Social and environmental influences on mate attraction, mate choice and territorial defence

Abstract

This thesis explores social and environmental influences on mate attraction, mate choice and territoriality across a range of model vertebrate and invertebrate species. Chapter 1 investigates context-dependent male mate choice in the eastern mosquitofish (Gambusia holbrooki). Theoretical models predict that male choice is strongly influenced by the level of male-male competition. I found, however, that males associated with larger females, irrespective of the presence of rivals or these rivals’ relative competitive ability. It seems, at least in this system, that males do not maximise their expected reproductive success in the immediate social setting. In Chapter 2 I explore who is the ideal neighbour for a male during the communal courtship displays of fiddler crabs (Uca mjoebergi) where females can encounter males at varying distances. The initial distance at which males are seen partly determined how neighbours’ sexual signals affected male mating success, suggesting that males should ideally court next to less attractive neighbours. Interestingly, fiddler crabs are also one of the few territorial species where larger (more attractive) males act to retain smaller (less attractive) neighbours by assisting them to repel intruders (defence coalitions). In Chapter 3 I show experimentally that males are indeed more likely to attract females if they court alongside smaller males. Chapters 4 and 5 examine the role of multiple male cues, namely the display rate, size and shape of the fiddler crab major claw, during female choice. I found that female U. mjoebergi selected mates based directly on wave rate but also indirectly on claw size because smaller males were less likely to wave. In a separate experimental study, controlling for the colour, wave rate and size of the major claw, I show that claw shape alone plays little or no role in female mate choice in this species. When male fiddler crabs (U. annulipes) lose their original major claw, they can regenerate a new one that looks nearly identical but reduces their fighting ability. In Chapter 6 I test whether claw regeneration has an effect on coalition formation. Males with regenerated claws are as likely to help their neighbours as are original clawed males. This suggests that even though males with regenerated claws are weaker competitors, they still benefit from retaining a smaller neighbour. Chapter 7 looks at the role that resource value plays in determining fight outcome for a territory centered on a burrow in U. annulipes. Here, I show that when the disputed resource is also required for breeding (i.e. during the mating period), individuals with low resource holding potential (RHP) can improve their chances of mating if they escalate fights. In the final chapter I test whether the social environment affects male advertisement calling in three populations of field cricket (Teleogryllus commodus). There is some evidence that males increase their calling effort in response to the presence of a rival. Males housed with a rival also experienced a significant reduction in adult longevity. My results highlight the potential importance of plastic behavioral changes in courtship by males to life history strategies.