Regulation of sexual receptivity of female Mediterranean fruit flies: old hypotheses revisited and a new synthesis proposed

The objective of this study was to examine the relative contributions of copula duration and sperm transfer to the inhibition of sexual receptivity of female Mediterranean fruit flies (Ceratitis capitata, Diptera: Tephritidae). Females choosing to remate had significantly fewer sperm in their spermathecae than females who chose not to remate. Duration of a female's first copulation did not affect her subsequent receptivity. Furthermore, on the first day following copulation significantly more females whose first mate was sterile and from a laboratory strain (sterile males transfer fewer sperm than wild males) chose to copulate than did females whose mate was fertile and recently derived from wild stock. Finally, we offer a synthesis of the available information on remating in this species, and suggest that while females are facultatively polyandrous, copula duration, sperm transfer and male accessory gland secretions act in succession to inhibit female receptivity.     

Prior oviposition, female receptivity and last-male sperm precedence in the cosmopolitan pest Callosobruchus maculatus (Coleoptera: Bruchidae)

Sperm competition studies have shown that P₂ (the proportion of ova fertilized by the last male to mate) increases as the interval between inseminations is experimentally increased. Variation in the number of sperm in storage is associated with sperm use (or loss) from the female's sperm stores between copulations (fewer sperm from previous mates at the time of the last copulation) and with the extent of prior oviposition and female receptivity to further copulation: females that lay many eggs tend to have few remaining sperm in storage and to be more receptive to further copulation. Using the bruchid beetle Callosobruchus maculatus, we examined the effect of prior oviposition and female receptivity to further copulation on the extent of last-male sperm precedence (measured as P₂). Extent of prior oviposition was experimentally manipulated independently of the intermating interval by altering the availability of oviposition sites between inseminations. Females given few or no oviposition sites laid fewer eggs, were less receptive and had a lower P₂ than females given abundant oviposition sites. To examine the effect of female receptivity on P₂ independently of prior oviposition, we examined the outcome of sperm competition experiments using (1) females from lines that had been selected for different latencies to copulation and (2) natural variation in female latency to receptivity. Female receptivity to further copulation had no detectable effect on P₂. When oviposition resource is abundant, female receptivity may be a poor predictor of current sperm load.     

Functional and nonfunctional female receptivity signals in the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae)

In many taxa, females signal during courtship when they are receptive. However, just because a female signals does not mean that the male responds to the signal. This study examines female signaling of receptivity (readiness to copulate) and male response in the parasitoid wasp Spalangia endius Walker. Females folded their antennae against their heads when they were receptive, and antennal folding has been shown to be effective in eliciting male copulation attempts in a confamilial. However, male S. endius did not respond to antennal folding: males did not contact the female's antennae during courtship, and how quickly a male attempted copulation was independent of whether or not the female had antennae. Males courted from on top of the female's abdomen and appeared to detect receptivity directly from the female's abdomen rising as her genital orifice opened. On females whose abdomens did not rise, initiation of male copulation attempts were delayed but not eliminated. Based on its current lack of function as a receptivity signal and on comparisons to published reports of mating behavior in confamilials, we hypothesize that female antennal folding at receptivity is a vestigial trait in S. endius.     

Remating inhibition in the melon fly,Bactrocera (=Dacus) cucurbitae (Diptera: Tephritidae): Copulation with spermless males inhibits female remating

Eight hour copulation of the melon fly,Bactrocera cucurbitae, which usually mates at dusk and finishes copulation at dawn, inhibited female remating, while 3 h copulation did not. Copulation of females with either normal or virgin sterile males inhibited female remating. Sperm-depleted sterile males inhibited female remating at the same rate as normal males when the copulation duration was 8 h, indicating that existence or amount of sperm in females' spermathecae is not important in remating inhibition. Females of a wild strain remated later than females of a mass-reared strain, irrespective of strains of 1st and 2nd males. This suggests that the females may control their own remating, or that there is a difference between wild and mass-reared strains in their sensitivity to a male substance that inhibits females' receptivity.     

