Nuptial feeding by male bushcrickets: an indicator of male quality?

Male bushcrickets transfer a spermatophore at mating that consistsof a sperm-containing ampulla and a product of the accessoryglands, the spermatophylax, that is consumed by the female duringinsemination. Male Requena verticalis produce functionally differentspermatophores depending on the availability of sexually receptivefemales. They will maintain high mating frequency by providinga gift sufficient to ensure sperm transfer, or will invest parentallyin females when their mating frequency is low. We examined therelationship between male quality and nuptial feeding underconditions where males invest in ejaculate protection or inparental investment. When investing in ejaculate protection,males reduced the quality of the spermatophylax meal by reducingboth the concentration of protein and the absolute amount ofprotein it contained. There was no relationship between malephenotype and gift size or quality. Moreover, we could findno evidence for the recently advanced hypothesis that femalescan exercise mate choice by interfering with insemination. However,when males were investing parentally, we found a positive associationbetween spermatophylax size and male size, but no relationshipbetween protein content and male size. Males with high levels offluctuating asymmetry invested more heavily in the nutritionalcontent of their spermatophylaxes than did symmetrical males.Thus, male quality does influence nuptial feeding, but in amanner predicted by a model of indirect fitness benefits frommate choice.     

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.     

The refractory period of female katydids (Orthoptera: Tettigoniidae): sexual conflict over the remating interval?

Female tettigoniids have a refractory period after mating duringwhich they are sexually unreceptive. Because females obtainvaluable nutrients as well as sperm at mating, there is likelyto be sexual conflict over the duration of the refractory period;females should accrue male donations, whereas males should preventtheir mates from accepting additional matings. We examined theeffects of ampulla attachment duration and female diet on theinduction of the refractory period of a zaprochiline tettigoniid.We find that, although the relationship between ampulla attachmentduration and duration of the refractory period holds for femalesmaintained on a high-pollen diet, poorly nourished females onlyshow the typical onset of the refractory period when allowedto consume the spermatophylax. These results suggest that femaleinterests may have a greater influence in determining the outcomeof sexual conflict. Under some circumstances spermatophylaxfeeding may compensate for poor female nutrition leading tothe typical refractory period. Sexual conflict over the rematinginterval could be instrumental in generating larger nutrientinvestments by male tettigoniids. [Behav Ecol 1991;2:276–282]     

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.     

Investigation of venereal, transplacental, and contact transmission of the Lyme disease spirochete, Borrelia burgdorferi, in Syrian hamsters.

A hamster was inoculated with the SI-1 strain of Borrelia burgdorferi and subsequently served as a host to larval Ixodes scapularis Say. Approximately 68% of the nymphs resulting from the fed larvae were infected. Nymphs from this group were fed on uninfected hamsters, and 3 of 4 males and 6 of 6 females became infected. The infected hamsters were allowed to mate with uninfected partners to test for venereal transmission. Six infected females were mated with 6 uninfected males, whereas 3 infected males were mated with 6 uninfected females. None of the uninfected hamsters became infected after mating. Two protocols were used to determine if transplacental transmission of B. burgdorferi occurred. One group included 6 nonpregnant infected females that were subsequently mated and became pregnant. Three of the females were allowed to carry to full term, whereas the other 3 were killed prior to parturition. All fetuses and offspring were negative for B. burgdorferi based on cultures and monoclonal antibody assays. Another group of 6 females was infected via tick bite after becoming pregnant; those females were allowed to carry fetuses to birth and all were negative. Attempts at contact transmission of B. burgdorferi from 2 infected females to 2 uninfected male and 2 uninfected female hamsters and from 2 infected males to 2 uninfected male and uninfected female hamsters via urine or feces failed.     

Juvenile hormone titre and egg production in Tenebrio molitor infected by Hymenolepis diminuta: effect of male and/or female infection,male age and mating

Infection of Tenebrio molitor with Hymenolepis diminuta induces curtailment of female fertility. We examined ovulation and oviposition, and associated titres of juvenile hormone (JH), in relation to parasitism and mating. Oviposition was significantly increased in infected mated and virgin beetles by days 6 and 9 post-emergence. Ovulation was not changed by infection; by the end of the 18-day experiment, the total number of laid eggs was not significantly altered. On day 6, JH levels were significantly higher in virgin infected insects, compared to non-infected controls (236+/-37.7 and 107+/-9.62 pg/g wet weight). Oviposition increased after mating, but total eggs ovulated remained the same. JH levels were higher in mated females on days 12 and 18 post-emergence, for infected and control insects. Previous studies suggested that male reproductive potential might rise following infection, because uninfected females lay more eggs when mated to infected males. We tested whether this caused an increase in female JH. Males were mated on days 5 or 12, when significant changes in their reproductive physiology begin to be observed, and are maximal, respectively. However, male age was of greater significance in promoting JH levels in females (p=0.001), than infection status of either partner (p=0.33).     

