title: The ecology of sex explains patterns of helping in arthropod societies.
abstract: Across arthropod societies, sib-rearing (e.g. nursing or nest defence) may be provided by females, by males or by both sexes. According to Hamilton's 'haplodiploidy hypothesis', this diversity reflects the relatedness consequences of diploid vs. haplodiploid inheritance. However, an alternative 'preadaptation hypothesis' instead emphasises an interplay of ecology and the co-option of ancestral, sexually dimorphic traits for sib-rearing. The preadaptation hypothesis has recently received empirical support, but remains to be formalised. Here, we mathematically model the coevolution of sex-specific helping and sex allocation, contrasting these hypotheses. We find that ploidy per se has little effect. Rather, the ecology of sex shapes patterns of helping: sex-specific preadaptation strongly influences who helps; a freely adjustable sex ratio magnifies sex biases and promotes helping; and sib-mating, promiscuity, and reproductive autonomy also modulate the sex and abundance of helpers. An empirical survey reveals that patterns of sex-specific helping in arthropod taxa are consistent with the preadaptation hypothesis.
authors.affiliation: Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
authors.forename: Nicholas G
authors.identifier: 0000-0002-1740-1412
authors.initials: NG
authors.lastname: Davies
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, King's Buildings, Edinburgh, EH9 3JT, UK.
authors.forename: Laura
authors.initials: L
authors.lastname: Ross
authors.affiliation: School of Biology, University of St Andrews, Dyers Brae, St Andrews, KY16 9TH, UK.
authors.forename: Andy
authors.identifier: 0000-0002-1304-3734
authors.initials: A
authors.lastname: Gardner
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D001181:Arthropods / Q000235:genetics* / Q000502:physiology*; D005075:Biological Evolution; D005260:Female; D008297:Male; D008954:Models, Biological; D012641:Selection, Genetic; D012727:Sex Characteristics; D012744:Sex Ratio; D012919:Social Behavior
keywords: Eusociality; haplodiploidy; inbreeding; inclusive fitness; local mate competition; local resource enhancement; manipulation; preadaptation; sex ratio; sib-mating