SPECIES ISOLATION,GENITAL MECHANICS,AND THE EVOLUTION OF SPECIES-SPECIFIC GENITALIA IN THREE SPECIES OF MACRODACTYLUS BEETLES (COLEOPTERA,SCARABEIDAE, MELOLONTHINAE)

The question asked was why male genitalic structures have diverged in three syntopic species of Macrodactylus beetles. Four hypotheses were evaluated: 1. The ways in which male genitalia mesh with internal female structures indicate that selection for species isolation via mechanical exclusion (“lock and key”) is unlikely to explain the genitalic differences. 2. The specific mate recognition hypothesis also clearly fails to explain genitalic differences due to the implausibility of postulated environmental effects on genitalia, and lack of postulated coevolution of male and female morphologies. 3. Selection for species isolation via differences in genitalic stimulation (sensory lock and key) is unlikely due to relatively infrequent cross-specific pair formation and intromission in the field, and “excessive” numbers of species-specific genitalic structures and male courtship behavior patterns which nevertheless occasionally fail. It also fails to explain the frequent failure of intraspecific copulations to result in sperm transfer. This hypothesis cannot, however, be rejected as confidently as the previous hypotheses. 4. Conditions under which sexual selection by cryptic female choice could take place are common. Females frequently exercise their ability to prevent sperm transfer by conspecific males even after intromission has occurred, and females generally mate repeatedly, probably with different males. Males behave as if cryptic female choice is occurring, courting assiduously while their genitalia are within the female. Sexual selection by female choice could thus contribute to the divergence in genitalic structures.     

Evolution of animal genitalia: morphological correlates of fitness components in a water strider

Rapid divergence of male genitalia is one of the most general evolutionary trends in animals with internal fertilization, but the mechanisms of genital evolution are poorly understood. The current study represents the first comprehensive attempt to test the main hypotheses that have been suggested to account for genital evolution (the lock-and-key, sexual selection and pleiotropy hypotheses) with intraspecific data. We measure multivariate phenotypic selection in a water strider species, by relating five different components of fitness (mating frequency, fecundity, egg hatching rate, offspring survival rate and offspring growth rate) to a suite of genital and non-genital morphological traits (in total 48). Body size had a series of direct effects in both sexes. Large size in females was positively related to both fecundity and egg hatching rate. There was positive sexual selection for large size in males (mating frequency), which to some extent was offset by a reduced number of eggs laid by females mated to large males. Male genitalic morphology influenced male mating frequency, but the detected directional selection on genitalia was due to indirect selection on phenotypically correlated non-intromittent traits. Further, we found no assortative mating between male intromittent genitalia and female morphology. Neither did we find any indications of male genitalia conveying information of male genetic quality. Several new insights can be gained from our study. Most importantly, our results are in stark disagreement with the long standing lock-and-key hypothesis of genital evolution, as well as with certain models of sexual selection. Our results are, however, in agreement with other models of sexual selection as well as with the pleiotropy hypothesis of genital evolution. Fluctuating asymmetry of bilaterally symmetrical traits, genital as well as non-genital, had few effects on fitness. Females with low fluctuating asymmetry in leg length produced offspring with a higher survival rate, a pattern most proba bly caused by direct phenotypic maternal effects. We also discuss the relevance of our results to sexual conflict over mating, and the evolution of sexual traits by coevolutionary arms races between the sexes.     

A phylogenetic analysis of the evolution of sexual dimorphism and mating systems in water striders (Hemiptera: Gerridae)

