Data from: Sex-biased cooperation among immature peers: It matters who helps whom

Our understanding of sex-biased helping has progressed from a historical
emphasis on relatedness differences caused by haplodiploidy to an
understanding of the role played by the rarer-sex effect. Theory to date
typically assumes that offspring help their mother. We show that an
alternative, peer-to-peer cooperation, can shed light on the interaction
of helpers and the recipients of help. In pine sawfly (Diprion pini)
larvae, larval peer-to-peer cooperation takes the form of collective, and
individually costly, antipredator behaviour. Larvae typically occur in
mixed-sex groups, but females can lay unfertilized eggs that develop into
haploid males, which produce male-only broods. Female-biased sex ratios
typically select for female-biased helping, and our model here matches
empirical findings. Alternative scenarios provide insight too: (1) if
genetic constraints permit no sex-specificity in behaviour beyond haploid
males expressing all alleles while helping in females can be recessive or
dominant, then the sex difference in helping simply reflects the effects
of dominance. (2) Female-biased helping can also emerge under male-biased
sex ratios, if males are mostly produced in single-sex broods by unmated
mothers. While this last example remains hypothetical for D. pini, it
highlights an underappreciated point: the rarer-sex effect impacts
solutions not only by modifying fitness prospects of the helper, but also
of the recipient of help.