A Neogene Moon

Back when I was a young lad, some time not so long after the end-Cretaceous extinction, we often spent part of the Christmas holidays camped at the estuary beach-front below my great-grandparents' house. Among the things I recall doing there was going out at low tide with my great-grandmother to dig up cockles for lunch. The New Zealand cockle Austrovenus stutchburyi is not an immediate relative of the bivalves of the family Cardiidae known as cockles in Europe but a member of a different bivalve family, the Veneridae. Venerids are shallowly burrowing bivalves that generally live buried below the sand or mud just shallowly enough to extend their short siphons to the surface for filter-feeding.

Dorsal (left) and lateral views of Marama hurupiensis, from Beu & Maxwell (1990).

Because they live pre-buried in this manner in fairly low-energy habitats, venerids have an excellent fossil record. Marama is a fossil genus of a dozen species of venerids known only from New Zealand and Tasmania (Beu & Maxwell 1990; Beu 2012). The genus was first recognised by Marwick (1927) who divided it between two subgenera, Marama sensu stricto and Hina. Both names derive from Maori names for the moon, presumably in reference to the clams' appearance. Marama species are similar in overall appearance to the modern New Zealand cockle, the primary defining characters of the genus reflecting features of the shell hinge. These include the presence of a moderate anterior lateral tooth or tubercle in the left valve. The size of the species varies from the small M. tumida, a bit less than two centimetres in length, to the relatively large M. hurupiensis which reaches six centimetres in length. The shells are sculpted with concentric lamellae, varying from fine and very dense in M. tumida to strong and widely spaced in M. pristina to weak and sparse in M. ovata.

Marama species are known from the Kaiatan to the Nukumaruan stages in the New Zealand stratigraphic system, corresponding to the ealy Late Eocene to the late Pliocene/earliest Pleistocene in the international stratigraphic divisions. Many regions of the world have their own local stratigraphic divisions that may be used in preference to the glocal system for various reasons. In some cases, this may be because of difficulties in correlating the local geological record to global events. There may not be suitable resources preserved for calculating a deposit's absolute age, or a geographically isolated region may lack fossils of cosmopolitan index species. As a result, it may be possible to recognise temporally successive biotas in a region's palaeontological record without being able to tell for sure whether a given biota is (for instance) Eocene or Oligocene. Alternatively, because stratigraphic divisions are commonly based on biotic turnovers such as mass extinctions, the major local biotic events may not exactly line up with the global average (for instance, the characteristic biota of a given geological period may have persisted longer in one region than it did in another). In the case of the New Zealand palaeontological record, Marama was one of a number of molluscan genera that became extinct towards the end of the Nukumaruan in relation to cooling temperatures representing the onset of the Pleistocene ice ages.

REFERENCES

Beu, A. G. 2012. Marine Mollusca of the last 2 million years in New Zealand. Part 5. Summary. Journal of the Royal Society of New Zealand 42 (1): 1–47.

Beu, A. G., & P. A. Maxwell. 1990. Cenozoic Mollusca of New Zealand. New Zealand Geological Survey Paleontological Bulletin 58: 1–518.

Marwick, J. 1927. The Veneridae of New Zealand. Transactions and Proceedings of the New Zealand Institute 57: 567-636.

Rove, If You Want To

Rove beetle Staphylinus erythropterus, copyright James K. Lindsey.

The Staphylinidae, rove beetles and related forms, is an absolutely massive array of insects. In fact, thanks to some relatively recent waves of the redefinition wand, the Staphylinidae is not only the largest recognised family of beetles but the largest family of animals of any kind. It even beats out the Curculionidae weevils that were the previous fore-runners. One might think that such a diverse group of animals would be the subject of extensive attention but that is simply not the case. I've commented before that part of the reason for this neglect is that staphylinids are a simply horrid group to work with but they still deserve a better look.

Devil's coach-horse Ocypus olens in a threat display, from Wildlife Insight. The white blebs visible at the end of the abdomen represent glands producing an unpleasant odour.

