Field of Science

Colpochila: The Chafing of a Mega-genus

Just a few weeks ago, I discussed the melolonthines, a hyperdiverse group of beetles including the chafers that have historically presented something of a taxonomic challenge. In the comments on that post, Adam Yates brought up one aspect of the difficulties presented by this group that I hadn't gotten around to discussing. This is the presence among melolonthines of a number of what may be called 'mega-genera', large genera containing literally hundreds of species that defy attempts to break them down into more manageable units. So on that note, it's only appropriate that I move on to an example of one of these mega-genera, Colpochila.

Colpochila obesa, from Insects of Tasmania.


Colpochila is an Australian genus of melolonthines belonging to a group currently recognised as the tribe Liparetrini (Britton 1986) though readers of the earlier post may recall that relationships between Australian melolonthines and taxa elsewhere in the world remains something of an open question. Liparetrins are, on the whole, a fairly generalised group: characters of the group include a lack of metallic coloration, a labrum which sits underneath and is not fused to the clypeus, simple claws, and relatively broad hind tibiae that end in a pair of widely separated spurs that are placed one above and one below so that the tarsus when moved from side to side can move between the spurs. The two largest genera in the tribe, by a significant margin, are Colpochila and Liparetrus. Somewhere in the region of 130 species are currently recognised in Colpochila whereas Liparetrus is even more diverse. However, both genera were referred to by Britton (1986) as 'polythetic': that is, both represent assemblages of species that, while clearly connected to each other overall, are difficult to characterise from a diagnostic perspective. Species of the genus possess enough features in common that we can readily recognise them as related but it is difficult to drill down on any individual feature or set of features that is shared between all species without exception. Similarly, while I can say from experience that it is generally easy to tell at a glance whether a given species is a Colpochila or a Liparetrus, it is a lot harder to actually define what separates the two genera. The most obvious distinction is size: Colpochila species are relatively large chafers, over a centimetre in length, whereas Liparetrus are smaller. Other features that each separate most Colpochila species from most (though not all) Liparetrus are circular eyes (most Liparetrus have eyes with flattened edges in back so the eye is closer to semi-circular), antennae with more segments in the terminal club, longer elytra that leave less of the end of the abdomen exposed, and hind coxae without the translucent margins found in many Liparetrus.

The lifestyles of Colpochila species are still not very well known. As with other melolonthines, most of the life is spent underground with mature adults only emerging very briefly to breed. The active adults fly at night and may be attracted to lights; it seems unclear whether they feed at maturity. This genus is mostly found in drier habitats such as open woodland, grasslands or semi-desert (mind you, this is Australia we're talking about; drier habitats are 90% of what's going). Of the known species, over half are found in Western Australia.

A second Colpochila species, from Friends of Queens Park Bushland.


So why are Colpochila and other melolonthine mega-genera so diverse? It should be noted that straight geographical and/or ecological divergence does not appear to be the reason: not only is it possible to find multiple species of a single genus in one location but one may even collect very similar species together. It might be that the diversity of the mega-genera is artefactual, a reflection of the failure of taxonomists to properly identify relationships: any study that wanted to explain their diversity would have to study their phylogenetic relationships with related smaller genera to confirm their evolutionary coherence and/or age of divergence. However, if the current generic classification of melolonthines reflects a real evolutionary pattern, a potential explanation was proposed by Britton (1986). Adult melolonthines do not emerge immediately upon maturing but remain dormant underground awaiting a suitable environmental signal such as rainfall. However, rainfall in the arid zone at any one time is often uneven. Dormant beetles at one spot may feel the urge to emerge while others nearby may be left to wait for the next shower. The first wave will have died off before the second wave emerges, and their offspring will not yet be mature. As a result, sub-populations in a single region may become temporally staggered allowing the possibility of divergence via genetic drift. Eventually, their emergence times may drift back into sync but by then they may no longer be able to breed successfully. Could this be the reason why so many species may be found in a single location or may other factors be more significant?

REFERENCE

Britton, E. B. 1986. A revision of the Australian chafers (Coleoptera: Scarabaeidae: Melolonthinae) vol. 4. Tribe Liparetrini: genus Colpochila. Australian Journal of Zoology, Supplementary Series 118: 1–135.