Conflicts over mating decisions characterize the sexual behaviour of many insects, in particular when males encounter females that already carry enough sperm to fertilize their eggs, since a mating often will inflict greater costs than benefits upon females. Therefore, coevolutionary models predict adaptation and counter-adaptation by the sexes in a battle to control the outcome of sexual encounters. A phylogenetic analysis was performed on patterns of sexual dimorphism and mating systems within water striders (Hemiptera, Gerridae). Phylogenetic effects or 'constraints' have significantly shaped patterns of sexual dimorphism in female/ male size ratios, legs and genitalia of males, and the structure of the female abdomen. Males of ancestral gerrids were probably slightly smaller than conspecific females, had powerful fore legs adapted to grasp the female's thorax during mating, and had clasping genitalic structures suited to grasp or pinch the female posteriorly. Most gerrids have a female/male size ratio between 1.05 and 1.14, but more pronounced sexual size ratios (above 1.25) have independently evolved several times in the family, usually in association with extended post-copulatory mate guarding. The comparative, phylogenetic analysis suggests coevolution of female anticlasper and male clasping devices for the clade comprising the subfamilies Cylindrostethinae, Ptilomerinae, and Halobatinae while female anticlasper devices have evolved in the absence of male clasping genitalia in the Gerrinae. The ancestral and most common mating system in gerrids is 'scramble competition polygyny' from which has evolved 'resource defence polygyny' at least four times independently of each other. The phylogenetic effects on patterns of mating behaviour are much less obvious, as exemplified by the large amount of interspecific variation in some genera.     

Genital and body allometry in two species of noctuid moths (Lepidoptera: Noctuidae)

One‐size‐fits‐all and related hypotheses predict that static allometry slopes for male genitalia will be consistently lower than 1.0 and lower than the slopes for most other body parts (somatic traits). We examined the allometry of genitalic and somatic morphological traits in males and females of two species of noctuid moths, Spodoptera exigua (Hübner, [1808]) and Helicoverpa armigera (Hübner, [1808]). The relationship between genitalic traits and body size was generally strongly negative‐allometric in males but with no significant differences from 1.00 in females of the two species examined. However, in females, the slope of genital traits was also lower than the slopes for somatic traits. The relationship between somatic traits and the body size indicator was approximately isometric in most cases in males, except in four traits in S. exigua, in which the slopes showed slight negative allometry, and the hind tibia in H. armigera, in which the slope had positive allometry. However, in females, some somatic traits showed isometric and some other showed negative allometry in both species. The coefficients of variation (CV) for all structures in the males were low, not exceeding 10%. Genitalic traits showed significantly lower CV than somatic traits in males. In females, somatic traits showed lower CV than genitalic traits but with no significant difference in the H. armigera. Our observations of strongly negative allometry for genitalic traits in males are consistent with stabilizing selection on genital size and we suggest that male performance in interactions with females is the source of selection on male genital allometry. The difference in the degree of phenotypic variation between genitalic and somatic traits in the two studied species is attributed to the different developmental‐genetic architectures of these traits. Female genitalia showed a similar trend to the males, although the difference between genital and somatic traits was not significant in females. This finding suggests that selection is acting differently on male and female genitalia. Positive allometry of hind tibia in H. armigera may be a result of secondary sexual function.     

A time-sequence functional analysis of mating behaviour and genital coupling in Drosophila: role of cryptic female choice and male sex-drive in the evolution of male genitalia

Male genitalia in Drosophila exemplify strikingly rapid and divergent evolution, whereas female genitalia are relatively invariable. Whereas precopulatory and post-copulatory sexual selection has been invoked to explain this trend, the functional significance of genital structures during copulation remains obscure. We used time-sequence analysis to study the functional significance of external genitalic structures during the course of copulation, between D. melanogaster and D. simulans. This functional analysis has provided new information that reveals the importance of male-driven copulatory mechanics and strategies in the rapid diversification of genitalia. The posterior process, which is a recently evolved sexual character and present only in males of the melanogaster clade, plays a crucial role in mounting as well as in genital coupling. Whereas there is ample evidence for precopulatory and/or post-copulatory female choice, we show here that during copulation there is little or no physical female choice, consequently, males determine copulation duration. We also found subtle differences in copulatory mechanics between very closely related species. We propose that variation in male usage of novel genitalic structures and shifts in copulatory behaviour have played an important role in the diversification of genitalia in species of the Drosophila subgroup.     

