Interpopulation variation in female remating is attributable to female and male effects in <Emphasis Type="Italic">Callosobruchus chinensis</Emphasis>

The evolution of female multiple mating is best understood by consideration of male and female reproductive perspectives. Females should usually be selected to remate at their optimum frequencies whereas males should be selected to manipulate female remating to their advantage. Female remating behavior may therefore be changed by variation of male and female traits. In this study, our objective was to separate the effects of female and male strains on female remating for the adzuki bean beetle, Callosobruchus chinensis, for which there is interstrain variation in female remating frequency. We found that interstrain variation in female remating is primarily attributable to female traits, suggesting genetic variation in female receptivity to remating in C. chinensis. Some interstrain variation in female remating propensity was attributable to an interaction between female and male strains, however, with the males of some strains being good at inducing nonreceptivity in females from one high-remating strain whereas others were good at inducing copulation in nonvirgin females from the high-remating strain. There is, therefore, interstrain variation in male ability to deter females from remating and in male ability to mate successfully with nonvirgin females. These results suggest that mating traits have evolved along different trajectories in different strains of C. chinensis.     

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.     

Female Age Determines Remating Behavior in Wild Mexican Fruit Flies

Male and female age are important factors that can influence mating and remating behavior. Females can discriminate against or prefer older males, but there have been relatively fewer studies on how female and male age influence female remating. Here we showed in wild flies of the Mexican fruit fly Anastrepha ludens (Loew), that when females were given a choice between males of different ages, younger females preferred to mate with younger males over older males, while older females were less selective. Also, when given a choice between males of different ages, older females had longer copulation durations than younger females. On the other hand, older males and females had lower mating success, compared with young and middle-aged flies under no choice conditions. However, middle-aged females mated faster compared to young females and young males mated faster compared to middle-aged males. Male age did not influence female remating, while female age strongly determined female remating, with no females remating when they were old. It is unclear if female receptivity mechanisms are switched off at older ages, or if females are reluctant to remate due to possible costs of mating. We discuss our results in terms of how male and female age can influence mating decisions.     

Disparity in sexual behaviour between wild and mass‐reared Mexican fruit flies

The sterile insect technique (SIT) is currently used to control Mexican fruit fly Anastrepha ludens Loew (Diptera: Tephritidae). However, mass‐rearing can alter the quality of released males. If males that are mass‐reared have behaviours different from those of their wild counterparts, then this may diminish the effectiveness of SIT. Questions remain as to whether wild females may be able to detect the male condition before, during and/or after copulation with a mass‐reared male. In the present study, copula duration, female remating, female fecundity and fertility of both mass‐reared and wild A. ludens are evaluated. Marked differences are found between mass‐reared and wild females. Specifically, mating latency is longer and copula duration is shorter for wild females compared with mass‐reared females. Importantly, there are no significant differences in mating latency, copula duration or remating probability between wild females paired with either mass‐reared or wild males. All mass‐reared females remate, whereas only approximately half of the wild females remate after first mating with either a wild or mass‐reared male. Fecundity of wild females mated to either wild or mass‐reared males is approximately one‐third lower than that of mass‐reared females, confirming that mass‐reared females may have been selected for high fecundity and are adapted to laboratory conditions. Fertility of females that mate with a wild male for only 10 min is not significantly different from that achieved via a full‐length copulation. By contrast, females mating with mass‐reared males need copulation durations of at least 40 min to achieve fertility comparable with that achieved via a full‐length copulation. The findings of the present study have important implications for A. ludens controlled through SIT and broaden our understanding on the copulatory and post‐copulatory behaviours between wild females and mass‐reared males.     

Sexual selection for large male size in a polyandrous butterfly: the effect of body size on male versus female reproductive success in Pieris napi

Sexual selection theory predicts that the larger sex shouldbe that for which fitness increases at the faster rate withsize. In butterflies, as in most invertebrates, females areusually the larger sex, but previous comparative analysis hasshown that relative male size increases with female polyandryamong butterflies. In agreement with this pattern, males arelarger than females in the strongly polyandrous green-veinedwhite butterfly, Pieris napi L., and in this article we assessthe size dependence of reproductive success in both sexes. Inan experiment where virgin males and females were released inthe field, we found no strong association between size and malemating success. However, laboratory experiments showed thatthere was a strong correlation between size and the ejaculatethat the male delivered to the female at mating and that largeejaculates delayed female remating for a longer time comparedto small ejaculates. Moreover, female P. napi utilize male-derivednutrients received at mating to increase their fecundity. Hence,large males sire more offspring both by way of donating morenutrients to female egg production and by way of delaying femaleremating (given that the last male to mate with the female willfather most of the offspring). Laboratory experiments showedthat the association between size and fecundity was low, ornonexistent, among P. napi females allowed to mate only once.However, weak size dependence was found for polyandrous females.We hypothesize that size dependence of female fecundity maybe especially weak among polyandrous butterflies because a fundamentalsource of variation in fecundity relates to their ability tofind nutrient giving males, an ability which may be unrelatedto female size. According to this hypothesis there is a causalassociation between weak size dependence of female fecundityand polyandry, and a strong size dependence of male reproductivesuccess that may underlie the comparative pattern of positivecorrelation between relative male size and polyandry.     