Austrotritia: Jack-in-the-Box Mites

We just keep coming back to the oribatids, don't we?

In an earlier post, I introduced you to Oribotritia, one of the genera of box mites. These, you may recall, are the armoured mites that have evolved the ability to curl the front of the body under themselves and tuck back their legs to form a solid case (in the Oribotritiidae, that mechanical defense is supplemented by the production of a defensive chemical, chrysomelidial, from glands in the cuticle—Shimizu et al. 2012). In the earlier post, I also gave you a quick overview of the families of what are known as the 'true' box mites. Today's post is for another component of the family Oribotritiidae, the genus Austrotritia.

Austrotritia lebronneci, copyright R. Penttinen.


Austrotritia accounts for nearly twenty species of box mite, the great majority of which are found in Australasia and southern and eastern Asia (Liu et al. 2009). Outliers are A. engelbrechti in South Africa, A. herenessica in the Canary Islands and, most unexpected of all, A. finlandica in Finland. Austrotritia differs from all other oribotritiids except the small Bornean genus Terratritia in lacking any division between the genital and aggenital plates on the underside of the body. The distinction between Austrotritia and Terratritia perhaps requires reassessment: Niedbała (2000) distinguished them by the presence of five-segmented palps and a single pair of exobothridial setae in Austrotritia versus three-segmented palps and two pairs of exobothridial setae in Terratritia (the bothridia are the structures bearing large sensory setae on the prodorsum of the mite; exobothridial setae are thus setae sitting alongside the bothridia). However, Liu & Zhang (2014) redescribed the widespread species Austrotritia lebronneci as having three-segmented palps but only a single pair of exobothridial setae. Note that classification of oribatids has mostly been conducted from a diagnostic rather than a phylogenetic perspective; it would not surprise me if Terratritia turned out to be a derived subgroup of Austrotritia.

Schematic of jump performance by Indotritia cf. heterotrichia from Wauthy et al. (1998); the solid line represents observed jumps, the dashed lines modelled jumps. Line drawings represent (a) body posture when beginning jump, (b) rotation during jump, and (c) enclosed posture after jumping.


As well as the aforementioned defenses standard for box mites, Austrotritia and the related genus Indotritia stand out from other oribotritiid genera in that at least some species have the ability to jump. The mechanics of jumping were described for a species of Indotritia by Wauthy et al. (1998) who recorded the mites jumping nearly a centimetre in height over a distance of just under an inch (for perspective, the mite itself is about half a millimetre in length). Jumping was preceded by compressing the notogaster while raising the ventral plates under the opisthosoma, together with lowering the prosoma and bringing the legs together under the body. Small hooks at the end of femur of the first pair of legs were used to catch ridges on the side of the prodorsum in order to hold the body compression. The force for the jump was presumably supplied by the release of the hydraulic compression of the body fluids when the legs disengaged from the prodorsum, propelling the mite backwards while the body rolled forwards: essentially, the mite would star-jump away. The mite would curl up after jumping to lie in an enclosed state.

Whether all Austrotritia species are jumpers is not entirely certain. The femoral hooks that seem to play a significant role in jumping have not been described in all species. However, it is not clear if this lack of observation represents an actual absence or whether this minute feature has simply been overlooked. I also wonder whether the aforementioned fusion of the ventral plates in Austrotritia is related to their jumping abilities (Indotritia species also have the genital and aggenital plates fused anteriorly though they retain a degree of separation at the rear of the plates; non-jumping Oribotritia have the plates entirely separated). As always, there's still a lot we could potentially find out.

REFERENCES

Liu, D., J. Chen & G. Qiao. 2009. Review of Austrotritia (Acari: Oribatida: Oribotritiidae), with descriptions of two new species from China. Zootaxa 2144: 54–64.

Liu, D., & Z.-Q. Zhang. 2014. Redescription of Austrotritia lebronneci (Oribotritiidae) and descriptions of two new species of Euphthiracaridae (Acari, Oribatida) from Australian region. International Journal of Acarology 40 (1): 43–51.

