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Polyandry can profoundly affect the strength of pre-copulatory sexual selection acting on males because each additional mate acquired by a female means that, all else being equal, a male’s paternity share declines. However, accruing additional mates could benefit male fitness if males with greater mating success also tend to have less promiscuous females as partners. If this is indeed the case, then males should experience strong sexual selection to acquire more mates. We tested these predictions by collecting detailed mating data on male and female Cook Strait giant weta (Deinacrida rugosa) in the wild via daily radio tracking. Our sexual network-based approach indeed revealed that the most polygynous male D. rugosa mated the least polyandrous females. This finding therefore suggests that the most successful males likely face lower intensities of sperm competition and so should be selected to accrue more mates. Further, our selection analysis revealed significant pre-copulatory sexual selection on males with those having relatively smaller body size, lighter body mass, and longer legs accruing more mates than otherwise. Thus, it appears that both pre- and post-copulatory episodes of sexual selection reinforce the same male phenotype.

The conopid fly Stylogaster neglecta Williston (Diptera: Conopidae) is a parasitoid with no known host. We report this species as the first recorded dipteran parasitoid of Oecanthus nigricornis Walker (Orthoptera: Gryllidae) (black-horned tree crickets). We reared field-collected O. nigricornis juveniles over several months in 2017 and found that larval S. neglecta emerged from them during late July into August. We estimated the incubation period for S. neglecta larvae to be around 30 days based on the length of time it took for them to emerge from the host and pupate (subsequently all hosts died). We documented several cases of multiple parasitism. In 2018, we dissected O. nigricornis sampled from four sites across southern Ontario, Canada and upstate New York, United States of America and found that the percentage of juvenile O. nigricornis parasitised ranged 2–39%. Further sampling will be necessary to determine whether this variation represents consistent population differences or between-year variation in parasitism.

Male genitalia are rapidly evolving structures, often driven by sexual conflict and/or sexual selection to increase fertilization success. Although sexual selection on females can be strong in systems where males provide offspring care or feed their mates, sometimes resulting in the evolution of female ornaments to acquire male investments, there are no studies of sexual selection on female genitalia. In New Zealand ground weta, Hemiandrus pallitarsis, females possess a genitalic device (the accessory organ) that is necessary for successful copulation and the acquisition of spermatophylax glandular gifts, which are probably important in avoiding starvation during a months-long period when caring for (their lifetime production of) eggs. Here, we test the hypothesis that the accessory organ is a sexually selected device in Hemiandrus pallitarsis by measuring the female Bateman gradient and directional sexual selection on the accessory organ (female mating frequency estimated from microsatellite analysis of offspring and/or stored sperm). As predicted, there was both positive Bateman gradients for females, and evidence of directional sexual selection on accessory organ length. Although organ length did not correlate well with female fecundity (eggs in abdomen), it may increase mating success by indicating maternal condition and thus quality of her offspring care.

The prevalence and diversity of female ornaments poses a challenge to evolutionary theory because males should prefer mates that spend resources on offspring rather than ornaments. Among dance flies, there is extraordinary variation in sexual dimorphism. Females of many species have conspicuous ornaments (leg scales and inflatable abdominal sacs). Meanwhile males of some species have regions of their eyes with larger ommatidial facets, common traits in many arthropod taxa that allow for regionally elevated photosensitivity and/or acuity. Here, we conduct a comparative study of these traits using both species descriptions available from the literature, as well as quantitative measures of eyes and ornaments from wild-caught flies. We show a conspicuous covariance between exaggerated male dorsal eye regions and the extent of female ornaments: species with highly ornamented females have males with more exaggerated eyes. We discuss this pattern in the context of competing hypotheses for their evolution.

