DOI: 10.5061/dryad.fqz612jpp
title: Anisogamy is unrelated to the intensity of sexual selection

description: Males and females often display different behaviours and, in the context
 of reproduction, these behaviours are labelled sex roles. The
 Darwin–Bateman paradigm argues that the root of these differences is
 anisogamy (i.e., differences in size and/or function of gametes between
 the sexes) that leads to biased sexual selection, and sex differences in
 parental care and body size. This evolutionary cascade, however, is
 contentious since some of the underpinning assumptions have been
 questioned. Here we investigate the relationships between anisogamy,
 sexual size dimorphism, sex difference in parental care and intensity of
 sexual selection using phylogenetic comparative analyses of 64 species
 from a wide range of animal taxa. The results question the first step of
 the Darwin–Bateman paradigm, as the extent of anisogamy does not appear to
 predict the intensity of sexual selection. The only significant predictor
 of sexual selection is the relative inputs of males and females into the
 care of offspring. We propose that ecological factors, life-history and
 demography have more substantial impacts on contemporary sex roles than
 the differences of gametic investments between the sexes.
description: We followed the PRISMA (Preferred Reporting Items for Systematic
 Reviews and Meta-Analyses) [1] statement to search systematically the
 literature using the exact same method given by Janicke et al. (2016) [2],
 to augment Janicke et al’s dataset. We searched the ISI Web of Knowledge
 (Web of Science Core Collection, from 1945 to 2017) in 2017 3rd of March
 the following “topic” search terms and format: (“Bateman*” OR
 “opportunit*for selection” OR“opportunit*for sexual selection”OR“selection
 gradient*”), where asterisk (*) represents any group of characters,
 including no character. We obtained 754 candidate publications for further
 investigation. We compared these studies to Janicke’s database, and we
 checked all the items absent in their database. We were able to extend the
 dataset of Janicke et al. only with one new species (Lamprotornis superbus
 where data was extract from the supplementary material of Apakupakul and
 Rubenstein(2015)), otherwise, we used their data. Hermaphrodite species
 (Physa acuta, Biomphalaria glabrata) were excluded. Overall, our dataset
 contains data from 64 species.  1. Moher D et al. 2009
 Preferred reporting items for systematic reviews and meta-analyses: The
 PRISMA statement (Chinese edition). J. Chinese Integr. Med. 7, 889–896.
 (doi:10.3736/jcim20090918) 2.  Janicke T, Ha derer IK,
 Lajeunesse MJ, Anthes N. 2016 Darwinian sex roles confirmed across the
 animal kingdom. Sci. Adv. 2, e1500983–e1500983.
 (doi:10.1126/sciadv.1500983)   This
 dataset contains the following information: 
       
 name description
 notes 
 species species latin
 name   
 sperm_head_length sperm head length
  (μm)   
 sperm_head_length_reference reference of
 sperm head length  (μm)   
 sperm_total_length sperm length
  (μm)   
 sperm_total_length_reference reference of
 sperm total length  (μm)   
 testis_mass combined testis mass
 (g)   
 testis_mass_reference reference of combined
 testis mass (g)   
 other_testis_size other testis size
 data   
 other_testis_size_reference reference
 of   
 egg_mass fresh egg mass (g)
 fresh egg mass or newborn mass (g) 
 egg_mass_reference reference
 of fresh egg mass (g)   
 other_egg_size other egg size
 data   
 other_egg_size_reference reference of other
 egg size data   
 clutch_size clutch size
   
 clutch_size_reference reference of clutch
 size   
 male_body_mass male body mass
 (g)   
 male_body_mass_reference reference of male
 body mass (g)   
 female_body_mass female body mass
 (g)   
 female_body_mass_references reference
 of female body mass (g)   
 female_body_length female body
 length (mm)   
 female_body_length_reference reference
 of female body length (mm)   
 male_body_length male body
 length (mm)   
 male_body_length_reference reference
 of male body length (mm)   
 other_body_size other body size
 data   
 other_body_size_reference reference
 of other body size data   
 sexual_size_dimorphism log(male
 size) - log(female size)   
 sexual_size_dimorphism_how_was_measured
 what kind of body size  
 dI_lnCVR effect size
 of opportunity of selection   
 dI_lnCVR_VAR measurement error
 variance for dIs_lnCVR   
 dIs_lnCVR effect size of
 opportunity of sexual selection  
 dIs_lnCVR_VAR
 measurement error variance for dIs_lnCVR
   dbeta_g
 effect size of Bateman gradient
   
 dbeta_g_VAR measurement error variance for
 dbeta_g   
 selection_indices_reference_Janicke_et_al
 reference of selection (from Janicke)
   
 sperm_mass sperm mass (g)
   
 sperm_mass_reference reference of sperm
 mass (g)   
 sperm_volume sperm head volume
 (μm3)   
 sperm_volume_reference reference of sperm
 head volume (μm3)   
 parental_care parental care bias: if care:
 0 - just female, 1- shared but rather female care, 2- equal care, 3-shared
 but rather male care, 4- just male care, - no parental care
   
 parental_care_reference reference of
 parental care   
      
  
description: To represent the phylogenetic relationships between species, we
 used the most recent comprehensive phylogeny (timetree.org [3] that
 included all but seven species in our dataset. 
 Species added to the phylogeny
 trees.<br> Added species    Source<br> Colpula
 lativentris    [4]<br> Gerris gilettei    [4]<br> Hippocampus
 subelongatus    [5]<br> Ischnura gemina    [6]<br> Labidomera
 clivicollis<br> Megabruchidius dorsalis    [7]<br>
 [7]<br> Strongylocentrotus purpuratus    [8]<br>  
   4.    Li M, Tian Y, Zhao Y, Bu W. 2012
 Higher level phylogeny and the first divergence time estimation of
 heteroptera (insecta: Hemiptera) based on multiple genes. PLoS One 7.
 (doi:10.1371/journal.pone.0032152)<br> 5.    Teske PR, Beheregaray
 LB. 2009 Evolution of seahorses’ upright posture was linked to Oligocene
 expansion of seagrass habitats. Biol. Lett. 5, 521–3.
 (doi:10.1098/rsbl.2009.0152)<br> 6.    Swaegers J, Janssens SB,
 Ferreira S, Watts PC, Mergeay J, McPeek MA, Stoks R. 2014 Ecological and
 evolutionary drivers of range size in Coenagrion damselflies. J. Evol.
 Biol. 27, 2386–2395. (doi:10.1111/jeb.12481)<br> 7.    Kergoat GJ,
 Le Ru BP, Genson G, Cruaud C, Couloux A, Delobel A. 2011 Phylogenetics,
 species boundaries and timing of resource tracking in a highly specialized
 group of seed beetles (Coleoptera: Chrysomelidae: Bruchinae). Mol.
 Phylogenet. Evol. 59, 746–760. (doi:10.1016/j.ympev.2011.03.014)<br>
 8.    Lee YH. 2003 Molecular phylogenies and divergence times of sea
 urchin species of Strongylocentrotidae, Echinoida. Mol. Biol. Evol. 20,
 1211–1221. (doi:10.1093/molbev/msg125)<br>