The Lithoglyphidae: Let's Get Fresh

Live individuals of Lithoglyphus naticoides, copyright Jan Steger.

In previous posts on this site (see here and here), I've introduced you to members of the Hydrobiidae, a diverse family of mostly freshwater gastropods. Hydrobiids have long been recognised as a tricky group to work with, because of their small size and general shortage of distinctive shell features. In recent years, an understanding has developed that the 'hydrobiids' may include a number of lineages that became independently adapted to fresh water, and a number of previously recognised subfamilies of the Hydrobiidae have come to be recognised as their own distinct families. One of these ascended subgroups is the Lithoglyphidae.

Flat pebblesnails Lepyrium showalteri with eggs, copyright Friends of the Cahaba River National Wildlife Refuge.

The Lithoglyphidae are a family of about 100 known species, mostly found in the Holarctic region (Strong et al. 2008), though they have also been recorded from South America. Most lithoglyphids have distinctively squat, relatively thick shells, and for a long time this was treated as one of the main defining features of the group. However, Thompson (1984) pointed out that the sturdy lithoglyphid shell was probably an adaptation to living in fast-flowing streams and rivers, and could also be found in other 'hydrobiid' groups. As well as reducing the shell profile, the lithoglyphid shell possesses a broad aperture that allows for a proportionately large foot, increasing the snail's clinging power. Thompson (1984) identified a number of other features characteristic of lithoglyphids, including a spirally sculptured protoconch and a simple, blade-like penis that lacks accessory lobes or glandular structures. As the soft anatomy of many 'hydrobiids' has not yet been described, it is still possible that some taxa currently identified as lithoglyphids are in fact impostors. Conversely, confirmed lithoglyphids now include some taxa more divergent in shell shape, such as the limpet-like Lepyrium showalteri from Alabama. This species is distinctive enough that when first described it was identified as a neritid, a member of a group of gastropods not even closely related to lithoglyphids (imagine a new species of rodent being identified as a ratfish). Sadly, Lepyrium is also now endangered, being extinct in one of the two river catchments it was historically known from (see here). Thompson (1984) notes that another North American lithoglyphid genus, Clappia, may be entirely extinct. For at least one species, the cause of extinction was pollution from coal mining; no cause was specified for the other species, but according to Wikipedia its native habitat in the Coosa River has been modified by the construction of hydroelectric dams.

Shells of Benedictia baicalensis, from Baikal.ru.

Also closely related to the lithoglyphids are the Benedictiinae, a group of 'hydrobiid' gastropods endemic to Lake Baikal in Russia. A single species of benedictiine has been described from Lake Hövsgöl in Mongolia, but has not been collected there since; it seems likely that its original location was an error (Sitnikova et al. 2006). Baikal is a remarkable place: one of the world's largest freshwater lakes (and easily the largest in terms of the volume of water it contains), it is basically a freshwater sea. While other large lakes such as the Rift Lakes of Africa are poorly oxygenated at deeper levels, effectively restricting most animal life to the surface layer, Baikal has oxygen-rich deeper waters allowing a rich deep-water animal community (this may also be related to the numerous hydrothermal vents in the depths of Baikal). Some of you may have heard of the endemic Baikal seal Phoca sibirica, but Baikal is also home to a wide diversity of endemic fish (including a dramatic radiation of sculpins), a remarkable array of endemic amphipods, and even its own endemic family of sponges. The Benedictiinae are currently classified as a separate subfamily of Lithoglyphidae, with the remainder of species in the Lithoglyphinae (Bouchet et al. 2005), but as the relationship between the two subfamilies has not yet been examined in detail it is possible that the lithoglyphines are paraphyletic to the benedictiines. The benedictiines generally have thinner shells the lithoglyphines, possibly related to the differences in their usual habitats.

REFERENCES

Bouchet, P., J.-P. Rocroi, J. Frýda, B. Hausdorf, W. Ponder, Á. Valdés & A. Warén. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1-2): 1-397.

Sitnikova, T., C. Goulden & D. Robinson. 2006. On gastropod mollusks from Lake Hövsgöl. In: Goulden, C. E., T. Sitnikova, J. Gelhaus & B. Boldgiv (eds) The Geology, Biodiversity and Ecology of Lake Hövsgöl (Mongolia), pp. 233-252. Backhuys Publishers: Leiden.

Strong, E. E., O. Gargominy, W. F. Ponder & P. Bouchet. 2008. Global diversity of gastropods (Gastropoda; Mollusca) in freshwater. Hydrobiologia 595: 149-166.

Thompson, F. G. 1984. North American freshwater snail genera of the hydrobiid subfamily Lithoglyphinae. Malacologia 25 (1): 109-141.

The Little Tike that is Tychus

Male (left) and female of Tychus niger, copyright Lech Borowiec.

Another brief beetle post for today. The species in the image above is the type species of Tychus, a genus of about 150 species of pselaphine beetles found in Eurasia and North America. Chandler (1988) regarded the North American species as a separate genus Hesperotychus but Kurbatov & Sabella (2008) felt that the differences between species from the two continents were not enough to warrant separation. There's probably still some work to be done here.

Like many other pselaphines, most of the work on Tychus has focused on the morphology of the various species, with relatively little having been said about its life habits. Heer (1841) described the habitat of T. niger as 'sub lapidibus et in graminosis' which I believe means 'under stones and among grass', and Kurbatov & Sabella (2008) recorded collecting a specimen of Atychodea pilicollis, a related species, in damp sand. The large, broad-ended palps (the appendages on the head behind the antennae) of Tychus species suggests that they are probably micropredators, like the pselaphine Bryaxis puncticollis whose hunting behaviour was described in an earlier post. Like most pselaphines, the small size of Tychus species means that they generally escape observation.

Tychus is the largest genus in the pselaphine tribe Tychini. Tychins are most diverse in the Holarctic region, with only a very few species found in southern and south-east Asia. Chandler (1988) characterised the Tychini by the shape of the third segment of the palp, which is invariably longer than wide, and by the antennae usually being inserted close together on a narrow rostrum, though this varies a lot in distinctiveness between species. Kurbatov & Sabella (2008) also identified a number of other features representing possible synapomorphies of the Tychini, and suggested that the Oriental genera Atychodea and Amorphodea represent the sister taxon of the remaining Holarctic genera. The genera of Tychini are all fairly similar in appearance; notable distinguishing features of Tychus include an asymmetrical aedeagus (the intromittent organ in the male genitalia) and the arrangement of foveae (hollows) on the elytra and sternites. Males of Tychus often have one of the antennal segments modified as in the male of T. niger shown above, with a median segment noticeably thicker and broader than those on either side. The purpose of this enlarged segment, as with so many other features of pselaphines, seems to be unknown.

REFERENCES

Chandler, D. S. 1988. A cladistic analysis of the world genera of Tychini (Coleoptera: Pselaphidae). Transactions of the American Entomological Society 114 (2): 147-165.

Heer, O. 1841. Fauna Coleopterorum Helvetica, pars 1. Impensis Orelii, Fuesslini et Sociorum: Turici.

Kurbatov, S. A., & G. Sabella. 2008. Revision of the genus Atychodea Reitter with a consideration of the relationships in the tribe Tychini (Coleoptera, Staphylinidae, Pselaphinae). Transactions of the American Entomological Society 134 (1-2): 23-68.

A Skinny Waist is Not That Important

Female Clitemnestra bipunctata carrying prey back to its nest. Copyright Bill Johnson.

It's time for another post on crabronid wasps! The hard-working individual in the photo above is Clitemnestra bipunctata, a species found in the United States of North America. This is the only species of this genus found north of Mexico; other species are found in South America and in Australasia (Australia, New Guinea and New Caledonia). Clitemnestra belongs to the Gorytini, a closely related tribe to the Bembicini featured in an earlier post, though C. bipunctata is smaller than the average bembicin. You can find a good description of the biology of C. bipunctata at Bug Eric's website.