Females of the Cellar Spider Discriminate Against Previous Mates

Mate choice for novel partners should evolve when remating with males of varying genetic quality provides females with fitness‐enhancing benefits. We investigated sequential mate choice for same or novel mating partners in females of the cellar spider Pholcus phalangioides (Pholcidae) to understand what drives female remating in this system. Pholcus phalangioides females are moderately polyandrous and show reluctance to remating, but double‐mated females benefit from a higher oviposition probability compared to single‐mated females. We exposed mated females to either their former (same male) or a novel mating partner and assessed mating success together with courtship and copulatory behaviours in both sexes. We found clear evidence for mate discrimination: females experienced three‐fold higher remating probabilities with novel males, being more often aggressive towards former males and accepting novel males faster in the second than in the first mating trial. The preference for novel males suggests that remating is driven by benefits derived from multiple partners. The low remating rates and the strong last male sperm precedence in this system suggest that mating with novel partners that represent alternative genotypes may be a means for selecting against a former mate of lower quality.     

Female remating in butterflies: interaction between female genotype and nonfertile sperm

Female mating rate is fundamental to evolutionary biology as it determines the pattern of sexual selection and sexual conflict. Despite its importance, the genetic basis for female remating rate is largely unknown and has only been demonstrated in one species. In paternally investing species there is often a conflict between the sexes over female mating rate, as females remate to obtain male nutrient donations and males try to prevent female remating to ensure high fertilization success. Butterflies produce two types of sperm: fertilizing, eupyrene sperm, and large numbers of nonfertile, apyrene sperm. The function of apyrene sperm in the polyandrous, paternally investing green‐veined white butterfly, Pieris napi, is to fill the female’s sperm storage organ thereby reducing her receptivity. However, there is large variation in number of apyrene sperm stored. Here, I examine the genetic basis to this variation, and if variation in number of apyrene sperm stored is related to females’ remating rate. The number of apyrene sperm stored at the time of remating has a genetic component and is correlated with female remating tendency, whereas no such relationship is found for fertilizing sperm. The duration of the nonreceptivity period in P. napi also has a genetic component and is inversely related to the degree of polyandry. Sexual conflict over female remating rate appears to be present in this species, with males using their apyrene sperm to exploit a female system designed to monitor sperm in storage. Ejaculates with a high proportion of nonfertile sperm may have evolved to induce females to store more of these sperm, thereby reducing remating. As a counter‐adaptation, females have evolved a better detection system to regain control over their remating rate. Sexually antagonistic co‐evolution of apyrene sperm number and female sperm storage may be responsible for ejaculates with predominantly nonfertile sperm in this butterfly.     

Natural variation in female mating frequency in a polyandrous butterfly: effects of size and age

In the polyandrous gift-giving butterfly Pieris napi, females mature at a smaller size than males under poor food conditions, so it has been suggested that females can compensate for their smaller size through nuptial feeding. We tested this hypothesis by assessing female polyandry in relation to female size in a study of a wild bivoltine population and in a laboratory experiment. Contrary to expectation, larger females had a higher mating frequency. In the wild population female polyandry was positively correlated with size and in the laboratory experiment larger females were also more polyandrous. Hence, smaller females cannot compensate for their size by increasing their mating frequency, perhaps because the rate of spermatophore breakdown sets the limit for polyandry and larger females are able to break down the spermatophore faster. In addition, the lifetime number of matings for wild females varied between one and five. As previous studies indicate that female fitness in P. napi appears to increase monotonically with number of mates as a result of the increase in spermatophore material received, it is surprising that 12% of the wild females in the oldest age classes had mated only once and that another 35-40% had mated only twice. This apparently maladaptive behaviour is discussed in terms of sexually antagonistic coevolution and whether environmental conditions influence optimal mating frequency. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Mating senescence and male reproductive organ size in the Mexican fruit fly