Receptivity of female remating and sperm number in the sperm storage organ in the bean bug,Riptortus clavatus (Heteroptera: Alydidae)

This study examines the relationship between the number of sperm in the seminal receptacle (spermatheca) and the receptivity of female remating in the bean bugRiptortus clavatus Thunberg. On the 21 st day after the first mating when receptivity to remating was > 70%, females receptive to remating had significantly fewer sperm ( < 40 on average) in the spermathecae than females reluctant to do (about 150 on average). However, averages of the number of eggs laid by receptive and reluctant females within 21 days were almost same. The proportion of fertilized eggs for receptive females at 15–21 days after copulation was significantly lower than that for reluctant females. Spermatozoa transferred from a male to a female’s spermatheca were detected 5 min after copulation and then increased continuously to about 500 with the first hour. When copulation durations were manipulated artificially, the shorter the copulation period (=females had less sperm in their spermathecae), the higher the remating rate became. Females may perceive the number of sperm in their seminal receptacles and then determine whether they copulate or not. These results support the hypothesis that females mate multiply in order to replenish inadequate sperm supplies to fertilize all eggs produced.     

Managing the invasive crayfish Procambarus clarkii: Is manual sterilisation the solution?

1. Management of invasive alien crayfish is challenging, as once established their eradication or control is difficult, even impossible in some areas. Sterile male release technique has been previously assessed in crayfish with encouraging results, however, the methods have not demonstrated the complete sterility of released competitive males. The present study explores whether manual removal of male gonopods, i.e. the appendages responsible for sperm transfer, as a sterilisation technique, might affect male competitiveness and sexual behaviour as well as reproductive potential in the red swamp crayfish Procambarus clarkii.
2. Under controlled laboratory conditions, we analysed the agonistic and sexual behaviour of 64 treated and 64 control males both coupled with a female in single pairs, and 40 treated and 40 control males together with 80 females in a natural-like social context.
3. Removal of gonopods partly altered sexual behaviour, affecting duration of copulation and competitiveness in treated males. However, male readiness to initiate sexual interaction with females was not affected by the treatment. Treated males needed to invest more in agonistic interactions with females to successfully dominate a female for the copulation to take place. Females coupled with treated males did not produce any offspring, compared to females coupled with control males. Treated males were able to regenerate removed gonopods, even if sometimes only partially or malformed. Females that mated with 11 treated males with regenerated gonopods did not produce any juveniles.
4. Although treated males managed to mate with females and impair their reproductive capability under the laboratory conditions, shorter copulation and elevated number of abdominal extensions were observed in treated couples. This indicates that males and/or females are able to sense the lack of gonopods and/or lack of the contact. We believe that female receptivity after an initial mating requires further investigation. Assessment of receptivity in an experimental setting where females are provided with refuges (e.g. burrows) would help us to elucidate whether there is a compensation for unsuccessful copulation. More research is needed on underlying biological mechanisms to better assess male competitiveness, technique effectiveness and limits of technique application.

     

Factors affecting female sexual receptivity in the planthopper, Prokelisia dolus

Abstract. The mating system of Prokelisia dolus Wilson (Homoptera: Delphacidae) was characterized by determining: if males and females multiply mate; when transitions occur in female sexual receptivity, what triggers sexual refractoriness; and what behaviours characterize unreceptive virgins, receptive virgins, and unreceptive mated females. Males copulated with up to six females in less than 1 h, but completely inseminate, on average, only the first four females. Females rarely mated more than once, unless males were depleted of sperm due to previous copulations or if copulation was interrupted (if duration was<2 min). Male and female calling was associated (100% and 91%, respectively) with sexual receptivity and resultant matings. The transition from unreceptive virgin to receptive (calling) mature virgin occurred 48 h posteclosion, and all were mated by day 4. Females that were sexually immature and those completely inseminated did not call. Rejection of males by females included walking away from approaching males (65%), female kicking (7%), and abdominal lifting (5%). Rejection of males was observed by immature, mature and calling, and mated females. Sexual refractoriness was not triggered by acoustic and visual stimuli or mechanical stimulation of genitalia. Refractoriness was also not triggered by reception of small quantities of sperm because some females laid a few viable eggs yet calling was not terminated. Sexual refractoriness was activated by a substance in the ejaculate as demonstrated by injection into the haemocoel of male accessory glands or testes and homogenates of seminal vesicles. This is the first study that documents the role of male ejaculate in inhibiting female sexual receptivity in Hemiptera (Homoptera).     