Niedbała, W. 2000. The ptyctimous mites fauna of the Oriental and Australian regions and their centre of origin (Acari: Oribatida). Polskie Towarzystwo Taksonomiczne: Wrocław (Poland).

Shimizu, N., R. Yakumaru, T. Sakata, S. Shimano & Y. Kuwahara. 2012. The absolute configuration of chrysomelidial: a widely distributed defensive component among oribotritiid mites (Acari: Oribatida). Journal of Chemical Ecology 38: 29–35.

The Cervini: Deer of Temperate Eurasia (and Beyond)

A couple of years back, I presented you with a post giving a quick overview of the classification of deer. For this post, I'm going to look a bit closer at a particular subgroup of deer: the species of the tribe Cervini.

Wapiti Cervus canadensis, photographed by Mongo.


For most people outside the Americas, a member of the Cervini will probably represent the first image that comes to mind when picturing a deer. The same goes for many Americans, for that matter, though in that part of the world they face a bit more competition. Cervins are the most diverse group of deer in temperate Eurasia, with representatives also being found in northernmost Africa, North America, India and southeast Asia (as well as introduced species in Australasia). The Monarch of the Glen was a cervin: specifically, a red deer Cervus elaphus. Bambi, in his Disney film incarnation, was also a cervin, a wapiti C. canadensis (in his original literary form, probably less familiar to modern audiences with little interest in Austrian novels about all the miserable ways that animals can die, he was a roe deer Capreolus capreolus and so not a cervin) (Edit: Scratch that, he's a apparently a non-cervin white-tailed deer, see comment below). The group has long been recognised by features of the skull and leg bones, and also is well supported by molecular data (Heckeberg 2020). Males produce antlers with multiple branches (at least in typical individuals) with the branches or tines usually directed forwards from the main shaft of the antler (the Père David's deer Elaphurus davidianus differs from other cervins in having the tines directed rearwards). The first of these branches, the brow tine, usually originates close to the base of the antler. In a number of Asian species, such as the chital Axis axis and sambar Cervus unicolor, there is usually on one more branch on the antler so each antler ends with three points. Species with such antlers are generally found in dense forests and their simpler antlers may represent an adaptation to these habitats (Heckeberg 2020). Other cervin species may have more extensively branched antlers with a tendency for antler complexity to correlate with overall body size; the largest living cervins, the red deer and wapiti, also have the most branched antlers. Larger extinct species had even more extravagant headgear with the apex of insanity being perhaps the bush-antlered deer Eucladoceros dicranios of the lower Pleistocene of Europe: each antler of this species might carry a dozen points.

Skull of Eucladoceros dicranios, photographed by Aldo Cavini Benedetti.


To describe the classification of cervins as having recently been in a state of flux is something of an understatement. A conservative presentation of the group may refer to thirteen or fourteen living species in four genera (e.g. Macdonald 1984). More recent authors, however, might refer to up to ten genera and nearly forty species. In a way, this difference is not really as dramatic as it may seem: multiple subspecies have long been recognised for most cervin species and some authors have argued for the recognition of many of these 'subspecies' as distinct species. Classification at generic level has mostly been affected by recognition that the genus Cervus as previously recognised is not monophyletic. Most recent authors agree on the recognition of at least four genera of Cervini (Cervus, Dama, Axis and Rucervus) with two further genera (Rusa and Elaphurus) also commonly recognised.

Persian fallow deer Dama mesopotamica, copyright Rufus46.


The genus Dama is usually recognised as including two species, the fallow deer D. dama and Persian fallow deer D. mesopotamica. These species are readily distinguished from other cervins by the form of their antlers which are distally palmate. Palmate antlers are also characteristic of the extinct giant Irish elk Megaloceros giganteus and many recent authors have regarded the two as closely related. The white spots that many deer species possess when young are commonly retained by fallow deer into adulthood though the coat will often become darker and the spots disappear during winter. Melanistic and leucistic individuals of fallow deer are also common. Defining the native range of the fallow deer is a bit of a tricky question. This inhabitant of open woodlands is currently widespread in Europe but was probably restricted to a region of the eastern Mediterranean during the last ice age. Its current range in northern Europe may in large part be the result of human transportation. The fallow deer has also been widely introduced elsewhere: herds may now be found in numerous locations in Africa, Australasia, North and South America. The Persian fallow deer, in contrast, is now endangered, its range restricted to a small number of localities in Iran. Indeed, it was once thought to be extinct prior to the rediscovery of a population of about two dozen individuals in the mid-1950s; the current population is perhaps only a few hundred.