Male copulatory sensory stimulation induces female ejection of rival sperm in a damselfly

Male damselflies possess very specialized genitalia. Females mate multiply and store sperm in two sperm storage organs, the bursa copulatrix and the spermatheca. During copulation, males physically remove the sperm stored in these organs using their genitalia. I document a novel mechanism by which males gain access to the spermatheca in Calopteryx haemorrhoidalis asturica. The mechanism is based on male stimulation of the female sensory system that controls egg fertilization and laying. During copulation, the aedeagus (a male genitalic structure indirectly involved in sperm transfer) distorts the cuticular plates in the female genital tract that bear mechanoreceptive sensilla. This stimulation results in sperm ejection from the spermatheca. Aedeagus width is positively correlated with the amount of sperm ejected. I propose that males have exploited a pre-existing female sensory bias to gain access to otherwise physically unreachable sperm. These results shed light on the issue of the origin of female preferences in current models of sexual selection and on the evolution of genitalia via sexual selection. It is postulated that females might use this process as a form of post-copulatory sexual selection on the basis of males'' genitalia.     

The function of female resistance behavior: intromission by male coercion vs. female cooperation in sepsis flies (Diptera: Sepsidae)

Female resistance behavior that occurs prior to intromission does not by itself imply forced copulation. Such behavior may function instead as a test of the male in order to favor some males over others, or to induce the male to desist. Thus, male persistence and forcefullness may sometimes be better described as persuasion rather than coercion. Under the persuasion hypothesis, the male only gains intromission due to an active response of the female. Under the coercion hypothesis, male and female are opposed in a physical battle which the female loses if copulation occurs. In species in which males are morphologically incapable of forcing intromission without active female cooperation (I argue here that this is probably a very common situation), data on the behavioral and ecological context in which resistance occurs can distinguish between the two possibilities. Partially congruent functions of resistance, seen from the female point of view, are female resistance to screen (male persuasion), and female resistance to avoid males non-selectively (male coercion). Sepsis flies illustrate these ideas. Females often struggle energetically in apparent attempts to dislodge mounted males and to prevent intromission, and males grasp females with powerful species-specific structures on their front legs and genitalia. This suggests the possibility of coerced intromission. But behavioral and morphological evidence demonstrate that active female cooperation occurs at the moment of intromission, and that males are probably dependent on this cooperation because they are not morphologically equipped to force their genitalia into those of an uncooperative female. Despite the impression from previous publications, male insects in general may seldom be able to achieve intromission by genitalic force. The species-specific forms of the grasping genitalia of male sepsis are probably not the result of an evolutionary arms race between coercive males and unselectively resistant females.     

HAVE MALE AND FEMALE GENITALIA COEVOLVED? A PHYLOGENETIC ANALYSIS OF GENITALIC MORPHOLOGY AND SEXUAL SIZE DIMORPHISM IN WEB‐BUILDING SPIDERS (ARANEAE: ARANEOIDEA)

Sexual size dimorphism (SSD) can strongly influence the evolution of reproductive strategies and life history. If SSD is extreme, and other characters (e.g., genitalic size) also increase with size, then functional conflicts may arise between the sexes. Spiders offer an excellent opportunity to investigate this issue because of their wide range of SSD. By using modern phylogenetic methods with 16 species of orb-weaving spiders, we provide strong evidence for the "positive genitalic divergence" model, implying that sexual genitalic dimorphism (SGD) increases as SSD increases. This pattern is supported by an evolutionary mismatch between the absolute sizes of male and female genitalia across species. Indeed, our findings reveal a dramatic reversal from male genitalia that are up to 87x larger than female genitalia in size-monomorphic species to female genitalia that are up to 2.8x larger in extremely size-dimorphic species. We infer that divergence in SGD could limit SSD both in spiders, and potentially in other taxa as well. Further, male and female body size, as well as male and female genitalia size, are decoupled evolutionarily. Finally, we show a negative scaling (hypoallometry) of male and female genitalic morphology within sexes. Evolutionary forces specific to each sex, such as larger female size (increased fecundity) or smaller male size (enhanced mate-searching ability), may be balanced by stabilizing selection on relative genitalic size.     

