the effect of pair formation on diel calling patterns in two cricket species,Gryllus veletis andGryllodes sigillatus (Orthoptera: Gryllidae)

After pair formation, male crickets should reduce calling to minimize the risks to males of attracting predators and/or rivals. We tested this hypothesis in two cricket species, one in which males exhibit a high mating propensity (Gryllus veletis)and another in which the mating propensity of males is constrained by the manufacture of elaborate, bipartite spermatophores (Gryllodes sigillatus).Calling durations of male G. veletisdeclined precipitously after the introduction of females but remained unchanged in G. sigillatus.We attribute the asymmetric effect of female proximity on male calling to differences in the mating propensity of males of the two species. Male G. veletisabstain from further calling in favor of repeated matings with the same female. Male G. sigillatusprobably lack the opportunity to mate repeatedly with the same female and, thus, resume calling shortly after mating to increase their probability of attracting additional mates.     

Hydration benefits to courtship feeding in crickets

The spermatophore transferred by male decorated crickets (Gryllodes sigillatus) at mating includes a large gelatinous spermatophylax that the female consumes after copulation. Although previous studies have shown that G. sigillatus females gain no nutritional benefits from consuming food gifts, there may be other benefits to their consumption. We examined potential hydration benefits to females by experimentally manipulating both the availability of water and the number of food gifts that females consumed, and by measuring their effect on female fitness. Analysis of the number of nymphs produced by females revealed a significant interaction between the number of spermatophylaxes consumed and water availability. When spermatophylaxes were not provided, females given water ad libitum produced significantly more nymphs than females subjected to water stress. Female longevity was significantly affected by water availability, with an increase in the availability of water corresponding to a significant increase in female longevity. These data suggest that female G. sigillatus accrue fitness benefits by consuming spermatophylaxes when alternative sources of water are unavailable. In addition, females appear to allocate water contained in spermatophylaxes towards reproduction as opposed to survival.     

Food fight: sexual conflict over free amino acids in the nuptial gifts of male decorated crickets

In decorated crickets, Gryllodes sigillatus, the spermatophore that a male transfers at mating includes a gelatinous spermatophylax that the female consumes, delaying her removal of the sperm‐filled ampulla. Male fertilization success increases with the length of time females spend feeding on the spermatophylax, while females may benefit by prematurely discarding the spermatophylaxes of undesirable males. This sexual conflict should favour males that produce increasingly appealing spermatophylaxes, and females that resist this manipulation. To determine the genetic basis of female spermatophylax feeding behaviour, we fed spermatophylaxes to females of nine inbred lines and found that female genotype had a major influence on spermatophylax feeding duration. The amino acid composition of the spermatophylax was also significantly heritable. There was a positive genetic correlation between spermatophylax feeding duration and the gustatory appeal of the spermatophylax. This correlation suggests that genes expressed in males that produce more manipulative spermatophylaxes are positively linked to genes expressed in females that make them more vulnerable to manipulation. Outbred females spent less time feeding on spermatophylaxes than inbred females, and thus showed greater resistance to male manipulation. Further, in a nonspermatophylax producing cricket (Acheta domesticus), females were significantly more prone to feeding on spermatophylaxes than outbred female Gryllodes. Collectively, these results suggest a history of sexually antagonistic coevolution over the consumption of nuptial food gifts.     

Paternity of offspring in multiply-mated,female crickets: the effect of nuptial food gifts and the advantage of mating first

The spermatophore transferred by male decorated crickets (Gryllodes sigillatus) includes a large gelatinous mass, the spermatophylax, that is consumed by the female after mating. This nuptial gift preoccupies the female while sperm are discharged from the remaining portion of the spermatophore, the sperm ampulla, into her reproductive tract. There is considerable variation in the mass of the spermatophylax, and about half of all males produce spermatophylaxes that are too small to ensure complete sperm transfer. We tested two hypotheses concerning the maintenance of this variation: (i) males trade-off investment in spermatophylaxes against copulation frequency; and (ii) males synthesize the largest spermatophylaxes of which they are physiologically capable. Males synthesizing large and small food gifts were permitted multiple mating opportunities with the same females, and allozyme markers were used to establish the paternity of offspring. There was a significant advantage to those males that mated first irrespective of gift size. This advantage probably arose, in part, because the sperm of first males would have had exclusive access to females'' eggs during the first 24 hours of oviposition, and underscores the benefits of matings with virgin females. The paternity of ''small-gift'' males increased with gift mass, but there was no such increase in ''large-gift'' males. This difference probably stems from the relationship between gift mass and sperm transfer: most of the gifts of the large-gift males would have been above the threshold needed to achieve complete inseminations, whereas those of small-gift males would have been below the threshold. Within mating-order positions, there was no significant difference in the paternity of large-gift and small-gift males, a result seemingly consistent with the ''trade-off'' hypothesis. However, there was no correlation between spermatophylax mass and male mating frequency, so that the mechanism by which small-gift males offset their fertilization disadvantage remains unknown.     