Thorold's deer Cervus albirostris, copyright Heather Paul.


The genus Cervus in its current, more restricted sense includes the red deer and wapiti as well as the sika C. nippon* of eastern Asia. Sika are generally smaller than the other two species and, like fallow deer, usually retain the juvenile spots into adulthood. Excluding occasional small accessory branches, the antlers of sika also possess no more than four tines (Heckeberg 2020) in contrast to the commonly further branched antlers of red deer and wapiti. Four-tined antlers are also characteristic of the Thorold's or white-lipped deer C. albirostris, an inhabitant of the Tibetan Plateau that has sometimes been treated recently as the only representative of a separate genus Przewalskium. White-lipped deers have broad, cow-like hooves for navigating the steep, rocky slopes of their homeland. More commonly accepted classification-wise is the separation of two species found in southern Asia, the rusa C. rusa and sambar C. unicolor, as the genus Rusa. Both these species have three-tined antlers and their fawns lack spots.

*Commonly referred to as the sika deer. 'Sika' (or, as it's more commonly transliterated these days, 'shika') is Japanese for deer, so the common vernacular name of Cervus nippon is, indeed, 'deer deer'. The same issue arises for the rusa deer in Malay.

Chitals Axis axis, copyright Charles J. Sharp.


Axis is a genus of four species of smaller forest-dwelling deer found in southern Asia. Antlers are generally three-tined with the upper beams curving inwards towards each other. The chital remains spotted at maturity whereas the other species loose their spots. These species include the hog deer A. porcinus, named for its low, short-legged build, and two closely related insular species. Recent years have seen some authors separate the hog deers as a separate genus Hyelaphus, restricting Axis to the chital, owing to molecular phylogenies casting doubt on the genus' monophyly. However, it seems that these studies may have been mislead by a contaminated sample for the hog deer (Gilbert et al. 2006) and other studies have retained a monophyletic Axis. The thamin Rucervus eldii and barasingha R. duvauceli are also found in southern Asia where they tend to be associated with marshy habitats. Their antlers curve outwards then inwards to form a bow-shaped curve; those of the thamin are three-tined whereas the barasingha possesses further tines, sometimes up to ten on each antler. Again, some studies have questioned the monophyly of Rucervus and suggested the thamin be moved to a separate genus Panolia.

Père David's deers Elaphurus davidianus, copyright Peter O'Connor.


Finally, there is Père David's deer, arguably the weirdest of all the cervins, most often placed in its own genus Elaphurus but sometimes included in Cervus. By the time this species became known to European naturalists, it was already extinct in the wild, surviving only as a herd kept in a hunting garden near Peking belonging to the emperor of China. This herd was exterminated during the Boxer Rebellion but specimens that had been transported to Europe saved the species from total extinction. It is now widely kept in captive herds and has also been returned to the wild in a couple of locations in China. Père David's deer has a number of features that make it stand out from other deer: as well as the aforementioned backwards antlers, it has wide, splayed hooves and a remarkably long tail. But in other regards, Père David's deer is not anywhere as weird as it should be. In particular, its karyotype is very similar to that of the red deer: close enough, in fact, that not only are the two species capable of hybridising in captivity but the resulting hybrids are fully fertile (such matings are unlikely in the wild owing to the two species normally having different breeding seasons). Heckeberg (2020) found that Père David's deer was associated with Cervus species in analyses of nuclear genes and cranial characters but with Rucervus species in analyses of mitochondrial genes and dentition; other authors had previously found similar results. It has been suggested that these schizoid tendencies with regard to phylogenetic analysis might indicate a hybrid origin for Père David's deer from ancestors related to the wapiti on one side and the thamin on the other. Such a hybridisation event would have happened some time ago—fossils related to Père David's deer seem to date back at least to the late Pliocene—allowing enough time to pass for the new population to develop its own idiosyncracies not acquired directly from either parent.