The original rove beetles belong to the tribe Staphylinini, a cosmopolitan group with more than 5300 known species and probably many more yet to be described. They are mostly active predators of other arthropods, hence the name 'rove beetle' in reference to their roving habits. One particularly large species (up to about three centimetres in length), Ocypus olens, has garnered the moniker of 'devil's coach-horse'. Several genera are found in association in ants and a termitophilous genus Sedolinus was recently described from South America (Solodovnikov 2006). The exact nature of its association with its termite hosts remains uncertain though it is worth noting that it shows less marked morphological adaptations than other termitophilous staphylinids. The South American Amblyopinus and closely related genera in South America and Australia are found amongst the fur of rodents and small marsupials. Because they are often attached to their host by the mandibles, they were long believed to be parasites feeding on blood or skin secretions. However, further studies found that they do not bite into the host but instead grip to its fur. And rather than feeding on the host itself, they feed on other, actually parasitic arthropods also present on the host (Ashe & Timm 1987).

Edrabius peruvianus, a member of the Amblyopinus group of mammal associates, copyright Stylianos Chatzimanolis.

The classification of Staphylinini is currently in the progress of going through a major shake-up. Not only were many of the taxa within the tribe previously poorly defined, what definition they had was mostly taken from Holarctic taxa. Species found in other parts of the world had largely been classified by finding what Holarctic taxon they most resembled, at least superficially, slotting them therein and then jumping on them until they could be made to fit. A prime example of this awkwardness revolves around the genus Quedius, to which species have been assigned from around the world. Molecular phylogenetic studies have found that a cosmopolitan Quedius represents a polyphyletic grouping (Brunke et al. 2016). Southern Hemisphere taxa assigned to Quedius or believed closely related are not only not immediate relatives of the true European Quedius, but they have been assigned to entirely distinct subtribes representing strongly divergent lineages in the Staphylinini.

REFERENCES

Ashe, J. S., & R. M. Timm. 1987. Predation by and activity patterns of 'parasitic' beetles of the genus Amblyopinus (Coleoptera: Staphylinidae). Journal of Zoology 212: 429–437.

Brunke, A. J., S. Chatzimanolis, H. Schillhammer & A. Solodovnikov. 2016. Early evolution of the hyperdiverse rove beetle tribe Staphylinini (Coleoptera: Staphylinidae: Staphylininae) and a revision of its higher classification. Cladistics 32 (4): 427–451.

Solodovnikov, A. 2006. Adult and larval descriptions of a new termitophilous genus of the tribe Staphylinini with two species from South America (Coleoptera: Staphylinidae). Proceedings of the Russian Entomological Society, St. Petersburg 77: 274–283.

Mesopsocus unipunctatus: an Intriguing Barklouse

I've maintained before that barklice or Psocoptera/Psocodea are the cutest of all insects, an opinion that I still stand by. Nevertheless, their small size and inoffensive habits mean that they don't get the attention that they deserve.

Female Mesopsocus unipunctatus, copyright Tom Murray.

Mesopsocus unipunctatus is a widespread barklouse species in Europe and North America (and possibly in Asia as well where a lack of records may reflect a lack of people looking). It is a relatively large species as barklice go, growing up to about half a centimetre in length. Mature males are fully winged but females have the wings reduced to rudiments and are flightless. Mesopsocus unipunctatus are found living on the bark of trees, primarily on branches rather than on the trunk, and their diet is predominantly made up of the micro-alga Pleurococcus and fungal spores. They are active in early summer: populations in Yorkshire had the first nymphs hatching during April and numbers of individuals reached a peak in late June to early July. The population survived over winter as eggs, laid in clusters of five to eight and covered with a protective layer of hard faecal matter (Broadhead & Wapshere 1966).

Mesopsocus unipunctatus shares much of its range with a closely related species, M. immunis, and the two are often found in association (Broadhead & Wapshere 1966). Differences between the two are slight: M. immunis tends to be paler in coloration but the two species are best distinguished by features of their terminalia. They both feed on the same diet and are active around the same time of year (conversely, other ecologically similar barklice species found in Yorkshire by Broadhead & Wapshere, 1966, were active later in the summer). So how do the two manage to persist without one excluding the other? As it turns out, they differ in oviposition behaviour. Mesopsocus unipunctatus prefers to lay its eggs right at the tips of tree branches whereas M. immunis mostly lays about 25 to 50 cm back from the tip. Mesopsocus immunis also covers its egg masses with a layer of silk in addition to the layer of faecal matter used by both species. These behaviours mean that M. immunis egg masses are better protected from one of their major threats, a mymarid wasp that parasitises them. However, M. unipunctatus compensates for its higher vulnerability to parasitoids through a greater resistance to cold, meaning that a higher proportion of its unparasitised eggs survive the winter. The greater cold resistance of M. unipunctatus means that it may also be found at altitudes and latitudes beyond the range of M. immunis.