Sexually transmitted nematodes affect spermatophylax production in the cricket, Gryllodes sigillatus

Parasites can influence various aspects of host reproductionand mating, including spermatophore production. In the cricket,Gryllodes sigillatus, males transfer to females a two-part spermatophorecontaining a sperm-filled ampulla and a gelatinous spermatophylax(nuptial gift). Here we investigate the effects of a sexuallytransmitted nematode on male spermatophylax production. Sexuallytransmitted diseases (STDs) have the potential to reduce hostfertility or fecundity in insect hosts. To our knowledge thisis the first empirical study on the effects of an insect STDon the reproductive physiology of a male host. Our results indicatethat infected males produced significantly smaller spermatophylacesthan healthy males; this effect was more apparent for smallermales. Spermatophylax size was inversely correlated with theintensity of infection. Spermatophylax replacement time, thetime between producing the first and second spermatophylax,did not differ significantly between infected and healthy males.This parasite-mediated reduction in spermatophylax size maybe a direct consequence of the physiological stress of parasitismor parasite manipulation.     

Virgin male mating advantage in a primitive acoustic insect (Orthoptera: Haglidae)

Male reproductive behavior in the relict flightless haglid, Cyphoderris strepitans,entails the generation of sound signals and the provision of nuptial gifts to mates. These food gifts take two forms: (1) a gelatinous mass (spermatophylax) augmenting the spermatophore and (2) fleshy metathoracic wings adapted to be eaten. The female consumes a portion of the male's underwings during courtship and copulation and the spermatophylax afterward. The incidence of wing-feeding wounds can be used to monitor the mating success of field-caught males. If, when a male mates, he compromises his ability to provide subsequent nutritive gifts, females would benefit by mating with virgin rather than nonvirgin males. To test this, mating success of virgin and nonvirgin males was compared in a field population. Virgins were found to obtain more matings than explained by their numbers relative to nonvirgins in the population. We conclude that, having mated, a male is at a disadvantage, relative to his virgin competitors, in securing further matings.     

Paternity Analysis in a Hexapod (Orchesella cincta; Collembola) with Indirect Sperm Transfer

In species where males and females interact during mating, the role of females in sexual selection cannot always be demonstrated unambiguously. Here we present a model system to study female choice for mates. Orchesella cinca is a soil-dwelling hexapod with indirect sperm transfer. Females and males do not interact physically for reproduction. We gave females the choice between spermatophores produced by two different males. Paternity analysis based on microsatellite variation revealed that offspring in one clutch were sired by one male only. Direct observations showed that after a female has taken up a spermatophore, the female's receptivity to further spermatophore uptake seem to end. Our results imply that the female is in full control of paternity.     

Sexual selection at varying population densities in male field crickets,Gryllus veletis andG. pennsylvanicus

Male field crickets call and attract females or they silently search for females in the vicinity of calling males. At high population densities, fewer calling sites are available, defense of calling sites is costly, and an increased proportion of matings should result from searching behavior. To test these predictions, individually marked field crickets, Gryllus veletisand G. pennsylvanicus,were observed for 10 h nightly in large outdoor arenas at relatively high and low densities (2020 and 55, males and females). Data were gathered on body weight, calling duration, movement, and mating frequency for individual crickets. These observations showed that variance in male mating success was significantly greater at a low density in G. pennsylvanicus,and calling duration correlated with mating success at this density. Direct selection on a trait was estimated as the partial regression coefficient (selection gradient, ) and the total selection was estimated (direct and indirect selection on correlated traits) as the covariance (standardized intensity of selection, s) of the trait on the relative mating success. Direct selection favored increased movement at a high density in G. veletis,and direct and total selection favored increased calling duration at a low density in G. pennsylvanicus.Most other comparisons were not statistically significant. The data are discussed in terms of density-dependent fluctuations in sexual selection on correlated male traits.     