Despite their prevalence in nature, the evolution of sex-specific female ornaments is still not well understood. Although in some cases (often carotenoid-based ornaments) they appear to honestly signal quality, such as fecundity, it has been suggested that some female ornaments have evolved to deceptively to obtain matings. We address these two hypotheses in the long-tailed dance fly ( Rhamphomyia longicauda ), where females possess two sex-specific ornaments: pinnate scales on the hind femur and tibia and abdominal sacs that are inflated in female-biased display swarms. Although several studies have suggested that female ornaments in this species are deceptive, evidence is mixed and requires further investigation. Here, we use static allometry (with body size as a proxy for condition) of both ornamental and non-ornamental traits in females (and homologous non-ornamental traits in males) in order to determine whether they are honest or deceptive signals of quality. Most male traits scaled isometrically with body size, however male leg hairs showed positive static allometry, probably because they are involved in nuptial-prey capture or in grasping mates. Ornamental traits in females (abdomen area and tibia scale length) showed significant positive allometry and had steep slopes relative to non-ornamental traits. As larger females invest more in ornamentation relative to smaller females, this suggests that these traits are likely honest, condition-dependent signals of quality. We note that honesty and deception are not mutually exclusive hypotheses. Individuals may vary in their signalling strategy, resulting in, for example, deception from some low condition individuals but honesty overall. Although our finding of positive allometry makes it unlikely this occurs in long tailed dance flies, simultaneous honesty and deception should be considered in future studies of female ornamentation.

Radiotransmitters have been used successfully to track and recapture giant wētā (Deinacrida species) in part to assess mating success. We report the successful use of very light transmitters (0.2 g) to track male Wellington tree wētā, Hemideina crassidens, over several nights to daytime refuges in burrows and tree galleries. Male Hemideina species sport lengthy mandibles used as weapons in fights with rivals over groups of females living in gallery refuges. Consistent with previous studies showing that males with the longest mandibles cohabit with the largest groups of females, our two largest radio-tagged males were the only ones relocated with adult females.

Sperm production is costly and so males are expected to prudently allocate sperm to matings in a manner that maximizes their fitness. Sperm competition hypotheses predict that when facing increased sperm competition risk males should increase their investment in ejaculates. In contrast, when facing high future mating opportunities, males are expected to decrease their sperm investment in the current mating. This is because males should keep in reserve an amount of sperm proportional to their expected future mating opportunities. We experimentally tested whether male Cook Strait giant weta (Anostostomatidae: Orthoptera: Deinacrida rugosa) phenotypically adjust their investment in ejaculates in relation to their perceived risk of sperm competition and future mating opportunities. D. rugosa is a large flightless orthopteran insect in which males pass multiple spermatophores to females during a day-long mating bout. Contrary to expectation, we found that low female availability (i.e. increased sperm competition risk) had no effect on male resource allocation to sperm (i.e. number of spermatophores) compared to controls whereas, contrary to expectation, males experiencing high female availability increased their ejaculate investment by transferring significantly more spermatophores to their mates. Our results might be a consequence of males being insensitive to increased presence of rival males, reducing their allocation to sperm under increasingly risky circumstances, or due to females prolonging copulations when their perceived future mating opportunities are low.

Most hypotheses to explain nonrandom mating patterns invoke mate choice, particularly in species that display elaborate ornaments. However, conflicting selection pressures on traits can result in functional constraints that can also cause nonrandom mating patterns. We tested for functional load-lifting constraints during aerial copulation in Rhamphomyia longicauda, a species of dance fly that displays multiple extravagant female-specific ornaments that are unusual among sexual traits because they are under stabilizing selection. R. longicauda males provide females with a nuptial gift before engaging in aerial mating, and the male bears the entire weight of the female and nuptial gift for the duration of copulation. In theory, a male's ability to carry females and nuptial gifts could constrain pairing opportunities for the heaviest females, as reported for nonornamented dance flies. In concert with directional preferences for large females with mature eggs, such a load-lifting constraint could produce the stabilizing selection on female size previously observed in this species. We therefore tested whether wild-caught male R. longicauda collected during copulation were experiencing load-lift limitations by comparing the mass carried by males during copulation with the male's wing loading traits. We also performed permutation tests to determine whether the loads carried by males during copulation were lighter than expected. We found that heavier males are more often found mating with heavier females suggesting that whereas R. longicauda males do not experience a load-lift constraint, there is a strong relationship of assortative mating by mass. We suggest that active male mate choice for intermediately adorned females is more likely to be causing the nonrandom mating patterns observed in R. longicauda.

