Experimental reduction of intromittent organ length reduces male reproductive success in a bug

It is now clear in many species that male and female genital evolution has been shaped by sexual selection. However, it has historically been difficult to confirm correlations between morphology and fitness, as genital traits are complex and manipulation tends to impair function significantly. In this study, we investigate the functional morphology of the elongate male intromittent organ (or processus) of the seed bug Lygaeus simulans, in two ways. We first use micro-computed tomography (micro-CT) and flash-freezing to reconstruct in high resolution the interaction between the male intromittent organ and the female internal reproductive anatomy during mating. We successfully trace the path of the male processus inside the female reproductive tract. We then confirm that male processus length influences sperm transfer by experimental ablation and show that males with shortened processi have significantly reduced post-copulatory reproductive success. Importantly, male insemination function is not affected by this manipulation per se. We thus present rare, direct experimental evidence that an internal genital trait functions to increase reproductive success and show that, with appropriate staining, micro-CT is an excellent tool for investigating the functional morphology of insect genitalia during copulation

The causes and consequences of reproductive interference in the Lygaeidae

Electronic version excludes material for which permission has not been granted by the rights holderReproductive interference occurs when individuals direct sexual behaviours towards other species and this causes a reduction in the fitness of one or both of the participants. While initially considered to be little more than an aberration, reproductive interference is increasingly recognised, not just as a factor in determining species co-existence and community dynamics, but also as an opportunity to further our understanding of sexual selection. In this thesis I investigate the causes and consequences of reproductive interference between several species of true bugs (Order: Hemiptera) in the family Lygaeidae. These species have a polygynandrous mating system, in which both males and females mate multiple times. I found that the interspecific mating attempts often witnessed in these bugs is likely a consequence of this mating system, as potential cues for species discrimination, in the form of cuticular hydrocarbons, are available and can be utilised by the bugs in some contexts. This is further supported by the finding that pre-copulatory selection on factors such as diet and chemical protection are weak in these insects. Furthermore, my work highlights the context-dependant nature of both the fitness costs associated with reproductive interference, and also of the bugs’ intra-specific behaviour. When housed in groups, female Lygaeus equestris did not show consistent fitness losses in response to harassment by either conspecific or heterospecific males, despite previous evidence showing that such males inflict costs on both egg production and longevity when interacting one-to-one. This, combined with the finding that male L. equestris alter their mate-guarding behaviour in the presence of other males, highlights the potential of behavioural flexibility to influence the outcome of inter-species interactions, and the importance of context when attempting to measure phenomena such as reproductive interference

Mate-guarding in a promiscuous insect : species discrimination influences context-dependent behaviour

Funding: NERC studentshipMating strategy is often informed by social context. However, information on social environment may be sensitive to interference by nearby heterospecifics, a process known as reproductive interference (RI). When heterospecific individuals are present in the environment, failures in species discrimination can lead to sub-optimal mating behaviours, such as misplaced courtship, misplaced rivalry behaviours, or heterospecific copulation attempts. All aspects of mating behaviour that are influenced by social context may be prone to RI, including copulatory behaviours associated with mate-guarding in the presence of possible competitors. Here we investigate the effect of three heterospecifics on the mate-guarding behaviour of male Lygaeus equestris seed bugs. We find that, despite previously reported heterospecific mating harassment amongst these species of lygaeid bug, male L. equestris are able to effectively distinguish rival conspecific males from heterospecifics. Thus, heterospecific mating attempts in this group may reflect selection on males to mate opportunistically, rather than a failure of species discrimination.Publisher PDFPeer reviewe

