How males respond to rivals: an integrated study of molecular mechanisms and fitness consequences

Males of many different mammal, bird and invertebrate species respond to their social and sexual environment. These responses have profound effects on their reproductive success. For example, males of many species that perceive rivals transfer more sperm to females during mating, to increase their share of paternity. However, the complete pathway from the detection of cues from rival males, to effects on the composition of the male ejaculate through to ultimate reproductive success is not known. Nor do we know the effects on ageing for males of responding to rivals. The discovery of the pathway between rival detection and paternity represents the next key stage in understanding the evolution of male mating success. In this proposal we aim to provide the first case study, using the fruitfly. The fruitfly offers a unique opportunity, its genome has been sequenced and there are many different genetic reagents available with which to manipulate a male's perception of the number of rivals present. We have also generated a substantial amount of relevant and novel background data. For example, males respond to the presence of rivals before mating, and subsequently mate for longer when they do meet a female. More importantly, during those longer matings they transfer more of key ejaculate components, which increase the overall number of offspring fathered. Males appear to detect rivals by smelling a particular male pheromone. Importance for pure research: The work tackles questions of fundamental importance: how do males respond to rivals and what are the fitness consequences of doing so. When ejaculates are limiting (e.g. when males that mate just a few times become exhausted), males partition their ejaculates among different matings and different females, according to how many rival males are present. However, despite the wealth of studies showing that males do this, key questions remain: (i) what are molecular mechanisms by which males signal and perceive rivals? and (ii) what are the overall consequences, particularly the impact on ageing, for males that respond to the presence of rivals. These are the questions we will answer. Importance for applied research: Of equal importance, our work will provide techniques to improve insect pest control. Insect pests are the source of the world's most serious agricultural (and health) problems. Research is focusing on methods whose basic principles lie in biological control. However, males produced for control often have poor mating success. We aim to provide methods to improve this (e.g. simple husbandry rules to increase exposure to rivals or pheromones) using the fruitfly, which is the only species in which the relevant background data and genetic reagents are available. We plan to apply our findings to pests in the future. Methodology: We will manipulate male numbers and length of exposure to rivals, and the smell pathways that our work has highlighted as important. We can test the amount of ejaculate proteins transferred to females during mating using a method developed by our project partner, Mariana Wolfner from Cornell University. We can test for sperm transfer by staining and counting the sperm transferred. To test for the effects of responding to rivals on male ageing, we will compare the lifespan and reproductive success of males that mate following exposure, or not, to rivals. Timeliness and originality: Our proposal will provide the first investigation of the complete pathway by which males respond to rivals. The work is timely given the recent elucidation of smell receptors, our recent discoveries of changes to ejaculate composition in the presence of rivals and the recent surge of developments in genetic insect pest control.

Males responses to rivals ultimately and profoundly affect their reproductive fitness. However, the complete, causal pathway from the detection of cues from rivals through to ultimate fitness effects is unknown. In this proposal we aim to provide the first case study, using the fruitfly (D. melanogaster). The overall rationale is to (i) understand the mechanisms underlying the fitness benefits of responding to rivals, (ii) determine the effects on male ageing / fitness of responding to rivals, and (iii) provide methods to implement in a pest control context. Importance of male reproductive fitness and male ageing: This proposal tackles questions of fundamental importance: how do males respond to rivals and what are the fitness consequences of doing so. Key questions remain: (i) what are molecular mechanisms by which variation in rival numbers is perceived, and (ii) what are the impacts on ageing, for males that respond to rivals. Importance of male reproductive fitness for insect pest control: Males produced for mass release insect control often have reduced mating ability. We aim to provide simple husbandry techniques (e.g. increased exposure to rivals and / or their pheromones) to improving male quality. We plan to extend into pests (e.g. Medfly) in future applications together with industrial partners. We will use manipulations of smells (the major volatile pheromone, cis vaccenyl acetate), smell receptors (odorant and gustatory receptors) and cuticular hydrocarbon biosynthesis mutants, to test the idea that males that cannot sense rivals or female mating status will not respond adaptively to the presence of rivals and will not show adaptive changes in ejaculate composition. We will also test the effect on male lifespan and ageing of responding to rivals. The work is timely given the recent discovery of odorant receptors, of the important fitness effects of male detection of rivals and of recent developments in the technology of genetic pest control.