Sticking Your Sulphur on the Outside

The ability to obtain energy from sunlight through photosynthesis is a feature of a range of bacterial lineages, using a number of different processes and growing under a variety of different conditions. Perhaps the best known such group is the oxygen-producing blue-green algae or Cyanobacteria, but there are other photosynthetic bacteria that do not release oxygen. One such group is the purple sulphur bacteria of the Ectothiorhodospiraceae.

Individual Ectothiorhodospira mobilis, from Trüper (1968).


Purple sulphur bacteria are members of the hyperdiverse array of bacteria known as the Proteobacteria, specifically of a subgroup known as the Gammaproteobacteria (other notable Gammaproteobacteria include such luminaries as the various Pseudomonas species, the plant-attacking Xanthomonas, and perhaps the single most intensely studied bacterial species of all, Escherichia coli). They are found growing under anoxic conditions, using light energy to assimilate carbon via the oxidation of sulphides to organic sulphur, which is in turn further oxidated to sulphate. Purple sulphur bacteria can be divided between two families, the Chromatiaceae and Ectothiorhodospiraceae, that may be distinguished by how they deposit the sulphur globules produced during photosynthesis. In Chromatiaceae, the sulphur globules are retained within the cell membrane but in Ectothiorhodospiraceae, they are deposited externally (one species of Ectothiorhodospiraceae, Thiorhodospira sibirica, does deposit sulphur both internally and externally, but the internal globules are restricted to the peripheral region of the cell within the periplasmic space). Photosynthetic pigments are bacteriochlorophyll a or b, together with carotenoids; these pigments are attached to intracellular membranes appearing as lamellar stacks. Ectothiorhodospiraceae species are found in marine and other saline habitats, often in environments with a more or less alkaline pH. Species of the genus Halorhodospira, which have been found in salt and soda lakes, require exceedingly saline conditions, being unable to grow at total salt concentrations below 10%.

Cross section of Ectothiorhodospira mobilis showing photosynthetic membrane stack, from Trüper (1968).


Though the genera Halorhodospira and Thiorhodospira are strictly anaerobic and invariably photosynthetic, some species of the genus Ectothiorhodospira are able to obtain energy heterotrophically from organic compounds, and may grow under microaerobic conditions in the dark. The range of organics they can utilise in this way is limited to relatively simple compounds: they generally cannot break down carbohydrates, for instance, but they can grow on organic acids such as acetates. Molecular analysis has also indicated the inclusion in the Ectothiorhodospiraceae of a number of non-photosynthetic bacteria. The species Arhodomonas aquaeolei was originally isolated from brine from a subterranean oil reservoir; it breaks down organic compounds using oxygen or nitrate but has the same limitations to simple molecules as Ectothiorhodospira. It seems easy to imagine it evolving from an Ectothiorhodospira-like ancestor but losing its photosynthetic capabilities due to its subterranean habitat, like an animal in a cave losing its eyesight. The genera Nitrococcus and Thioalkalivibrio are lithoautotrophs (that is, they synthesis organic compounds like photosynthetic forms but use the energy from chemical reactions using minerals rather than from light) and generally aerobic (at least one strain of the species Thioalkalivibrio denitrificans is facultatively anaerobic). Thioalkalivibrio species oxidise sulphur, sulphides and other sulphur-containing compounds whereas Nitrococcus convert nitrate to nitrite. Despite their lack of photosynthetic abilities, Nitrococcus still carry indications of their photosynthetic ancestry in the presence of tubular intracellular membranes, the repurposed derivatives of the original stacks.

REFERENCE

Brenner, D. J., N. R. Krieg & J. R. Staley (eds) 2005. Bergey’s Manual of Systematic Bacteriology 2nd ed. vol. 2. The Proteobacteria pt B. The Gammaproteobacteria. Springer.

Chondria: Turf of the Surf

Of the major groups of multicellular algae (or 'seaweeds' in the common parlance) found in the world today, the red algae are unquestionably the most speciose. In this post, I'm looking at a widespread genus of red algae going by the name of Chondria.

Chondria coerulescens, copyright Alan Thurbon.