When Bohart & Menke (1976) prepared their revision of the Sphecidae (which then included the current Crabronidae), they included Clitemnestra in the genus Ochleroptera. Ochleroptera was recognised as closely related to Clitemnestra, but the two genera were distinguished by the shape of the metasoma (the effective abdomen). In Ochleroptera, the first segment of the metasoma is relatively long and narrow, and there is a distinct constriction between it and the remainder of the metasoma (you can see this clearly in the picture above). In Clitemnestra, this segment is shorter and broader, and it is not so divided from the other segments. Because the latter arrangement is the more primitive, Bohart & Menke suggested that Ochleroptera was descended from Clitemnestra, and because both genera were found in both South America and Australasia, they suggested that the two genera had both originated in Australasia and dispersed independently to South America.

Habitus of Clitemnestra noumeae, from Ohl (2002).

However, it was soon realised that the distinction between the two genera was not as clear as had been thought. A number of species were identified in South America in which the segment shape was intermediate: a bit long and narrow for 'Clitemnestra', but not narrow enough for 'Ochleroptera'. As there were no other significant features distinguishing the genera, they were eventually synonymised. Subsequently, Ohl (2002) described another species, Clitemnestra noumeae, from New Caledonia that also has an intermediate metasomal form. Though no formal analysis has yet been done to confirm things one way or another, it seems likely that 'Clitemnestra' and 'Ochleroptera' do not represent independent dispersals between Australasia and the Americas. Instead, 'Ocheroptera' species have probably arisen independently within Clitemnestra on more than one occasion.

To date, Clitemnestra bipunctata is the best studied species in the genus natural history-wise; other species have only been described on sporadic occasions. Clitemnestra species nest in burrows in vertical banks, which they primarily stock with various species of leafhoppers. In the case of one Australian species, C. plomleyi, it was suggested that the burrows it was seen using were not dug by the wasp itself, but had been left behind by beetles or other wasps (Evans & O'Neill 2007). It remains to be seen whether this is typical behaviour for the species, or it may have represented opportunistic behaviour by one enterprising individual.

REFERENCES

Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World: a generic revision. University of California Press.

Evans, H. E., & K. M. O'Neill. 2007. Sand Wasps: Natural History and Behavior. Harvard University Press.

Ohl, M. 2002. A new species of the wasp genus Clitemnestra Spinola, 1851 from New Caledonia (Hymenoptera, Apoidea, Crabronidae, Bembicinae). Deutsche Entomologische Zeitschrift 49 (2): 275-278.

Hunter Balls: The Hydrachna Water-Mites

Hydrachna sp., copyright J. C. Schou.

Hydrachnae are among the most rapacious of living animals, bold, fierce and cruel, the natural and inveterate enemies of all their congenera; they are no less hostile to each other, against which is waged a permanent war of extermination. Neither do they hesitate in attacking such animals as are suitable to their appetites, though double the size of their assailant.

This lurid description was applied to the water-mites by John Graham Dalyell in his 1851 book, The Powers of the Creator displayed in the Creation, or observations on life amidst the various forms of the humbler tribes of animated nature. The water-mites are a diverse group found mostly in fresh waters around the world; Dalyell probably intended the name Hydrachna to cover all water-mites, but modern authors recognise a large number of genera and families in addition to Hydrachna (which is distinctive enough that it is placed in its own family. Whether Hydrachna proper deserves the full force of Dalyell's description may be debatable, but there is no denying that they are predators.

As explained in an earlier post, water-mites belong to a group of mites, variously referred as Parasitengonae, Parasitengonina or some variation thereof (depending where you look), that is characterised by a life cycle including parasitic larvae and predatory adults. In the case of Hydrachna, the adults, which are nearly spherical in shape and bright red in colouration, feed on the eggs of aquatic bugs such as water boatmen or backswimmers that they find attached to submerged plants (so for all his charcterisation of Hydrachna as 'bold, fierce and cruel', Dalyell probably committed no less horrific an act of cruelty to chickens when he sat down to a fried breakfast). Despite their aquatic habits, Hydrachna are only clumsy swimmers themselves. After all, it does not require any great athleticism to hunt down an egg.

Larvae of Hydrachna, copyright Pfliegler Walter.

As well as finding their food on submerged plants, female Hydrachna lay their own eggs in them. They have needle-like chelicerae that they use to cut into the plant's stem, and then lay their eggs in air spaces within the plant cells (up to 1500 at a time: Walter et al. 2009). When the eggs hatch, the emerging larvae (which are kind of rugby ball-shaped) swim in search of a suitable host. Usually, this is a water-bug of much the same sort whose eggs were being devoured by the larvae's parents, though some Hydrachna species have also been recorded parasitising aquatic beetles. While some water-mites are quite picky about where exactly they choose to attach to a host, Hydrachna are not so: they may attach pretty much anywhere. They also do not exclude each other: a single host insect may end up with a large number of Hydrachna larvae attached to it (enough to have a serious impact on the host's health). The palps on either side of the chelicerae are used to initially hold on to the host before the larva cuts into the host cuticle with its chelicerae; once its hold with the chelicerae is firm, the palps are folded out of the way (Redmond & Lanciani 1982). Once attached, feeding on the host's haemolymph may not commence immediately: if the larva has found itself on a host that has not yet reached maturity, it will often wait until after the host has moulted. This is because the feeding larva becomes massively engorged and may swell up to hundreds of times its original size. In this swollen state, it obviously becomes immobile (one cannot walk if one's legs no longer touch the ground); should the host shed its cuticle with the engorged larva attached, the larva would be unable to reattach itself to the host.

After about two weeks of feeding, the larva is ready to mature, but this does not necessarily mean leaving the host. In parasitengonines, the first nymphal instar (the protonymph) after the larval stage is dormant as the mite metamorphoses into something closer to its adult form, the first of the two 'pupal' stages that the mite will go through in its life (the second comes between the active deutonymphal instar and maturity, but involves less of a radical change in morphology). Hydrachna passes this 'pupal' stage while still attached to the host, only detaching when it becomes an active deutonymph. As well as saving the larva the inconvenience (and danger) of dropping off the host while in an engorged state, this helps ensure that the deutonymph emerges in a suitable habitat. Hydrachna prefers still waters, such as ponds and lakes. Some species of Hydrachna prefer to breed in temporary seasonal pools, and may remain attached to the host for several months while their home pools are dry. Somehow they can tell the difference between the temporary pools and the more permanent waters in which the hosts spend the rest of their time.

REFERENCES

Redmond, B. L., & C. A. Lanciani. 1982. Attachment and engorgement of a water mite, Hydrachna virella (Acari: Parasitengona), parasitic on Buenoa scimitra (Hemiptera: Notonectidae). Transactions of the American Microscopical Society 101 (4): 388-394.

Smith, I. M., D. R. Cook & B. P. Smith. 2010. Water mites (Hydrachnidiae) and other arachnids. In: Thorp, J. T., & A. P. Covich (eds) Ecology and Classification of North American Freshwater Invertebrates, pp. 485-586. Academic Press.

Walter, D. E., E. E. Lindquist, I. M. Smith, D. R. Cook & G. W. Krantz. 2009. Order Trombidiformes. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology, 3rd ed., pp. 233-420. Texas Tech University Press.

Black Yeasts, Black Lichens and Rotting Wood: the Chaetothyriomycetidae

Pyrenula cruenta, copyright Gary Perlmutter.

There is no denying that the advent of molecular phylogenetic analysis has been a boon for fungal systematics. It has allowed a much greater resolution of relationships than was previously possible (especially for comparisons between asexually- and sexually-reproducing fungi), and has even lead to the identification of a number of major lineages that probably could have never been recognised from morphological data alone. One such lineage is the Chaetothyriomycetidae, whose members vary from lichens on tropical tree trunks, to saprobes living in the deep sea, to pathogens in the brains of humans.

