The ecology of a continental evolutionary radiation: Is the radiation of sigmodontine rodents adaptive?

Abstract

Evolutionary radiations on continents are less well-understood and appreciated than those occurring on islands. The extent of ecological influence on species divergence can be evaluated to determine whether a radiation was ultimately the outcome of divergent natural selection or else arose mainly by nonecological divergence. Here, we used phylogenetic comparative methods to test distinct hypotheses corresponding to adaptive and nonadaptive evolutionary scenarios for the morphological evolution of sigmodontine rodents. Results showed that ecological variables (diet and life-mode) explain little of the shape and size variation of sigmodontine skulls and mandibles. A Brownian model with varying rates for insectivory versus all other diets was the most likely evolutionary model. The insectivorous sigmodontines have a faster rate of morphological evolution than mice feeding on other diets, possibly due to stronger selection for features that aid insectivory. We also demonstrate that rapid early-lineage diversification is not accompanied by high morphological divergence among subclades, contrasting with island results. The geographic size of continents permits spatial segregation to a greater extent than on islands, allowing for allopatric distributions and escape from interspecific competition. We suggest that continental radiations of rodents are likely to produce a pattern of high species diversification coupled with a low degree of phenotypic specialization.

Divergent selection along elevational gradients promotes genetic and phenotypic disparities among small mammal populations

“…Such conflicting patterns might reflect idiosyncratic responses due to inherent ecological, physiological, and evolutionary constraints (Adams & Church, 2008;Itescu et al, 2018). This manyto-one mapping scenario predicts that complex morphological structures, such as the skull, can perform similar functions with divergent forms (Maestri et al, 2017;Renaud et al, 2018;Wainwright, 2007;Wainwright, Alfaro, Bolnick, & Hulsey, 2005). Sampling part of a species' (altitudinal) range may fail to reveal the real trend, as shown by Adams and Church (2008) At high elevations, the reduced species richness and predation pressure (Fu et al, 2007;Kumar, Longino, Colwell, & O'Donnell, 2009; (Liao et al, 2006), while that of the high-altitude plateau pika (Ochotona curzoniae) presents a positive trend (Lin, Ci, Zhang, & Su, 2008).…”

Diversification of the climatic niche drove the recent processes of speciation in Sigmodontinae (Rodentia, Cricetidae)

“…We estimated the rates of speciation of Sigmodontinae species based on the phylogenetic hypothesis of Maestri et al. (), using Bayesian analysis of macroevolutionary mixtures software BAMM 2.5 (Rabosky et al. , ).…”

“…Although the group has been thought to represent an adaptive radiation because of its apparent ecological diversification, recent studies pointed to the possibility that the subfamily did not undergo that process (Maestri et al. ). The aim of the present work was to analyse the role of the climatic niche in the diversification of the species of Sigmodontinae (Cricetidae).…”

Using phylogenetic clade composition to understand biogeographical variation in functional traits

“…Trait variation was explored by applying geometric morphometrics to analyze the skulls and mandibles of nearly 3,000 sigmodontine specimens (Maestri 2017). At the species level, geographical and historical process were found likely to be more important than ecological variables to explain the morphological evolution of skull and mandible size and shape (Maestri et al 2017b). High functional versatility and limited morphological specialization of skulls and mandibles may account for this pattern (Maestri et al 2016b(Maestri et al , 2017b.…”

“…At the species level, geographical and historical process were found likely to be more important than ecological variables to explain the morphological evolution of skull and mandible size and shape (Maestri et al 2017b). High functional versatility and limited morphological specialization of skulls and mandibles may account for this pattern (Maestri et al 2016b(Maestri et al , 2017b. Moreover, size and shape variation can be linked to different sets of predictors Elton 2009, Maestri et al 2016c), suggesting that an analysis of both traits is necessary.…”