The costs of copulating in the dung fly Sepsis cynipsea

Finding, assessing, rejecting, and copulating with a mate isassumed to carry fitness costs, particularly for females, thathave to be traded off against fitness benefits of mating suchas increased fecundity, fertility, longevity, or better qualityoffspring. Female dung flies, Sepsis cynipsea (Diptera: Sepsidae),typically attempt to dislodge mounted males harassing themby vigorous shaking. Shaking duration has been shown to reflect both direct and indirect female choice in this species. Thelatter is an expression of the females' general reluctanceto mate due to presumed costs of mating. We investigated thecosts of copulation in the laboratory. Females were randomlyassigned to one of three treatment groups and allowed to copulateeither not at all, once, or twice. The males' armored genitalia injured females internally during copula. Injuries were visibleas sclerotized scars in the female ovipositor, and their occurrenceincreased with mating frequency. Presumably due to these injuries,mated females showed higher mortality. This effect was statisticallyindependent from additional costs of reproduction related tooviposition, as copulation also increased lifetime egg productionand tended to augment oviposition rate (eggs per day), while fertility (proportion of offspring emerged) was unaffected.We thus found high mortality costs of copulating, indicatingsubstantial sexual conflict, which helps explain female reluctanceto mate in this species.     

Mating strategies based on foraging ability: an experiment with grasshoppers

Female mate choice and the benefits of this behavior are criticalaspects of Darwinian sexual selection, but they are seldom documentedbecause it is difficult to identify the male trait(s) that femalesmay be seeking. We conducted experiments with grasshoppers (Melanoplussangutnipes: Orthoptera, Acrididae) to examine this behavior.Males that feed more intensively and select a diet mix thatpermits greater food intake (food intake per body mass per time)in laboratory trials were preferentially selected by females.These better foraging males on average provide greater paternalinvestment (greater spermatophore mass) to the female, whichincreases her reproductive rate (eggs produced per body massper time). However, paternal investment may not entirely explainfemale choice of better foraging males, because these maleswere still selected even if they had their food intake restrictedor had been allowed to recently mate, which reduces spermatophoreproduction. Furthermore, males change their mating strategyin response to female choice and the foraging abilities of surroundingmales. Poorer foraging males attempt forcible copulation ratherthan displaying and allowing female choice. A male will facultativelyswitch between these strategies depending on the foraging abilitiesof the surrounding males. While females attempt to reject forciblecopulation, forcible copulation reduces the frequency with whichfemales successfully copulate with better foraging males. Therefore,males that are less "attractive" to females adopt alternativemating strategies to counter female choice which would excludethem from mating.[Behav Ecol 7: 438–444 (1996)]     

Interacting effects of predation risk and male and female density on male/female conflicts and mating dynamics of stream water striders

We used a factorial experiment to examine interacting effectsof male density, female density, and sunfish (predation risk)on mating dynamics of the stream water strider (Aquarius remigis).Many of our results corroborated earlier studies on the isolatedeffects of each factor on mating behavior. The effect of eachfactor, however, depended on the other factors. For example,in low density pools, predation risk decreased male generalactivity, male/female harassment rates, mating activity, andmating duration and increased the large male mating advantage.At higher densities, however, water striders apparently enjoyed"safety in numbers" and did not alter their mating dynamicsin response to the presence of predators. Female activity showeda particularly complex response to male density and fish. Whenmales were scarce, fish caused females to reduce their activity.However, when males were abundant, fish increased female activity,probably because fish decreased male activity thus releasingfemales from harassment by males. The three treatment factorsalso had interacting effects on male mating success. In theabsence of fish, when females were scarce, increased male densityresulted in a decrease in mean male mating success; however,when females were abundant, increased male density enhancedmean male mating success. In contrast, in the presence of fish,male density had little effect on male mating success. Manyof the observed mating patterns can be explained by the effectsof ecological and social factors on male/female conflicts; thatis, on male harassment of females and female reluctance to mate.     

