Extinction, Ecological Opportunity, and the Origins of Global Snake Diversity

Abstract

Snake diversity varies by at least two orders of magnitude among extant lineages, with numerous groups containing only one or two species, and several young clades exhibiting exceptional richness (>700 taxa). With a phylogeny containing all known families and subfamilies, we find that these patterns cannot be explained by background rates of speciation and extinction. The majority of diversity appears to derive from a radiation within the superfamily Colubroidea, potentially stemming from the colonization of new areas and the evolution of advanced venom-delivery systems. In contrast, negative relationships between clade age, clade size, and diversification rate suggest the potential for possible bias in estimated diversification rates, interpreted by some recent authors as support for ecologically mediated limits on diversity. However, evidence from the fossil record indicates that numerous lineages were far more diverse in the past, and that extinction has had an important impact on extant diversity patterns. Thus, failure to adequately account for extinction appears to prevent both rate-and diversity-limited models from fully characterizing richness dynamics in snakes. We suggest that clade-level extinction may provide a key mechanism for explaining negative or hump-shaped relationships between clade age and diversity, and the prevalence of ancient, species-poor lineages in numerous groups.

Evidence for determinism in species diversification and contingency in phenotypic evolution during adaptive radiation

“…For more ancient groups, ecological limits have been detected using phylogenetic methods but here the impact of increasing extinction over speciation may confound interpretation [6,76,77]. The taxa examined here are relatively young and extinction rates are always estimated to be much less than speciation rates (table 1).…”

“…Table 1. Tests of models of diversification for each of the four groups of squamates that account for constant rates and diversity dependence (DD) with and without extinction using TreePar [6,34]. For the DD models, estimates of speciation (l), extinction (m) and carrying capacities (K) were unconstrained or constrained with m equal to 10-50% of the initial unconstrained l. Models with the lowest AICc values and highest AIC weights are marked with an asterisk.…”

Evolutionary stability of sex chromosomes in snakes

“…Caenophidian snakes with highly differentiated sex chromosomes include more than 3000 recent species, while there are only around 400 species of non-caenophidian snakes [7], where sex chromosomes are likely to be only poorly differentiated. Nevertheless, it is important to note that identification of the key evolutionary novelty connected with enlarged diversification of a group is a difficult task, and that other candidate mechanisms such as the colonization of new areas and the evolution of advanced venom-delivery systems were suggested to be responsible for the large diversity of caenophidian and colubroid snakes, respectively [33]. Future research should be carried out to determine to what extent the superradiation of this clade is connected to the so-called 'fast Z', and likewise 'fast X' phenomena (i.e.…”

Out of Asia: Natricine snakes support the Cenozoic Beringian Dispersal Hypothesis

“…Although many of the species are associated with aquatic habitats and have diets consisting of amphibians or fish, many others are found in dry habitats and may consume invertebrates and mammals (Rossman et al, 1996;Gibbons and Dorcas, 2004;Vitt and Caldwell, 2009). Estimates using molecular phylogenies place the origin of the natricines from other colubrids in the Eocene/Oligocene, indicating they are young enough to have encountered the same environmental conditions as the ratsnakes, skinks and crotaline snakes (Pyron and Burbrink, 2012).…”