The function and evolution of male and female genitalia in Phyllophaga Harris scarab beetles (Coleoptera: Scarabaeidae)

Genitalia diversity in insects continues to fuel investigation of the function and evolution of these dynamic structures. Whereas most studies have focused on variation in male genitalia, an increasing number of studies on female genitalia have uncovered comparable diversity among females, but often at a much finer morphological scale. In this study, we analysed the function and evolution of male and female genitalia in Phyllophaga scarab beetles, a group in which both sexes exhibit genitalic diversity. To document the interaction between male and female structures during mating, we dissected flash‐frozen mating pairs from three Phyllophaga species and investigated fine‐scale morphology using SEM. We then reconstructed ancestral character states using a species tree inferred from mitochondrial and nuclear loci to elucidate and compare the evolutionary history of male and female genitalia. Our dissections revealed an interlocking mechanism of the female pubic process and male parameres that appears to improve the mechanical fit of the copulatory position. The comparative analyses, however, did not support coevolution of male and female structures and showed more erratic evolution of the female genitalia relative to males. By studying a group that exhibits obvious female genitalic diversity, we were able to demonstrate the relevance of female reproductive morphology in studies of male genital diversity.     

We do not select,nor are we choosy: reproductive biology of Strepsiptera (Insecta)

The cryptic entomophagous parasitoids in the order Strepsiptera exhibit specific adaptations to each of the 34 families that they parasitize, offering rich opportunities for the study of male–female conflict. We address the compelling question as to how the diversity of Strepsiptera (where cryptic speciation is common) arose. Studying 13 strepsipteran families, including fossil taxa, we explore the genitalic structures of males, the free‐living females of the Mengenillidia (suborder), and the endoparasitic females of the Stylopidia (suborder). Inferring from similarity between aedeagi of males either between congeners, heterogeners, or between species within the same taxonomic family, the same of which is true of the cephalothoraces of females, we predict that male–female conflict and a co‐evolutionary morphological arms race between sexes is not likely to exist in most species of Strepsiptera. We then review the non‐genitalic structures that play a role during sexual communication, and present details of copulatory behaviour. We conclude that Strepsiptera fall within the synchronous sensory exploitation model where short‐lived males take advantage of a pre‐existing sensory system involving pheromone signals emitted by females.     

Hierarchical comparative analysis of genetic and genitalic geographical structure: testing patterns of male and female genital evolution in the scarab beetle Phyllophaga hirticula (Coleoptera: Scarabaeidae)

It is generally accepted that genitalia are among the fastest evolving characters in insects and that selection on these structures may increase speciation rates in groups with polygamous mating systems. If selection is causing genitalic divergence between or among populations of a species, one prediction is that geographical structure of genitalic morphology would be in place before genetic structure of a rapidly evolving neutral marker. The current study tests this hypothesis in the geographically widespread scarab beetle Phyllophaga hirticula by evaluating whether standing variation in male and female genitalia is more or less geographically structured than a mitochondrial genetic marker. Geographical structure of mitochondrial (mt)DNA and male and female genitalic shape were analysed using analysis of variance, multivariate analysis of variance, Mantel tests, and tests of spatial autocorrelation. The results show that, although female genitalia are more geographically structured than mtDNA, male genitalia are not. This pattern suggests that selection on female genitalic variation may be causing divergence of these structures among populations.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 135–149.     

Social preferences based on sexual attractiveness: a female strategy to reduce male sexual attention

Male sexual harassment of females is common across sexually reproducing species and can result in fitness costs to females. We hypothesized that females can reduce unwanted male attention by constructing a social niche where their female associates are more sexually attractive than themselves, thus influencing the decision-making of males to their advantage. We tested this hypothesis in the Trinidadian guppy (Poecilia reticulata), a species with high levels of male sexual harassment. First, we confirmed that non-receptive females were harassed less when they were paired with a more sexually attractive (receptive) female than with another non-receptive female. We then found that, indeed, females exploit this as a strategy to reduce sexual harassment; non-receptive females actively preferred to associate with receptive over non-receptive females. Importantly, when given access only to chemosensory cues, non-receptive females still showed this preference, suggesting that they use information from chemical cues to assess the sexual attractiveness of potential female partners. Receptive females in contrast showed no such preferences. Our results demonstrate that females can decrease male harassment by associating with females that are more sexually attractive than themselves and that they perform active partner choices based on this relative attractiveness. We propose that this strategy is likely to represent an important pathway by which females can construct social niches that influence the decision-making of others to their advantage; in this case, to reduce the sexual harassment they experience.     