Female mate choice and mating costs in the polyandrous butterflyPieris napi (Lepidoptera: Pieridae)

Males of the green-veined white butterfly (Pieris napi L.) transfer large ejaculates that represent on average 15% of their body mass when mating for a first time. Shortly after mating a male is able to transfer only a small ejaculate when mating a second time. Male ejaculate production plays a crucial role in the mating system ofP. napi because females use male-derived nutrients for egg production and somatic maintenance. Here we study how timing of female rematings and copulation duration are influenced by the mating history of their mates and, also, study if females exert mate choice to minimize their mating costs. Mating with a recently mated male increased female mating costs by increasing time in copula and mating frequency. Virgin females that mated with virgin males remated after an average of 6 days, whereas virgin females that mated with recently mated males remated after an average of 2 days. Moreover, copulations involving recently mated males lasted on average almost 7 h, whereas copulations involving virgin males lasted on average 2 h. Recently mated males were eager to remate, in spite of the fact that the size of the ejaculate they transfer is small and that they remain in copula for a long time. Hence it seems that males are more successful in the sexual conflict over mating decisions and that females do not minimize mating costs by choosing to mate preferentially with virgin males.     

Costs of loading associated with mate-carrying in the waterstrider, Aquarius remigis

When one sex carries the other during some phase of courtshipor mating, the associated loading may entail a significant costto the carrier. This paper presents a series of laboratory experimentsdesigned to identify the costs of mate-carrying in Aquariusremigis. Female A. remigis mate repeatedly and carry each matefor several hours. Dead males and lead weights were used tosimulate normal mating and loading associated with mate-carrying,respectively. Females carrying weights equivalent to the weightof an average male showed no detectable reductions in survival,lipid reserves, or foraging success, and maintained themselveson the water surface for more than 10 days without access toresting sites. Weights equivalent to two males were supportedfor 6.1 ± 4.9 days. Thus, female A. remigis appear tobe very well adapted to carrying their mates and are unlikelyto be near their load limits when carrying a single mate. However,females carrying males or equivalent weights suffered a significantreduction in maximum mobility (stride length and speed), andan increased risk of predation by frogs (Rana clamitans). Femalescarrying weights were more susceptible to predation than unburdenedfemales but were less susceptible than females carrying males,suggesting that loading contributes significantly to, but doesnot fully explain, the increased predation risk. This risk probablyresults from both reduced mobility due to loading and greatervisibility (size). Possible influences of the costs of loadingon mating behavior and sexual size dimorphism are discussed.     

Hemolymph loss during nuptial feeding constrains male mating success in sagebrush crickets

Although costs of mating have been widely documented in females,intrinsic costs of copulation have been poorly documented inmales, and there is little evidence that such costs constrainmale mating success under natural conditions. Male sagebrushcrickets, Cyphoderris strepitans, offer females an unusual somaticfood gift at copulation that may constitute a significant costof copulation: females chew on the ends of the males' fleshyhind wings and ingest hemolymph seeping from the wounds theyinflict. Previous studies have shown that once a male has mated,his probability of obtaining an additional copulation is reducedrelative to that of a virgin male seeking to secure his firstmating. If the future mating prospects of nonvirgin males arediminished because of the costs of copulation, this could stemeither from the resources required to manufacture a new spermatophoreor through the energy needed to replenish hemolymph lost throughfemale wing-feeding. To distinguish between these two alternatives,we experimentally depleted virgin males of varying amounts hemolymphin a way that mimicked hemolymph loss of nonvirgin males, withoutthe attendant costs of spermatophore production. After theyhad been treated, males were released in the field and recapturedover the course of the breeding season to monitor their matingsuccess. Control males mated significantly sooner than did malesdepleted of hemolymph. We conclude, therefore, that the depletionof hemolymph that occurs through female wing feeding is sufficientby itself to diminish a nonvirgin male's ability to secure anothermating.     

