Steell, E. M. | bioRxiv Science

bioRxiv2023

Geographic patterns of living tetrapod diversity reveal the signature of global diversification dynamics

AimBiodiversity is distributed unevenly among lineages and regions, and understanding the processes generating these global patterns is a central goal in evolutionary research, particularly in light of the current biodiversity crisis. Here, we integrate phylogenetic relatedness with species diversity patterns in four major clades of living tetrapods (amphibians, squamates, birds, and mammals) to approach this challenge. LocationGlobal. Time period300 million years ago - Present. Major taxa studiedTetrapods. MethodsWe studied geographic patterns of richness-corrected phylogenetic diversity (residual PD), identifying regions where species are phylogenetically more closely or distantly related than expected by richness. We explored the effect of different factors in residual PD: recent speciation rates, temporal trends of lineage accumulation, and environmental variables. Specifically, we searched for evolutionary and ecological differences between regions of high and low residual PD. ResultsOur results show heterogeneous spatial patterns of diversity dynamics across tetrapods. They reveal an overall negative relationship between recent speciation rates and residual PD, underscoring the role of recent speciation events in structuring current biogeographic patterns. Furthermore, we found differences between endothermic and ectothermic tetrapods in response to temperature and precipitation, highlighting the pivotal role of thermal physiology in shaping diversity dynamics. Main conclusionsGeographic patterns of diversity dynamics are heterogeneous across tetrapod clades and help us disentangle the evolutionary and ecological processes underlying them. By illuminating the multifaceted factors underpinning global diversity patterns, our study represents a significant advancement towards better understanding of how the present-day diversity of tetrapods was formed and how speciation rates influenced their species and phylogenetic diversity across clades and regions.

evolutionary biology↗

bioRxiv2023

Relative Homoplasy Index: A New Cross-comparable Metric for Quantifying Homoplasy in Discrete Character Datasets

Homoplasy is among the main hinderances to phylogenetic inference. However, investigating patterns of homoplasy can also improve our understanding of macroevolution, for instance by revealing evolutionary constraints on morphology, or highlighting convergent form-function relationships. Several methods have been proposed to quantify the extent of homoplasy in discrete character matrices, but the consistency index (CI) and retention index (RI) have remained the most widely used for decades, with little recent scrutiny of their function. Here, we test the performance of CI and RI using simulated and empirical datasets and investigate patterns of homoplasy with different matrix scenarios. In addition, we describe and test a new scaled metric, the relative homoplasy index (RHI), implemented in the R statistical environment. The results suggest that, unlike the RI, the CI does not constitute a direct measure of homoplasy. However, the RI consistently underestimates the extent of homoplasy in phylogenetic character-taxon matrices, particularly in datasets characterised by high levels of homoplasy. By contrast, RHI--the newly proposed metric--outperforms both methods in sensitivity to homoplasy levels, and is scaled between zero and one for comparison of values between different datasets. Using both simulated and empirical phylogenetic datasets, we show that relative levels of homoplasy remain constant with the addition of novel characters, and, in contrast to earlier work, decrease with the addition of taxa. Our results help illuminate the inherent properties of homoplasy in cladistic matrices, opening new potential avenues of research for investigating patterns of homoplasy in macroevolutionary studies.

evolutionary biology↗