Friday, January 17, 2014

The ancient blindsnake family Xenotyphlopidae becomes monotypic

Madagascar has a unique phylogenetic representation of reptiles that includes the enigmatic Malagasy blind snake of the family Xenotyphlopidae established by Vidal et al., 2010. The family currently contains one genus Xenotyphlops with the two species X. grandidieri Mocquard, and X. mocquardi  both are presumably endemic to the same area in northwest Madagascar. 
Photo to the left. The three reptile species originally described by Mocquard (1905, 1906) which were re-discovered in syntopy at Baie de Sakalava in northern Madagascar after more than 100 years without records. Xenotyphlops grandidieri (pink), together with the two skink species Paracontias minimus (brown with longitudinal lines of dark spots) and P. rothschildi (beige with black flanks).

François Mocquard, a French herpetologist described a number of species from Madagascar at the turn of the 20th century, including the two limbless skinks Paracontias minimus and Paracontias rothschildi and the typhlopid snake Xenotyphlops grandidieri.  None of the three species was rediscovered and their status remained enigmatic and their Malagasy origin was in doubt. The type specimens remained the only known specimens.

Within the worm-like snakes (Scolecophidia), Xenotyphlopidae is most closely related to the species-rich and almost globally distributed family Typhlopidae. Together with the Asian family Gerrhopilidae, these three families form the superfamily Typhlopoidea. They have a biogeographic pattern characterized by major vicariance events, such as the break-up of Gondwana and the separation of  India and Madagascar, events that might have promoted the diversification of major lineages. A recent molecular phylogeny of the Scolecophidia suggested a Cretaceous split between the genus Xenotyphlops and its sister group, the family Typhlopidae.

Considering the almost cosmopolitan distribution and species richness of the family Typhlopidae, the blind snake fauna of Madagascar appears species-poor, consisting of the three genera Ramphotyphlops  (one species), Typhlops  (11 species) and Xenotyphlops (two species). And, since 1980, only three new species of Malagasy blind snakes have been described (Xenotyphlops mocquardi, Typhlops rajeryi and Typhlops andasibensis). Their discovery has been opportunistic rather than in the framework of a comprehensive revisionary work.With the exception of the probably introduced and parthenogenetic Ramphotyphlops braminus, all species of Malagasy blind snakes are endemic to the island and occur in a wide variety of habitats, ranging from xeric savanna at the coast to deciduous forest and rainforest Most of the species are known only from a few localities.

None of Mocquard the three species were rediscovered and their status remained enigmatic and even their Malagasy origin was considered questionable by somke authors. The type specimens remained the only representatives for more than a century, until Köhler and colleagues discovered all three of Mocquard’s taxa at the same locality within the same habitat confirming their Malagasy origin, in 2007-2008.

Prior to this  Wallach & Ineich had noticed the morphological uniqueness of Typhlops grandidieri and placed it in the genus Xenotyphlops with X. mocquardi, based on differences in morphological and anatomical characters to X. grandidieri.

In general appearance, Xenotyphlops are purple to pinkish, thin, medium-sized blind snakes (SVL 163-276 mm), with a strongly pointed rostral scale and a complete lack of eyes. They are also unique in having a large, circular and nearly vertical rostral, and a single anal shield. Internally, it lacks a tracheal lung, has a type G foramen in the right bronchus, an anteriorly positioned heart and a large heart-liver gap.

In a new paper Wegener et al. (2013) used DNA from the 2007 specimens and found the two species of Xenotyphlops genetically similar and the morphological variability of X. grandidieri is thus greater than formerly thought. DNA sequences of the cytochrome b gene provide no indication of the occurrence of more than one species of Xenotyphlops in the Baie de Sakalava area despite the morphological variation found in specimens from this site. Due to the absence of clear diagnostic characters they consider X. mocquardi a junior synonym of X. grandidieri resulting in a monotypic genus Xenotyphlops and a monotypic family Xenotyphlopidae. This conclusion is supported by the distribution of both taxa, which are in close geographic proximity. To protect this unique relic species as well as other presumed endemics classified as Critically Endangered by the IUCN the authors  suggest establishing a littoral (coastal) nature reserve along the coast east and southeast of Antsiranana.

Wegener, Johanna E., Sebastian Swoboda, Oliver Hawlitschek, Michael Franzen, Van Wallach, Miguel Vences, Zoltán T. Nagy, S. Blair Hedges, Jörn Köhler, and Frank Glaw. "Morphological variation and taxonomic reassessment of the endemic Malagasy blind snake family Xenotyphlopidae." Spixiana 36:269-283

No comments:

Post a Comment