Ejaculate expenditure by malebush crickets decreases with sperm competition intensity

Male bushcrickets transfer a spermatophore at mating that consists of a sperm-containing ampulla and a sperm-free mass, the spermatophylax, that is consumed by the female during insemination. The costs of spermatophore production for males and benefits of consumption for females result in reversals in courtship roles in nutrient limited populations that increase both the risk and intensity of sperm competition. Here we show that under conditions characteristic of courtship role reversal, male expenditure on the spermatophore is dependent on female size. When mating with small females, males increase the amount of spermatophylax material and sperm, as expected from the increased sperm competition risk associated with courtship role reversal. However, males reduce the amount of spermatophylax material and sperm transferred to larger females. Since larger females have a higher mating success when competing for nurturant males, the intensity of sperm competition covaries with female size. Reduced ejaculate expenditure under increased sperm competition intensity is in accord with theoretical expectation.     

Condition-dependent spermatophore size is correlated with male's age in a bushcricket (Orthoptera: Phaneropteridae)

During mating, male bushcrickets transfer a spermatophore that consists of a sperm-containing ampulla and a product of the accessory glands, the spermatophylax, which females directly ingest. In the present study, we demonstrate male spermatophore allocation in the bushcricket Poecilimon zimmeri . Males of this species show condition-dependent spermatophore investment. This investment depended upon the age at first mating of males, with older individuals transferring larger spermatophores than younger ones of the same body mass. Independently of age, heavier males transfer larger spermatophores, but the size of males (as measured by femur length) was not a good predictor. Heavier males allocate a lower proportion of their mass to spermatophores and reach their maximal investment point earlier than less heavy males. Spermatophylax production levelled off to a species specific maximum earlier than that of sperm investment (measured as ampulla mass), suggesting that males face high levels of sperm competition.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 354–360.     

Unpredictable environments,nuptial gifts and the evolution of sexual size dimorphism in insects: an experiment

Many insects have a mating system where males transfer nutrients to females at mating, which are often referred to as ''nuptial gifts''. Among butterflies, some of the characteristic features of these species are polyandry (females mate multiple times), and relatively large male ejaculates. When males produce part of the resources used for offspring, the value of body size might then increase for males and decrease for females. The male/female size ratio is also observed to increase when the degree of polyandry and gift size increase. Butterfly species where gift-giving occurs are generally more variable in body size, suggesting that food quality/quantity fluctuates during juvenile stages. This will cause some males to have much to provide and some females to be in great need, and could be conducive to the evolution of a gift-giving mating system. In such a system, growing male and female juveniles should react differently to food shortage. Females should react by maturing at a smaller size since their own lack of reproductive resources can partly be compensated for by male contributions. Males have to pay the full cost of decreased reproduction if they mature at a small size, making it more important for males to keep on growing, even when growth is costly. An earlier experiment with the polyandrous and gift-giving butterfly, Pieris napi, supported this prediction. The pattern is expected to be absent or reversed for species with small nuptial gifts, where females do not benefit from mating repeatedly, and will thus be dependent on acquiring resources for reproduction on their own. To test this prediction, we report here on an experiment with the speckled wood butterfly, Pararge aegeria. We find that growth response correlates with mating system in the two above species, and we conclude that differences in environmental conditions between species may act as an important factor in the evolution of the mating system and sexual size dimorphism.     

Costs of Reproduction in Male Bicyclus anynana and Pieris napi Butterflies: Effects of Mating History and Food Limitation

Life history theory predicts trade‐offs arising from the costs of reproduction: individuals investing more into reproduction should have less energy available for their own somatic demands. Despite a wealth of research on such costs for females, very few studies have looked at the male side. We investigated the costs of reproduction in males of two butterfly species, Bicyclus anynana and Pieris napi. The males of these species differ tremendously in their allocation of nutrients to reproduction: virgin male spermatophores were 18.5 times larger in the latter compared with those in the former. Based on this striking difference, we expected to find a longevity cost of mating in P. napi, but not necessarily in B. anynana. In line with our predictions, we found no evidence for a survival cost of mating in B. anynana, while there was some evidence for such a cost in P. napi. Here, virgin males lived longer than once‐ or twice‐mated ones. However, this overall trend did not hold for all treatment groups, and there was no linear relationship between the number of copulations and longevity. Adult food limitation reduced longevity throughout, but had otherwise very little impact. Spermatophore dry mass decreased in later compared with first spermatophores, while water content increased, indicating that spermatophore production is indeed physiologically costly. Additionally, adult food limitation tended to reduce spermatophore fresh and dry mass, and tended to increase spermatophore water content. Based on our results we tentatively conclude that longevity and reproduction may not always be traded off against each other, as in our study organisms’ longevity seems to depend in first place on adult carbohydrate income, while male reproduction seems to be primarily (although not entirely) fuelled by larval storage reserves.     