Nutritional condition is important to the function and performance of several facets of male reproduction such as searching for mates and producing ejaculates. Nutritional status should be important to male success in the Cook Strait giant weta (Deinacrida rugosa), a flightless orthopteran insect, in which males invest considerable effort in mate searching during scrambles and transfer multiple ejaculates to female partners during a single mating bout. In this study, we hypothesize that success in scrambles for mates is related to nutritional status and thus predict that males in better nutritional condition will: (1) be more successful at finding a female, (2) find her more quickly, and (3) cover more distance per unit time during their search (i.e., have greater speed). We also predict that males in better nutritional condition will transfer more spermatophores than starved males. Although we found that critical facets of mate searching (e.g., speed) were not significantly affected by body condition, we did discover that spermatophore transfer to females was significantly related to female size and the interaction between male search effort and male body condition. We posit that perhaps males transfer spermatophores based on their current body condition and perceived mate availability. Nutritional conditon is an important factor in determining the expression of sexually selected traits in males; well-fed males produce better sexual ornaments and larger ejaculates than poorly fed males. Most studies that address this hypothesis, however, focus on species in which males display to potential female partners and then, if successful, transfer a single ejaculate to their mate. In contrast, condition could be more critical to male success in species in which males search for mates over long distances. Such scramble competition is shown by Cook Strait giant weta, where male leg length is a sexually selected trait. In this enormous insect (of conservation importance), males pass multiple ejaculates (spermatophores) to each mate; so condition in this species is also expected to be important to copulation success. Our study supports this hypothesis, but we found no evidence that mate searching speed is condition-dependent.

Sex-specific ornaments typically occur in males, but they can also develop in females. While there are several models concerning the evolution of male-specific ornaments, it is not clear how, or under what circumstances, those models apply to female-specific ornament evolution. Here, we present a manipulative field experiment that explores the theoretical ‘trait space’ of multiple female-specific ornaments to study how these unusual traits evolved. We measured the attractiveness of two female-specific ornaments (pinnate leg scales and inflatable abdominal sacs) in the dance fly Rhamphomyia longicauda in a wild mating swarm. We found significant directional preferences for larger ornaments of both types; however, variation in one of the ornaments (abdominal sacs) was almost three times more effective at improving attractiveness. The abdominal ornament was consistently effective in increasing attractiveness to males regardless of leg ornament expression, while leg ornament size was only effective if abdominal ornaments were very small. These results are consistent with predictions from a sexual conflict model of ornament expression in supporting the probable role of deception in the evolution of female-specific ornaments among dance flies. Sexual conflict can be an important force in generating elaborate sex-specific ornaments in females as well as males.

Female ornaments have evolved in a few taxa in which females compete for access to important resources provided by their mates. However, the effects of these sexually selected traits on survival have not been studied. Elaborate leg-scale and/or abdominal ornaments are displayed by females of some Rhamphomyia dance flies (Diptera: Empididae) to flying males carrying prey gifts (females do not hunt). Previous analyses have shown significant sexual selection on these female traits. We studied viability selection on the traits by sampling the webs of two spider species and comparing prey R. longicauda females to survivors. We also investigated viability selection from one of the spiders over two seasons. We found that the direction of viability selection on R. longicauda from sticky Tetragnatha spider webs was consistent over two seasons. For abdominal ornaments the form of viability selection was positive and primarily directional (linear). Viability selection also favoured shorter tibiae but there was no significant selection on the size of residual tibial scale area. However, with the addition of dance fly kills from the non-sticky, leaf-covering webs of a Dictyna spider, abundant in only one of the seasons, the overall direction of viability selection favoured larger tibial ornaments. While noting that this viability selection on tibial scale ornaments may be a statistical artefact of the fewer traits in the two-predator analysis (abdominal structures were missing from most Dictyna prey), we suggest that simple differences in the natural history of selective agents causing mortality may partly explain the variation in whether sexual traits are under viability selection. Viability selection on ornamental traits may vary greatly between seasons with changes in the abundances of different natural enemies so that net directional selection on these traits over many generations may be weak.