The Chaetothyriomycetidae (or Chaetothyriomycetes in many older references: the botanical code goes rather all out in the rather irritating practice of changing the endings of names to indicate arbitrary taxonomic ranks) has been divided by Gueidan et al. (2014) into four major lineages. Two of these, the Pyrenulales and Verrucariaceae, are mostly comprised of lichens. Lichenised fungi in the Pyrenulales associate with green algae of the family Trentopohliaceae (which, despite being 'green algae', are generally orange in colour), and are most commonly found on tree bark in tropical forests. Only one lichenised genus, Strigula, is also found growing on leaves; non-lichenised Pyrenulales are found on bark, leaves or wood (Geiser et al. 2006).

Verrucaria maura on coastal rocks, copyright A. J. Silverside.

The Verrucariaceae, in contrast, associate with different symbiotic algae, and prefer to grow on rocks. Lichens of this family are often blackish; their hyphae are darkened by a melanin-like compound which allows them to tolerate quite exposed conditions. Certain species are particularly prominent around the marine shoreline. Gueidan et al. (2014) also identified a small as-yet-unnamed lineage close to Verrucariaceae including rock-dwelling and moss-associated non-lichenised fungi, but support for this grouping requires further testing.

Another somewhat novel lineage identified by Gueidan et al. (2014) was the Celotheliaceae. The type genus, Celothelium, is a lichenised fungus that associates with the alga Trentepohlia in the manner of Pyrenulaceae. Other members of the Celotheliaceae, however, are quite different in ecology, being mostly pathogens of woody plants. Phaeomoniella chlamydospora is a causative agent of grapevine trunk disease, resulting in conditions such as esca, and the rather ominously named 'black goo decline' (so-called because the stems become filled with 'black goo', as the xylem vessels become clogged with fungal hyphae). Dolabra nepheliae causes canker in lychee and rambutan trees. These pathogenic taxa are commonly largely anamorphic (that is, they produce asexual reproductive structures).

Culture of black yeast Exophiala dermatitidis, from here.

The last and most diverse lineage (so far as we know, anyway) is the Chaetothyriales. Like the Verrucariaceae, the Chaetothyriales have melanised hyphae and often grow on exposed substrates such as rocks. Indeed, molecular analyses have supported a closer relationship between Verrucariaceae and Chaetothyriales than the other major lineages. However, members of the Chaetothyriales are not lichenised. Many are saprobic; others, such as the Chaetothyriaceae, grow on plant leaves but in many cases it is unclear whether they are saprobic or parasitic. The mostly saprobic family Herpotrichiellaceae also includes a number of asexually-reproducing forms that grow as yeasts and are opportunistic pathogens, including in humans. Infections by black yeasts (Exophiala) are most commonly cutaneous and relatively superficial, but they can also cause severe and life-threatening infections of deeper organ systems. These infections are most common in patients with pre-existing conditions affecting the immune system, but at least one species, E. dermatitidis, has been recorded causing fatal brain infections in otherwise healthy individuals.

And I referred at the beginning of this post to the deep sea? Well, the Chaetothyriomycetidae samples from there are, I believe, yet to be described. It is possible that this diverse group of fungi still has surprises for us.

REFERENCES

Geiser, D. M., C. Gueidan, J. Miadlikowska, F. Lutzoni, F. Kauff, V. Hofstetter, E. Fraker, C. L. Schoch, L. Tibell, W. A. Untereiner & A. Aptroot. 2006. Eurotiomycetes: Eurotiomycetidae and Chaetothyriomycetidae. Mycologia 98 (6): 1053-1064.

Gueidan, C., A. Aptroot, M. E. da Silva Cáceres, H. Badali & S. Stenroos. 2014. A reappraisal of orders and families within the subclass Chaetothyriomycetidae (Eurotiomycetes, Ascomycota). Mycol. Progress 13: 1027-1039.

Teasels and Scabious: the Dipsacaceae

Scabiosa cretica, copyright Ori Fragman Sapir.

As recognised plant families go, the Dipsacaceae is not a particularly large one. It includes only a few hundred species, of which the majority are found in arid regions around the Mediterranean and the remainder elsewhere in Africa and Eurasia. The economic significance of the family is also relatively low. Some species are cultivated as ornamental plants. Dipsacus fullonum, teasel, gets its vernacular name because its bottle-brush-like flower-heads were used to tease the fibres of woollen cloth. Various species of Dipsacaceae, particularly the genus Scabiosa, are known as 'scabious' because they were apparently once used somehow in treating scabies. I also came across a reference in Duke (2008) to Syrian scabious Cephalaria syriaca having had a certain notoriety in the past due to its seeds being similar in appearance to wheat grain, meaning that they could be inadvertently sown into fields, or impart an unpleasant taste if ground into flour.

Flowers and fruits of Sixalix atropurpurea, copyright Manuel M. Ramos. Members of this genus grow on sand; their fruits have a reduced membranous wing, and disperse by rolling.

Nevertheless, the Dipsacaceae are not without their points of interest. One intriguing characteristic of the family is that they bear numerous small flowers clustered onto a single shared receptacle, similar to those of the much more diverse Asteraceae. Like Asteraceae, there may even be a differentiation in the appearance of flowers on the inner part of the receptacle from those around the outer rim. The Dipsacaceae are not directly related to the Asteraceae; rather, the two families have developed their capitate flower-heads independently. Which is not to say that they are incomparable: species of both Asteraceae and Dipsacaceae exhibit duplications of genes that are believed to affect the development of floral symmetry (Carlson et al. 2011), and it is possible that similar processes have lead to the evolution of compound flower-heads in both.

Flowers and fruits of Scabiosa sicula, copyright Jose Rodriguez. The fruiting head in focus shows the membranous wings that function in dispersal.

Past authors have divided the Dipsacaceae into three tribes, largely on the basis of characters related to seed dispersal. Each of the small flowers on a dipsacacean flower-head develops into a dry fruit containing a single seed. The epicalyx (an outer protective layer of the flower base) persists as an outer coating of the mature fruit, like a second skin. In the largest of the three previously recognised tribes, the Scabioseae, the epicalyx is often modified for wind dispersal, either by plumose hairs on top of a dorsal tube (the same sort of set-up as seen in dandelions) or by a membranous wing around the fruit. In contrast, the fruit of the genus Knautia, widow flowers, which has been placed in its own separate tribe, bears an elaiosome, a fleshy, hemispherical lump. The elaiosome attracts ants, who carry the fruit away to their nest; after the ants have eaten the elaiosome, the remaining seed is able to germinate where they leave it. Finally, the third tribe Dipsacaceae includes only the genera Dipsacus and Cephalaria; the mature fruit of these genera lack adaptations for either wind or ant dispersal, and seed dispersal is largely controlled by the break-up of the flower-head itself.

Bassecoia bretschneideri, copyright Dave Boufford.

More recent molecular analyses, however, have not entirely supported this three-way division of the Dipsacaceae (Carlson et al. 2009). While Knautia and the Dipsaceae are both likely to be monophyletic, the Scabioseae are not. Instead, a small clade including the eastern Asian genus Bassecoia is sister to the remaining members of the family. These fall into two major clades: one, that has been referred to as the Scabioseae 'sensu stricto', includes the majority of the taxa previously included in the Scabioseae, such as Scabiosa, Lomelosia and Pterocephalus. The other clade, which has been dubbed the 'dipknautids', includes Knautia and the Dipsaceae, together with a few smaller 'ex-Scabioseae' genera. While the original Dipsacaceae may have been wind-dispersed, they have not been above looking at alternatives.