Sexual transmission of a plant pathogenic bacterium, Candidatus Liberibacter asiaticus, between conspecific insect vectors during mating

Candidatus Liberibacter asiaticus is a fastidious, phloem-inhabiting, gram-negative bacterium transmitted by Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae). The bacterium is the presumed causal agent of huanglongbing (HLB), one of the most destructive and economically important diseases of citrus. We investigated whether Las is transmitted between infected and uninfected D. citri adults during courtship. Our results indicate that Las was sexually transmitted from Las-infected male D. citri to uninfected females at a low rate (<4%) during mating. Sexual transmission was not observed following mating of infected females and uninfected males or among adult pairs of the same sex. Las was detected in genitalia of both sexes and also in eggs of infected females. A latent period of 7 days or more was required to detect the bacterium in recipient females. Rod shaped as well as spherical structures resembling Las were observed in ovaries of Las-infected females with transmission electron microscopy, but were absent in ovaries from uninfected D. citri females. The size of the rod shaped structures varied from 0.39 to 0.67 μm in length and 0.19 to 0.39 μm in width. The spherical structures measured from 0.61 to 0.80 μm in diameter. This investigation provides convincing evidence that a plant pathogenic bacterium is sexually transmitted from male to female insects during courtship and established evidence that bacteria persist in reproductive organs. Moreover, these findings provide an alternative sexually horizontal mechanism for the spread of Las within populations of D. citri, even in the absence of infected host trees.     

Paternity costs from polyandry compensated by increased fecundity in the hide beetle

Polyandry-induced sperm competition is assumed to impose costson males through reduced per capita paternity success. In contrast,studies focusing on the consequences of polyandry for femalesreport increased oviposition rates and fertility. For thesespecies, there is potential for the increased female fecundityassociated with polyandry to offset the costs to males of sharedpaternity. We tested this hypothesis by comparing the proportionand number of offspring sired by males mated with monandrousand polyandrous females in the hide beetle, Dermestes maculates,both for males mating with different females and for males rematingwith the same female. In 4 mating treatments, monandrous femalesmated either once or twice with the same male and polyandrousfemales mated either twice with 2 different males or thricewith 2 males (where 1 male mated twice). Polyandrous and twice-matingmonandrous females displayed greater fecundity and fertilitythan singly mating monandrous females. Moreover, males rematedto the same female had greater paternity regardless of whetherthat female mated with another male. In both polyandrous treatments,male mating order did not affect paternity success. Finally,although the proportion of eggs sired decreased if a male matedwith a polyandrous female, multiply mating females or femalesthat remated with a previous mate laid significantly more eggsand thus the actual number of eggs sired was comparable. Thus,males do not necessarily accrue a net fitness loss when matingwith polyandrous females. This may explain the absence of anyobvious defensive paternity-protection traits in hide beetlesand other species.     

Sex‐dependent infection causes nonadditive effects on kissing bug fecundity

The influence of parasites on host reproduction has been widely studied in natural and experimental conditions. Most studies, however, have evaluated the parasite impact on female hosts only, neglecting the contribution of males for host reproduction. This omission is unfortunate as sex‐dependent infection may have important implications for host–parasite associations. Here, we evaluate for the first time the independent and nonindependent effects of gender infection on host reproductive success using the kissing bug Mepraia spinolai and the protozoan Trypanosoma cruzi as model system. We set up four crossing treatments including the following: (1) both genders infected, (2) both genders uninfected, (3) males infected—females uninfected, and (4) males uninfected—females infected, using fecundity measures as response variables. Interactive effects of infection between sexes were prevalent. Uninfected females produced more and heavier eggs when crossed with uninfected than infected males. Uninfected males, in turn, sired more eggs and nymphs when crossed with uninfected than infected females. Unexpectedly, infected males sired more nymphs when crossed with infected than uninfected females. These results can be explained by the effect of parasitism on host body size. As infection reduced size in both genders, infection on one sex only creates body size mismatches and mating constraints that are not present in pairs with the same infection status. Our results indicate the fitness impact of parasitism was contingent on the infection status of genders and mediated by body size. As the fecundity impact of parasitism cannot be estimated independently for each gender, inferences based only on female host infection run the risk of providing biased estimates of parasite‐mediated impact on host reproduction.     

