Small lizards of South America

Three readers made comments about the apparent identity of yesterday's ID challenge; none of them, I'm afraid, even came close.


The gymnophthalmid lizard Leposoma hexalepis, photographed in Venezuela by Carl Franklin.

Gymnophthalmids are a family of nearly 200 species (new ones continue to be described at a steady rate) of small (4-15 cm excluding the tail) insectivorous lizards from South America. So little regarded is this family that no really good vernacular name exists for it and its members are generally referred to by what they are not: they are referred to as 'microteiids' in contrast to the related but physically larger family Teiidae. Today's Taxon of the Week is a clade within the Gymnophthalmidae known as the Ecpleopini or Ecpleopinae*, depending on whom you ask.

*Technically, that should be 'Ecpleopodini', but all recent publications have used the 'incorrect' spelling (so far I've only seen one publication from 1887 use the correct spelling). The online page for one recent article includes a footnote mentioning the correct spelling but the note does not appear to be present in the printed article.

The Ecpleopini include (at present) about thirty species, about half of which are placed in the genus Leposoma. The clade is currently supported by molecular analyses without any identified morphological synapomorphies (Pellegrino et al., 2001; Rodrigues et al., 2005). Different analyses recover different relationships between the constituent genera except for a small clade of the genera Colobosauroides, Dryadosaura and Anotosaura (Rodrigues et al., 2005). This clade represents one of a number of lineages within Gymnophthalmidae to develop an elongate body form and reduced limbs together with a fossorial lifestyle. Anotosaura has also lost its external ear openings.


Another ecpleopin, Arthrosaura reticulata, photographed in Peru by Thomas Stromberg.

The species of the genus Leposoma are more generalised in their overall appearance but still not without their intrigues. Leposoma species can be divided between two groups distinguished by their chromosome number and arrangement. The L. scincoides group possess 52 chromosomes of a range of sizes while species of the L. parietale group ancestrally possess 44 chromosomes with a clear size distinction between 20 major and 24 minor chromosomes. The only exception to this pattern is L. percarinatum, a parthenogenetic species* from Mato Grosso in Brazil with 66 chromosomes: one of the few known examples of a triploid genome in vertebrates. When the triploid nature of L. percarinatum was identified, it was suggested that it might be derived from a hybridisation event between two diploid parents. Since then, a diploid form of L. percarinatum has also been identified that may represent one of the parents of the triploid form; perhaps the other is the sympatric bisexual** diploid L. ferreirai (Laguna et al., 2010). Which does still leave the question of how the usual parthenogenesis of the diploid L. percarinatum came to be in the first place.

*Or, as it seems to be called, a 'parthenoform' (presumably to avoid having to refer to a parthenogenetic taxon as a 'species').

**In the sense of possessing two sexes, not the other sense.

REFERENCES

Laguna, M. M., M. T. Rodrigues, R. M. L. dos Santos, Y. Yonenaga-Yassuda, T. C. S. Ávila-Pires, M. S. Hoogmoed & K. C. M. Pellegrino. 2010. Karyotypes of a cryptic diploid form of the unisexual Leposoma percarinatum (Squamata, Gymnophthalmidae) and the bisexual Leposoma ferreirai from the lower Rio Negro, Amazonian Brazil. Journal of Herpetology 44 (1): 153-157.

Pellegrino, K. C. M., M. T. Rodrigues, Y. Yonenaga-Yassuda & J. W. Sites Jr. 2001. A molecular perspective on the evolution of microteiid lizards (Squamata, Gymnophthalmidae), and a new classification for the family. Biological Journal of the Linnean Society 74: 315-338.

Rodrigues, M. T., E. M. X. Freire, K. C. M. Pellegrino & J. W. Sites Jr. 2005. Phylogenetic relationships of a new genus and species of microteiid lizard from the Atlantic forest of north-eastern Brazil (Squamata, Gymnophthalmidae). Zoological Journal of the Linnean Society 144 (4): 543-557.

Name the Bug #27

Tomorrow's post will relate to this little fellow and his nearest and dearest:



Anyone out there recognise him?

