Why colour in subterranean vertebrates? Exploring the evolution of colour patterns in caecilian amphibians

Abstract

The proximate functions of animal skin colour are difficult to assign as they can result from natural selection, sexual selection or neutral evolution under genetic drift. Most often colour patterns are thought to signal visual stimuli; so, their presence in subterranean taxa is perplexing. We evaluate the adaptive nature of colour patterns in nearly a third of all known species of caecilians, an order of amphibians most of which live in tropical soils and leaf litter. We found that certain colour pattern elements in caecilians can be explained based on characteristics concerning above‐ground movement. Our study implies that certain caecilian colour patterns have convergently evolved under selection and we hypothesize their function most likely to be a synergy of aposematism and crypsis, related to periods when individuals move overground. In a wider context, our results suggest that very little exposure to daylight is required to evolve and maintain a varied array of colour patterns in animal skin.

Population Genetics of the São Tomé Caecilian (Gymnophiona: Dermophiidae: Schistometopum thomense) Reveals Strong Geographic Structuring

“…Our study confirms previous hypotheses concerning clinal latitudinal variation [36] and philopatry [38], but was inconclusive about the importance of color for crypsis [84] using our geological proxy for soil type and vegetation type. Taxonomically, our results were inconclusive because we could not investigate a clear zone of admixture present on the island between two deeply divergent clades (which would correspond to S. thomense and S. ephele ), although applying genetic barcoding standards to 16S [82], [106], our 4.3% divergence would not be considered deep enough to warrant taxonomic differentiation.…”

“…We selected these explanatory variables based on previous hypotheses or from proxies when data was unavailable. Specifically, latitude was postulated by Nussbaum and Pfrender [36], altitude was found to be important in clinal variation in size [38], geology was selected as a proxy for soil type and vegetation, which are expected to influence caecilian color crypsis [84], and genetic groupings are expected to reveal any taxonomic explanation [34]. Our global model included all main effects described above.…”

Evolution of Cranial Shape in Caecilians (Amphibia: Gymnophiona)

“…Yet attributing a direct, causal relationship is advised against at this time because the scanty available data do not demonstrate a clear correlation. For example, although comparative and experimental evidence suggest that Schistometopum thomense (with a relatively terminal mouth, perhaps secondarily) is a relatively poor burrower that prefers to use existing tunnels (Ducey et al 1993;Nussbaum and Pfrender 1998;Wollenberg and Measey 2009;Herrel and Measey 2010), many caecilians with strongly countersunk mouths (e.g. Scolecomorphus, Geotrypetes, Uraeotyphlus, Caecilia) have also been found in leaf litter rather than deeper soil (Burger et al 2004;Gower et al 2004;pers.…”

The kinematics of locomotion in caecilians: effects of substrate and body shape

“…San Mauro et al, 2004;Roelants et al, 2007;Wollenberg and Measey, 2009). Associated with the transition to an aquatic lifestyle, these animals have lost their skin-vertebral independence and are unable to move through narrow tunnels (Summers and O'Reilly,'97).…”