Ageing can reduce the probability that individuals reproduce. The present study investigates whether ageing influences the mating frequency of mass‐reared fertile and sterile Mexican fruit flies Anastrepha ludens (Loew). The ability of males of different ages to inhibit female remating is also determined, and the growth of male reproductive organs is measured as they age. Young males (6 days old) have a lower mating frequency than older males, and also have a lower capacity to inhibit female remating than older males. However, 7‐day‐old males are as likely to inhibit female remating as older males. Young males also have smaller reproductive organs than middle‐aged (21‐day‐old) or senescent males (57‐day‐old). These results have implications for the sterile insect technique because sterilized males of A. ludens are released in the field 6 days after emergence. The highest mating frequency, the lowest mating latency and the largest size of testes are observed at 21 days of age. Older males (57 days old) have more sperm in their seminal vesicles than young males (6 and 9 days old). Accessory glands take longer to grow to their complete size compared with testes, and mating frequency is more closely associated with accessory gland size than testes size. Furthermore, there are more sperm in the seminal vesicles during the afternoon period of peak sexual activity than during the morning when sexual activity is absent. These results indicate that, even at the onset of reproductive senescence, mass‐reared males of A. ludens are still capable of mating, as well as inhibiting remating in females.     

Remating Behavior of Cnephasia jactatana Walker Females (Lepidoptera: Tortricidae)

Cnephasia jactatana Walker is an important pest of kiwifruit in New Zealand. We investigated, under laboratory conditions, the effects of multiple mating on the reproductive performance of C. jactatana females and how such effects varied with male virginity and larval nutrition. We found that in permanent pairs, remating increased female fecundity and fertility but suboptimally fed females benefited more from remating. Regardless of this benefit, mass-reared pairs had a lower remating frequency. Females remating with a virgin male or a male that had delivered a spermatophore presented similar fecundity and fertility; however, females receiving a second ejaculate from a virgin male had increased daily fecundity. Female weight clearly affected remating behavior since those that received a second ejaculate were significantly heavier. Neither mating length nor size of the first spermatophore influenced female remating. Further, mass-reared and individually reared males produced spermatophores of similar size.     

Evaluating female remating rates in light of spermatophore degradation in Heliconius butterflies: pupal‐mating monandry versus adult‐mating polyandry

1. Butterflies are frequently used in comparative studies of sexual selection because of their diverse mating systems. In Heliconius, the two major clades in the genus are characterised by contrasting pupal‐mating and adult‐mating strategies. Adult‐mating females are considered to be promiscuous whereas pupal‐mating females are thought to be monandrous. 2. Counting spermatophores in female Lepidoptera is a common method for assessing patterns of female remating. However, in pupal‐mating Heliconius butterflies spermatophores can become completely degraded, potentially leading to underestimation of female remating rates. 3. We qualitatively characterised the different states of spermatophore degradation, and showed that complete degradation takes approximately 3 weeks in captive‐bred H. erato females. 4. We counted spermatophores and/or assayed spermatophore degradation in > 500 Heliconius females across 28 species sampled from natural populations. Among pupal‐maters these observations yielded a few rare observations of double mating by recently eclosed females, but generally indicated a lack of rematings. In contrast, approximately 25% of sampled adult‐mating females remated at least once. 5. Using a novel statistical analysis, we estimated remating rates from patterns of spermatophore degradation or from counts stratified by age, as indicated by wing‐wear. This analysis showed no statistically significant evidence for remating for the pupal‐mating H. erato whereas significant remating rates were detected for adult‐mating species. 6. The present results support the established view of Heliconius mating systems in which pupal‐maters are largely monandrous, whereas adult‐maters are polyandrous.     

Long-term study of female multiple mating indicates direct benefits in Tribolium castaneum

Polyandry or female mating with several different partners in a single fertile period is a widespread phenomenon possibly involving both costs and benefits. This study tested whether remating after weeks of initial copulation (periodic multiple mating) has fitness consequences for females of red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), a cosmopolitan storage pest. We hypothesize that females benefit from higher mating frequency and more mates through sperm replenishment and/or compatible sperm. Thus, offspring production and survivorship were examined of females that were mated to multiple males or the same male repeatedly at variable intervals (every 2 weeks, 1, 3, and 5 months). Our results suggest that remating, after months of initial copulation, confers direct benefits to females, likely by providing additional sperm or through an alternative mechanism such as better ability of fresh sperm to fertilize eggs, stimulation of oviposition from copulation itself, and/or hydration benefit of the ejaculate. We did not detect any additional benefit of female multiple mating.     