Attribution, as always, to follow.

Update: Identity now available here. Photo from here.

Gender's Just a State of Gonads

It didn't take long for Adam Yates to recognise this animal:


Juvenile Pagrus auratus. Photo by Richard Ling.

This is the fish that goes by the name of 'snapper' in New Zealand, though that name is used for different kinds of fish elsewhere. In older references, you'll find this species under the name of Chrysophrys auratus, but the genera Chrysophrys has since been synonymised with Pagrus (Paulin, 1990). However, the molecular phylogenetic analysis of Chiba et al. (2009) failed to recover monophyly for Pagrus, so we may yet see Chrysophrys make a comeback some day.


Mature individuals of Pagrus major, a north-west Pacific species regarded by some authors as a synonym of P. auratus. These two are probably engaging in courtship behaviour. Photo from here.

As this young snapper gets older, its body will change in numerous ways. One is that the blue spots along its side will fade away and it'll become more evenly pink. Its head will become deeper, and if it may develop a large supraorbital boss on its forehead. And one other significant change that it may go through is a reassignment of gender. Members of the marine fish family Sparidae, to which Pagrus belongs, show a bewildering range of sexual development, including forms which show protandrous hermaphroditism (they start life as males before developing into females), protogynous hermaphroditism (starting as females, developing into males) and gonochorism (completely separate males and females, as we have ourselves). Other species start life with the rudiments of both male and female gonads but have only one or the other develop to maturity, without any subsequent sex changes, while a single species has been recorded as possessing simultaneously functional gonads of both sexes (Buxton & Garratt, 1990).

Different species of sparids feed on a variety of different diets, from predators of other fish such as the Dentex species to herbivores on algae such as Sarpa salpa. This variation in diet is reflected in a variety of dental morphologies. Predators such as Dentex possess pointed caniniform teeth while invertebrate feeders such as Pagrus auratus have a combination of pointed teeth in the front and round molariform teeth in the back. Algal feeders have flat-topped incisiform dentition, leading to occassional reports on fish with human teeth:


Teeth of sheepshead, Archosargus probatocephalus. Photo from Nathan Thurston.

In the past, dentition has been used as the basis for dividing sparids into a number of subfamilies, but both molecular (Chiba et al., 2009) and morphological (Day, 2002) analyses indicate multiple polyphyletic origins of the various dentition types. Contrast that to the situation in the possibly related* family Lethrinidae where trophic type and phylogeny show a much closer fit.

*A relationship between the two has been suggested on morphological grounds; molecular analyses have so far not supported such a relationship, but nor have they produced any strong relationships for either family.

REFERENCES

Buxton, C. D., & P. A. Garratt. 1990. Alternative reproductive styles in seabreams (Pisces: Sparidae). Environmental Biology of Fishes 28: 113-124.

Chiba, S. N., Y. Iwatsuki, T. Yoshino & N. Hanzawa. 2009. Comprehensive phylogeny of the family Sparidae (Perciformes: Teleostei) inferred from mitochondrial gene analyses. Genes and Genetic Systems 84 (2): 153-170.

Day, J. J. 2002. Phylogenetic relationships of the Sparidae (Teleostei: Percoidei) and implications for convergent trophic evolution. Biological Journal of the Linnean Society 76 (2): 269-301.

Paulin, C. D. 1990. Pagrus auratus, a new combination for the species known as "snapper" in Australasian waters (Pisces: Sparidae). New Zealand Journal of Marine and Freshwater Research 24: 259-265.

Name the bug # 26

I haven't put up any posts earlier this week as I was at the Australian Entomological Society conference, but now it's back to work. Tomorrow's post will be related to this animal:



Attribution to follow.

Update: Identity now available here. Photo from here.