Sexual functionality of Leptopilina clavipes (Hymenoptera: Figitidae) after reversing Wolbachia-induced parthenogenesis

Females infected with parthenogenesis-inducing Wolbachia bacteria can be cured from their infection by antibiotic treatment, resulting in male production. In most cases, however, these males are either sexually not fully functional, or infected females have lost the ability to reproduce sexually. We studied the decay of sexual function in males and females of the parasitoid Leptopilina clavipes. In western Europe, infected and uninfected populations occur allopatrically, allowing for an investigation of both male and female sexual function. This was made by comparing females and males induced from different parthenogenetic populations with those from naturally occurring uninfected populations. Our results indicate that although males show a decay of sexual function, they are still able to fertilize uninfected females. Infected females, however, do not fertilize their eggs after mating with males from uninfected populations. The absence of genomic incompatibilities suggests that these effects are due to the difference in mode of reproduction.     

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.     

Female assessment of male functional fertility during mate choice in a promiscuous fish

Sexual selection should favour females that can assess the functional fertility of available sexual partners and avoid mating with recently mated, sperm‐depleted males. Our current understanding of the sensory mechanism(s) underlying female assessment of males based on their functional fertility and avoidance of sperm‐depleted males is incomplete. Female Trinidadian guppies (Poecilia reticulata) are known to avoid mating with males that they had previously observed mating with other females. Here, we investigated experimentally the proximate sensory cues that they use to distinguish between paired size‐ and colour‐matched mated and unmated males in the absence of visual public information on their prior mating histories. When only water‐borne chemical cues from the males were available, females avoided the previously mated male and preferred the unmated one, but they chose randomly when only male visual cues (and no chemical cues) were available. They also preferred unmated over mated males when freely swimming with them in a more sensorially complex environment with multiple male cues (i.e., visual, chemical and mechanical cues) concurrently available. Females exhibited no preference for either stimulus males when both were unmated, irrespectively of the sensory environment. These novel results suggest that, in the absence of prior visual public information on the recent mating histories of males, female guppies use olfactory cues putatively emitted by mated males to avoid mating with them. The source and nature of the implicated olfactory cues and the fitness benefits gained by female guppies in sexually preferring males that have not recently mated remain unknown and warrant further research.     

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.     

Male Drosophila melanogaster show adaptive mating bias in response to female infection status

Given the non-trivial cost of reproduction for males and substantial variation in female quality, males have been predicted to show mating bias as an evolved strategy. Using a large outbred population of Drosophila melanogaster, we test this prediction and show that males may adaptively bias their mating effort in response to the infection status of females. Given a simultaneous choice between females infected with pathogenic bacteria and sham infected females, males preferentially mated with the latter, who had a higher reproductive output compared to infected females. This may provide evidence for pre-copulatory male mate choice. Assessment of the reproductive behaviour ensured that the observed pattern of mating bias was not due to differences in receptivity between females infected with pathogenic bacteria and sham infected females. Further, there was no evidence for post-copulatory male mate choice measured in terms of copulation duration.     

Parasites reduce attractiveness and reproductive success in male grain beetles

Sexual characters may reveal the quality of a potential mate, including the mate's level of infection with parasites. Females that prefer males with low levels of infection or no infection may benefit in several ways. Direct benefits may include avoidance of infection, acquistition of larger nuptial gifts or enhancement in fecundity due to differences in male fertility. Females may also benefit indirectly by producing offspring that are more resistant to infections. We measured female preference for odours produced by male grain beetles, Tenebrio molitor, that were either infected by a tapeworm, Hymenolepis diminuta, or uninfected. This parasite is not transmitted directly between conspecifics. Females were attracted to odours of all males, but they were less attracted to those from parasitized males. To the contrary, females were preferentially attracted to infected females. Males did not show any biased attraction to odours from infected and uninfected male beetles. Females that mated with highly infected males produced fewer offspring than females mated to uninfected males, indicating parasitic infection inflicts multiple costs to males. These results are consistent with models of parasite-mediated sexual selection. Copyright 2000 The Association for the Study of Animal Behaviour.     

