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.
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.
A triploid vertebrate. Wow.
ReplyDeleteDon't lizards go parthenogenetic pretty much at the drop of an evolutionary hat? Perhaps they're somehow preadapted for it?
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