Female Choice, Female Reluctance to Mate and Sexual Selection on Body Size in the Dung Fly Sepsis cynipsea

We investigated the mechanisms of sexual selection in the common dung fly Sepsis cynipsea and how these affect selection on body size at the population level. Because of the presumed costs associated with mating, we predicted that there would be a decrease in the general reluctance of females to mate with any particular male at higher male densities at the mating site, a fresh cow pat, resulting in indirect female choice and a decrease in the strength of sexual selection. In contrast, classical direct female choice and male‐male competition should result in increased selection intensities because more opportunities for choice and competition exist at higher densities. Female reluctance to mate and female assessment of males are expressed in prominent female behaviour to repel mates in several insect species, including S. cynipsea. Laboratory pair‐wise choice experiments showed that large males were more likely to obtain copulations, which also ensued more promptly, suggesting female assessment of male quality (direct female choice). There was a basic influence of male activity but little further effect of male scramble competition on the outcome of mating. Another laboratory experiment showed a decrease in female shaking duration per male, associated with an asymptote in the shaking duration per female, as male density and harassment increased, but did not show the increase in mating frequency predicted by the female reluctance hypothesis. A study estimating sexual selection differentials in the field showed that directional selection for larger males was present overall and was negatively related to seasonally mediated variation in male density. Our study suggests that direct female choice in combination with indirect female choice (due to an interaction of female reluctance to mate and male persistence) is most consistent with the behavioural and selection patterns observed in S. cynipsea, but male effects cannot be definitively excluded.     

Male mate choice in the chameleon grasshopper (Kosciuscola tristis)

In many species, males can increase their fitness by mating with the highest quality females. Female quality can be indicated by cues, such as body size, age and mating status. In the alpine grasshopper Kosciuscola tristis, males can be found riding on subadult females early in the season, and as the season progresses, males engage in fights over ovipositing females. These observations suggest that males may be competing for females that are either unmated (early season) or sperm‐depleted (late season). We thus hypothesised that male K. tristis may be choosy in relation to female mating status, and specifically, we predicted that males prefer females that are unmated. We conducted behavioural experiments in which males were given the choice of two females, one mated and one unmated. Contrary to our prediction, males did not mate preferentially with unmated females. However, copulation duration with unmated females was, on average, 24 times the length of copulation with mated females. While female K. tristis can reject mates, we did not observe any evidence of overt female choice during our trials. Females may gain additional benefits from mating multiply and may therefore not readily reject males. While our experiment cannot definitively disentangle female from male control over copulation duration, we suggest that males choose to invest more time in copula with unmated females, perhaps for paternity assurance, and that male mate assessment occurs during copulation rather than beforehand.     

The role of functional constraints in nonrandom mating patterns for a dance fly with female ornaments

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.     

FEMALES RECEIVE A LIFE-SPAN BENEFIT FROM MALE EJACULATES IN A FIELD CRICKET

Abstract.— Mating has been found to be costly for females of some species because of toxic products that males transfer to females in their seminal fluid. Such mating costs seem paradoxical, particularly for species in which females mate more frequently than is necessary to fertilize their eggs. Indeed, some studies suggest that females may benefit from mating more frequently. The effect of male ejaculates on female life span and lifetime fecundity was experimentally tested in the variable field cricket, Gryllus lineaticeps. In field crickets, females will mate repeatedly with a given male and mate with multiple males. Females that were experimentally mated either repeatedly or multiply lived more than 32% longer than singly mated females. In addition, multiply mated females produced 98% more eggs than singly mated females. Because females received only sperm and seminal fluid from males in the experimental matings, these life‐span and fecundity benefits may result from beneficial seminal fluid products that males transfer to females during mating. Mating benefits rather than mating costs may be common in many animals, particularly in species where female mate choice has a larger effect on male reproductive success than does the outcome of sperm competition.     

