Genetic variation within Trogonophis wiegmanni Kaup 1830

The fossorial Amphisbaenid Trogonophis wiegmanni is the only extant representative of the family Trogonophidae in North Africa, occurring in the North of the Maghreb, from southwest Morocco to northeast Tunisia. Its elongate limbless body, reduced vision, compact skull and enhanced hearing and olfactory capabilities are morphological adaptations for burrowing (1). It is not commonly observed due to its fossorial habits and thus the distribution remains poorly known. Most authors accept the existence of two subspecies: T. w. wiegmanni and T. w. elegans (2;3). Morphologically, the two subspecies are very similar except for their colouration patterns. Trogonophis w. wiegmanni presents a ground yellow colour and T. w. elegans a whitish, grey or pink one (3). Nevertheless, the yellow pigmentation of T. w. wiegmanni disappears after a very short period of time in alcohol, so the two forms in preserved specimens cannot be separated morphologically (3). Trogonophis w. wiegmanni is found in central and eastern Morocco and into western Tunisia (3). The western range limit is thought to be the oriental mountains of the Rif and Medium Atlas (2). It is rarely found above 900m (3). This subspecies occupies relatively dry regions, with its western range limit apparently coinciding with the 600mm isohyet (3). Trogonophis w. elegans is endemic to Morocco, found in the north and west of the Atlas mountain chains up to an altitude of 1600m (2;3). This form lives in relatively moist regions influenced by the temperate Atlantic climate with an eastern limit apparently coinciding with the 700mm isohyet (3). These apparently very different ecological demands of both forms suggest a considerable step towards speciation (3). In fact, in a recent checklist, GANS (4) considers them as two different species: T. wiegmanni and T. elegans. There are two principal mountain chains in Morocco, the Rif mountains in the north of the country and further south in the country the Atlas, Medium Atlas, High Atlas and Anti-Atlas mountains that extend in a northeast/southwest direction. The two forms are considered to be separated by the Atlas mountains and there is no evidence of hybridization (2). The Atlas mountain chain was formed towards the end of the Miocene and at this time the Rif formed an island, separated from continental Africa (5). The Miocene Atlas uplift may provide a general explanation of differentiation and speciation in many northwest African species (6). Such a hypothesis of vicariance has been suggested to explain the observed differentiation in various species such as Acanthodactylus erythurus (7) and Agama impalearis (6). Many reptile species in this area, that have been studied phylogeographically, revealed unexpected high levels of mitochondrial DNA (mtDNA) sequence variation. In Lacerta perspicillata 12s rRNA uncorrected distances detected were between 5.2 and 6.6% (8) and in Tarentola mauritanica the 16s rRNA uncorrected genetic distances between subspecies reached 8%, and 5% between the north and south Morocco populations (9;10). In all studies the authors suggest that some of the genetic lineages identified were probably distinct species. In Acanthodactylus erythrurus, genetic distances between all populations range up to 3.1% within 12s rRNA, which was considered as substantial intraspecific variation (11). In Agama impalearis, the Agamid lizard, the 16s rRNA maximum uncorrected intraspecific divergence was 2.6% (6) which the authors considered that, combined with other factors, supported the recognition of two species. Thus there is a real need to assess other species in this region for cryptic genetic variation.