REFERENCES

Carlson, S. E., D. G. Howarth & M. J. Donoghue. 2011. Diversification of CYCLOIDEA-like genes in Dipsacaceae (Dipsacales): implications for the evolution of capitulum inflorescences. BMC Evolutionary Biology 11: 325. doi:10.1186/1471-2148-11-325.

Carlson, S. E., V. Mayer & M. J. Donoghue. 2009. Phylogenetic relationships, taxonomy, and morphological evolution in Dipsacaceae (Dipsacales) inferred by DNA sequence data. Taxon 58 (4): 1075-1091.

Duke, J. A. 2008. Duke's Handbook of the Medicinal Herbs of the Bible. CRC Press.

Friend and/or Foe: Separating Rhizobium and Agrobacterium

Roots of cowpea Vigna unguiculata with nodules containing Rhizobium, copyright Dave Whitinger.

For as far back as we have records to know, farmers have recognised the value of crop rotation: varying the crops grown on a particular patch of land in order to avoid exhausting the soil of nutrients. It also did not take these ancient farmers long to realise the value of one of these rotated crops being a legume, the group of plants including peas, beans, lentils and the like. What these pioneers of agriculture did not know was that the rejuvenating effect that legumes seemed to have on the soil was due to bacteria living in their roots, the organisms that we now know as Rhizobium.

The value of Rhizobium to agriculture comes from its ability to fix nitrogen. Nitrogen compounds are essential for all living organisms (proteins, for instance, contain nitrogen). But while nitrogen is also the most abundant element in our planet's atmosphere, most of it exists in a form that cannot be used directly by most organisms. Nitrogen-fixing bacteria are the exception, able to extract the nitrogen directly from the atmosphere and 'fix' it into more tractable compounds. Rhizobium is not the only genus of bacteria able to fix nitrogen, but it is certainly one of the most predominant. One of the limitations of nitrogen fixation is that it generally involves enzymes that do not work well in the presence of oxygen. Rhizobium cells induce the growth of nodules on legume roots, within which they are sheltered from that polluting gas. Not all Rhizobium live in legumes, however: they may also be found in large numbers free in the soil, with concentrations of tens of millions of cells per gram of soil having been recorded (Kuykendall et al. 2005).

Crown gall caused by Agrobacterium tumefaciens, copyright Christoph Müller.

Rhizobium has been regarded as closely related to another bacterial genus called Agrobacterium, whose significance for agriculture has been seen somewhat less favourably. As classically distinguished, Agrobacterium species do not fix nitrogen like Rhizobium, but they do resemble Rhizobium in causing growths on plant roots. These might be tumours, as in Agrobacterium tumefaciens (which can also cause galls to form elsewhere on the plant), or an overabundance of small rootlets, as in A. rhizogenes. While not necessarily fatal to the host plant, these deformities do often stunt growth, causing a loss in yield. A third species, A. radiobacter, has been recognised for non-pathogenic Agrobacterium.

However, as microbiologists gained a better understanding of the underlying genetics of Rhizobium and Agrobacterium, the picture became more complicated. The ability of Rhizobium to fix nitrogen, and of Agrobacterium to cause root deformities, is due to particular sets of genes in each. These genes are not contained in the main chromosome of each bacterium, but are held in little 'mini-chromosomes' called plasmids. And plasmids can be readily transferred from one bacterial cell to another. Through the transfer of the right plasmids, an Agrobacterium might gain the ability to fix nitrogen, or a Rhizobium might start inducing tumours. Phylogenetic analyses of the genera also indicated that some 'Rhizobium' were more closely related to 'Agrobacterium', and vice versa. As a result, at least one group of researchers has proposed uniting the two genera into one, Rhizobium. But others have been loathe to abandon a name as long-used in both the microbiological and agricultural literature as Agrobacterium (Farrand et al. 2003). There are recognisably distinct phylogenetic lines within the family Rhizobiaceae that includes the two genera, and even differences in plasmids are not entirely uninformative: not all strains can utilise all plasmids.

Cells of Rhizobium trifolii on root hair of clover, copyright Frank Dazzo.

There are also some significant genomic differences involved. Some of you may have learnt in biology class that the normal arrangement for bacterial cells is to have the bulk of the genome contained in a single circular chromosome, possibly with a scattering of small plasmids. The difference between the two is that the cell can function without the plasmids, but not without the chromosome. Rhizobium leguminosarum, the type species of Rhizobium, keeps to this arrangement, as do most other Rhizobium (though the plasmid containing the nitrogen-fixation genes is a bit of a whopper by usual standards). However, Agrobacterium tumefaciens*, the type species of its genus, is more unusual in having not one but two chromosomes: some of its vital genes have been transferred to what was originally a large plasmid (Slater et al. 2009). What is more, this second chromosome is not formed as a circle like other bacterial chromosomes, but is linear like the chromosomes of eukaryotes. Another 'Agrobacterium' species, A. vitis, has the second chromosome like A. tumefaciens but it remains circular. The type strain of A. rhizogenes, on the other hand, has only a single circular chromosome, and appears to be closer to Rhizobium.

*The type strains of 'Agrobacterium tumefaciens' and 'A. radiobacter' are close enough that the two names should be synonymised into a single species. However, there seems to be an on-going dispute over which of the two names should be used for the combined taxon. I'm using A. tumefaciens for convenience, but I wouldn't be able to judge which of the sides is correct.

Phylogenetic analysis also supports the recognition of a further genus of Rhizobiaceae, Ensifer, sitting outside the clade including Rhizobium and Agrobacterium. The type species of Ensifer, E. adhaerens, is a soil-dwelling bacterium that can live as a predator of other bacteria. It attaches to them end-wise (when multiple E. adhaerens attach to a single target cell, they may form a palisade) and causes them to burst open. Ensifer adhaerens is not an obligate predator—when suitable prey is not available, it can survive on free nutrients in the soil—and when analysed it turns out to be related to a clade of nitrogen-fixing bacteria previously recognised as the genus 'Sinorhizobium'. Indeed, one species of this genus turned out to be simply a non-parasitic form of E. adhaerens (Young 2003).

REFERENCES

Farrand, S. K., P. B. van Berkum & P. Oger. 2003. Agrobacterium is a definable genus of the family Rhizobiaceae. International Journal of Systematic and Evolutionary Microbiology 53 (5): 1681-1687.

Kuykendall, L. D., J. M. Young, E. Martínez-Romero & H. Sawada. 2005. Genus I. Rhizobium Frank 1889, 337^AL. In: Garrity, G., D. J. Brenner, N. R. Krieg & J. T. Staley (eds) Bergey's Manual of Systematic Bacteriology vol. 2. The Proteobacteria, Part C. Springer.

Slater, S. C., B. S. Goldman, B. Goodner, J. C. Setubal, S. K. Farrand, E. W. Nester, T. J. Burr, L. Banta, A. W. Dickerman, I. Paulsen, L. Otten, G. Suen, R. Welch, N. F. Almeida, F. Arnold, O. T. Burton, Z. Du, A. Ewing, E. Godsy, S. Heisel, K. L. Houmiel, J. Jhaveri, J. Lu, N. M. Miller, S. Norton, Q. Chen, W. Phoolcharoen, V. Ohlin, D. Ondrusek, N. Pride, S. L. Stricklin, J. Sun, C. Wheeler, L. Wilson, H. Zhu & D. W. Wood. 2009. Genome sequences of three Agrobacterium biovars help elucidate the evolution of multichromosome genomes in bacteria. Journal of Bacteriology 191 (8): 2501-2511.

Young, J. M. 2003. The genus name Ensifer Casida 1982 takes priority over Sinorhizobium Chen et al. 1988, and Sinorhizobium morelense Wang et al. 2002 is a later synonym of Ensifer adhaerens Casida 1982. Is the combination ‘Sinorhizobium adhaerens’ (Casida 1982) Willems et al. 2003 legitimate? Request for an Opinion. International Journal of Systematic and Evolutionary Microbiology 53 (6): 2107-2110.