Inheritance of species differences in female receptivity and song requirement between Drosophila virilis and D. montana

Females of two Drosophila virilis group species, D. virilis and D. montana, have different requirements for the courting males. In the present study we have examined species differences in female receptivity and male courtship song requirement using females' acceptance signal instead of copulation for measuring female readiness to mate. Behavior of D. virilis and D. montana females and F1 and backcross hybrid females was observed in a single-pair courtships with D. virilis and D. montana males and normal and wingless (mute) F1 hybrid males. D. virilis females were very receptive and they commonly accepted the courtship of males unable to produce courtship song. D. montana females, on the contrary, had a low receptivity and these females accepted the courting male only after hearing his song. Interspecific F1 and backcross (BCm) females resembled D. virilis more than D. montana in their receptivity. These females, however, resembled D. montana in their song requirement. These findings suggest that female song requirement and female receptivity are determined by different genetic factors.     

Androgens and the social behavior of male and female lizards (Anolis carolinensis)

This study investigated the androgen specificity of aggressive and sexual behavior in the lizard Anolis carolinensis and the capacity of females of this species to exhibit male-typical copulation. Gonadectomized males and females were injected with testosterone propionate (TP) or dihydrotestosterone propionate (DHTP) or were implanted with Silastic tubing containing TP or DHTP. Either TP or DHTP activated male-typical sexual behavior in both males and females and activated aggressive behavior in males; DHTP activated aggressive behavior in females. Thus conversion of androgen to estrogen is not essential for these behavior patterns, and endogenous dihydrotestosterone may be important. TP but not DHTP stimulated receptivity in females, suggesting that conversion of testosterone to estrogen may underlie TP-stimulated receptivity. Females treated with TP did not differ from males in their display of male-typical courtship, neck-clasping, and intromission.     

Mating Behavior of Cephalonomia tarsalis (Ashmead) (Hymenoptera: Bethylidae) and the Effect of Female Mating Frequency on Offspring Production

The courtship behavior of Cephalonomia tarsalis, a solitary semiectoparasitoid of Oryzaephilus surinamensis, was investigated in the laboratory. Courtship behavior includes a series of stereotypic movements. Males play the most active role, executing the majority of courtship action, and females respond with relatively limited observable behaviors. Males typically keep antennae still during encounters with females prior to mounting, which may be correlated with recognition of the female's sexual status. After mounting, males display a series of movements on females, such as antennae touching female's antennae, antennae or mouth touching female's head or thorax, and walking around on female, which may serve to stimulate females towards increased receptivity. Females signal receptivity by assuming a stereotypical posture of remaining stationary, with head down, and antennae still in front of the body. The male then inserts his aedeagus and the pair copulates. After an average of 40.4 s of copulation, females signal the end of copulation by waving the antennae and moving away from the copulation site. Males continue copulating for a short time after females start moving but dismount soon thereafter. After dismounting, the two wasps move away from each other immediately, and they typically begin grooming. Neither males nor females exhibit mating preference based on mate's mating status in both choice and no-choice tests. The male is polygynous and the mated female can mate multiple times within the first 3 days after starting oviposition. However, female mating frequency does not affect the production of female progeny.     