Influence of Female Copulation Calls on Male Sexual Behavior in Captive Macaca fascicularis

We investigated the function of copulation calls—vocalizations by females during mating—in captive groups of long-tailed macaques. We tested predictions of the contest-competition, sperm competition, synchronized orgasms, mate again, alpha-male notification and graded-signal hypotheses. We observed 371 copulations of 36 females wherein the presence or absence of a copulation call was clear. Females call equally often with different males and shortly after ejaculation. Copulation calls occurred equally with copulations with and without ejaculation. Calls did not incite disruptions of the mating. Following calls females mated again, more often than expected, with their mating partner. Both pregnant and fertile females uttered copulation calls. Two females conceived and mated mainly with the alpha male then. We conclude that copulation calls do not incite male contest competition for sexual access to females and that it is unlikely that calls synchronize male and female orgasms. Several hypotheses remain plausible, but not all predictions are borne out unequivocably. This alerts us to the possibility that the calls could have multiple beneficial effects; natural selection might strike a compromise among functions. Investigation of the mate again, sperm competition and alpha-male notification hypotheses, and of hypotheses not tested in our study concerning female breeding overlap and female-female agonism, is required.     

Size Dependent Sexual Selection in Drosophila ananassae

Mate choice based on body size is widespread and can have numerous consequences. We present data, which show the effect of male and female body size on sexual selection in Drosophila ananassae. The relationships between wing size, locomotor activity, mating latency, courtship pattern, fertility and mating success were studied. Mating latency was negatively correlated with wing length and with locomotor activity, while wing length and locomotor activity was positively correlated in males as well as in females. In female- and male-choice, we found that mate choice influenced size-assortative mating by: (1) large and small males preferring to mate with large females, (2) large males successfully competing for large females, leaving small males to mate with small females. Males increased their reproductive success by mating with large and more fecund females. In addition, in pairs of long/short winged flies, long winged flies courted and mated more successfully than short winged flies and they also have longer duration of copulation and more progeny than short winged flies. We found sterile mating in pairs of small winged males and females.     

Female reproductive strategies in orangutans,evidence for female choice and counterstrategies to infanticide in a species with frequent sexual coercion

Intersexual conflicts over mating can engender antagonistic coevolution of strategies, such as coercion by males and selective resistance by females. Orangutans are exceptional among mammals for their high levels of forced copulation. This has typically been viewed as an alternative mating tactic used by the competitively disadvantaged unflanged male morph, with little understanding of how female strategies may have shaped and responded to this behaviour. Here, we show that male morph is not by itself a good predictor of mating dynamics in wild Bornean orangutans but that female conception risk mediated the occurrence and quality of male–female interactions. Near ovulation, females mated cooperatively only with prime flanged males who they encountered at higher rates. When conception risk was low, willingness to associate and mate with non-prime males increased. Our results support the hypothesis that, together with concealed ovulation, facultative association is a mechanism of female choice in a species in which females can rarely avoid coercive mating attempts. Female resistance, which reduced copulation time, may provide an additional mechanism for mate selection. However, coercive factors were also important as prime males were frequently aggressive to females and females used mating strategies consistent with infanticide avoidance.     

Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection

The nuptial prey gift in the spider Pisaura mirabilis has been suggested to function as a male protection against sexual cannibalismduring courtship and mating. This hypothesis together withtwo alternatives—male mating effort and paternal investment hypotheses—were tested in a laboratory experiment withsexually inexperienced males and females. One group of malesoffered no gift to the female while three groups of males offeredsmall, medium, or large sized gifts, respectively. No malewas cannibalized among 82 trials. Aggression was observed onlyin encounters where a gift was presented. Males without a gift courted females, and 40% of these males managed to copulate,compared to 90% of males offering a gift. The copulation durationwas positively correlated with gift size. In general, the femaleterminated the copulation and ran away with the gift. The proportionof eggs fertilized increased with copulation time. Presenceor size of the nuptial gift did not affect female fecundityor spiderling size significantly. The results refute the hypothesesof sexual cannibalism and paternal investment. The nuptialgift represents a male mating effort; it entices the femaleto copulate, facilitates coupling during copulation, and byprolonging copulation it may increase the amount of sperm transferred.I conclude that the nuptial prey gift in Pisaura mirabilisis maintained by sexual selection.     