Chondria is a genus of fifty or more known species of marine algae belong to the Rhodomelaceae, one of the most diverse families of red algae, found in tropical and temperate regions of the world. Species vary in size and are found in a range of habitats from intertidal to subtidal. They may live attached to rock or growing over other seaweeds. Turfs of Chondria may form a significant part of local habitats, but like many smaller red algae they tend not to receive a great deal of attention from humans (I did come across webpages referring to it as a weed in marine aquaria). In the majority of Chondria species, the thallus is erect; more rarely, it grows prostrately against its substrate or free-floating. The thallus is attached to the substrate by a discoid holdfast or by haptera growing from stolons. The greater part of the thallus is filamentous and more or less irregularly branched. The branches may be cylindrical and compressed; the younger branches are often constricted at their bases. The tips of the branches may end in a depression or in a tapering filament. Structure-wise, filaments are solid in cross-section without internal hollows. A central axial cell is surrounded by a ring of five pericentral cells, with the outside of the filament composed of smaller cortical cells.

Like other red algae, Chondria species have a complicated triphasic life cycle. The haploid gametophytes are dioecious: that is, there are separate male and female individuals. Males produce flat, disc-shaped or slightly lobed spermatangia that release male gametes. Female gamete-producing structures grow from the base of lateral filaments on the thallus; fertilised female gametes grow into a diploid, more or less ovoid cystocarp that remains attached to the parent gametophyte. Diploid spores released by the cystocarp grow into independent tetrasporophytes. These produce haploid spores by meiosis that will be released and grow into new gametophytes, and the cycle begins again.

REFERENCE

Womersley, H. B. S. 2003. The Marine Benthic Flora of Southern Australia. Rhodophyta—Part IIID. Ceramiales—Delesseriaceae, Sarcomeniaceae, Rhodomelaceae. Australian Biological Resources Study: Canberra, and State Herbarium of South Australia: Adelaide.

Crystal Butterflies of the Sea

All chains of life in the open ocean are ultimately dependent on plankton. Photosynthetic micro-plankton convert the energy of sunlight into their own stores that are in turn commandered by animal plankton through consumption and digestion. Both animal and photosynthetic plankton provide food sources for larger animals, both plankton and nekton, and even deeper dwelling organisms may take their sustenance from the rain of planktonic corpses settling from above. A wide range of animal lineages may be identified among oceanic plankton, one of the most prominent being the gastropod group known as the Thecosomata.

An orthoconch thecosomatan, Clio pyramidata, copyright Russ Hopcroft.


The Thecosomata are small gastropods, rarely exceeding a couple of centimetres in size at their largest. Many marine molluscs will spend at least part of their lives as planktonic larvae but relatively few mollusc groups have taken the route that the Thecosomata have, remaining part of the plankton through their entire life cycle. They maintain their position in the plankton by means of broad expansions of the foot on either side of the mouth, known as parapodia. The appearance and movement of these parapodia have given the Thecosomata the vernacular name of 'sea butterflies'. They also inspired the name Pteropoda ('wing-foot'), used for a clade that unites the Thecosomata with another group of planktonic gastropods, the Gymnosomata. Historically, many authors have questioned the association of the pteropods, in part because of the differing dispositions of the parapodia in the two component groups (Gymnosomata, commonly known as 'sea angels', have the wings of the parapodia located further back on the body rather than around the mouth). Nevertheless, more recent studies have corroborated pteropod monophyly (Klussmann-Kolb & Dinapoli 2006). The Thecosomata themselves fall between two major sublineages, known as the Euthecosomata and Cymbulioidea (or Pseudothecosomata). Members of the Euthecosomata have well-divided parapodia and the viscera are contained within a delicate, translucent, calcareous shell. In some euthecosomes such as the genus Limacina, this shell is coiled like that of other gastropods, but in others the shell has become straight and bilaterally symmetrical, being conical or globular with lateral projections. Recent phylogenetic analysis suggests that the straight-shelled sea butterflies may form a single monophyletic lineage known as the Orthoconcha* (Corse et al. 2013). In the Cymbulioidea, the parapodia are fused around the front of the animal to form a single swimming plate. Of the three families of cymbulioids, the Peraclidae have a calcareous shell as in the euthecosomes. The Cymbuliidae shed the larval calcareous shell over the course of their development and replace it with a pseudoconch, a hardened gelatinous, slipper-shaped structure that is still secreted by the mantle. In the third family, the Desmopteridae, the shell has been lost entirely.

