Zigzags in the White Sand Belt: A new, highly divergent lineage of sand-swimmer skink from Madagascar (Squamata: Scincidae)

Abstract

The present work reports on the discovery of a new sand swimming lizard (Scincidae: Scincinae) in Madagascar. This limbless and eyeless skink was found during fieldwork in the northern part of the “great white sand belt”, a series of patchy white sand areas encircling the island’s western sedimentary basins. The new taxon shows a distinctive combination of derived morphological traits (miniaturized, limbless, elongated body, with absent or scale-covered eyes and ear openings, and a reduced head scale pattern) reminiscent of other Malagasy fossorial skinks adapted to sandy habitats (e.g. Voeltzkowia, Grandidierina and some Paracontias). Phylogenetic analyses based on two datasets (multilocus DNA from Sanger sequencing and genome-wide DNA sequences derived from double-digest Restriction Associated DNA [ddRAD]) reveal a highly divergent phylogenetic position of this taxon and, given its distinct morphology, justify its description as a new species in a new genus, Zig zag gen. nov. & sp. nov. This marks the first genuine field discovery of a new genus of Scincidae in Madagascar since the 19th century, i.e., the discovery of a formerly unknown deep clade rather than an identification (and split) from an already recognized genus. Our results also shed light on the ancient evolutionary history of this taxon and its sister clade, Paracontias. Finally, the present work explores the factors that may explain why ecosystems characterized by white sand substrates, an ecosystem often neglected in biodiversity research, but present in various regions of the globe (e.g., Florida sand scrub, South American WS savannah, Indonesian Keranga) have seemingly so frequently promoted the convergent evolution of fossorial squamates.