The systematics and independent evolution of cave ecomorphology in distantly related clades of Bent-toed Geckos (Genus Cyrtodactylus Gray, 1827) from the Mekong Delta and islands in the Gulf of Thailand

Abstract

An integrative taxonomic analysis of the distantly related Cyrtodactylus condorensis and intermedius species complexes of the Mekong Delta revealed that C. paradoxus is a junior synonym of C. condorensis and that C. thochuensis is a junior synonym of C. leegrismeri. Additionally, the analysis revealed that a cave-dwelling ecomorpholgy has evolved independently early on in the evolution of both complexes (represented by C. hontreensis in the intermedius complex and C. grismeri and C. eisenmani in the condorensis complex) and cave ecomorphs exist in sympatry-but not syntopy-with general scansorial ecomorphs. Multiple, recent, cyclical, glacioeustatic driven changes in sea levels across the Sunda Shelf are hypothesized to account for the evolution and distribution of the widely separated, conspecific insular populations of C. condorensis and C. leegrismeri. The independent evolution of cave ecomorphology is proposed to have been driven by competition avoidance. Habitat islands across the Mekong Delta are an important source of endemism and in need of protection.

A novel hotspot of vertebrate endemism and an evolutionary refugium in tropical Australia

“…On the one hand, regions of karstic limestone in many tropical areas have been shown to be characterized by a depauperate, but highly distinctive biota (especially flora), reflecting the challenges of poor water retention and low nutrient levels (Proctor et al ., ; Polak, ). Other specializations may be associated with utilizing habitats that combine very complex three‐dimensional microhabitats with wide exposed rockfaces (Grismer et al ., ). In the endemic lizard lineages of the DRS, we have not yet assessed whether there is morphological evidence for specializations linked to using this habitat; however, the morphological similarity of many endemic lineages to relatives occurring elsewhere (their divergence was in most cases only revealed by genetic analyses) suggests they are generally merely isolates of other saxicoline lineages, not karst specialists.…”

“…Better understanding of patterns of diversity in these regions, and the processes underlying them, is therefore a high research priority (Wong et al ., ; Clements et al ., ; Grismer et al ., , ). Many karst taxa are characterized by specializations to cope with unique local conditions including poor, nutrient‐deficient soils that retain little water and/or extremely complex three‐dimensional microhabitats (Polak, ; Clements et al ., ; Grismer et al ., ). On the other hand, some karst endemics also appear to be relicts, showing evidence of long‐term persistence in evolutionary refugia from climatic extremes and/or biotic competition (e.g.…”

Historical demography of four gecko species specializing in boulder cave habitat: Implications in the evolutionary dead end hypothesis and conservation

“…Among a total of 55 species in Cnemaspis , there are more than 30 rocky habitat specialists, most of which have restricted distributions (Grismer et al, ; Grismer, Wood, Quah et al, ; Grismer, Wood, Tri et al, ; Kurita, Nishikawa, Matsui, & Hikida, ; Wood et al, ). In addition to Cnemaspis species, several Cyrtodactylus geckos also occupy these small hills in the Mekong Delta; and all show extremely limited distributional ranges (Grismer, Wood, Quah et al, ; Grismer, Wood, Tri et al, ). These observations suggest that surrounding unsuitable habitats limit the dispersal of specialist geckos, which are isolated in their “habitat islands” even without rising sea level.…”

“…Despite this region's faunal uniqueness and diversity, its biodiversity inventory remains incomplete (Grismer & Ngo, ; Grismer, Wood, Quah et al, ; Grismer, Wood, Tri et al, ). Integrative practices, combining scientific research with suitable conservation management, are desperately needed to protect this critically threatened habitat.…”

“…Despite this region's faunal uniqueness and diversity, its biodiversity inventory remains incomplete (Grismer & Ngo, 2007;Grismer, Wood, Quah et al, 2015;Grismer, Wood, Tri et al, 2015).…”