INTERSEXUAL ARMS RACE? GENITAL COEVOLUTION IN NEPHILID SPIDERS (ARANEAE,NEPHILIDAE)

Genital morphology is informative phylogenetically and strongly selected sexually. We use a recent species-level phylogeny of nephilid spiders to synthesize phylogenetic patterns in nephilid genital evolution that document generalized conflict between male and female interests. Specifically, we test the intersexual coevolution hypothesis by defining gender-specific indices of genital complexity that summarize all relevant and phylogenetically informative traits. We then use independent contrasts to show that male and female genital complexity indices correlate significantly and positively across the phylogeny rather than among sympatric sister species, as predicted by reproductive character displacement. In effect, as females respond to selection for fecundity-driven fitness via giantism and polyandry (perhaps responding to male-biased effective sex ratios), male mechanisms evolve to monopolize females (male monogamy) via opportunistic mating, pre- and postcopulatory mate guarding, and/or plugging of female genitalia to exclude subsequent suitors. In males morphological symptoms of these phenomena range from self-mutilated genitalia to total castration. Although the results are compatible with both recently favored sexual selection hypotheses, sexually antagonistic coevolution, and cryptic female choice, the evidence of strong intersexual conflict and genitalic damage in both sexes is more easily explained as sexually antagonistic coevolution due to an evolutionary arms race.     

Costly sexual harassment in a beetle

Abstract The optimal number of mating partners for females rarely coincides with that for males, leading to sexual conflict over mating frequency. In the bruchid beetle Callosobruchus maculatus, the fitness consequences to females of engaging in multiple copulations are complex, with studies demonstrating both costs and benefits to multiple mating. However, females kept continuously with males have a lower lifetime egg production compared with females mated only once and then isolated from males. This reduction in fitness may be a result of damage caused by male genitalia, which bear spines that puncture the female’s reproductive tract, and/or toxic elements in the ejaculate. However, male harassment rather than costs of matings themselves could also explain the results. In the present study, the fitness costs of male harassment for female C. maculatus are estimated. The natural refractory period of females immediately after their first mating is used to separate the cost of harassment from the cost of mating. Male harassment results in females laying fewer eggs and this results in a tendency to produce fewer offspring. The results are discussed in the context of mate choice and sexual selection.     

Male harassment drives females to alter habitat use and leads to segregation of the sexes

Sexual conflict is ubiquitous across taxa. It often results in male harassment of females for mating opportunities that are costly for females, in some cases reducing reproductive success and increasing mortality. One strategy that females may employ to avoid sexual harassment is to segregate spatially from males. In fact, we do find sexual segregation in habitat use in species that have high levels of sexual conflict; however, the role of sexual harassment in driving such segregation remains poorly understood. Here, we demonstrate experimentally in a population of wild Trinidadian guppies Poecilia reticulata that male sexual harassment drives females into habitats that they otherwise do not prefer to occupy. In support of the social factors hypothesis for sexual segregation, which states that social factors such as harassment drive sexual segregation, this female behaviour leads to segregation of the sexes. In the presence of males, females actively select areas of high predation risk, but low male presence, and thus trade off increased predation risk against reduced sexual harassment.     

Sexually antagonistic coevolution in insects is associated with only limited morphological diversity

Morphological traits involved in male-female sexual interactions, such as male genitalia, often show rapid divergent evolution. This widespread evolutionary pattern could result from sustained sexually antagonistic coevolution, or from other types of selection such as female choice or selection for species isolation. I reviewed the extensive but under-utilized taxonomic literature on a selected subset of insects, in which male-female conflict has apparently resulted in antagonistic coevolution in males and females. I checked the sexual morphology of groups comprising 500-1000 species in six orders for three evolutionary trends predicted by the sexually antagonistic coevolution hypothesis: males with species-specific differences and elaborate morphology in structures that grasp or perforate females in sexual contexts; corresponding female structures with apparently coevolved species-specific morphology; and potentially defensive designs of female morphology. The expectation was that the predictions were especially likely to be fulfilled in these groups. A largely qualitative overview revealed several surprising patterns: sexually antagonistic coevolution is associated with frequent, relatively weak species-specific differences in males, but male designs are usually relatively simple and conservative (in contrast to the diverse and elaborate designs common in male structures specialized to contact and hold females in other species, and also in weapons such as horns and pincers used in intra-specific battles); coevolutionary divergence of females is not common; and defensive female divergence is very uncommon. No cases were found of female defensive devices that can be facultatively deployed. Coevolutionary morphological races may have occurred between males and females of some bugs with traumatic insemination, but apparently as a result of female attempts to control fertilization, rather than to reduce the physical damage and infections resulting from insertion of the male's hypodermic genitalia. In sum, the sexually antagonistic coevolution that probably occurs in these groups has generally not resulted in rapid, sustained evolutionary divergence in male and female external sexual morphology. Several limitations of this study, and directions for further analyses are discussed.     

