A highly polymorphic South American collared lizard (Tropiduridae: Tropidurus) reveals that open–dry refugia from South-western Amazonia staged allopatric speciation

Abstract

Research on Pleistocene Amazonian refugia has predominantly targeted forest-dwelling taxa, although evidence suggests that endemic species have also evolved in peripheral Amazonian enclaves of open–dry habitats. In Rondônia, Brazil, Tropidurus lizards are restricted to savannah relicts that were once connected to the core Cerrado biome. These populations are currently allocated under Tropidurus oreadicus but hypothesized to comprise allopatric species that evolved in response to landscape changes induced by Pleistocene climatic fluctuations. Phylogenetic analyses support the monophyly of populations from savannah enclaves from Rondônia but place them as distantly related to T. oreadicus. We describe these populations as a new species with unprecedented levels of chromatic polymorphism. A pre-Pleistocene origin is inferred for this new taxon, and dating analysis indicates that Tropidurus species endemic to savannah enclaves diverged from relatives distributed in core open–dry biomes in a non-temporally overlapping fashion. Species distribution models estimate vast climatically suitable areas for the new species during the Last Interglacial, followed by significant contraction during the Last Glacial Maximum, and subsequent expansion and northward displacement towards the Holocene and the present. We conclude that landscape transformations played an important role in the evolution of lizards from enclaves, but their speciation history is temporally deeper than previously thought.