Male Mesopsocus unipunctatus, copyright Ken Schneider.

Another feature of M. unipunctatus worth mentioning is that it shows variation in coloration attributed to industrial melanism. This phenomenon is better known in Lepidoptera: you may have heard of one of the most famous animals supposed to exhibit it, the peppered moth Biston betularia. Individuals of M. unipunctatus in England vary in the degree of dark markings on the abdomen, from some that are almost entirely dark through those with a mottled pattern of dark patches and stripes to some in which the dark markings are restricted to the primary transverse stripe on the fourth abdominal segment. The head and thorax are also darker in some individuals than others though it is notable that not all individuals with darkened abdomens also have darkened heads and thoraces (Popescu et al. 1978). Industrial melanism is so-called because this variation in colour pattern is supposed to be related to industrial pollution. It is supposed that the original paler, broken coloration provided camouflage on lichen-covered bark but selection came to favour darker color patterns as trees became blackened with soot. Studies on melanism in M. unipunctatus did indeed find a correlation between the number of dark individuals in a population and the degree of pollution in the environment (Popescu 1979). However, aviary studies of predation rates on M. unipunctatus individuals released into simulated habitats were a bit more equivocable: survival rates of light-coloured individuals were better among branches taken from rural locations but neither morph was definitely favoured among branches from urban environments. Also, darker individuals exhibited faster growth rates in polluted environments than lighter individuals, perhaps due to better absorption of heat despite sunlight being blocked by smog. Are there more dark-coloured individuals in industrial locations because they die less, or because they live more? Another question I don't know the answer to: has M. unipunctatus also reflected Biston betularia in seeing a drop in melanistic individuals with the reduction of smog levels in England in recent decades?

REFERENCES

Broadhead, E., & A. J. Wapshere. 1966. Mesopsocus population on larch in England—the distribution and dynamics of two closely-related coexisting species of Psocoptera sharing the same food resource. Ecological Monographs 36 (4): 327–388.

Popescu, C. 1979. Natural selection in the industrial melanic psocid Mesopsocus unipunctatus (Müll.) (Insecta: Psocoptera) in northern England. Heredity 42 (2): 133–142.

Popescu, C., E. Broadhead & B. Shorrocks. 1978. Industrial melanism in Mesopsocus unipunctatus (Müll.) (Psocoptera) in northern England. Ecological Entomology 3: 209–219.

Psoraceae

Psora decipiens, copyright Troy McMullin.

Just a very quick one today. The photo above is of a member of the Psoraceae, a group of lichens sometimes referred to as 'fishscale lichens'. As their vernacular name indicates, Psoraceae are characterised by a scaly appearance, together with a preference for growing on soil or rock crevices (Ekman & Blaalid 2011). The scaly appearance also gives the family its botanical name: Psora comes from the Greek for 'itch'.

Psora vallesiaca, copyright Leif Stridvall.

Molecular phylogenetic analyses have supported the inclusion of three genera in the Psoraceae, Psora, Protoblastenia and Brianaria (Ekman & Svensson 2014). The last genus was only described recently to include a group of species previously included in a different genus Micarea belonging to an entirely different lichen family, the Pilocarpaceae. Micarea lichens closely resemble Brianaria species in overall appearance but differ in some features including the nature of their algal symbiont. Past authors often assumed that symbiont associations provided little guidance to lichen relationships; it was thought that a germinating lichen fungus would pretty much form a connection with whatever algal species was available. However, more recent investigations have found that the tastes of lichen fungi are more discriminating. Micarea species form associations with small algal cells, four to seven microns in diameter, with thin cell walls that are often found in pairs within the lichen thallus. Brianaria species, in contrast, have larger algal symbionts that are always isolated in the thallus (Andersen & Ekman 2005).

REFERENCES

Andersen, H. L., & S. Ekman. 2005. Disintegration of the Micareaceae (lichenized Ascomycota): a molecular phylogeny based on mitochondrial rDNA sequences. Mycological Research 109 (1): 21–30.

Ekman, S., & R. Blaalid. 2011. The devil in the details: interactions between the branch-length prior and likelihood model affect node support and branch lengths in the phylogeny of the Psoraceae. Systematic Biology 60 (4): 541–561.

Ekman, S., & M. Svensson. 2014. Brianaria (Psoraceae), a new genus to accomodate the Micarea sylvicola group. Lichenologist 46 (3): 285–294.