The potential viability costs of sexually selected traits are central to hypotheses about the evolution of exaggerated traits. Estimates of these costs in nature can come from selection analyses using multiple components of fitness during the same time frame. For a population of tree crickets (Oecanthus nigricornis: Gryllidae), we analyzed viability and sexual selection on male traits by comparing Oecanthus prey of a solitary wasp to those that survived, and comparing mating individuals to solitary males. We measured forewing width (sexually size dimorphic and used for singing), head width, pronotum length, and size of hind jumping legs as potential targets of selection. Supporting the hypothesis that sexually selected traits have viability costs, we found that significant directional sexual selection for wider heads was opposed by significant viability selection for narrower heads. Nonlinear selection revealed that individuals with wide heads and small legs were most attractive, but individuals with narrow heads, large legs, and intermediate pronotum length were most likely to survive. Successful mating may put males at greater risk of predation, especially if copulation per se is risky. Such balancing selection in tree crickets may have constrained the evolution of sexual dimorphism in head size—a condition seen in other gryllids and orthopterans.

In a role-reversed beetle, in which sexual selection acts primarily on females, females evolved to more rapidly court and copulate after many generations of experimentally increased female sexual competition.

Multiple mating by individuals successful in sexual competition results in other individuals failing to mate. This leads to sexual selection within a sex, typically the males. However, more species are coming to light in which females are subject to sexual selection. We review the contexts for and nature of sexual selection on females in several insect species where female mating failures have been noted. We then examine evidence of mating failures in two groups of insects, empidid flies (Diptera) and tettigoniid Orthoptera (katydids), in which sexual selection is expected to be relatively stronger on females. Using data from the field, we show for two species of katydids that, as predicted, there are mating failures by females in populations in which the direction of sexual selection appears to be reversed, but not in populations where sexual selection appears to be stronger on males.

Ornamental traits function by improving attractiveness and are generally presumed to experience directional selection for mating success. However, given the greater investment of females in offspring than males, female-specific ornaments can in theory signal fecundity yet be constrained by fecundity costs. Theoretical work predicts that such constraints can lead to stabilizing selection via male choice for intermediately ornamented females. Female dance flies Rhamphomyia longicauda (Diptera: Empididae) display two female-specific ornaments in mating swarms – inflatable abdominal sacs and pinnate tibial scales. We investigated the intensity and form of sexual selection on female traits including ornaments and found no evidence for directional sexual selection. Instead, we found marginally nonsignificant quadratic selection for all three measures of ornament expression. Canonical analysis confirmed that the strongest vectors of nonlinear selection were associated with ornamental traits, although the significance of the quadratic coefficients associated with these vectors depended on the statistical approach. Direct Mitchell-Olds and Shaw tests for the location of the maximum fitted fitness value for both raw morphological traits and canonical axes revealed only one marginally nonsignificant result for the multivariate axis loading most heavily on pinnate leg scales. Together, these results provide the first tentative support for stabilizing selection on female-specific ornaments.

During mating, the female Carolina ground cricket ( Eunemobius carolinus (Scudder, 1877)) chews specialized spurs on the male’s hind tibia for access to his hemolymph. One potential benefit to spur chewing includes nutritional acquisition from male hemolymph. A method for testing this hypothesis is to manipulate food quality or quantity, with the prediction that mating rate will increase as food quality or quantity decreases. We manipulated diet quality in adult females and provided them with four consecutive mating opportunities. We measured four aspects of mating behaviour (mating rate, latency to copulate, copulation duration, and spur chewing duration) and three of female fitness (egg number, egg-laying rate, and life span). Females of the two diet treatments did not differ significantly in any of the measured mating behaviours, although females fed a low-quality diet lived longer. Male life span did not correlate with any measured variable, although males that experienced more matings and longer total times of copulation and spur chewing lost more mass. These results suggest that spur chewing may be costly for males, although we detected no evidence that this behaviour was a benefit to the female or represented a form of male coercion.

Although many studies examine the form of sexual selection in males, studies characterizing this selection in females remain sparse. Sexual selection on females is predicted for sex-role-reversed Mormon crickets, Anabrus simplex, where males are choosy of mates and nutrient-deprived females compete for matings and nutritious nuptial gifts. We used selection analyses to describe the strength and form of sexual selection on female morphology. There was no positive linear sexual selection on the female body size traits predicted to be associated with male preferences and female competition. Instead, we detected selection for decreasing head width and mandible length, with stabilizing selection as the dominant form of nonlinear selection. Additionally, we tested the validity of a commonly used instantaneous measure of mating success by comparing selection results with those determined using cumulative mating rate. The two fitness measures yielded similar patterns of selection, supporting the common sampling method comparing mated and unmated fractions.

