RESUMEN
Biotic and abiotic factors often are treated as mutually exclusive drivers of diversification processes. In this framework, ecological specialists are expected to have higher speciation rates than generalists if abiotic factors are the primary controls on species diversity but lower rates if biotic interactions are more important. Speciation rate is therefore predicted to positively correlate with ecological specialization in the purely abiotic model but negatively correlate in the biotic model. In this study, I show that the positive relationship between ecological specialization and speciation expected from the purely abiotic model is recovered only when a species-specific trait, digestive strategy, is modeled in the terrestrial, herbivorous mammals (Mammalia). This result suggests a more nuanced model in which the response of specialized lineages to abiotic factors is dependent on a biological trait. I also demonstrate that the effect of digestive strategy on the ecological specialization-speciation rate relationship is not due to a difference in either the degree of ecological specialization or the speciation rate between foregut- and hindgut-fermenting mammals. Together, these findings suggest that a biological trait, alongside historical abiotic events, played an important role in shaping mammal speciation at long temporal and large geographic scales.
Asunto(s)
Fermentación/fisiología , Especiación Genética , Herbivoria , Mucosa Intestinal/metabolismo , Mamíferos/clasificación , Mamíferos/fisiología , Animales , Evolución Biológica , Dieta , Ecosistema , Intestinos/microbiología , FilogeniaRESUMEN
Several theories predict that rapidly diversifying clades will also rapidly diverge phenotypically; yet, there are also reasons for suspecting that diversification and divergence might not be correlated. In the widely distributed squirrel clade (Sciuridae), we test for correlations between per lineage speciation rates, species richness, disparity, and a time-invariant measure of disparity that allows for comparing rates when evolutionary modes differ, as they do in squirrels. We find that species richness and speciation rates are not correlated with clade age or with each other. Disparity appears to be positively correlated with clade age because young, rapidly diversifying Nearctic grassland clades are strongly pulled to a single stable optimum but older, slowly diversifying Paleotropical forest clades contain lineages that diverge along multiple ecological and morphological lines. That contrast is likely due to both the environments they inhabit and their phylogenetic community structure. Our results argue against a shared explanation for diversity and disparity in favor of geographically mediated modes of speciation and ecologically mediated modes of phenotypic evolution.
Asunto(s)
Evolución Molecular , Especiación Genética , Polimorfismo Genético , Sciuridae/genética , Adaptación Fisiológica , Animales , EcosistemaRESUMEN
A large number of published phylogenetic estimates are based on a single locus or the concatenation of multiple loci, even though genealogies of single or concatenated loci may not accurately reflect the true history of species diversification (i.e., the species tree). The increased availability of genomic data, coupled with new computational methods, improves resolution of species relationships beyond what was possible in the past. Such developments will no doubt benefit future phylogenetic studies. It remains unclear how robust phylogenies that predate these developments (i.e., the bulk of phylogenetic studies) are to departures from the assumption of strict gene tree-species tree concordance. Here, we present a parametric bootstrap (PBST) approach that assesses the reliability of past phylogenetic estimates in which gene tree-species tree discord was ignored. We focus on a universal cause of discord-the random loss of gene lineages from genetic drift-and apply the method in a meta-analysis of East African cichlids, a group encompassing historical scenarios that are particularly challenging for phylogenetic estimation. Although we identify some evolutionary relationships that are robust to gene tree discord, many past phylogenetic estimates of cichlids are not. We discuss the utility of the PBST method for evaluating the robustness of gene tree-based phylogenetic estimations in general as well as for testing the clade-specific performance of species tree estimation methods and designing sampling strategies that increase the accuracy of estimated species relationships.
Asunto(s)
Cíclidos/clasificación , Filogenia , África Oriental , Animales , Cíclidos/genética , Genes , Sitios GenéticosRESUMEN
Exceptional species and phenotypic diversity commonly are attributed to ecological opportunity (EO). The conventional EO model predicts that rates of lineage diversification and phenotypic evolution are elevated early in a radiation only to decline later in response to niche availability. Foregut fermentation is hypothesized to be a key innovation that allowed colobine monkeys (subfamily Colobinae), the only primates with this trait, to successfully colonize folivore adaptive zones unavailable to other herbivorous species. Therefore, diversification rates also are expected to be strongly linked with the evolution of traits related to folivory in these monkeys. Using dated molecular phylogenies and a dataset of feeding morphology, I test predictions of the EO model to evaluate the role of EO conferred by foregut fermentation in shaping the African and Asian colobine radiations. Findings from diversification methods coupled with colobine biogeographic history provide compelling evidence that decreasing availability of new adaptive zones during colonization of Asia together with constraints presented by dietary specialization underlie temporal changes in diversification in the Asian but not African clade. Additionally, departures from the EO model likely reflect iterative diversification events in Asia.