Does Sex Speed Up Evolutionary Rate and Increase Biodiversity?

Most empirical and theoretical studies have shown that sex increases the rate of evolution, although evidence of sex constraining genomic and epigenetic variation and slowing down evolution also exists. Faster rates with sex have been attributed to new gene combinations, removal of deleterious mutations, and adaptation to heterogeneous environments. Slower rates with sex have been attributed to removal of major genetic rearrangements, the cost of finding a mate, vulnerability to predation, and exposure to sexually transmitted diseases. Whether sex speeds or slows evolution, the connection between reproductive mode, the evolutionary rate, and species diversity remains largely unexplored. Here we present a spatially explicit model of ecological and evolutionary dynamics based on DNA sequence change to study the connection between mutation, speciation, and the resulting biodiversity in sexual and asexual populations. We show that faster speciation can decrease the abundance of newly formed species and thus decrease long-term biodiversity. In this way, sex can reduce diversity relative to asexual populations, because it leads to a higher rate of production of new species, but with lower abundances. Our results show that reproductive mode and the mechanisms underlying it can alter the link between mutation, evolutionary rate, speciation and biodiversity and we suggest that a high rate of evolution may not be required to yield high biodiversity

The contribution of temperature and continental fragmentation to amphibian diversification

International audienceAim: Abiotic factors such as global temperature or continental fragmentation mayfavour speciation through the ecological and geographical isolation of lineages, butmacroevolutionary quantifications of such effect with both fossil and phylogeneticdata are rarely performed. Here, we propose to use biogeographical estimations andpalaeo‐environmental diversification models to estimate whether and how palaeotemperatureand the sequential break‐ups of Pangaea, Gondwana and Laurasiahave affected the diversification of amphibians through time.Location: Global.Methods: Using a time‐calibrated phylogeny for 3,309 amphibian species and agenus‐level fossil record, we estimated the diversification rates of the group withbirth–death models allowing rates to depend on the temporal variations of the environment.We used estimates of global palaeotemperature and an index of continentalfragmentation through time to test the association between speciation and/or extinctionrates and past temperature and fragmentation. We also estimated the biogeographicalhistory based on a time‐stratified parametric model informed by theglobal palaeogeography. We inferred whether vicariance or dispersal events explainedthe ancient and current geographical distribution of amphibians.Results: The diversification analyses on the whole amphibians showed that temperature‐dependent models are better supported than tectonic‐dependent, time‐dependentand constant‐rate models for both the fossil and phylogenetic data. Thebest‐fitting temperature‐dependent model indicated a positive dependence of bothspeciation and extinction rates with the temperature through time. Biogeographicalanalyses indicated a Pangaean origin for amphibians and also showed that allopatricspeciation (vicariance) explained important phases of the evolution of geographicalranges in the Mesozoic.Main conclusions: Our results support that palaeotemperatures have positively impactedamphibian diversification. Our study provides additional insights into how toquantify the effect of the landmass fragmentation on the diversification processesand shows with biogeographical reconstruction that continental fragmentation islinked to allopatric speciation in the early history of the clade