Observations were made on the behaviour of male Philanthus bicinctus (Mickel) which defend territories around the nesting burrows of ♀♀. ♂♂ were individually identified with small number tags and focal-animal samples were taken of the behaviour of these ♂♂. Intense interactions were observed between territorial ♂♂ and 1) conspecifics and 2) intruding insects which resembled conspecifics. Evidence is presented which suggests that ♂♂ scent mark their territories.

Intrinsic factors such as female age and mating status have been found to affect female choosiness. However, as these factors are often confounded in the wild because mated females are usually older individuals, the relative influence of these two factors on female behaviour is unclear. Using a fully factorial design, we tested the relative effects of age and mating status of female field crickets ( Gryllus pennsylvanicus Burmeister, 1838) on both (i) the probability that she would mate and (ii) her latency to mate. We found that virgin females were both more likely to mate and copulated more quickly than mated females, but female age had no significant effect on either the probability of mating or the latency to copulate. These results clearly show that mating status is more important in determining female mating behaviour than age. We suggest that previous work which showed an age effect on female choosiness in virgins alone might be of reduced relevance if most females do not remain unmated for long.

Despite widespread evidence for the benefits of polyandry, there are costs associated with each mating for females, and for many species, it is unknown whether the costs of extra matings outweigh the benefits. In the seed beetle Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae), costs might come from male harassment during mating attempts or from injuries that females sustain during copulation. Benefits of mating might come from nutrients or water transferred in the ejaculate. If mating is costly overall, male presence (sexual harassment) and multiple mating in C. maculatus is expected to reduce female fitness. Females were housed with differing numbers of males (1–4) and differing opportunities for copulation. When females were both harassed by and could remate with more than one male, they had lower lifetime reproductive rates and reduced life span relative to monandrous females. These results indicate that when females are continually exposed to multiple males, the direct benefits of multiple mating do not compensate for the costs.

Female seed beetles, Callosobruchus maculatus, mate multiply even though association with males and copulations carry costs, such as injury to the genital tract. Multiple mating (polyandry) may, however, offset these costs through the acquisition of food and water, two material benefits hypothesized to be obtained from the large ejaculates produced by males. The material benefits hypothesis can be tested by increasing female access to nutrients and water, with the prediction that female mating frequency will decrease as copulation is no longer required to derive these materials. Females were given water, 5% sugar-water or baker's yeast, and were compared with females deprived of these. We presented females with virgin males daily for 8 days and recorded female mating frequency, survivorship, and fecundity. Females provided with water and sugar-water decreased mating frequency. Thus, water, rather than nutrients in the ejaculate, appears to be important to females of this species. In addition, both life span and fecundity were extended for females in the sugar-water and water treatments. Since water is scarce in the arid environment in which this species is found, we conclude that polyandry provides material benefits to females that may offset some of the costs of associating with males.

Female-biased size dimorphism, in which females are larger than males, is prevalent in many animals. Several hypotheses have been developed to explain this pattern of dimorphism. One of these hypotheses, the mobility hypothesis, suggests that female-biased size dimorphism arises because smaller males are favored in scramble competition for mates. Using radiotelemetry, we assessed the mobility hypothesis in the Cook Strait giant weta (Deinacrida rugosa), a species with strong female-biased size dimorphism, and tested the prediction that male traits promoting mobility (i.e., longer legs, smaller bodies) are useful in scramble competition for mates and thus promote reproductive success. Our predictions were supported: males with longer legs and smaller bodies exhibited greater mobility (daily linear displacement when not mating), and more mobile males had greater insemination success. No phenotypic traits predicted female mobility or insemination success. In species with female-biased size dimorphism, sexual selection on males is often considered to be weak compared to species in which males are large or possess weaponry. We found that male giant weta experience sexual selection intensities on par with males of a closely related harem-defending polygynous species, likely because of strong scramble competition with other males.