The Gordian Mouse

North American deer mouse from near Santa Fe, New Mexico, possibly Peromyscus sonoriensis. Copyright J. N. Stuart.

The North American deer mouse Peromyscus maniculatus has been recognised as one of the most widespread mammal species in North America. It has been recorded from most of the continent, with the main areas of absence being northern Canada and Alaska, the south-eastern corner of the United States (where it is replaced by a closely related species, the smaller Oldfield deer mouse Peromyscus polionotus) and coastal regions of Mexico. They are highly adaptable animals, eating a wide range of foods, and their tendency to gnaw just about anything available for food or nesting has not always endeared them to their human compatriots. In recent years, they have also received their fair share of unwelcome attention as vectors for pathogens such as the Sin Nombre hantavirus*, which causes a devastating (and commonly fatal) pulmonary disease in humans. It is therefore not surprising that the deer mouse has become one of the most extensively studied mammal species out there (not quite in house mouse or black rat territory, maybe, but still definitely up there). A search for 'Peromyscus maniculatus' on Google Scholar brings back well over 16,000 results. Surely with this degree of attention, this is at least one taxon for which I cannot deploy my usual 'the taxonomy is uncertain'?

*'Sin nombre' is, of course, Spanish for 'without name'. The reason for this coy appellation is that the virus in question was first labelled the 'Four Corners' virus after being identified from patients in that region of the United States in 1993, but was renamed after residents of the region protested.

Of course it isn't. Quite the opposite, in fact. With a range this large, it is not surprising that a fair amount of variability has been recognised in the North American deer mouse over the years. Over sixty subspecies of Peromyscus maniculatus have been recognised from various regions. This variability has also been part of the deer mouse's appeal as a study animal, as evolutionary scientists have examined the relationships between subspecies. The problem comes when you realise that in some places you may find two distinct 'subspecies' of deer mouse in a single locality. If a 'subspecies' is defined as a geographical sub-unit of a reproductively coherent species (as it traditionally has been), then that ain't right. Two taxa occupying a single range and not interbreeding should be separate species, surely? But travel to another location nearby, and you'll find the two 'species' interbreeding and merging into one. One case that has been cited as a classic example of a 'ring species' is around the Rocky Mountains, where the subspecies P. maniculatus artemisiae and P. m. nebrascensis do not interbreed with each other, but both interbreed with other subspecies to the north and south.

Part of the problem, of course, is that the 'species' is just a horrendously messy concept. There are a wealth of different species concepts out there, but the essential ideal underlying most is that a 'species' represents the point at which the reticulating relationships between interbreeding individuals become less important for understanding relationships than the branching relationships between population lineages. Which is not a point at all. Lineages diverge at multiple, quasi-independent levels in the process of speciation—they separate geographically, behaviourally, genetically, morphologically—and there is no magic point at which they suddenly change from 'one species' to 'separate species'. Nevertheless, as the recent trend has been to recognise species on a finer level than in the past, it seems likely that the future will see a subdivision of the current Peromyscus maniculatus.

Figure showing distributions of lineages of Peromyscus maniculatus from Kalkvik et al. (2012).

Over much of its range, Peromyscus maniculatus can be divided between two main morphotypes: a forest form with larger ears and a longer tail, and an open-country form with smaller ears and a shorter tail. Where the two forms are found in one region, they maintain their ecological distinctiveness. However, because of the aforementioned hybridisation between geographically adjacent populations, it is unlikely that any subdivision of P. maniculatus will be directly between these two morphotypes. One split that has already been widely accepted was proposed by Hogan et al. (1993), who found that certain populations in coastal north-west North America were genetically quite distinct from other P. maniculatus, and recommended the recognition of a separate species P. keeni. Peromyscus keeni is also generally larger and longer-tailed than P. maniculatus. However, more recent studies of the phylogeography of North American deer mice by Dragoo et al (2006) and Kalkvik et al. (2012) have found that even with the removal of P. keeni, P. maniculatus remains paraphyletic to both that species, to the south-west species P. polionotus (whose distinction from P. maniculatus has not generally been questioned), and possibly to the Mexican P. melanotis. Both the later studies identified six major lineages within P. maniculatus, and Dragoo et al. (2006) suggested that it may need to be divided between at least three species. The 'true' Peromyscus maniculatus, under this scheme, includes the two lineages found in the north-east of North America (the original type locality of the species being in Labrador). A coastal lineage found in the south-west was identified by both studies as related to P. keeni, and it remains to be seen whether it would be better included in that species or recognised as its own separate species. A lineage identified in southern New Mexico could be recognised under the name of Peromyscus blandus. The remaining two lineages, one found around the Rocky Mountains and one in the Great Plains, formed a clade that Kalkvik et al. (2012) identified as the sister lineage of P. polionotus. Dragoo et al. suggested that the name Peromyscus sonoriensis was available for this clade. However, Kalkvik et al. recognised that the Rocky Mountain lineage was a forest form and the Great Plains lineage a open-country form, so there may be grounds for their recognition as distinct species.

While the correlation between these studies appears promising, it must be stressed that both were analysing the same gene (cytochrome b) and it remains to be seen whether the lineages they identified continue to be supported by other sources of data. It also needs to be seen whether they stand up to the inclusion of further populations: western Canada and Mexico stand out as poorly sampled areas in both studies. Peromyscus maniculatus in its current form may represent one species, it may represent four, or it may yet refer to even more than that.

REFERENCES

Dragoo, J. W., J. A. Lackey, K. E. Moore, E. P. Lessa, J. A. Cook & T. L. Yates. 2006. Phylogeography of the deer mouse (Peromyscus maniculatus) provides a predictive framework for research on hantaviruses. Journal of General Virology 87: 1997-2003.

Hogan, K. M., M. C. Hedin, H. S. Koh, S. K. Davis & I. F. Greenbaum. 1993. Systematic and taxonomic implications of karyotypic, electrophoretic, and mitochondrial-DNA variation in Peromyscus from the Pacific Northwest. Journal of Mammalogy 74 (4): 819-831.

Kalkvik, H. M., I. J. Stout, T. J. Doonan & C. L. Parkinson. 2012. Investigating niche and lineage diversification in widely distributed taxa: phylogeography and ecological niche modeling of the Peromyscus maniculatus species group. Ecography 35: 54-64.

Bits of Cucumber in the Fossil Record

Aggregation of Eocaudina septaforminalis sclerites from Boczarowski (2001). Scale bar = 200 µm.

Echinoderms are a dream group of animals for invertebrate palaeontologists (that's palaeontologists who study invertebrates, not palaeontologists who are invertebrates). Their calcified skeletons mean that their fossil record is extensive and detailed. When most of the body is covered in plates, looking at the fossil can give you an instant idea of what the animal looked like when alive. But as with all things in biology, there are notable exceptions. The sea cucumbers are one group of echinoderms that has significantly reduced the original skeleton, sacrificing a hard outer skeleton for increased flexibility. Instead of solid plates, the sea cucumber skeleton is made up of many minute sclerites embedded in the skin. And while this may be all well and good for the sea cucumber, it is not so convenient for the palaeontologists. In the fossil record, these minute sclerites become separated, and one separated sclerite does not tell you much about the appearance of the sea cucumber as a whole.

As a result, palaeontologists looking at sea cucumber remains have found themselves presented with a conundrum. The classification of modern sea cucumbers is largely based on features of the soft body that are usually not preserved in the fossil record, making comparison of living and fossil cucumbers difficult. Also, the skeleton of a single sea cucumber may include different forms of sclerite, performing different roles. If two different types of sclerite are found close together in the fossil record, did they come from a single sea cucumber or from two different sea cucumbers that died close together? To bypass these barriers, palaeontologists have often used what are referred to as 'parataxa'. A single type of sclerite is treated as a single 'parataxon', with the recognition that there may not be a perfect correlation between the parataxon and the theoretical taxon that it originally came from.