Female Reproductive Status and Mate Choice in the Hide Beetle, Dermestes maculatus

Models of mutual mate choice predict that when the costs of mating indiscriminately increase, so may the choosiness of the conventionally non-choosy sex. In a series of behavioral trials, we tested both male and female chemo-reception and mate choice in the hide beetle, Dermestes maculatus. Using olfactometer bioassays we found that males detected and responded more rapidly to individual mated females but had a limited ability to detect virgin females or discriminate between virgin and mated females when presented simultaneously. Both mated and virgin females were unable to detect the presence of virgin males. Copulation behaviors were comparable when males were presented with a virgin or mated female either individually or simultaneously. However, when presented simultaneously, virgin females had a higher probability of receiving a copulation than their mated counterparts. Our data show that males respond to variation in female reproductive status, but that female propensity to mate does not change. We suggest that mutual mate choice may be an important force, even in systems in which there is apparently strong selection for female mate discrimination.     

Why do male Callosobruchus maculatus harm their mates?

Males of the bruchid beetle Callosobruchus maculatus have spineson their intromittent organs that puncture the female reproductivetract during mating. Females kick their mates during copulation.If females are prevented from kicking the males, copulationslast longer and the injuries females sustain are more severe.We tested whether or not these injuries represent real fitnesscosts that can be mitigated by kicking and also what males gainby inflicting them. Our results show that females do indeedsuffer lowered lifetime fecundity if they are prevented fromkicking. However, we could find no evidence that males gainbenefits through harming their mates. It has been suggestedthat the way females respond to the harm may benefit the malecausing it. Injured females may be less willing to remate toavoid sustaining further injuries, or they may respond by increasingtheir rate of oviposition if they perceive the injuries as athreat to their survival. In our study, however, females thatwere prevented from kicking did not respond by delaying rematingor increasing their rate of oviposition. Furthermore, preventingfemales from kicking during their second copulation did notmake their second mates more successful in sperm competition.This suggests that the spines have evolved for other reasonsthan harming the females, such as serving as an anchor duringcopulation, and that the harm they cause is a side effect ofa male adaptation and is not itself adaptive for either sex.     

Female remating propensity contingent on sexual cannibalism in sagebrush crickets, Cyphoderris strepitans: a mechanism of cryptic female choice

Male sagebrush crickets (Cyphoderris strepitans) permit femalesto engage in an unusual form of sexual cannibalism during copulation:females feed on males' fleshy hind wings and ingest hemolymphoozing from the wounds they inflict. These wounds are not fatal,and normally only a portion of the hind wings are eaten at anyone mating, so that mated males are not precluded from matingagain. As a result, nonvirgin males have fewer material resources tooffer females than do virgin males, such that females shouldbe selected to preferentially mate with high-investment virginmales. We tested the hypothesis that female mating preferencesfavor males capable of supplying females with the highest materialinvestment. Our results indicate that both female diet and opportunitiesfor sexual cannibalism influence female mating behavior. Femalesmaintained on a low-nutrient diet mounted males significantlysooner than females maintained on a high-nutrient diet, indicatingthat a female's overall nutrient intake may determine her propensityto mate. In addition, females were significantly more reluctantto mount and mate with males whose hind wings had been surgicallyremoved and thus were incapable of providing females with awing meal. Finally, females initially mated to dewinged malesremated with winged males significantly sooner than femalesallowed to feed freely during their initial mating, resultingin cryptic female choice of investing males.     