Female Remating Behavior in a Lekking Moth

In polyandrous species, male reproductive success will at least partly be determined by males' success in sperm competition. To understand the potential for post‐mating sexual selection, it is therefore important to assess the extent of female remating. In the lekking moth Achroia grisella, male mating success is strongly determined by female choice based on the attractiveness of male ultrasonic songs. Although observations have indicated that some females will remate, only little is known about the level of sperm competition. In many species, females are more likely to remate if their first mating involved an already mated male than if the first male was virgin. Potentially, this is because mated males are less well able to provide an adequate sperm supply, nutrients, or substances inhibiting female remating. This phenomenon will effectively reduce the strength of pre‐copulatory sexual selection because attractive males with high mating success will be more susceptible to sperm competition. We therefore performed an experiment designed both to provide a more precise estimate of female remating probability and simultaneously to test the hypothesis that female remating is influenced by male mating history. Overall, approximately one of five females remated with a second male. Yet, although females mated to non‐virgin males were somewhat more prone to remate, the effect of male mating history was not significant. The results revealed, however, that heavier females were more likely to remate. Furthermore, we found that females' second copulations were longer, suggesting that, in accordance with theory, males may invest more sperm in situations with an elevated risk of sperm competition.     

Receptive females mitigate costs of sexual conflict

Males typically gain fitness from multiple mating, whereas females often lose fitness from numerous mating, potentially leading to sexual conflict over mating. This conflict is expected to favour the evolution of female resistance to mating. However, females may incur male harassment if they refuse to copulate; thus, greater female resistance may increase costs imposed by males. Here, I show that the evolution of resistance to mating raises fitness disadvantages of interacting with males when mating is harmful in female adzuki bean beetles, Callosobruchus chinensis. Females that were artificially selected for higher and lower remating propensity evolved to accept and resist remating, respectively. Compared with females that evolved to accept remating, females that evolved to resist it suffered higher fitness costs from continuous exposure to males. The costs of a single mating measured by the effect on longevity did not differ among selection line females. This study indicates that receptive rather than resistant females mitigate the fitness loss resulting from sexual conflict, suggesting that even though mating is harmful, females can evolve to accept additional mating.     

Remating in Ceratitis capitata sterile males: Implications in sterile insect technique programmes

Sterile insect technique (SIT) is used, among other biological control tools, as a sustainable measure for the management of Ceratitis capitata Wiedemann (Diptera: Tephritidae) in many agricultural regions where this pest can trigger severe economic impacts. The tendency of wild females to remate multiple times has been deeply studied; it has been a common point of controversy when evaluating SIT programmes. Nevertheless, the remating potential of the released sterile males remains unknown. Here, under laboratory conditions, the remating capability of mass-reared sterile males was determined. Wild-type virgin females were offered to sterile males (Vienna-8 strain), which had the opportunity to mate up to four consecutive times. The remating assays were carried out at 24 hr, 48 hr, 4 days and 7 days after the first mating. At the end of each tested time period, males were divided according to their mating response, mated or unmated, and subsequently reused for the next round of mating assays. The frequency of successful remating in each tested time period was obtained. Insemination was confirmed by determining the sperm transfer in mated female spermathecae by quantitative real-time PCR. Our results demonstrate that 73% of the mass-reared sterile males were able to remate 24 hr after the first mating, 55% of which remated again the day after. Close to 25% of the V8 sterile males tended to copulate in all of the four mating opportunities. The qPCR analysis of the spermathecae contents verified an effective transfer of V8 sperm to wild females with every mating; 99% of copulations resulted in sperm transfer. These findings shed light on the remating potential of V8 sterile males, an aspect until now underestimated in many SIT programmes.     

Sperm precedence in <Emphasis Type="Italic">Callosobruchus chinensis</Emphasis> estimated using the sterile male technique

P₂, the proportion of offspring sired by the second male to mate, is an indicator of the outcome of postcopulatory sexual selection, which occurs through sperm competition and/or cryptic female choice. We determined the appropriate dose of gamma radiation for sterilization of adult males and, using the sterile male technique, measured P₂ in the adzuki bean beetle, Callosobruchus chinensis. Adult males of C. chinensis were almost completely sterilized when irradiated at 80 Gy. Thus, we obtained sterile males through irradiation at this dose. Neither the probability of female first mating nor the probability of female remating was affected by whether females were paired with normal or sterile males. The P₂ calculated from the hatching success of eggs laid by females that mated both with normal and sterile males did not differ between reciprocal mating sequences, indicating that the sterilization has no effect on sperm fertilizing ability. The P₂ was estimated at 0.25. This study shows that female remating in C. chinensis means the coexistence of sperm from two males and thus the occurrence of postcopulatory sexual selection within the female reproductive tract, resulting in first-male sperm precedence.     