Individual calclamnine sclerite, Priscocaudina crucensis, from Boczarowski (2001).

The Calclamnidae has been recognised as one such 'parafamily' of sea cucumber sclerites. As defined by Frizzell & Exline (1966), the Calclamnidae grouped together rounded or polygonal sclerites that are perforated with holes like a sieve, and that don't have any sort of stalk or other ventral protrusion. This is a very common sort of sclerite for echinoderms: 'calclamnid' sclerites have been identified as far back as the Ordovician (Boczarowski 2001), and sclerites of this sort are still found in sea cucumbers today (just to confuse matters, the skeletons of some brittle stars also include very similar sclerites, raising the spectre of misidentification). Boczarowski (2001) recognised two subfamilies of Calclamnidae: in one, the Eocaudininae, the perforations of the sclerite are all more or less even in size, while in the other, Calclamninae, the pores towards the centre of the plate are larger and arranged in a cross-shape. The eocaudinines include the earliest calclamnid plates, with the calclamnines appearing during the Devonian.

Recognition of parataxa is a convenient tool for keeping records of things like biostratigraphy without getting bogged down, but what sort of sea cucumber did calclamnids actually come from? The calclamnids resemble sclerites found in the group of modern sea cucumbers called the Dendrochirotacea, so they have often been classified with this group. However, a number of features of the dendrochirotaceans, including perforated calclamnid-like sclerites, have been suggested to be primitive for sea cucumbers, so similarities between calclamnids and dendrochirotaceans may represent shared ancestral features rather than true affinities. Haude (1992) commented on a number of cases of sclerites found preserved in assemblages that he believed represented original life associations, including some containing calclamnids. One of these contained sclerites that Haude identified as similar to Calclamna germanica, the type species of the family, in association with large hook-shaped sclerites. Hooks are not characteristic of dendrochirotaceans, but of Apodacea, a different group of sea cucumbers characterised by the loss of tube feet (with the hooks working to provide mobility in their place). Haude suggested the possibility that Calclamna might represent a stem-group apodacean that retained some primitive sclerite features. In other fossil groups such as conodonts, the identification of preserved assemblages has allowed palaeontologists to progress beyond the use of parataxa and integrate more recognition of evolutionary relationships. Hopefully we get the same opportunity with sea cucumbers.

REFERENCES

Boczarowski, A. 2001. Isolated sclerites of Devonian non-pelmatozoan echinoderms. Palaeontologia Polonica 59: 1-219.

Frizzell, D. L., & H. Exline. 1966. Holothuroidea—fossil record. In: Moore, R. C. (ed.) Treatise on invertebrate Paleontology pt U. Echinodermata 3 vol. 2, pp. U646-U672. The Geological Society of America, Inc., and The University of Kansas Press.

Haude, R. 1992. Fossil holothurians: sclerite aggregates as 'good' species. In: Scalera-Liaci, L., & C. Canicatti (eds) Echinoderm Research 1991, pp. 29-33. Balkema: Rotterdam.

The Mighty Limpets

The limpet Nacella concinna on bull kelp Durvillea, copyright David Cothran.

I am Clamp the mighty limpet,
I am solid, I am stuck.
I am welded to the rockface
with my super-human suck.

The hero of Pam Ayres' "Clamp the Mighty Limpet" is a misanthropic Napoleon, threatening would-be harassers with lost fingernails and the danger of attachment (if they would only be willing to stand in one place for two weeks). In reality, 'limpet' is a name that has been applied to a number of unrelated groups of gastropod with cap-like, more-or-less uncoiled shells. The most prominent group of limpets, however, and the one that Ayres almost certainly had in mind, is the 'true limpets' of the Patellogastropoda.

Owl limpet Lottia gigantea, copyright Jerry Kirkhart.

The Patellogastropoda are a mostly marine group of molluscs, though one species in south-east Asia, Potamacmaea fluviatilis, is found in rivers and brackish waters adjoining the Bay of Bengal (Lindberg 2008). The group takes its name from the north-east Atlantic genus Patella, which has been featured on this site in an earlier post. Patellogastropods are particularly prominent in the intertidal zone, where they can be found clinging to rocky surfaces, but there are also many subtidal or deep-water limpets. Some limpets are specialised for living on macro-algae or marine vegetation; one such species, the North Atlantic Lottia alveus, has previously been mentioned on this site due to its unfortunate extinction as a result of the wasting epidemic that devastated sea-grass populations in the 1930s. Deep-water patellogastropods may be found on sunken wood, or they may live in association with hydrothermal vents or cold seeps. One such genus, Serradonta, is restricted to the tubes of vestimentiferan worms (Nakano & Sasaki 2011).

Whitecap limpet Acmaea mitra, copyright Mary Jo Adams.

Phylogenetically speaking, patellogastropods are a very interesting group indeed. Morphological studies have identified them as the sister group to all other living gastropods. They have a distinctive radula morphology, known as 'docoglossan', with each tooth-row of the radula containing a median tooth flanked by a small number of relatively simple lateral and marginal teeth (up to three pairs of each). This contrasts with the radulae of other gastropods, in which the teeth are more numerous and/or more specialised, but resembles the radula of other molluscan groups such as chitons. As such, patellogastropods may retain the plesiomorphic radula morphology of gastropods as a whole. Patellogastropods also have a shell microstructure that differs from that of other gastropods, and they have their gonads in a ventral position relative to the visceral mass instead of the dorsal position of other gastropods (Lindberg 2008). Some have even suggested that patellogastropods may represent a remnant lineage that never underwent the coiling that characterises other gastropods, but this seems unlikely. Patellogastropods do have some features, such as an asymmetrical position of the protoconch (larval shell) on the mature shell, that suggest coiled ancestors. Molecular studies, on the other hand, have been more equivocal in positioning the patellogastropods. Some have given results consistent with the morphological analyses, but a few have failed to place patellogastropods with the other gastropods at all (e.g. Giribet et al. 2006), while many have placed them in a more nested position deeper within the gastropods (Zapata et al. 2014).

Ringed blind limpet Cryptobranchia concentrica, copyright L. Schroeder.

At face value, the fossil record might actually appear to support a more nested position for patellogastropods. The fossil record for gastropods as a whole extends back to the Cambrian, but the oldest definite record of patellogastropods goes back no further than the late Triassic (Frýda et al. 2009). If patellogastropods were indeed the earliest surviving gastropod lineage to diverge, where were they hiding for the intervening 200 million years or so? One possibility is that they were there, but did not get preserved. Phylogenetic analysis of living limpets suggests that the immediate ancestors of the patellogastropods clung to rocks in high-energy environments, with deep-water lineages occupying more nested positions in the tree (Nakano & Sasaki 2011). Such environments are not favourable to the fossil record, as the shells of dead limpets tend to get broken up by wave action before they have the chance to be fossilised. Another, more likely, possibility is that we have failed to recognise the coiled ancestors of the Patellogastropoda for what they are. The Palaeozoic gastropod fauna included a number of groups that are not present in the modern day; it is quite possible that one of these groups gave rise to the patellogastropods. One group that has specifically been nominated as a possible relative of the patellogastropods is the euomphaloids. But for now, Clamp the Mighty Limpet is holding the secrets of his affinities well hidden, and it will not be easy prising them off him.

REFERENCES

Frýda, J., P. R. Racheboeuf, B. Frýdová, L. Ferrová, M. Mergl & S. Berkyová. 2009. Platyceratid gastropods—stem group of patellogastropods, neritimorphs or something else? Bulletin of Geosciences 84 (1): 107-120.