Tinned Psammon

Psammonobiotus communis, copyright Hugh MacIsaac.

In several previous posts on this site, I have discussed representatives of the remarkable group of organisms that are the Foraminifera. However, forams are not the only group of unicellular amoeboids to encase themselves in a shell. Today, I want to consider another such group, the Psammonobiotidae.

Psammonobiotids are a group of testate amoeboids forming part of (as their name suggests) the psammon, the community of organisms inhabiting the interstitial spaces between sand grains along the edge of the sea. Until the 1960s and '70s, most authors who encountered amoebae tests in marine samples assumed that they were the remains of freshwater organisms washed downstream (Golemansky 2008). Eventually, though, it was realised that there is quite a diversity of amoeboids that not only tolerate salty conditions, they prefer it. The Psammonobiotidae was recognised in the 1970s for a number such organisms. They produce a proteinaceous test without regular scales, the test structure being amorphous or composed of irregular plates. The test is generally more or less flattend to help the organism fit into the narrow spaces between grains. An aperture at one end of the test allows the organism access to the outside world; in many cases, this aperture may be bent to one side to allow the test to lie close to its substrate.

Campascus minutus, from Microworld.

Many psammonobiotids inhabit the supralittoral zone, just above the high tide mark. Groundwater in this region forms the contact zone between fresh water flowing out from under the land and salt water coming in from the sea. As a result, psammonobiotids and other inhabitants of this region need to be able to handle constantly shifting salinity levels. Many interstitial amoeboids can handle variations from 2% salinity in merely brackish waters to 37% in warm tropical seas (Golemansky 2008). Some normally marine psammonobiotids have even been recorded from entirely freshwater streams (Golemansky & Todorov 2007) though I personally suspect misidentifications may be involved.

The relationships of psammonobiotids to other testate amoeboids requires research (Adl et al. 2012). They possess filose rather than lobose pseudopodia, indicating relationships with other testate amoeboid groups in the Cercozoa. A leading possibility is a relation to the Euglyphida, which resemble psammonobiotids in many features but have tests with distinct scales. I haven't found any references to any psammonobiotids being covered by molecular analyses which may reveal where they really come from.

REFERENCES

Adl, S. M., A. G. B. Simpson, C. E. Lane, J. Lukeš, D. Bass, S. S. Bowser, M. W. Brown, F. Burki, M. Dunthorn, V. Hampl, A. Heiss, M. Hoppenrath, E. Lara, E. Le Gall, D. H. Lynn, H. McManus, E. A. D. Mitchell, S. E. Mozley-Stanridge, L. W. Parfrey, J. Pawlowski, S. Rueckert, L. Shadwick, C. L. Schoch, A. Smirnov & F. W. Spiegel. 2012. The revised classification of eukaryotes. Journal of Eukaryotic Microbiology 59 (5): 429-493.

Golemansky, V. 2008. Origin, phylogenetic relations, and adaptations of the marine interstitial testate amoebae (Rhizopoda: Lobosea, Filosea, and Granuloreticulsea). In: Makarov, S. E., & R. N. Dimitrijević. Advances in Arachnology and Developmental Biology. Papers dedicated to Prof. Dr. Božidar Ćurčić pp. 87–100. Inst. Zool, Belgrade; BAS, Sofia; Fac. Life Sci., Vienna; SASA, Belgrade & UNESCO MAB Serbia.

Golemansky, V., & M. Todorov. 2007. Taxonomic review of the genus Centropyxiella (Rhizopoda: Filosea) with data on its biology and geographical distribution. Acta Zoologica Bulgarica 59 (3): 227–240.

Moustached Bats, Ghost-faced Bats

In the theatre of mammal diversity, there are two groups that loom above all their competitors. The most diverse of the generally recognised mammalian orders, by a healthy margin, is the rodents. Nevertheless, they are still given a good run for their money by the silver medalist, the bats. There is somewhere in the region of 1100 known living species of bat, a number that has continued to increase in recent years as study progresses. This post will focus on one particular group of bats, the Mormoopidae.

Ghost-faced bat Mormoops megalophylla, copyright Merlin Tuttle.

Mormoopids are a group of bats found in warmer parts of the Americas. They commonly go by the names of moustached bats or funnel-eared bats, at least to the extent that any type of bat can be said to 'commonly' go by anything. They are fast-flying, insectivorous bats that roost in colonies in hot, humid caves. These colonies can be sizable: at least one colony of Wagner's moustached bat Pteronotus personatus was estimated to include more than 16,000 individuals (de la Torre & Medellín 2010). In the United States, mormoopids are currently restricted to the south-west (in the form of the ghost-faced bat Mormoops megalophylla) but subfossil from Florida indicate a wider distribution in the past (Simmons & Conway 2001).