Sexually transmitted parasites and host mating behavior in the decorated cricket

Sexually transmitted diseases play a potentially important rolein the ecology and evolution of host mating behavior. Here,we use a sexually transmitted nematode-cricket (Mehdinema alii–Gryllodessigillatus) system to examine the effects of parasitism on hostmating activity and female choice. Previous work has shown thatinfected male crickets produce a significantly smaller nuptialgift (spermatophylax) than uninfected males. This is expectedto result in reduced spermatophylax feeding duration and earlyampulla removal. Here, we hypothesize that the parasite-mediatedreduction in spermatophylax size will consequently shorten femaleintercopulatory interval. We predict that females mated to infectedmales will exhibit a shorter intercopulatory interval than femalesmated to uninfected males. To test this hypothesis, we experimentallymeasured the behavioral responses of females mated to uninfectedand infected males. We found no significant difference betweenfemale handling of the spermatophylax and ampulla from infectedversus uninfected males. Although the duration of spermatophylaxconsumption is positively correlated with the duration of ampullaattachment, neither of these variables is correlated with femaleintercopulatory interval. Intercopulatory intervals for femalespreviously mated with uninfected versus infected males are notstatistically different. We conclude that parasitism in maleG. sigillatus does not influence female intercopulatory intervalor male mating success. We found no evidence for female matechoice based on male infection status. The lack of female choiceis consistent with theoretical predictions involving parasitesthat are sexually transmitted.     

Extreme Costs of Mating for Male Two-Spot Ladybird Beetles

Male costs of mating are now thought to be widespread. The two-spot ladybird beetle (Adalia bipunctata) has been the focus of many studies of mating and sexual selection, yet the costs of mating for males are unknown. The mating system of A. bipunctata involves a spermatophore nuptial gift ingested by females after copulation. In this study, we investigate the cost to males of mating and of transferring spermatophores in terms of lifespan, ejaculate production and depletion of nutritional reserves. We found that males faced a strong trade-off between mating and survival, with males that were randomly assigned to mate a single time experiencing a 53% reduction in post-mating lifespan compared to non-mating males. This is among the most severe survival costs of a single mating yet reported. However, spermatophore transfer did not impact male survival. Instead, the costs associated with spermatophores appeared as a reduced ability to transfer spermatophores in successive matings. Furthermore, males ingested more food following spermatophore transfer than after matings without spermatophores, suggesting that spermatophore transfer depletes male nutritional reserves. This is to our knowledge the first report of an effect of variation in copulatory behaviour on male foraging behaviour. Overall, our study highlights the advantages of assessing mating costs using multiple currencies, and suggests that male A. bipunctata should exhibit mate choice.     

Cryptic sexual conflict in gift-giving insects: chasing the chase-away

The chase-away model of sexual selection posits that elaborate male sexual displays arise because they exploit preexisting biases in females' sensory systems and induce females to mate in a suboptimal manner. An essential element of this hypothesis is that such manipulation should quickly lead to female resistance to male displays. Nuptial food gifts may be a frequent conduit by which males attempt to influence the mating behavior of females against females' own reproductive interests. In decorated crickets Gryllodes sigillatus, such inducements come in the form of a spermatophylax, a gelatinous mass forming part of the male's spermatophore and consumed by the female after mating. We conducted experiments in which spermatophylaxes obtained from male G. sigillatus were offered as novel food gifts to females of a non-gift-giving species (Acheta domesticus) having no evolutionary history of spermatophylax consumption. Female A. domesticus that were allowed to consume the spermatophylax took significantly longer to remate than when given no such opportunity. In contrast, when female G. sigillatus were prevented from consuming their partners' nuptial gifts, there was no difference in their propensity to remate relative to females permitted to consume a food gift after mating. These results suggest that the spermatophylax synthesized by male G. sigillatus contains substances designed to inhibit the sexual receptivity of their mates but that female G. sigillatus have evolved reduced responsiveness to these substances.     