Remating by female Mediterranean fruit flies (Ceratitis capitata, Diptera: Tephritidae): Temporal patterns and modulation by male condition

We determined the temporal pattern of female remating in the Mediterranean fruit fly, Ceratitis capitata, and how mating with sterile males affects remating. In addition, we examined the hypotheses that sterile male nutrition and age affect the subsequent receptivity of their mates. Temporally, female receptivity varied significantly throughout the experimental period. Relatively high levels of remating (14%) on the days following the first copulation were followed by a decline, with a significantly low point (4.1%) 2 weeks after mating. Subsequently, receptivity is gradually restored (18%) 3 and 4 weeks after the initial copulation. When females were first mated to sterile males, significantly higher remating percentages were recorded. The ability of sterile males to inhibit receptivity of both wild and laboratory reared females on the day of first mating was significantly improved when they were fed a nutrient rich diet. Male age at first mating also affected female receptivity: sterile males of intermediate age (11 days old) inhibited female remating significantly more than younger or older flies. Although further studies are needed to determine the relative roles of natural and sexual selection in modulating patterns of female sexual receptivity, the Sterile Insect Technique may be improved by releasing well nourished, older sterile males.     

Can patterns of chromosome inversions in Drosophila pseudoobscura predict polyandry across a geographical cline?

Female multiple mating, known as polyandry, is ubiquitous and occurs in a wide variety of taxa. Polyandry varies greatly from species in which females mate with one or two males in their lifetime to species in which females may mate with several different males on the same day. As multiple mating by females is associated with costs, numerous hypotheses attempt to explain this phenomenon. One hypothesis not extensively explored is the possibility that polyandrous behavior is captured and “fixed” in populations via genetic processes that preserve the behavior independently of any adaptive benefit of polyandry. Here, we use female isolines derived from populations of Drosophila pseudoobscura from three locations in North America to examine whether different female remating levels are associated with patterns of chromosome inversions, which may explain patterns of polyandry across the geographic range. Populations differed with respect to the frequency of polyandry and the presence of inversion polymorphisms on the third chromosome. The population with the lowest level of female remating was the only one that was entirely comprised of homokaryotypic lines, but the small number of populations prevented us investigating this relationship further at a population level. However, we found no strong relationship between female remating levels and specific karyotypes of the various isolines.     

Oviposition and refractory periods of the small water strider Microvelia horvathi (Heteroptera: Veliidae) after a single mating event

Multiple mating can be costly, but also beneficial for females. When the costs outweigh the benefits, mated females can be reluctant to remate for some time. Conversely, females will be likely to remate when they need to replenish sperm and/or receive nutrients contained in the accessory ejaculate substances. Water striders have been commonly used in mating studies as many show a vigorous struggle between the sexes. Generally, water strider females frequently mate with many males and lay many eggs during mating period. However, little is known about their oviposition and refractory periods after an initial mating event. In this study, we revealed that single-mated females of the small water strider, Microvelia horvathi, could lay eggs for 40 days, reflecting approximately half of their potential oviposition periods. It suggested that M. horvathi females do not need to mate to replenish sperm for some time once they mate. Our results also showed that no female remated after 1 or 3 days of an initial mating event. The proportion of female remating increased with time after the initial mating, however, remating levels reached 26.7% even after 14 days. In this sense, any significant cost of mating outweighs the benefit, which might be one of the factors lowering their remating levels.     

Multiple mating in Anastrepha fraterculus females and its relationship with fecundity and fertility

The occurrence of female remating has been widely reported in insects and the frequency at which it occurs and the factors driving females’ remating behavior have been shown to be both species specific and variable within species. Herein, we studied the remating behavior of females from a well established laboratory colony and a wild population of the South American fruit fly, Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae), under laboratory conditions. Latency to first mating (number of days from the onset of the experiment until the first copula) was shorter for remating females than for females that did not remate. Two‐day fecundity was higher for females that did remate than for monogamous females. Egg hatch was sustained after remating and was not affected by the number of times the female mated. However, when females willing to remate were prevented from doing so, percent egg hatch showed a significant drop. These results and the fact that remating occurred more often in more fecund females than in less fecund ones suggest that remating may be a response to sperm depletion. Remating frequency was similar in laboratory and wild flies, but 2‐day fecundity was higher for laboratory than for wild females of similar mating status. Also, the length of the refractory period (time between first and second copulation) was longer for wild than for laboratory females. Differences between strains could be the result of artificial selection. Results are discussed from a theoretical and applied perspective in the context of direct benefits to females.