*In the early days of invertebrate palaeontology, pteropod affinities were suggested for a number of groups of early Palaeozoic conical shells of uncertain affinities, such as the hyoliths and tentaculitoids. It is worth noting that, at the time, the pteropods themselves were often thought to represent a distinct molluscan class independent of the gastropods. Such proposals have long since fallen by the wayside. Not only is there nothing to connect such Palaeozoic forms with modern pteropods but the most superficial of resemblances in overall shape to certain Orthoconcha, but all indications now are that the Orthoconcha themselves did not evolve until some time in the Cenozoic (Corse et al. 2013), leaving a gap of some hundreds of millions of years between them and their erstwhile forebears.

Cymbulia peronii, copyright Vincent Maran.


Live sea butterflies feed on a wide range of organisms, including both micro-algae and other planktonic animals. The ancestral radula is reduced or lost and prey is captured by means of a mucous web, globular in euthecosomes and a funnel-shaped sheet in cymbulioids (Gilmer & Harbison 1986). This web may be absolutely gigantic relative to the animal itself, reaching up to two meters in diameter. While the web is extended, the sea butterfly does not swim actively but hangs suspended in the water column below, drawing food into the mouth by means of tracts of cilia on lobes of the foot. A further mucous array may trail away from the animal containing faecal particles and/or particles rejected as food; this may keep such particles from re-entering the feeding web. Should the animal be disturbed, the mucous web is rapidly ingested or abandoned before swimming away. Sea butterflies have commonly been referred to as suspension feeders but Gilmer & Harbison (1986) noted that a case could potentially be made for considering them as predators. Though micro-algae make up a large proportion of thecosome gut contents, the mucous web allows them to also capture active prey such as copepods that might have otherwise eluded them. It is possible that such prey is in fact more important overall for satisfying the sea butterfly's nutritional requirements. A number of sea butterflies possess brightly coloured mantle appendages that may lure active prey; the faecal trails may also assist in this way.

Limacina helicina, copyright Russ Hopcroft.


Sadly, any discussion of Thecosomata is forced to end on a tragic note. Recent increases in atmospheric carbon dioxide have lead to oceanic waters becoming more acidic than previously, which in turn reduces the concentration of dissolved carbonate. Because carbonate is a vital component of molluscan shells, ocean acidification compromises shell production. Studies of recent thecosome samples show that their shells have become thinner and more porous as acidification increases (Roger et al. 2012). If this trend continues, we may reach a point where shell secretion becomes impossible for these animals, leading to tragic consequences both for the thecosomes themselves and for the countless other organisms ecologically dependent on them. In recent years, concern has been expressed that ecological degredation may mean that we can no longer see butterflies flying in our gardens; their marine analogues are no less vulnerable.

REFERENCES

Corse, E., J. Rampal, C. Cuoc, N. Pech, Y. Perez & A. Gilles. 2013. Phylogenetic analysis of Thecosomata Blainville, 1824 (holoplanktonic Opisthobranchia) using morphological and molecular data. PLoS One 8 (4): e59439.

Gilmer, R. W., & G. R. Harbison. 1986. Morphology and field behavior of pteropod molluscs: feeding methods in the families Cavoliniidae, Limacinidae and Peraclididae (Gastropoda: Thecosomata). Marine Biology 91: 47–57.

Klussmann-Kolb, A., & A. Dinapoli. 2006. Systematic position of the pelagic Thecosomata and Gymnosomata within Opisthobranchia (Mollusca, Gastropoda)—revival of the Pteropoda. Journal of Zoological Systematics and Evolutionary Research 44 (2): 118–129.

Roger, L. M., A. J. Richardson, A. D. McKinnon, B. Knott, R. Matear & C. Scadding. 2012. Comparison of the shell structure of two tropical Thecosomata (Creseis acicula and Diacavolinia longirostris) from 1963 to 2009: potential implications of declining aragonite saturation. ICES Journal of Marine Science 69 (3): 465–474.