Mate selection in the fly Scatophaga stercoraria: female choice in a male-controlled system

Sexual pairing in the fly Scatophaga stercoraria involves ‘capture’ of females by males. Sizerelated choice by males and females is considered, because these flies are highly variable in size, and size strongly affects reproductive success. Results show that males do not discriminate among females on the basis of size. Females choose large males when free to select mates. They move toward larger males when contronted by more than one possible mate, and their movement on the oviposition site takes them to areas where large males are more common. Females paired with large males gain from (1) reduced harm in struggles; (2) more rapid copulation and oviposition, with lower risk to the female and her progeny; and (3) greater ability to escape danger during copulation. These benefits may account for female preference for large males.     

Female reproductive responses to photoperiod and male odours in the subterranean rodentCtenomys talarum

The tuco-tucoCtenomys talarum Thomas, 1898 is a solitary subterranean rodent that breeds seasonally in coastal sand-dune grasslands from Argentina. We assessed whether short-day photoperiod determines the onset of reproduction by an increase in female’s receptivity and whether male odour interacts with photoperiod as a cue by producing a greater response in receptivity. Receptivity was measured by an increase in the percentage of vaginal epithelial cells, particularly cornified cells. Females were trapped during their non-reproductive season (summer-long days) and randomly assigned to different day-length experimental groups: constant summer (CS), early winter (EW), and natural (NA) photoperiod. We examined the vaginal epithelium using vaginal smears during the first experimental phase (120 days) to test the effect of photoperiod. In the second experimental phase (15 days), we presented the females with male-soiled shavings to test the effect of photoperiod and male odor.Ctenomys talarum females showed some evidence of reproductive responsiveness to photoperiodic cuing. The proportion of epithelial cells peaked earlier in females when winter day-length was advanced than in females under natural photoperiod. Contrary to that expected, male odours did not stimulate female receptivity. These results suggest that, while photoperiod may participate in regulating reproduction, the integration of other environmental and social factors, as well as the identification of bodily conditions that lead to differences in individual response needs further consideration.     

The Effects of Experimentally Induced Polyandry on Female Reproduction in a Monandrous Mating System

Females of most insect species maximize their fitness by mating more than once. Yet, some taxa are monandrous and there are two distinct scenarios for the maintenance of monandry. While males should always benefit from inducing permanent non‐receptivity to further mating in their mate, this is not necessarily true for females. Since females benefit from remating in many species, cases of monandry may reflect successful male manipulation of female remating (i.e. sexual conflict). Alternatively, monandry may favor both mates, if females maximize their fitness by mating only once in their life. These two hypotheses for the maintenance of monandry make contrasting predictions with regards to the effects of remating on female fitness. Here, we present an experimental test of the above hypotheses, using the monandrous housefly (Musca domestica) as a model system. Our results showed that accessory seminal fluid substances that males transfer to females during copulation have a dual effect: they trigger female non‐receptivity but also seem to have a nutritional effect that could potentially enhance female fitness. These results suggest that monandry is maintained in house flies despite potential benefits that females would gain by mating multiply.     

Sexual receptivity and age in Glossina pallidipes Austen (Dipt., Glossinidae)

The recent success of the sterile insect technique (SIT) in eradicating Glossina austeni from Zanzibar has stimulated interest in applying this technology to control Glossina pallidipes. However, little is known about the mating behaviour of this species in relation to the development and implementation of an effective SIT programme. The effect of age on male and female receptivity to mating was evaluated together with copulation duration, sperm transfer and the growth of the accessory gland and follicle A in males and females, respectively. Females and males reached their optimal sexual receptivity 9–13 days after emergence. Mean copulation duration was 20–30 min for mature males and females. The growth of follicle A and the accessory gland (apical body) was a function of age of females and males, respectively. Ovulation was not observed in virgin females up to 15 days of age whereas mated females ovulated by day 9. Males aged 7–15 days were equally effective in inseminating. Cages of males and females of different ages were set up to monitor puparial production in relation to optimization of mass rearing. The results are discussed in relation to the development of an efficient mass rearing protocol for this species and an optimal release strategy for sterile males.     