Sexually selected traits are thought to impose survival costs on showy males. Recent empirical work found a negative relationship between male display and survival in a field cricket species (Orthoptera, Gryllidae, Gryllinae) where there is no evidence of a mating bias toward older males. In most species, however, male survival and ornamentation are positively correlated, and older males often have a mating success advantage over younger males. These findings suggest that male quality and survival are positively correlated, but more tests of this hypothesis are needed. We measured the condition dependence of male survival and calling effort in another grylline, Gryllus pennsylvanicus, where older males have previously been shown to have greater mating success. We varied condition by manipulating diet, and measured male life span and calling effort to assess the relative condition dependence of these traits. High- and medium-condition males survived longer than low-condition males, and high-condition males called more than medium- and low-condition males. Differences in calling effort among the condition treatments were not apparent early in life, but emerged as males aged. We discuss possible explanations for the differences between our study and contrasting results such as the previous grylline work.

Summary Sex differences in the correlation between number of offspring and number of mates likely drive much of the evolution of morphological and behavioral sexual differences. These correlations have traditionally been represented by slopes from regressions of number of offspring on number of mates (Bateman gradients). Typically the Bateman gradient is assumed to be large for males and zero for females. However, five of nine examples where male and female gradients have been measured show appreciable gradients for females. Difference in these 'actual' gradients reflect sex differences in the force driving sexual selection. In the lab it is simple to estimate the 'upper limits' on these Bateman gradients. Differences between male and female upper limits can be used to quantify the potential for sexual dimorphism. We demonstrate how to estimate these upper limits in a katydid (Conocephalus nigropleurum) where males provide females with a large food gift (nuptial gift) during mating. By mating males and females to either one or two virgin mates, we estimated the way maximum fecundity increased with additional mates for each sex, giving an estimate of the upper limit of sexual selection on each sex. We compared these estimates to predictions based on the relative value of the nuptial gift and female pre-mating fecundity. Contrary to expectation, the male upper limit did not exceed the female upper limit. Both the fact that a male's second nuptial gift was smaller than his first and that many matings failed to transfer appreciable numbers of sperm seem to have contributed to the unexpected result.

The sexes usually differ in their behavior and morphology in predictable ways: males typically compete for mates and females are often choosy. However, these sex differences, known as the ‘sex roles,’ can vary substantially among and within species. We summarize the main characters that comprise sex roles, review the evolutionary causes of general patterns of sex differences, and explore how systems that deviate from these patterns can provide strong tests of sexual selection theory.

Long-tailed dance flies, Rhamphomyia longicauda (Diptera: Empididae), show a striking reversal in the typical pattern of animal sexual dimorphism. Whereas male R. longicauda are mosquito-like in appearance, females sport rows of scales on their legs and have elaborate eversible pleural (abdominal) sacs that are inflated just prior to entry into a female competitive mating swarm. Both sets of ornaments appear to exaggerate female size to choosy males ascending through the swarm. To explain previous results showing a female bias in R. longicauda caught in spider webs near swarm sites, we hypothesized that females either encounter spider webs more frequently than do males because female flight patterns are more risky (e.g. there are usually more flying females than males in mating swarms) or that the ornaments per se inhibit escape from webs. We tested the hypothesis that female ornaments are an encumbrance and we provide evidence that secondary sexual devices hinder escape from predators. We also briefly discuss the implications of sex-biased mortality for male mating preferences and the evolutionary maintenance of female ornaments.

In many katydids, the male feeds his mate with a large gelatinous spermatophore. Males of most species also produce elaborate calling songs. We predicted a negative relationship between spermatophore size and call frequency because of trade-offs between these two costly traits. Our comparative analysis controlling phylogeny and body size supported this prediction. Although call frequency is expected to decrease with increasing body size, after controlling for phylogeny, both variables were not related. Finally, given that song frequency and spermatophore size are likely targets of sexual selection, we examined the relationship between these variables and sexual size dimorphism (SSD) which can be influenced by sexual selection on body size. We found that only female body size was positively related to SSD, suggesting that natural and/or sexual selection on female body size may be stronger than sexual selection on male and spermatophore size.