Wolbachia affects oviposition and mating behaviour of its spider mite host

Wolbachia bacteria are transmitted from mother to offspring via the cytoplasm of the egg. When mated to males infected with Wolbachia bacteria, uninfected females produce unviable offspring, a phenomenon called cytoplasmic incompatibility (CI). Current theory predicts that ‘sterilization’ of uninfected females by infected males confers a fitness advantage to Wolbachia in infected females. When the infection is above a threshold frequency in a panmictic population, CI reduces the fitness of uninfected females below that of infected females and, consequently, the proportion of infected hosts increases. CI is a mechanism that benefits the bacteria but, apparently, not the host. The host could benefit from avoiding incompatible mates. Parasite load and disease resistance are known to be involved in mate choice. Can Wolbachia also be implicated in reproductive behaviour? We used the two‐spotted spider mite – Wolbachia symbiosis to address this question. Our results suggest that uninfected females preferably mate to uninfected males while infected females aggregate their offspring, thereby promoting sib mating. Our data agrees with other results that hosts of Wolbachia do not necessarily behave as innocent bystanders – host mechanisms that avoid CI can evolve.     

Sexual Inhibition in <Emphasis Type="Italic">Spalangia endius</Emphasis> Males After Mating and Time for Ejaculate Replenishment

Although males are often stereotyped as always sexually responsive, a previous study with the parasitoid wasp Spalangia endius showed that males exhibit a post-mating decrease in sexual responsiveness. The present study examined the duration of the decrease and whether waiting to remate increased the amount of ejaculate that a male provided to his second mate. Mated males were back to being as sexually responsive as virgin males by about 5 min after mating. The amount of ejaculate that females received from already mated males was not significantly related to the duration between the male’s first and second mating. The short-term decrease in sexual responsiveness of a mated male may prevent him from immediately trying to remate with the same female because it gives her time to get away.     

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     

Pairing success of male Gammarus lacustris infected by two acanthocephalans: a comparative study

The costs of parasitism to host reproduction can be best assessedusing field studies to determine overall mating success andexperimental studies to examine how parasites may affect matingbehavior. We compared the influence of two parasites, Polymorphusparadoxus and P. marilis (Acanthocephala), on the pairing successof their intermediate host (Gammarus lacustris, Crustacea) inboth the field and laboratory. Parasitism significantly loweredthe pairing success of male gammarids. In the field, P. paradoxus-infectedmales paired significantly less often than P. marilis-infectedor uninfected males. Those infected by P. marilis were alsofound in precopula significandy less often than uninfected ones.In the laboratory, the pairing success of males infected byeither parasite was significantly reduced in both competitiveand noncompetitive situations. As in the field studies, thepairing success of P. paradoxus-infected males was significantlylower than that of P. marilis-infected and uninfected males.Polymorphus marilis-infected males were also outcompeted byuninfected individuals, however, their pairing success improvedwhen alone with a female (noncompetitive experiments). We relatethe differential influence of the two parasites on the pairingsuccess of male gammarids to their effects on the physiologyand behavior of G. lacustris.     

Polyandry in grain beetles, Tenebrio molitor, leads to greater reproductive success: material or genetic benefits?

Females that mate with more than one male may derive both materialand genetic benefits, and differentiating between the two benefitsis often difficult. We tested for both material and geneticeffects associated with multiple mating in the highly promiscuousyellow mealworm beetle, Tenebrio molitor. Females that matedfour times to the same male laid more eggs and produced morelarvae than females that mated only once. Whether copulationsoccurred on the same day or over several days, the result wasan immediate increase in the production of eggs by females.Some females were kept on a restricted diet to test whethernutrients in the spermatophore disproportionately benefittedfood-deprived females. Although females on poor diets producedfewer and smaller offspring, diet did not significantly affect the proportional benefit of mating treatment on female fecundity.By controlling for male mating history, we were able to separatethe effects of mating with different males from the effectsof receiving multiple spermatophores from the same male. Femalesthat mated with four different males achieved substantial gainsin numbers of eggs produced (32% increase) beyond those offemales that mated an identical number of times with the same male. We found no evidence that males allocate fewer sperm toprevious mates. Egg hatchability was unaffected by mating behavior,suggesting that genetic incompatibility at that stage is notresponsible for the low reproductive success of females matedwith a single male. These results suggest that females maydelay or reduce oviposition or may be incapable of achieving maximal fecundity until they have gained the material and/orgenetic benefits of mating with multiple males.