The Trouble with Coelosclerites

A couple of years ago, I posted a brief review of the chancelloriids, mysterious sessile animals from the Cambrian period. As explained in that post (which I'd recommend reading before this one), chancelloriids are remarkable for how much we know about them while still being unable to place them anywhere in the animal family tree. However, there are two main options that are currently supported: one is that chancelloriids are sponge-grade animals, probably in the stem-group of modern Epitheliozoa (the clade including coelenterates and bilaterians, which differ from sponges in having a differentiated external skin around their bodies); the other is that chancelloriids are related to other Cambrian animals such as halkieriids, which have themselves been shown to be closely related to molluscs (Vinther & Nielsen, 2005).


Diagram of coelosclerite microstructure from Porter (2008).

The sponge interpretation of chancelloriids has some strong points marshalling in its favour: chancelloriids lack any sign of bilateral symmetry and no sign has been recognised in them of differentiated organ systems. The main feature associating them with halkieriids is the microstructure of their sclerites. Chancelloriids and halkieriids (and a couple of other Cambrian families) possessed sclerites with a microstructure unknown for any other animal group. Known as coelosclerites, these structures were hollow and would have been secreted as a single unit without any subsequent growth*. The greater part of the sclerite was formed of aragonite fibres, arranged parallel to the axis of the sclerite. External protrusions on the sclerite were formed by aragonite bundles sitting at an angle to the main body. A thin layer, probably originally organic, covered the outer surface of the sclerite (Porter, 2008).

*But see Jakob Vinther's comment on the earlier post.

Porter (2008) felt that the similarity between chancelloriid and halkieriid sclerites was so great that it was unlikely that they had evolved independently. The coelosclerite was far from being the only way to develop such a structure: the Cambrian and subsequent periods have seen the evolution of many other sclerite-possessing animals, all of which exhibited different sclerite microstructures. Nor could any convergence be explained by selective pressures: the sessile chancelloriids and slug- or chiton-like halkieriids would have ecologically very different animals. If the coelosclerite structure arose independently in the two groups, the similarities would have to be accepted as pure coincidence.

However, if we accept that coelosclerites had a single origin, we have to explain the complete absence of apparent bilaterian traits in chancelloriids. Many groups of bilaterians have lost their ancestral bilateral symmetry: tunicates, entoprocts, echinoderms, for instance. None of them, however, have lost all trace of their ancestry to quite the same degree that chancelloriids would have had to. Porter (2008) proposed two options: (1) chancelloriids were indeed highly derived bilaterians forming a clade with halkieriids, or (2) chancelloriids were sponge-grade stem-epitheliozoans; coelosclerites arose in the common ancestor of chancelloriids and bilaterians but were subsequently lost by bilaterians other than halkieriids.

Option 2 might appear tempting if halkieriids were close to the base of bilaterians, but it is well-established that they are not. If halkieriids are interpreted as stem-trochozoans (a fairly conservative interpretation) then coelosclerites would have had to have been lost at least six times, in the ancestors of ctenophores, cnidarians, deuterostomes, ecdysozoans, bryozoans and platyzoans (and that is ignoring more phylogenetically contentious groups such as acoelomorphs and chaetognaths that could potentially increase the number even further). If, as seems more likely, halkieriids are stem-molluscs, we have to factor in another two losses for brachiozoans and annelids (and, again, I'm ignoring phylogenetic renegades such as entoprocts). And in the case of brachiozoans, the greater part of the brachiozoan stem group appear to have themselves possessed sclerites; Porter's hypothesis 2 would require the stem-brachiozoans to have lost coelosclerites, only to re-evolve a distinct new sclerite form shortly afterwards.

So, in my opinion, the only really viable options are coelosclerites evolved convergently in two entirely separate lineages, or coelosclerite-possessing animals formed a single monophyletic clade. My personal inclination would be to favour the latter; the examples of ascidians and others demonstrate that significant re-organisations of the bilaterian body plan are not a priori impossible. Of course, the supporting evidence either way remains shaky, and the whole structure could still come tumbling down tomorrow.

REFERENCES

Porter, S. M. 2008. Skeletal microstructure indicates chancelloriids and halkieriids are closely related. Palaeontology 51 (4): 865-879.

