Macroevolution of arboreality in salamanders

Abstract

Evolutionary theory predicts that selection in distinct microhabitats generates correlations between morphological and ecological traits, and may increase both phenotypic and taxonomic diversity. However, some microhabitats exert unique selective pressures that act as a restraining force on macroevolutionary patterns of diversification. In this study, we use phylogenetic comparative methods to investigate the evolutionary outcomes of inhabiting the arboreal microhabitat in salamanders. We find that arboreality has independently evolved at least five times in Caudata and has arisen primarily from terrestrial ancestors. However, the rate of transition from arboreality back to terrestriality is 24 times higher than the converse. This suggests that macroevolutionary trends in microhabitat use tend toward terrestriality over arboreality, which influences the extent to which use of the arboreal microhabitat proliferates. Morphologically, we find no evidence for an arboreal phenotype in overall body proportions or in foot shape, as variation in both traits overlaps broadly with species that utilize different microhabitats. However, both body shape and foot shape display reduced rates of phenotypic evolution in arboreal taxa, and evidence of morphological convergence among arboreal lineages is observed. Taken together, these patterns suggest that arboreality has played a unique role in the evolution of this family, providing neither an evolutionary opportunity, nor an evolutionary dead end.

Convergent evolution of olfactory and thermoregulatory capacities in small amphibious mammals

“…Furthermore, because the shift between foraging in water and in terrestrial environments is abrupt, we suggest that the morphological changes occurred quickly to adapt to new sensorial and physiological environments. Indeed, vertebrates can evolve faster when they are confronted with rapid environmental modifications (56)(57)(58). The consistent (17 times) and highly convergent loss of olfactory capacities and the gain of thermoregulatory capacities at the order level is surprising.…”

Macroevolution of desiccation‐related morphology in plethodontid salamanders as inferred from a novel surface area to volume ratio estimation approach

“…In this study, we presented strong evidence of a morphological response to ecological selective pressures in a family of salamanders whose morphology is not often associated with differences in habitat (Kozak and Wiens 2016). Previous investigations into the macroevolution of morphology have largely concluded that variation in plethodontid body proportions across taxa do not always correspond to what is predicted by selection across environmental gradients (Adams et al 2009;Blankers et al 2012;Baken andAdams 2019, but see Bonett andBlair 2017). The uniquely compelling results of our study suggest that SA:V may represent a key morphological trait that does respond predictably to environmental selective pressures, as much of the physiology of plethodontids, and thus their organismal performance, is mitigated through the consequences of cutaneous respiration and possible desiccation risk (see Feder 1983).…”

“…; Blankers et al. ; Baken and Adams , but see Bonett and Blair ). The uniquely compelling results of our study suggest that SA:V may represent a key morphological trait that does respond predictably to environmental selective pressures, as much of the physiology of plethodontids, and thus their organismal performance, is mitigated through the consequences of cutaneous respiration and possible desiccation risk (see Feder ).…”

“…Rather, they utilized surrogates of SA:V, such as body size (snout-vent length [SVL]) or surface area (SA) proxies derived from body mass alone, both of which assume a uniform body shape for every individual. Unfortunately, such an assumption directly contradicts empirical patterns of body shape variation in salamanders that has been observed across sizes (Hanken 1982;Wake 1989), within species (Adams 2011), and among species (Adams et al 2009;Blankers et al 2012;Baken and Adams 2019), as demonstrated through quantitative morphometric analyses. However, at present, we lack a direct method for efficiently quantifying SA:V variation.…”

“…; Blankers et al. ; Baken and Adams ), as demonstrated through quantitative morphometric analyses. However, at present, we lack a direct method for efficiently quantifying SA:V variation.…”