The role of mating history and male size in determining mating behaviours and sexual conflict in a water strider

We conducted three experiments to test the effects of mating history of both sexes and of male body size on mating behaviours in the water strider, Gerris buenoi. Our manipulations influenced the interests of both sexes and, thus, the degree of conflict over mating behaviours. Mating history was a dichotomous variable (deprived/mated), depending on holding conditions in the laboratory. Experiment 1 considered and found independent effects of male and female mating history on latency to copulation and copulation duration. In experiment 2, we manipulated only female mating history, using unsuccessful struggle rates as evidence for female reluctance and conflict over mating. Finally, we investigated the relation between male body size and mating history on copulation duration. We predicted that intersexual conflict over mating would be lowest when females were deprived, because female interests under these conditions should more closely match those of males. Deprived females began mating in half the time of mated females and were twice as likely to mate because of reduced reluctance. Furthermore, copulation duration for deprived males was about one and a half times longer than that for mated males. Although previous studies examining nonrandom mating patterns by size predicted longer copulations for small males, we found that small males prolonged copulation when deprived more than large males. We conclude that females primarily influence copulation frequency, but males primarily influence copulation duration. Our results favour the hypothesis that reduced mating opportunity for small males accounts for their extended copulation duration. Finally, our findings provide evidence for strong effects of male body size on selection mechanisms in water striders, and support the hypothesis of conflicting pre- and postcopulatory selection mechanisms in this group. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.     

The effects of exposure to seaweed on willingness to mate, oviposition, and longevity in seaweed flies

Abstract  1. Large male seaweed flies (Diptera: Coelopidae) are more likely to mate than smaller males. This is due to sexual conflict over mating, by which females physically resist male attempts to copulate. In some species, large males are simply more efficient at overpowering female resistance.
2. Female reluctance to mate is likely to have evolved due to the costs of mating to females. In many dipterans, males manipulate female behaviour through seminal proteins that have evolved through sperm competition. This behavioural manipulation can be costly to females, for example forcing females to oviposit in sub-optimal conditions and increasing their mortality.
3. Previous work has failed to identify any ubiquitous costs of mating to female coelopids. The work reported here was designed to investigate the effects of exposure to oviposition sites ( Fucus algae) on the reproductive behaviour of four species of coelopid. Algae deposition in nature is stochastic and females mate with multiple males in and around oviposition sites. Spermatogenesis is restricted to the pupal stage and there is last-male sperm precedence. It was predicted that males would avoid wasting sperm and would be more willing to mate, and to remain paired with females for longer, when exposed to oviposition material compared with control males. Females were predicted to incur longevity costs of mating if mating increased their rate of oviposition, especially in the presence of algae.
4. The behaviour of males of all four species concurred with the predictions; however mating did not affect female receptivity, oviposition behaviour, or longevity. Exposure to algae induced oviposition and increased female mortality in all species independently of mating and egg production. The evolutionary ecology of potential costs of mating to female coelopids are discussed in the light of these findings.     

Sexual harassment in live-bearing fishes (Poeciliidae): comparing courting and noncourting species

Sexual harassment by males has been reported from several live-bearingfishes (Poeciliidae) and has been shown to inflict costs onfemales. For example, poeciliid females have reduced feedingopportunities when accompanied by a male because females dedicateattention to avoiding male copulation attempts. Poeciliid speciesdiffer considerably in male mating behavior, such as the presenceor absence of courtship. Courting males display in front ofthe females, but males attempting to sneak-copulate approachfemales from behind, that is, in the blind portion of theirvisual field, and force copulations, which can be viewed asa male persistence trait. We predicted that poeciliid femalesneed to be more vigilant in the presence of noncourting males,and costs of harassment by noncourting males might be stronger.In a comparative approach we examined the costs of male sexualharassment for females as reduced feeding time in 9 speciesof live-bearing fishes, including courting (Poecilia latipinna,Poecilia reticulata, Xiphophorus cortezi, Xiphophorus variatus)and noncourting species (Poecilia mexicana [surface- and cave-dwellingform], Poecilia orri, Gambusia affinis, Gambusia geiseri, Heterandriaformosa). In all species examined except for the cave form ofP. mexicana, focal females spent significantly less time feedingin the presence of a male than when together with another female.The time females spent feeding was found to significantly declinewith increasing male mating activity (sum of all sexual behaviors),but there was no support for the idea that females would spendmore time feeding in the presence of courting males comparedwith noncourting ones.