Vinther, J., & C. Nielsen. 2005. The Early Cambrian Halkieria is a mollusc. Zoologica Scripta 34: 81-89.

Freak of the Week: Wingless, Legless Flies

I found this while looking up identification info for phorid flies, of which we currently seem to be receiving something of an influx in our samples.


Photoes from here.

Most of what you see in the lower of the two photoes above are larvae of army ants of the genus Aenictus. The odd one out is the whiter 'larva' in the centre—which is not a larva at all, but a fully adult female of the phorid fly Vestigipoda longiseta! (The upper photo shows the same animal in close-up.) This bizarre animal makes its living by imitating its host larvae and being fed by the larvae's deluded carers. Five species of Vestigipoda have been described to date from Malaysia (Disney et al., 1998; Murayama et al., 2008).


Close-up of head of Vestigipoda maschwitzi, from Disney et al. (1998).

Cases of neoteny, where insects develop full sexual maturity while still 'larvae', are not unknown among holometabolous insects (I earlier described a case involving the beetle Micromalthus). However, Vestigipoda cannot be regarded as neotenous because the female has a fully developed adult head.

So far, Vestigipoda seems to only be known from females. It is possible that males, when found, may turn out to be much more normal phorid flies. The challenge would be recognising them as related to their bizarre females.

REFERENCES

Disney, R. H. L., A. Weissflog & U. Maschwitz. 1998. A second species of legless scuttle fly (Diptera: Phoridae) associated with ants (Hymenoptera: Formicidae). Journal of Zoology 246 (3): 269-274.

Maruyama, M., R. H. L. Disney & R. Hashim. 2008. Three new species of legless, wingless scuttle flies (Diptera: Phoridae) associated with army ants (Hymenoptera: Formicidae) in Malaysia. Sociobiology 52 (3): 485-496.

A Little Bit of Gastrocopta

Gastrocopta armigerella, from Okinawa in Japan. Photo by Hiroshi Ishikawa.

Gastrocopta is a genus of terrestrial snail found pretty much throughout the world, mostly in drier habitats. Despite its abundance, it is not hugely familiar to most people by virtue of the fact that most species are only a couple of millimetres in size. Shells of Gastrocopta species are whitish and somewhat translucent, and have a number of distinct projections around the shell aperture. These projections may function for protection or they may help to reduce water loss: both important functions for a tiny snail.

Gastrocopta is a member of the superfamily Pupilloidea. All pupilloids are small, cylindrical snails, and authors have differed significantly as to how the group is divided up: some authors have recognised only a single family Pupillidae, others have recognised a number of families. The classification of Bouchet et al. (2005) (which is as good a baseline as any) includes the subfamily Gastrocoptinae in the family Vertiginidae. As well as the cosmopolitan Gastrocopta, Gastrocoptinae includes a number of genera with more restricted distributions (Pokryszko, 1996). The relationships between these genera do not appear to have been studied in detail; while I haven't found an explicit statement of such, there seems to be something of an implied suspicion that Gastrocopta in its current sense may represent a plesiomorphic paraphylum to at least some of the other gastrocoptines.


Live specimen of Gastrocopta contracta. Photo by Aydin Örstan.

There is certainly no shortage of described species for Gastrocopta, with probably at least as many species waiting to be described. However, the taxonomy of this genus is not on the firmest of grounds. Soft-anatomy characters such as genitalic features have been little studied within Gastrocopta, and have generally not shown much variation when they have been studied (Pokryszko, 1996). As such, species are distinguished by features of the shell, particularly the arrangement of teeth around the aperture. Unfortunately, at least some species have been shown to vary between individuals in these features, making species identification potentially difficult without access to multiple specimens (of course, Gastrocopta is hardly exceptional in this regard). Also, while the genus has been divided between a number of subgenera, the boundaries between these subgroups tend to be somewhat blurry and not all authors have accepted their validity.

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.

Pokryszko, B. M. 1996. The Gastrocoptinae of Australia (Gastropoda: Pulmonata: Pupilloidea): systematics, distribution and origin. Invertebrate Taxonomy 10: 1085-1150.