Female sexual receptivity and male copula guarding during prolonged copulations in the damselflyIschnura senegalensis (Odonata:Coenagrionidae)

Laboratory experiments were conducted to clarify the relationship between female sexual receptivity and male copula guarding inI. senegalensis, a species that copulates for several hours. In insectaries, most copulations were initiated early in the morning, and terminated relatively synchronously between 11 00 and 13 00. Females refused males with wing-flutter display and oviposited alone in the afternoon regardless of copulation events of that morning. Females could sexually receive males only in the morning. Males copulated for several hours until 12 00 after which females could oviposit. To determine whether copulations that last for hours function as male copula guarding or only of sperm displacement, emerged males were kept at various densities and permitted to copulate with virgin and mated females in insectaries. Both with virgin and mated females, “social” (not solitary; 2–4 males / insectary) males initiated copulations early in the morning and always terminated at around 12 00. However, both with virgin and mated females, solitary (one male / insectary) males terminated copulations in the morning. In both cases, duration of copulations did not significantly differ for virgin females and mated females. Therefore, long (several hour) copulation is more likely to function as male copula guarding than as sperm displacement, and duration of copulations is predicted to be shortened when male density is very low.     

Identification of Brain Sites Controlling Female Receptivity in Mosaics of DROSOPHILA MELANOGASTER

We have identified cells in the brain of Drosophila melanogaster that are required to be of female genotype for receptivity to copulation with males. To do this, we determined experimental conditions in which female flies virtually always copulate, then measured the minimum amount of male courtship that is required to stimulate females to indicate their receptivity to copulation. We then observed gynandromorphs with female genitalia to determine whether the sex mosaics elicited at least the minimum amount of courtship and, if so, whether they copulated. By analyzing these gynandromorphs, in which the genotype of external and internal tissues could be ascertained, we were able to identify a group of cells in the dorsal anterior brain that, when bilaterally female, is necessary and sufficient for receptivity to copulation. This group of cells is anatomically distinct from those that are required to be of male genotype for the performance of courtship behaviors.     

Mated Redback Spider Females Re-Advertise Receptivity Months after Mating

In many species, selection acts on males to recognize female reproductive status at a distance using pheromones. Unmated females may actively seek to attract males; however, mated females may become cryptic to avoid attracting additional males if multiple matings are costly. Although females of many species cease pheromone production after mating, it is often unclear whether this is a strategic part of a female reproductive strategy, or whether this is because of chemical manipulation by males. If variation in pheromone production is part of the female’s strategy, then we predicted mated females should eventually re‐advertise receptivity if the benefits of multiple mating increase with time since copulation (e.g. because of sperm depletion). Here, we tested this prediction in Australian redback spiders (Latrodectus hasselti). First, we replicated earlier results by showing that virgin males discriminate female maturity and mating status based exclusively on web‐borne chemicals. Our results show this difference must arise from a change in chemical deposition in the web as we controlled for web volume differences between mated and virgin females. Male activity on extracts from webs of virgin females exceeded activity on a solvent control and on extracts of webs of just‐mated females—confirming that female redbacks cease pheromone production immediately after mating. Second, we tested a new prediction that mated females might re‐advertise receptivity near the end of their normal breeding season to replenish diminished sperm stores prior to overwintering. Consistent with the prediction of strategic advertisement, we show that male activity on extracts from females’ webs increased significantly 3 mo after the female first mated (typical length of the breeding season). Thus, these females had begun to add pheromone to their web again. At this time, 26% of these females re‐mated with a second male. If females re‐advertise receptivity to ensure adequate sperm stores, then we predicted a positive relationship between female reproductive output during the 3‐mo interval after copulation and the subsequent intensity of male response to web extracts. However, differences in male activity time were not related to the total number of spiderlings or the number of egg sacs a female had produced during the 3‐mo interval after the first copulation. This result could arise if male chemical manipulation of female receptivity decreases with time after copulation, or if the testing interval used in our study was too long to reveal variation in sperm depletion in females. Thus, although our results are consistent with the idea that females strategically alter pheromonal advertisement, we cannot distinguish this from the hypothesis that female receptivity arises from chemical manipulation by males.     