The Halictidae: Short Tongues and Waxy Chambers

In an earlier post, I introduced you to the diverse group of bees known as the Halictinae. In this post, I'm going to take a step back and consider the family of bees to which the halictines belong, the Halictidae.

Nomia sp. feeding at a flower, copyright Graham Wise.


The Halictidae are one of the families of what are known as 'short-tongued bees' (the other short-tongued families recognised by Michener, 2007, are the Andrenidae, Colletidae and Stenotritidae). Bees have their mouthparts modified compared to those of other wasps to form a mobile proboscis. The tongue works in three main sections from base to tip. The first two sections work like the upper and lower parts of your arm, or of the arm of a crane, to extend and fold back the proboscis against the underside of the head. The third section beyond these two includes a flexible structure, the glossa, that may be thought of as working like the tongue proper to collect nectar and pollen from the inside of flowers. Somewhat self-explanatorily, this glossa is extremely long and slender in the families of 'long-tongued bees' (the Apidae and Megachilidae) but relatively shorter and broader in short-tongued bees. Naturally, these differences in tongue structure may be reflected in differences in which types of flowers the different types of bees chose to visit. Just to confuse matters, some species of Halictidae may have relatively long proboscides overall, but in this case the extra length is achieved by extending the length of the middle 'arm' section rather than of the glossa itself. The primary features separating Halictidae from the other families of short-tongued bees relate to the structure of particular sclerites incorporated into the proboscis that I'm not going to go into here, but notable points include that the glossa of Halictidae is pointed at the tip and hairs on it are usually branched or bifid at the tips.

Male Halictus tetrazonianellus with proboscis extended (the glossa is the orange structure at the end of the proboscis), copyright Gideon Pisanty.


For the most part, halictids are moderately built bees: neither remarkably slender nor particularly robust. Halictids vary extensively in size: many are small, even minute, but some may be relatively large by bee standards. Coloration is similarly variable, with both metallic and non-metallic species belonging to the family. Members of the genus Nomia (which tend to be relatively large for halictids) often bear contrasting bright bands across the back of the metasoma. Michener (2007) recognised four subfamilies within the halictids: the Rophitinae, Nomiinae, Nomioidinae and Halictinae, with the Halictinae being considerably more diverse species-wise than the other three. Nomioidines have sometimes been included by other authors within the Halictinae but, as there is a general agreement that nomioidines form the sister lineage of the halictines in the strict sense, the question of whether to combine them or not is purely a matter of semantics. Rophitines differ from other halictids in having a relatively large labrum whose tip remains visible between the mandibles when they are closed (other subfamilies have the labrum hidden by the closed mandibles). Rophitines, as well as kleptoparasitic halictines, also have the tip of the labrum simply truncate or rounded; in other subfamilies, the tip of the labrum in females is produced into a distinct process. Rophitines also have the scopa (the array of long pollen-carrying hairs on the hind leg) less developed on the trochanter and femur than on the tibia whereas other subfamilies (excluding, again, kleptoparasitic forms in which the scopa is reduced) generally have the longest scopal hairs on the femur. Nomiines commonly have the third submarginal cell on the wing (if present) as long as the first submarginal cell or at least more than twice the length of the second. In nomioidines and halictines, the third submarginal cell is much shorter. Another notable feature of the last two subfamilies is that the basal vein (the upper of the three veins radiating from the basal midline of the wing) is much more strongly curved near the base than in other bee families; this feature may or may not be discernable in rophitines and nomiines.

Just to show that bees can sometimes get insane: a male of the Colombian species Chlerogella anchicaya, from Engel et al. (2014).


For the most part, halictids construct their nests in burrows in the ground (some halictines nest in rotting wood). Cells of the burrows are generally lined with a wax-like membrane secreted by the parent bee. The membrane is duller and less watertight in Rophitinae than in other subfamilies; one rophitine genus, the southwest North American Protodufourea, appears to not produce such a membrane. Most non-halictine halictids are solitary nesters though some nomiines are known to work communally, and may even show low levels of division of labour. Kleptoparasitism is not known outside the Halictinae.

REFERENCE

Michener, C. D. 2007. The Bees of the World 2nd ed. John Hopkins University Press: Baltimore.