Giribet, G., A. Okusu, A. R. Lindgren, S. W. Huff, M. Schrödl & M. K. Nishiguchi. 2006. Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons. Proceedings of the National Academy of Sciences of the USA 103 (20): 7723-7728.

Lindberg, D. R. 2008. Patellogastropoda, Neritimorpha, and Cocculinoidea. In: Ponder, W. F., & D. R. Lindberg (eds) Phylogeny and Evolution of the Mollusca, pp. 271–296. University of California Press.

Nakano, N., & T. Sasaki. 2011. Recent advances in molecular phylogeny, systematics and evolution of patellogastropod limpets. Journal of Molluscan Studies 77 (3): 203-217.

Zapata, F., N. G. Wilson, M. Howison, S. C. S. Andrade, K. M. Jörger, M. Schrödl, F. E. Goetz, G. Giribet & C. W. Dunn. 2014. Phylogenomic analyses of deep gastropod relationships reject Orthogastropoda. Proceedings of the Royal Society of London Series B 281: 20141739.

Sybra punctatostriata

Sybra punctatostriata, from here.

Just a very brief post today, because once again I've drawn a species that I haven't been able to find too much about. Sybra punctatostriata is a member of the Cerambycidae, the longicorn beetles, a diverse but (usually) fairly distinctive group of beetles whose larvae burrow into wood and plant stems. This species was first described by H. W. Bates in 1866 as part of a collection of beetles from Taiwan. Since then, it has been recorded over a wide area stretching from Japan in the north to Hainan in the south (though mostly in Japanese and Chinese sources that I don't have access to, and probably couldn't follow if I did). However, Samuelson (1965) indicated that S. punctatostriata was one of a number of very similar species in the genus Sybra, hinting that its range may require revision. Samuelson himself only identified a single specimen of S. punctatostriata from Okinawa in collections of beetles from the Ryukyus, which he described as showing some small differences from Taiwan specimens.

Another view of Sybra punctatostriata from the same site.

Sybra punctatostriata has been recorded feeding on Gossypium, the genus that includes cotton. However, other Sybra species are known to have wide host ranges. Sybra alternans, a species that has been recorded infesting bananas, has also been known to feed on fig trees, pineapple plants, passionfruit vines, beans... (Chen et al. 2001). It is possible that S. punctatostriata's host range may also be wider than recorded.

REFERENCES

Bates, H. W. 1866. On a collection of Coleoptera from Formosa, sent home by R. Swinhoe, Esq., H.B.M. Consul, Formosa. Proceedings of the Zoological Society of London 1866: 339-355.

Chen, H., A. Ota & G. E. Fonsah. 2001. Infestation of Sybra alternans (Cerambycidae: Coleoptera) in a Hawaii banana plantation. Proc. Hawaiian Entomol. Soc. 35: 119-122.

Samuelson, G. A. 1965. The Cerambycidae (Coleopt.) of the Ryukyu Archipelago II, Lamiinae. Pacific Insects 7 (1): 82-130.

Wasps in the Sand

Sand wasp Bembix oculata with prey (a bombyliid, I think), copyright Carlos Enrique Hermosilla.

The sand wasps of the tribe Bembicini are a diverse group of about 500 species of wasp that get their name because, obviously, of their habit of constructing burrows in sand-banks. Like other members of the wasp family Crabronidae, sand wasps provision these burrows with food for their larvae in the form of other insects. The adults themselves feed on nectar. Some of the Bembicini are among the larger members of the Crabronidae, and most of them are strikingly marked in black and yellow, white or red. Other characteristics of the group include an elongate labrum above the mouth, and the reduction of the ocelli, often to simple scars.

Bembicins are divided between a reasonable number of genera (Bohart & Menke, 1976, listed fifteen, but subsequent authors have recognised more) but the greater number of species are included in just one of these, the cosmopolitan Bembix with over 300 species (some older sources spell this name 'Bembex', but Bembix seems to be correct). Bembix is also the only genus found outside the Americas. Bohart & Menke (1976) suggested three main lineages within the Bembicini: one containing the relatively plesiomorphic genera Microbembex and Bicyrtes, a group of four genera including Stictiella and Glenostictia in which the ocelli are sunken into pits, and a large group containing genera related to Bembix with a raised welt at the front of the scutum on the thorax.

Sand Wasp - Bembix americana from Dick Walton on Vimeo.

While other wasps will lay their egg(s) on a paralysed insect in a brood chamber and then fly off never to return, many bembicins continue to bring fresh food items to the burrow throughout their larvae's development (take a look at the video above, by Dick Walton). The majority of bembecins provide their larvae with flies as food, which they paralyse with their sting and then carry back to the burrow between their mid-legs. Only a small number of genera regularly use other prey, though notably these genera include both Bicyrtes and Microbembex (so predation on flies is possibly ancestral for a clade excluding these two genera rather than for the tribe as a whole). Bicyrtes species stock their burrows with bugs (Heteroptera), most commonly nymphs. Microbembex species are the gourmands of the tribe, taking prey ranging from mayflies to midges. They are also somewhat unusual in that they stock their burrows with dead as well as paralysed insects (because they are providing food continuously, freshness over an extended period is less important than it is for other wasps). Females may compete for dead insects: in the words of J. Parker (as quoted by Bohart & Menke, 1976): "The struggles at the mouth of the burrow for the possession of a dead insect are frequent and furious, the contestants grappling and rolling over and over on the sand. Frequently it happens that the prey is dropped in the struggle, and while the pair of contestants are rolling on the sand a third wasp comes along and settles the quarrel by quietly carrying off the coveted treasure". Of the other bembecin genera, species of the genera Stictiella and Editha are predators of Lepidoptera. Editha species are found in southern South America, and include the largest of the bembecins. Xerostictia longilabris, a member of the Stictiella-group from southern North America that gets its own genus, has been recorded stocking its burrow with ant-lions and flatid bugs (Evans 2002). Members of other genera may also stock their burrows with prey other than flies, though in the majority of cases they do not do so exclusively (Evans 2002).

Sand wasp, possibly Microbembex monodonta, burying the entrance to her burrow. Copyright Tim Lethbridge.

Many bembecins (most notably in the genera Microbembex and Bembix) nest gregariously, and may form sizable colonies. Species of Bembix will maintain the same colony from year to year. In some species, such as B. pallidipicta, the females may dig accessory burrows near the main burrow without laying eggs in them; these have been presumed to act as decoys to discourage parasitoids or kleptoparasites. Males perform prolonged 'sun dances' above the colony in which they fly in circles or figures-of-eight, looking out for attractive females (O'Neill 2001). Males of many species have a serrated mid-femur that they use to hold down the female's wings while mating; in species without these leg serrations, mating may involve more of a struggle (Bohart & Menke 1976). The male produces a loud chirping during mating, presumably just to add atmosphere.

REFERENCES

Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World: a generic revision. University of California Press.

Evans, H. E. 2002. A review of prey choice in bembicine sand wasps (Hymenoptera: Sphecidae). Neotropical Entomology 31 (1): 1-11.

O'Neill, K. M. 2001. Solitary Wasps: behavior and natural history. Cornell University Press.

Continued Adventures with Rake-legged Mites

Dorsal view of Neocaeculus kinnearae; photo modified for Taylor (2014).

It's been a noteworthy couple of weeks here at chez CoO. My contract at the university has reached its end, and I've become a Free Agent ('free' as in 'I don't get paid for any of this stuff'). That bit in the sidebar where I describe myself as "an entomologist working on the identification of terrestrial invertebrates" is, for the nonce, more of an aspiration. Or, to put another way, a lie. And my lunch breaks have gotten a lot more generous. Time will tell how long this state of affairs will continue, but in the meantime, there's still research to be done and papers to produce. Which segue's nicely into the subject of today's post: my newest paper, "Two further Neocaeculus species (Acari: Prostigmata: Caeculidae) from Barrow Island, Western Australia".