The relationship between sexual and viability selection in females is necessarily different than that in males, as investment in sexual traits potentially comes at the expense of both fecundity and survival. Accordingly, females do not usually invest in sexually selected traits. However, direct benefits obtained from mating, such as nuptial gifts, may encourage competition among females and subsidize investment into sexually selected traits. We compared sexual and viability selection on female tree crickets Oecanthus nigricornis, a species where females mate frequently to obtain nuptial gifts and sexual selection on females is likely. If male choice determines female mating success in this species, we expect sexual selection for fecundity traits, as males of many species prefer more fecund females. Alternatively, intrasexual scramble or combat competition on females may select for larger jumping legs or wider heads (respectively). We estimated mating success in wild caught crickets using microsatellite analysis of stored sperm and estimated relative viability by comparing surviving female O. nigricornis to those captured by a common wasp predator. In support of the scramble competition hypothesis, we found sexual selection for females with larger hind legs and narrower heads. We also found stabilizing viability selection for intermediate head width and hind leg size. As predicted, traits under viability and sexual selection were very similar, and the direction of that selection was not opposing. However, because the shape of sexual and viability selection differs, these episodes of selection may favour slightly different trait sizes.

1. Outbreaks of insect pest populations are common and can have devastating effects on natural communities and on agriculture. Little is known about the causes of these outbreaks or the causes of en masse migrations during outbreaks. 2. Flightless Mormon crickets (Anabrus simplex) were the focus of this study. They are a katydid species that forms large, dense, mobile groups (migratory bands) during outbreak periods, eating vegetation in their path. 3. Radiotelemetric methods were used to measure differences in movement rate and directionality in outbreak and non-outbreak populations, testing the hypothesis that these populations differ in their travel rate and consistency of direction. 4. Daily individual movement in outbreak populations differs substantially from non-outbreak populations that are at much lower density. In addition to large differences in distances travelled (1.6 km as compared with 1 m) and rates of travel, there is evidence for collective movement among individual Mormon crickets travelling in migratory bands. 5. These data suggest that the direction of group movement may be influenced by local environmental conditions such as wind direction and movement of nearby band members. This work forms the basis for ongoing work testing hypotheses about mass migrations in outbreak populations.

Female tree crickets (Oecanthus nigricornis) prefer large males but do not receive larger glandular courtship gifts from these males. This finding is puzzling from both the male and female perspectives, because females should prefer males providing more direct benefits, and because males who provide larger gifts achieve higher insemination success. We tested for differences in the quality of male secretions and found that larger males provided more proteinaceous food gifts than did rivals, which could explain why they are preferred by females. The preference in turn could cause depletion of food gift reserves in favored males, because natural remating rates are high and because even a single feeding bout negatively affects glandular stores. Most intriguingly, we showed that preferred males can adaptively decrease the size of courtship food-gifts provided (in order to conserve gifts for future mating events) when they perceive that the probability of multiple future mating opportunities is high. Thus, the elevated mating rates of preferred males (both before and after a focal mating event) could account for the small size of their courtship food-gifts. Key words: courtship-feeding, direct benefits, Gryllidae, mate choice, multiple mating, operational sex ratio. [Behav Ecol]

Compared to other ensiferan Orthoptera such as true crickets (Gryllidae) and katydids (Tettigoniidae) relatively little is known about the reproductive behavior of Anostostomatidae (formerly Stenopelmatidae), the king crickets, weta and allies. Moreover, although the New Zealand species (the weta) are best known, there is little knowledge of the biology of ground weta (Hemiandrus species), a variable genus especially with regard to ovipositor length. This paper presents observations of mating and post-mating behavior of several Hemiandrus species with short ovipositors. Sexually active males and females drum their abdomens on the substrate, apparently as local signals for mate attraction (pheromones may be involved in long distance communication). After mating there is both maternal and paternal investment. Females provide care to eggs and young larvae and males provide a spermatophylax to the female, a mating meal that, in other ensiferan Orthoptera can be an important source of nutrition. In co...

The extent to which a trait deteriorates in response to stress can indicate its fitness importance. Food limitation is a naturally-occurring stress in the katydid Kawanaphila nartee (Orthoptera: Tettigoniidae) and should cue larvae as to the level of sexual competition expected; hunger drives adult females to compete for copulations and thus acquire spermatophore meals. This increases sexual selection on females relative to males for increased body mass. As predicted, under experimental food-stress larval female K nartee showed little loss of mass whereas male mass decreased. In contrast, the sizes of body parts less critical to mating success showed similar decreases in males and females. For katydids such as Conocephalus nigropleurum, where reversals in mating roles do not occur, larval food stress should result in a greater preservation of male body mass, an important trait in male mating success. This prediction was supported; male mass decreased less than that of females.