A model of sexual selection and female use of refuge in a coercive mating system

In many non-monogamous systems, males invest less in progeny than do females. This leaves males with higher potential rates of reproduction, and a likelihood of sexual conflict, including, in some systems, coercive matings. If coercive matings are costly, the best female strategy may be to avoid male interaction. We present a model that demonstrates female movement in response to male harassment as a mechanism to lower the costs associated with male coercion, and the effect that female movement has on selection in males for male harassment. We found that, when females can move from a habitat patch to a refuge to which males do not have access, there may be a selection for either high, or low harassment male phenotype, or both, depending on the relationship between the harassment level of male types in the population and a threshold level of male harassment. This threshold harassment level depends on the relative number of males and females in the population, and the relative resource values of the habitat; the threshold increases as the sex ratio favours females, and decreases with the value of the refuge patch or total population. Our model predicts that selection will favour the harassment level that lies closest to this threshold level of harassment, and differing harassment levels will coexist within the population only if they lie on the opposite sides of the threshold harassment. Our model is consistent with empirical results suggesting that an intermediate harassment level provides maximum reproductive fitness to males when females are mobile.     

Social implications of the battle of the sexes: sexual harassment disrupts female sociality and social recognition

Across sexually reproducing species, males and females are in conflict over the control of reproduction. At the heart of this conflict in a number of taxa is male harassment of females for mating opportunities and female strategies to avoid this harassment. One neglected consequence that may result from sexual harassment is the disruption of important social associations. Here, we experimentally manipulate the degree of sexual harassment that wild female guppies (Poecilia reticulata) experience by establishing replicated, semi-natural pools with different population sex ratios. We quantify the effects of sexual harassment on female social structure and the development of social recognition among females. When exposed to sexual harassment, we found that females had more disparate social networks with limited repeated interactions when compared to females that did not experience male harassment. Furthermore, females that did not experience harassment developed social recognition with familiar individuals over an 8-day period, whereas females that experienced harassment did not, an effect we suggest is due to disruption of association patterns. These results show that social network structure and social recognition can be affected by sexual harassment, an effect that will be relevant across taxonomic groups and that we predict will have fitness consequences for females.     

Linking intra‐ and interspecific assortative mating: Consequences for asymmetric sexual isolation

Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within‐species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here, we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments, and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male–male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry indicates that sexual selection currently opposes a species boundary.     

The genetic architecture of sexual conflict: male harm and female resistance in Callosobruchus maculatus

Males harm females during mating in a range of species. This harm is thought to evolve because it is directly or indirectly beneficial to the male, despite being costly to his mate. The resulting sexually antagonistic selection can cause sexual arms races. For sexually antagonistic co-evolution to occur, there must be genetic variation for traits involved in female harming and susceptibility to harm, but even then intersexual genetic correlations could facilitate or impede sexual co-evolution. Male Callosobruchus maculatus harm their mates during copulation by damaging the female's reproductive tract. However, there have been no investigations of the genetic variation in damage or in female susceptibility to damage, nor has the genetic covariance between these characters been assessed. Here, we use a full-sib/half-sib breeding design to show that male damage is heritable, whereas female susceptibility to damage is much less so. There is also a substantial positive genetic correlation between the two, suggesting that selection favouring damaging males will increase the prevalence of susceptible females. We also provide evidence consistent with intralocus sexual conflict in this species.