Effects of male mating interval on spermatophore formation,transfer, and subsequent female receptivity and fecundity in the sorghum plant bug,Stenotus rubrovittatus

Males of the sorghum plant bug, Stenotus rubrovittatus (Matsumura) (Heteroptera: Miridae), transfer a spermatophore to females during copulation. After a 1‐day interval between the first and second copulation, males transferred both sperm and a spermatophore to females during the second copulation. However, when male mating interval was <1 h, they transferred sperm but no spermatophores to females during the second copulation. Therefore, the male mating interval probably produces two types of mated females, those with and those without a spermatophore. Mated females of S. rubrovittatus do not remate for at least 3 days after mating, even when courted, and lay more eggs than virgin females at the beginning of the oviposition period. The effects of spermatophores on female sexual receptivity and fecundity were examined using mated females with or without a spermatophore. Only one of the 40 (2.5%) mated females with a spermatophore remated, whereas 10 of the 26 (38.5%) without a spermatophore remated. Furthermore, mated females with a spermatophore laid more eggs than those without a spermatophore. These results suggest that spermatophores participate in reducing female sexual receptivity and enhancing female fecundity in S. rubrovittatus.     

Female control in yellow-legged gulls: trading paternity assurance for food

Females in many socially monogamous birds copulate hundreds of times more than necessary for fertilization, although little is known about the benefits of this excess. Females may not directly benefit from high copulation rates, but instead may exploit male interest in copulating to obtain benefits. In species with courtship feeding, females may trade copulations for food (immediate benefits hypothesis). I tested this hypothesis by analysing female behaviour during courtship in yellow-legged gulls, Larus cachinnans. Female gulls to some extent controlled sperm transfer, because they moved during copulation bouts, and this behaviour influenced the number of cloacal contacts per mounting that the male achieved. Female control was related to previous feeding by the male, and hence the male courtship feeding rate correlated with the cloacal contact rate. Males that give more food probably enhance their chances of fathering offspring. By analysing within-individual female behaviour, I also found that the number of cloacal contacts was higher when the male fed the female than when he did not, which indicates that female gulls followed a decision rule to resist copulation when food is not given. Overall, these results support the hypothesis that female gulls manipulate their mates to obtain food.     

True deception during extra‐pair courtship feeding: cheating whiskered tern Chlidonias hybrida females perform better

Males of many bird species feed their mates during the pre‐incubation period. The food provisioned by males during these courtship feedings (CFs) represents the key source of energy for the female during egg formation. Non‐pair males may trade food for extra pair copulations (EPC) with females during extra pair courtship feeding (EPCF), while females may trade copulations for food with non‐pair males to obtain additional resources. Because EPCs can be costly to the females, they are expected to behave in ways that will deceive non‐pair males to obtain additional resources at no cost to themselves. We investigated EPCFs in whiskered terns Chlidonias hybrida breeding in food‐rich conditions, on carp ponds in southern Poland. Almost all CFs (n = 2751) took place during the female's fertile period and peaked just before clutch initiation. 10% of all CFs were performed by non‐pair males. Females tried to obtain food from the non‐pair male during 39% of EPCFs, by swindling (the female solicits a non‐social male for copulation and tries to swindle food with no cloacal contact) or by snatching (the female tries to take the gift without engaging in copulation). In the remaining 61% of EPCFs, females did not react or chased the visiting male away. The probability of a female's obtaining food during EPCF was much higher (0.69, 95% CI: 0.47–0.85) if she swindled rather than snatched (0.08, 95% CI: 0.02–0.22). Only 0.7% of EPCFs were followed by EPCs. The high availability of food in the study area allows males to perform frequent EPCFs, despite the very low probability of obtaining EPCs. This is the first time that ‘true deception’ during EPCFs has been reported in birds: swindling females obtain food from non‐pair males at no immediate detectable cost to themselves.