Effects of female deprivation on mating propensity and mate selectivity by maleRequena verticalis (Orthoptera: Tettigoniidae)

This study examined the effects of female deprivation on the mating propensity and size selectivity of male Requena verticalis,an Australian katydid in which males provide a large spermatophylax to females during mating. Specifically, I tested the hypotheses that mating readiness would increase, while mate discrimination would decrease (i. e., females would be accepted independently of their size, an indicator of fecundity) as the period of female deprivation increased. Fieldcaught males were held in isolation for 1, 5, or 14 days in the laboratory and then presented with virgin females. As expected, males held for 5 and 14 days were more likely to mate than males held only a single day. However, in none of the treatments did males discriminate among females on the basis of size. These results are compared with those obtained in a similar study on a zaprochiline katydid.     

Cryptic female choice predicated on wing dimorphism in decorated crickets

Male decorated crickets, Gryttodes sigllatus, normally lackbind wings and are incapable of flight (short-winged males),but occasionally exhibit fully developed hind wings that makerudimentary flight possible (long-winged males). Long-wingedmales bear a cost of flight in the form of decreased inseminationsuccess, which arises as a consequence of two interrelated factors:(1) long-winged males exhibit a lower reproductive investmentrelative to short-winged males, as measured by the mass of amale's spermatophore and reproductive organs and (2) the postcopulatorybehavior of females favors males that maximize their reproductiveinvestment. Of particular importance to male mating successis the spermatophylax, a large gelatinous mass forming partof the spermatophore and consumed by the female after mating.Consumption of the spermatophylax keeps the female preoccupiedwhile sperm are discharged from the remaining portion of thespermatophore (sperm ampulla) into her repro ductive tract.The spermatophylax of long-winged males is significantly smallerthan that of short-winged males and consequently requires lesstime to consume. As a result, the sperm ampulla of long-wingedmales is frequently removed before its complete evacuation andsignificantly sooner than that of short-winged males. Becausethe spermatophore-removal behavior of females mediates the relativeinsemination success of short-winged and long-winged males,it can be considered a form of cryptic female choice     

Ejaculate expenditures of male crickets in response to varying risk and intensity of sperm competition: not all species play games

Costs incurred in the manufacture of ejaculates may constrainthe number of sperm that males can produce, so males shouldshow some economy in their allocation of sperm across multiplematings. In species in which females mate with multiple malesand are capable of storing sperm for extended periods, spermallocation of males should be tailored to the risk of spermcompetition. Recent game theory predicts that males shouldtransfer the least sperm when there are no other rivals, andthe most sperm when only one other rival is likely to inseminatethe female. However, as the numbers of competitors increasesbeyond two, the models predict a corresponding decrease in ejaculate expenditure. We tested these predictions in three cricket species, Gryllodes sigillatus, Gryllus veletis, and Gryllus texensis, assessing the sperm allocation of males held under three levelsof apparent interrival competition: no rivals, one rival andsix rivals. Sperm allocation of G. veletis varied accordingto theory: males increased their sperm allocation with an increasedrisk of sperm competition (no rivals vs. one), but decreasedtheir allocation with an increased intensity of sperm competition(one rival vs. six). Sperm allocation of male G. texensis showedno significant response to the density of rivals, and spermallocation in G. sigillatus was influenced by an unexpectedinteraction between treatment density and the order in whichmales experienced the three treatments. The observed interspecificvariation in facultative sperm allocation may be due to interspecificdifferences in population density, rearing environment, orfemale mating behavior.     

Neither Mating Rate Nor Spermatophore Feeding Influences Longevity in a Ladybird Beetle

Females of many species experience costs associated with mating. Seminal products, including nuptial gifts, may mitigate these mating costs or exacerbate them. For example, nuptial gifts derived from male accessory glands may transfer nutrition or potentially harmful seminal proteins to females. In this study, we assay the costs of multiple mating and the consumption of seminal products in a ladybird beetle. We compared longevity in females mated singly or multiply, while allowing or preventing spermatophore consumption at each mating. In order to distinguish a cost of mating per se from a cost of elevated reproduction, we prevented reproduction by using nutrient‐stressed females. Mating singly or multiply had no effect on female longevity, nor did spermatophore feeding influence longevity. The results imply, first, that intermediate mating rates do not directly harm females, though females may experience other indirect costs of mating (e.g. reduced foraging efficiency) or costs of reproduction; and second, that spermatophores transfer neither food nor directly harmful substances to female ladybirds.