The adaptive value of males in simple eusocial insect societies

Abstract

In the Hymenoptera (ants, bees, and wasps), female inclusive fitness is maximised directly by reproducing or indirectly through helping kin. By contrast, males have mainly evolved to disperse and mate, limiting fitness opportunities to direct reproduction. However, there are reports across the social Hymenoptera of natal males helping, by distributing food to brood, as well as defending and thermoregulating nests. It is not fully understood under what circumstances male help, how it is regulated, or whether helping carries indirect fitness benefits. Here, the hypothesis is tested that males are more than just ‘flying sperm’, and may have diversified pathways to maximising inclusive fitness. In achieving this aim, two tropical simple eusocial Polistinae paper wasps are studied, Polistes canadensis and Polistes lanio. First, through discovery and validation of new single-nucleotide polymorphism (SNP) markers, it is shown that siblings on the nest are fully related; suggesting indirect fitness opportunities for brothers. Second, using captive studies of P. canadensis, it is found that females are long-lived; suggesting short-term male investments have the potential to be assured by sisters after males depart. Third, males of P. lanio are delayed dispersers: in field studies males remained on the natal nest whilst sexually maturing; eventual dispersal was regulated by juvenile hormone. Delayed dispersal with immaturity suggests a life history phase in which direct fitness gains are not achievable for adult males. Finally, by experimentally offering food to natal P. lanio males in field trials, males were shown to help by distributing food to brood; but this effort diminished with age, suggesting male helping is temporary. In conclusion, it is proposed that males have the potential to exploit two different fitness strategies in their life, of a young helper that may benefit from indirect fitness gains and old reproductive that invests in mating and direct fitness.

Date of Award	25 Sep 2018
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Seirian Sumner (Supervisor) & Andrew N Radford (Supervisor)