Arboreality constrains morphological evolution but not species diversification in vipers

Abstract

An increase in ecological opportunities, either through changes in the environment or acquisition of new traits, is frequently associated with an increase in species and morphological diversification. However, it is possible that certain ecological settings might prevent lineages from diversifying. Arboreality evolved multiple times in vipers, making them ideal organisms for exploring how potentially new ecological opportunities affect their morphology and speciation regimes. Arboreal snakes are frequently suggested to have a very specialized morphology, and being too large, too small, too heavy, or having short tails might be challenging for them. Using trait-evolution models, we show that arboreal vipers are evolving towards intermediate body sizes, with longer tails and more slender bodies than terrestrial vipers. Arboreality strongly constrains body size and circumference evolution in vipers, while terrestrial lineages are evolving towards a broader range of morphological variants. Trait-dependent diversification models, however, suggest similar speciation rates between microhabitats. Thus, we show that arboreality might constrain morphological evolution but not necessarily affect the rates at which lineages generate new species.

Associated evolution of fruit size, fruit colour and spines in Neotropical palms

“…The Ornstein–Uhlenbeck (OU) models assume a constrained random walk where trait values change towards an optimum θ with strength of selection α and evolutionary rate σ 2 (Hansen, 1997). We fitted seven evolutionary models derived from BM and OU models (Table 1) to estimate parameter values that best describe the evolution of fruit length given the phylogeny and each ancestral state reconstruction (Alencar, Martins, Burin, & Quental, 2017; Onstein & Linder, 2016). These models differ in whether the rate of evolution, evolutionary optima and strength of selection are allowed to vary, thus differing in their assumptions on how the evolution of fruit length is associated with the evolution of fruit colours or the presence/absence of spines.…”

“…We excluded reconstructions for which model fit resulted in negative eigenvalues of the Hessian matrix, which indicates that the model failed in obtaining reliable parameter estimates (Beaulieu & O'Meara, 2016), and those which returned very unrealistic fruit size optima (θ > 20 cm or θ < 0.1 cm). We also excluded statistical outliers for the remaining parameters, since these may also be produced when the model fails to converge (Alencar et al, 2017). All these cases are referred herein as analyses with convergence problems.…”

Evolução correlacionada de caracteres de frutos e defesas em palmeiras neotropicais

“…Interactions between frugivores and angiosperms have a long history, of at least 80 million years (Eriksson 2016). Phylogenetic and fossil evidence suggest that these interactions had a major influence on the evolution and diversification of several plant and animal clades (Gómez & Verdú 2012, Burin et al 2017, including palms (Onstein et al 2017, Onstein et al 2018. Phylogenetic comparative methods can help us to understand how this long history of plant-vertebrate interaction affected trait evolution (Cornwell and Nakagawa 2017).…”

“…To investigate the evolutionary relationship between (1) fruit length and fruit color, and (2) fruit length and the presence of spines we used a maximum likelihood approach implemented in the "OUwie" R package (Beaulieu & O'Meara 2016 estimate parameter values that best describe the evolution of fruit length given the phylogeny and each ancestral state reconstruction (e.g. Alencar et al 2017, Onstein et al 2016). These models differ in how the rate of evolution, evolutionary optima, and strength of selection are allowed to vary, thus differing in their assumptions on how fruit color or the presence/absence of spines could have affected the evolution of fruit length (table 1).…”

“…We excluded fitted reconstructions with negative eigenvalues of the Hessian matrix and those which returned very unrealistic fruit size optima ( > 20 cm or < 0.1 cm). We also excluded statistical outliers, for the remaining parameters, since these may be produced when the model fails in converging (Alencar et al 2017). Because OUMA and OUMVA models often failed to converge we report the results for the remaining models and present the results for OUMA and OUMVA in the Supplementary material.…”