DOI: 10.5061/dryad.573n5tb6n
title: Male-biased sexual selection, but not sexual dichromatism, predicts speciation in birds

description: Sexual selection is thought to shape phylogenetic diversity by affecting
 speciation or extinction rates. However, the net effect of sexual
 selection on diversification is hard to predict, because many of the
 hypothesised effects on speciation or extinction have opposing signs and
 uncertain magnitudes. Theoretical work also suggests that the net effect
 of sexual selection on diversification should depend strongly on
 ecological factors, though this prediction has seldom been tested. Here,
 we test whether variation in sexual selection can predict speciation and
 extinction rates across passerine birds (up to 5,812 species, covering
 most genera) and whether this relationship is mediated by environmental
 factors. Male-biased sexual selection, and specifically sexual size
 dimorphism, predicted two of the three measures of speciation rates that
 we examined. The link we observed between sexual selection and speciation
 was independent of environmental variability, though species with smaller
 ranges had higher speciation rates. There was no association between any
 proxies of sexual selection and extinction rate. Our findings support the
 view that male-biased sexual selection, as measured by frequent predictors
 of male-male competition, has shaped diversification in the largest
 radiation of birds.
description: We obtained estimates of species range size using expert range
 maps (BirdLife International and Handbook of the Birds of the World 2017).
 The names of 1,230 species in the Birdlife database (Hoyo and Collar 2016)
 have been recently changed, so we manually matched these taxa with the
 names used in the sexual dichromatism dataset (Hoyo and Collar 2016).
 For each species’ range, we obtained estimates of climatic conditions by
 extracting 1,000 random point samples of each bioclimatic variable. We
 extracted 19 present-day bioclimatic variables (representing a variety of
 biologically relevant annual trends in temperature and precipitation) with
 30-second (~1 km2) spatial resolution (Fick and Hijmans 2017). From the
 1000 values of each bioclimatic variable, we obtained means and standard
 deviations for each species. Using the same spatial sampling, we extracted
 means and standard deviations of bioclimatic variables from the
 paleoclimate during the last interglacial (LIG; 120,000 - 140,000 years
 ago) (Otto-Bliesner et al. 2006). To estimate variability in the energy
 available to species, we obtained the mean and standard deviation of net
 primary productivity (NPP) values between 2000 - 2015 across each species
 distribution. Estimates of NPP had 30-second resolution and were obtained
 through MODIS (Moderate Resolution Imaging Spectroradiometer) primary
 production products stage 3 (MOD17A3) (Zhao et al. 2005).
 <strong>References</strong>
 BirdLife International and Handbook of the Birds of the World.
 2017. Bird species distribution maps of the world.
 http://datazone.birdlife.org/species/requestdis. Fick,
 S. E., and R. J. Hijmans. 2017. WorldClim 2: New 1-km spatial resolution
 climate surfaces for global land areas. International Journal of
 Climatology 37:4302–4315. Hoyo, J. del, and N. J.
 Collar. 2016. HBW and birdlife international illustrated checklist of the
 birds of the world. Lynx Edicions; BirdLife International.
 Otto-Bliesner, B. L., S. J. Marshall, J. T. Overpeck, G. H.
 Miller, A. Hu, and. 2006. Simulating arctic climate warmth and icefield
 retreat in the last interglaciation. Science 311:1751–1753.
 Zhao, M., F. A. Heinsch, R. R. Nemani, and S. W. Running. 2005.
 Improvements of the modis terrestrial gross and net primary production
 global data set. Remote Sensing of Environment 95:164–176.
description: The data, with relevant code relating to its usage and analysis
 is available on
 Github: https://github.com/JustinCally/SexualSelection_Speciation