Mormoopids belong to the Noctilionoidea, a distinctly Neotropical group of bats that also includes the leaf-nosed bats of the Phyllostomidae and the Noctilio bulldog bats (and also possibly the short-tailed bat Mystacina of New Zealand, because why make things simple?) The biggest difference between mormoopids and other noctilionoids lies in the structure of their shoulders. In most bats, the trochiter (one of the tubercles at the top of the humerus) is enlarged to form a secondary articulation with the scapula. This strengthens the shoulder joint, presumably allowing the production of more power for flight. Mormoopids, however, lack this enlarged trochiter. I must confess to being unsure just what is the significance of this alteration; mormoopids remain fast fliers (de la Torre & Medellín 2010). Are they perhaps sacrificing a bit of endurance for the sake of higher mobility?

Wagner's moustached bat Pteronotus personatus, copyright Bernard Dupont.

Current classifications of the mormoopids recognise two genera in the family, Mormoops and Pteronotus. Mormoops species have a shorter head than Pteronotus species (so short, in fact, that the braincase is wider than it is long), with a markedly upturned snout. Basically, they have a skull like a pug dog. In a revision of the family, Simmons & Conway (2001) recognised two living species of Mormoops and six of Pteronotus, plus an additional species of each described from subfossil remains from Cuba. Pteronotus was also divided between three subgenera. The type subgenus included two species, Pt. davyi and Pt. gymnonotus, known as naked-backed bats because the membrane for their wings attaches close to the spine so the body fur is not visible in dorsal view (in other mormoopids, the wings attach along the sides of the body). Three of the remaining species (Pt. personatus, the sooty moustached bat Pt. quadridens and Macleay's moustached bat Pt. macleayi) were placed in a morphologically generalised subgenus Chilonycteris. The remaining living species was Parnell's moustached bat Pt. parnellii, placed in its own subgenus Phyllodia.

Pteronotus parnellii was the only known mormoopid, and in fact the only Neotropical bat of any kind, to use high duty cycle echolocation. Echolocation, of course, works through the bat emitting calls and listening for when they bounce back from surrounding objects. The problem is that the noise produced while emitting calls can drown out returning echoes. As a result, most echolocating bats use what is called low duty cycle echolocation. Individual echolocation calls are spaced apart so the bat has time between each call to listen for echoes. High duty cycle echolocation is used by two Old World bat families, the Rhinolophidae and Hipposideridae, as well as Pteronotus parnellii. These bats have learnt the trick of emitting calls continuously and recognising returning echoes by their different frequency. This allows each bat to build up a more detailed picture of its surrounds, allowing for greater mobility in complex environments such as around dense forest.

Parnell's moustached bat Pteronotus parnellii, copyright Alex Borisenko.

In recent years, however, mormoopid systematics have been given a shake-up. Many of the mormoopid species recognised by Simmons & Conway (2001) could be divided between multiple subspecies. Recently, a molecular analysis of Pteronotus species by Pavan & Marroig (2016) found strong genetic divergence between most of these subspecies. As a result, they proposed raising the distinct subspecies to species level, effectively raising the number of living Pteronotus species from six to fifteen. Some of these species could also be separated on the basis of morphometric and acoustic data; others exhibited morphometric overlap but were geographically distinct. 'Pteronotus parnellii' was the most diverse, being divided into eight named species plus an unnamed population that may warrant species recognition. The question that this immediately raises: is the use of high duty cycle echolocation a feature of all nine of these species, or might it turn out that not all members of the P. parnellii group are high duty echolocators?

REFERENCES

de la Torre, J. A., & R. A. Medellín. 2010. Pteronotus personatus (Chiroptera: Mormoopidae). Mammalian Species 42 (869): 244–250.

Pavan, A. C., & G. Marroig. 2016. Integrating multiple evidences in taxonomy: species diversity and phylogeny of mustached bats (Mormoopidae: Pteronotus). Molecular Phylogenetics and Evolution 103: 184–198. Simmons, N. B., & T. M. Conway. 2001. Phylogenetic relationships of mormoopid bats (Chiroptera: Mormoopidae) based on morphological data. Bulletin of the American Museum of Natural History 258: 1–97.