Sexual behaviour and responses to the cues of mates and rivals in males of the parasitoid wasp, Mastrus ridens (Hymenoptera; Ichneumonidae)

Abstract

Behavioural flexibility can be advantageous when environments vary. When external conditions select for different strategies over time and space, species and individuals capable of evaluating these changes and modifying their behaviour are able to maximise their reproductive success in a variety of contexts. One factor that can alter selection on reproductive strategies is changes in the social environment, where demographic variation in populations may modify inter and intrasexual competition. Flexible male responses to shifts in intrasexual competition have been extensively studied in polyandrous species, providing many examples of male responses to sperm competition, depending on risk or intensity. Less is known about flexible male responses in species where males mate with multiple females but females mate only once. In these mating systems, male competition for mates is intense, but sperm competition does not occur. Parasitoid wasps provide ideal study systems to test the flexibility of male reproductive strategies as this group is mostly monandrous, their behaviour is often highly flexible, and laboratory populations are available to use in controlled manipulative experiments. In this thesis, I aim to explore the potential flexibility of mating behaviours and sperm investment strategies in a monandrous parasitoid wasp. I investigated the use of volatile chemical information in the parasitoid wasp M. ridens via Y-maze olfactometer experiments and provide the first behavioural evidence for a female-derived sex attractant pheromone in this species. In addition, I used mating experiments to test for male responses to varying sociosexual environments in terms of behaviour and sperm allocation. I found that volatile signals appear to be produced by females regardless of mating status and are innately attractive to males, regardless of whether males had previously cohabited with conspecifics. Moreover, males in my mating experiments did not appear to change their mating behaviour in response to exposure to males or females. They did, however, seem to alter sperm allocation: males that were exposed to rivals prior to mating appear to deplete their sperm stocks faster than isolated males or males that had been exposed to females. This novel research provides an investigation of behavioural flexibility and sperm investment strategies in an understudied mating system.