Back in December, I commented on the publication by myself and my colleagues of the rake-legged mite Neocaeculus imperfectus. In the comments for that post, I indicated that N. imperfectus was not the only new rake-legged mite species that I had on hand*. As it turns out, there was a total of five different species of caeculid in our collection (including N. imperfectus). Two of these were species that had already been described by Coineau & Enns (1969), but two more were new. The first of these I have dubbed Neocaeculus kinnearae, after my colleague Adrianne Kinnear, to whom I owe all of my understanding of mites. Adrianne first identified many of the Barrow Island mites, and trained me in mite identification prior to her recent retirement. Neocaeculus kinnearae is very similar to a species originally described from the Kimberley region of northern Western Australia, N. knoepffleri (some of you not familiar with Australian geography may still know the Kimberley as one of the few regions that diamonds come from). The two primarily differ in size (N. kinnearae is distinctly smaller) and while the large leg-spines in N. knoepffleri end in sharp points, those of N. kinnearae are blunter. Interestingly, N. knoepffleri is also present on Barrow Island, which did lead me to wonder if the specimens I ended up assigning to N. kinnearae might be just smaller individuals of N. knoepffleri. But I have seen several specimens of both from Barrow by now, and I'm yet to see any overlap between the two, so I do think that they are both good species.

*You may wonder why, if I knew that there was more than one species present, I didn't just put them all in the one paper. The reason was that, because I had never prepared a mite taxonomic paper before, I wanted to just do the one species at first as a test run, and then do the others once I felt a bit more confident that I knew what I was doing.

Neocaeculus knoepffleri also has a particular claim on my affections in that I've seen it alive. This is a bigger deal than it sounds: caeculids are cryptic and slow-moving, so observing them in the field is notoriously difficult. I already explained in my earlier post how I've never seen Neocaeculus imperfectus out and about, despite it turning up in samples in numbers that suggest absolute plagues of the things. But on my last trip to Barrow back in March, we were out collecting at night near the shore when I spotted a small grey point on a grey rock move slightly. Closer inspection revealed a caeculid sitting on the rock with spiny front legs outstretched, in the classic caeculid ambush pose. If I moved my forceps close to it, the mite would turn towards them as if warding them off. Having found one, I looked a bit further, and found several more, all perfectly camouflaged against the rock.

Dorsal view of Neocaeculus nudonates; original version of photo used in Taylor (2014).

The second new species was the smallest caeculid I had seen from Barrow so far, but was none the less remarkable. For a start, it didn't have the slender spines on its front legs of other rake-legged mites; instead, the spines were modified into rounded paddles. There are a few other caeculids known to have this feature (one of them, Neocaeculus bornemisszai, is another Kimberley species now also known from Barrow). Where their habits are known, it seems to be an adaptation for digging in sand, something that I can assure you Barrow Island has no shortage of. The other interesting feature of the new species is that the dorsal plates that usually cover the rear half of the body in other caeculids are unusually small. It was the appearance given by these small plates that inspired the name I gave this species: nudonates, from the Latin nudus, naked, and nates, buttocks. This is, literally, the bare-arsed mite.

So Barrow Island is now officially home to five different species of caeculid mite (and shortly after submitting this paper, I came across specimens of a sixth). While only one of these species has actually been observed alive, we can still infer some things about the likely habits of the others. Two, Neocaeculus bornemisszai and N. nudonates, are probably diggers of some sort. They may prefer different substrates: while N. nudonates has the afore-mentioned reduced plates, N. bornemisszai is more heavily armoured than usual. There may be a difference in preferred substrate between N. knoepffleri and N. kinnearae as well, to explain the blunter leg spines of the latter. In the paper, I suggested that N. imperfectus was probably a climber on vegetation, to explain it mostly being found in suction samples while the other species all came from pitfall traps. Since the paper was submitted, I have seen a few N. kinnearae specimens in suction samples, but I still think that it is most likely not a climber because these have been few and far between.

The other main point to be made is that there are probably a lot more caeculids out there than we realise. Though only eight species of caeculid have been recorded from Australia so far, Barrow Island is home to at least six (one of which may or may not be a further undescribed species). Caeculids are generally regarded as associated with warmer, drier habitats, and Australia is almost entirely warmer, drier habitat. I would not be surprised if, once we looked further, we would find a lot more undescribed caeculids out there.

Stunning Central American Millipedes

Blue cloud forest millipede Pararhachistes potosinus, copyright Luis Stevens.

For my semi-random selection of taxon to write about this week, I drew the millipede family Rhachodesmidae. Rhachodesmids are members of the millipede group called the Polydesmida, characterised by the presence of lateral keels on each segment of the body. The presence of these keels had lead to platydesmidans sometimes being referred to as 'flat-backed millipedes' though depending on how strong the keels are, not all species are necessarily 'flat-backed'.

In an earlier post on millipedes, I stressed the importance of genitalia in characterising millipedes, and the Rhachodesmidae are no exception. In polydesmidans, it is the front pair of legs on the seventh segment that is modified into the gonopods in males (with one notable exception that I may refer to later). Gonopods of rhachodesmids lack the solenite or coxal spur found in many other polydesmidans, and the inner side of the gonopod has a distinct elongate or oval concavity that is densely setose. Other noteworthy features of rhachodesmids are that they are often relatively large, with a conical terminal segment and more or less thickened rims to the lateral keels (Loomis 1964).

An unidentified rhachodesmid, copyright Sergio Niebla.

Beyond that, rhachodesmids become a little more difficult to characterise. Though they are not a widespread group, being restricted to Mexico and Central America, they are very diverse in appearance. Loomis & Hoffman (1962) commented that, "Rhachodesmoids collectively are members of a group notable for great variability and the development of bizarre features. Among their ranks we find millipeds which are bright blue, green, orange, and even pure white as adults; here the gonopod structure ranges from the normal polydesmoid appearance down to monoarticular fused remnants. Body form varies from a slender juliform shape to broad, flat, limaciform contour. Within the limits of this so-called single family occurs more variation than in all of the remaining polydesmoids." They also noted that the group was in need of review, something that apparently remains undone to this day (though there is someone working on it). If the photographs I've commandeered in this post are any indication, this is definitely a group that deserves more love.

Paratype of Tridontomus procerus, from Loomis & Hoffman (1962).

Loomis & Hoffman (1962) made their comments in comparing the Rhachodesmidae to another Central American polydesmidan family they were then describing as new, the Tridontomidae, and if I'm referring to the rhachodesmids then I should probably give a shout-out to these remarkable beasts as well. So far as I've found, this family is still only known from two species, Tridontomus procerus and Aenigmopus alatus, from Guatemala. Not only is the appearance of tridontomids striking, with long spinose processes on either side of the body, but the genital morphology of one species, A. alatus, is especially bizarre: it doesn't have any where it should. Where males of other polydesmidans have the legs of the seventh segment modified into gonopods, those of A. alatus have a perfectly ordinary pair of walking legs. In normal polydesmidans, the gonopods are used to transfer sperm from seminal processes on the coxae of the second pair of legs to the female's genital opening (more details are available here), but obviously Aenigmopus must do things differently. The seminal processes are still present, and the second legs themselves are thickened compared to other millipedes; it is possible that they are somehow used to transfer sperm directly from process to female without the use of gonopods. However it does it, there is no question that Aenigmopus is unique in the world of polydesmidans.

REFERENCES

Loomis, H. F. 1964. The millipeds of Panama (Diplopoda). Fieldiana: Zoology 47 (1): 1-136.

Loomis, H. F., & R. L. Hoffman. 1962. A remarkable new family of spined polydesmoid Diplopoda, including a species lacking gonopods in the male sex. Proceedings of the Biological Society of Washington 75: 145-158.