The extent and costs of reproductive interference among four species of true bug

ERB-S is supported by a Natural Environment Research Council (NERC) studentship and DMS was in part supported by a NERC Advanced Fellowship.Reproductive interference arises when individuals of one species engage in reproductive activities with individuals of another, leading to fitness costs in one or both species. Reproductive interference (RI) therefore has two components. First, there must be mis-directed mating interactions. Second, there must be costs associated with these mis-directed interactions. Here we consider RI between four species of true bug in the family Lygaeidae, focusing in particular on the fitness consequences to Lygaeus equestris. The species we consider vary in their relationships with each other, including species in the same or different genus, and with or without natural overlap in their geographic ranges. First we show that inter-specific mating interactions, although not a certain outcome, are common enough to perhaps influence mating behaviour in these species (arising in up to 10 % of inter-specific pairings). Second, we show that reproductive interference can seriously reduce female fitness in L. equestris. Importantly, different species impose different costs of RI on L. equestris, with interactions with male Spilostethus pandurus inflicting fitness costs of similar magnitude to the costs of mating with con-specifics. On the other hand, mating interactions with male Oncopeltus fasciatus appear to have no effect on female fitness. In a follow-up experiment, when we allowed competition amongst just females of S. pandurus and L. equestris, the fitness of the latter was not reduced, arguing more strongly for the role of reproductive interference. However, in our final experiments under mass mating conditions with extended ecological interactions (including scope for competition for resources and cannibalism), the costs of RI were less apparent. Our data therefore suggest that the costs of RI will be context-specific and may act in concert with, or be swamped by, other ecological effects. We suggest that comparative studies of this sort that both mimic naturally occurring reproductive interference events, and also artificially generate new ones, will be necessary if we are to better understand the ecological and evolutionary significance of reproductive interference.Publisher PDFPeer reviewe

Sexual stereotypes:the case of sexual cannibalism

There is a long-standing debate within the field of sexual selection regarding the potential projection of stereotypical sex roles onto animals by researchers. It has been argued that this anthropomorphic view may be hampering research in this area, for example by prioritizing the study of male sexual adaptations over female ones. We investigated how males and females are described in the sexual cannibalism literature. Sexual cannibalism is a specific form of sexual conflict and is highly gendered, with females generally cannibalizing males. We found that females were more likely to be described using active words and males with reactive words. This is contrary to recent results from a survey of the sexual conflict literature. While this reversed gender bias may arise from the nature of sexual cannibalism, our results nevertheless indicate an alternative form of sexual stereotyping. A number of the words used to describe cannibalistic females were highly loaded and suggestive of a negative stereotype of sexually aggressive females. To make progress we suggest first that animal behaviour researchers recognize both the costs and benefits of looking for general patterns as part of the scientific method. Although necessary, the search for general patterns may validate existing stereotypes or provide the basis for new ones. Additionally, we suggest that the field of sexual behaviour research is neither wholly bad nor good in terms of language use but that we should work towards a consensus of how and when we use particular terms to describe sexual behaviour. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.</p

Testing the effectiveness of pyrazine defences against spiders

Insects live in a dangerous world and may fall prey to a wide variety of predators, encompassing multiple taxa. As a result, selection may favour defences that are effective against multiple predator types, or target-specific defences that can reduce predation risk from particular groups of predators. Given the variation in sensory systems and hunting tactics, in particular between vertebrate and invertebrate predators, it is not always clear whether defences, such as chemical defences, that are effective against one group will be so against another. Despite this, the majority of research to date has focused on the role of a single predator species when considering the evolution of defended prey. Here we test the effectiveness of the chemical defences of the wood tiger moth, a species previously shown to have defensive chemicals targeted towards ants, against a common invertebrate predator: spiders. We presented both live moths and artificial prey containing their defensive fluids to female Trichonephila senegalensis and recorded their reactions. We found that neither of the moth’s two defensive fluids were able to repel the spiders, and confirmed that methoxypyrazines, a major component of the defences of both the wood tiger moth and many insect species, are ineffective against web-building spiders. Our results highlight the variability between predator taxa in their susceptibility to chemical defences, which can in part explain the vast variation in these chemicals seen in insects, and the existence of multiple defences in a single species.peerReviewe