Mate acquiring activities often expose males to increased risks of predation. In species where females are more competitive than males (i.e. a reversal in the conventional mating roles), the mate-acquiring biology of females is expected to increase their exposure to predators. Our observational study of a role-reversed dance fly, Rhamphomyia longicauda Loew (Empididae), supports this prediction. Within predominantly female swarms, R. longicauda display structures in flight that are assessed by males. Structural and behavioural components of the display should increase the risk of predation on females. We found more females than males captured in spider webs. This bias in predation was not due to a female-bias in population sex-ratios of the dance fly and the nature of web predation appears to rule out the hypothesis that spiders actively favour females as prey.

The potential viability costs of sexually selected traits are central to hypotheses about the evolution of exaggerated traits. Estimates of these costs in nature can come from selection analyses using multiple components of fitness during the same time frame. For a population of tree crickets (Oecanthus nigricornis: Gryllidae), we analyzed viability and sexual selection on male traits by comparing Oecanthus prey of a solitary wasp to those that survived, and comparing mating individuals to solitary males. We measured forewing width (sexually size dimorphic and used for singing), head width, pronotum length, and size of hind jumping legs as potential targets of selection. Supporting the hypothesis that sexually selected traits have viability costs, we found that significant directional sexual selection for wider heads was opposed by significant viability selection for narrower heads. Nonlinear selection revealed that individuals with wide heads and small legs were most attractive, but individuals with narrow heads, large legs, and intermediate pronotum length were most likely to survive. Successful mating may put males at greater risk of predation, especially if copulation per se is risky. Such balancing selection in tree crickets may have constrained the evolution of sexual dimorphism in head size-a condition seen in other gryllids and orthopterans.

In katydids such as Kawanaphilanartee, a female bias in the operational sex ratio (OSR) results in female competition for mates and male choice of mates. Previous work showed that the excess of sexually active females occurs when food availability is low, in part because less food increases the propensity of females to mate as they forage for the large edible spermatophores produced by males. In this study with K.nartee, a pollen-feeding species, we estimate natural variation in numbers of sexually active males and females by assessing male calling activity and the propensity of females to respond to experimental calling males. We found an excess of sexually active males at a site with many flowers and an excess of sexually active females at a site with few flowers about 900 m away. Between-site differences in gut masses of calling males were consistent with the hypothesis that pollen availability controls OSR. Finally, at a third site where flowers were at first scarce, we found that the initial excess in sexually active females changed to an excess of sexually active males after a clump of grass-trees flowered. The mean gut mass of all sampled males from this site increased after flowering. The large variation in OSR that we document for K. nartee highlights the importance of identifying the appropriate spatial and temporal scales over which OSRs are measured in studies of factors controlling sexual selection.

Uniquely positioned at the intersection of sexual selection, nutritional ecology and life-history theory, nuptial gifts are widespread and diverse. Despite extensive empirical study, we still have only a rudimentary understanding of gift evolution becausewe lack a unified conceptual framework for considering these traits. In this opinion piece, we tackle several issues that we believe have substantively hindered progress in this area. Here, we: (i) present a comprehensive definition and classification scheme for nuptial gifts (including those transferred by simultaneous hermaphrodites), (ii) outline evolutionary predictions for different gift types, and (iii) highlight some research directions to help facilitate progress in this field. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Females generally choose mates that produce the loudest, brightest or most elaborate sexual displays, and these costly male displays are predicted to be condition dependent. However, mate choice itself is a costly behaviour also expected to be condition dependent. Male fall field crickets, Gryllus pennsylvanicus, produce a conspicuous long-distance calling song that attracts females and is condition dependent. In this study, we tested the condition dependence of female preferences (preference function and choosiness) for male calling effort in G. pennsylvanicus. We manipulated female condition by raising crickets from hatching on either a low- or high-quality diet. In a series of two-speaker phonotaxis trials, both low- and high-condition females preferred playbacks reflecting greater calling effort. However, relative to low-condition females, high-condition females took significantly longer to make a choice, were more likely to fail to choose within the time allotted for a phonotaxis trial and significantly increased their latency to choose over the course of multiple trials. We discuss these results with respect to the possibility that female G. pennsylvanicus may be foraging for direct benefits when they choose their mates.