Data from: Population density and structure drive differential investment in pre- and postmating sexual traits in frogs

Sexual selection theory predicts a trade-off between premating (ornaments and armaments) and postmating (testes and ejaculates) sexual traits, assuming that growing and maintaining these traits is costly and that total reproductive investments are limited. The number of males in competition, the reproductive gains from investing in premating sexual traits, and the level of sperm competition are all predicted to influence how males allocate their finite resources to these traits. Yet, empirical examination of these predictions is currently scarce. Here, we studied relative expenditure on pre- and postmating sexual traits among frog species varying in their population density, operational sex ratio and the number of competing males for each clutch of eggs. We found that the intensifying struggle to monopolize fertilizations as more and more males clasp the same female to fertilize her eggs shifts male reproductive investment toward sperm production and away from male weaponry. This shift, which is mediated by population density and the associated level of male–male competition, likely also explains the trade-off between pre- and postmating sexual traits in our much broader sample of anuran species. Our results highlight the power of such a multi-level approach in resolving the evolution of traits and allocation trade-offs.Estimates of population density and operational sex ratioIndividual estimates of population density (individuals/m2) and operational sex ratio (proportion of males among all individuals) for each of our 10 focal species. The date indicates the first of three consecutive days of data collection for each estimate.PopulationDensity_and_OSR.txtGenbank accession numbersGenbank accession numbers for the gene sequences used to generate the phylogenyAccessionNumbers.txtSpecies-specific dataSpecies-specific data of all 30 species, including morphological data, mating system (monandry, polyandry), temporal breeding pattern (explosive breeder, prolonged breeder), oviposition site (aquatic, terrestrial/arboreal), and male competition and female choice (yes, no).SpeciesSpecificData.txtPhylogenyPhylogeny with branch lengths of the 30 anuran species used.phylogeny.nexMorphological data of individual males of 10 focal speciesMorphological data (body mass, testes mass, forelimb muscle mass) of all males males used to calculate intra-specific allometries.IndividualMorphologicalData.tx