Mating Effort and Cryptic Sperm Choice in Scorpionflies: Male Investment Strategy vs. Female Control

In this study, we examined which sex controls sperm transfer during copulation in scorpionflies. Therefore male scorpionflies were doubly mated to females of high and low fecundity to explore whether they allocate sperm according to female quality. While mating order had no effect males transferred sperm at higher rates when mating with low‐quality instead of high‐quality females. As there is no obvious benefit from providing low‐fecundity females with more sperm, we suggest a condition‐dependent female ability to counteract sperm transfer. Therefore, we disabled females at the beginning of copulations using the insecticide Propoxur which leads to total paralysis caused by tremors. While the provoked muscle contractions led to significantly smaller numbers of sperm transferred, Propoxur treatment had no effect on males. We suggest female counteracting of sperm transfer to be adaptive by decreasing the relative amount of sperm transferred by low‐quality males and increasing the proportion of offspring sired by high‐quality males.     

All that Glisters is not Gold: Sensory Bias, Sexual Conflict and Nuptial Feeding in Insects and Spiders

It is becoming increasingly clear that the evolutionary interests of the sexes are often in conflict when it comes to mating. Sexual encounters involving nuptial gifts, however, have often been viewed as prime examples of sexual co‐operation, rather than conflict. In this review, I explore the proposition that nuptial gifts act as sensory traps: by exploiting the female's gustatory responses, the male may be able to entice females to accept superfluous matings and/or transfer greater volumes of ejaculate than are in the female's reproductive interests. Evidence suggests that the females’ sensory biases may have played an important role in shaping gift characteristics in at least four different systems, although relatively few forms of nuptial feeding have so far been examined from this perspective. I argue that gift composition is more likely to be tailored to increasing the attractiveness of the gift to the female and/or maximizing gift handling time than to suit the female's nutritional needs and that the fecundity‐enhancing benefits of nuptial gifts are often questionable and have been over‐stated in the literature. Fertilization biases associated with the female's attraction to the nuptial gift, however, could lead to in‐direct benefits for the female. On the other hand, nuptial feeding may also lead to significant costs to the female. Evidence suggests that some types of gift entice the female to mate, but it is not clear whether the resultant degree of polyandry is higher than optimal for the female. In other cases, evidence suggests that the gift enables the male to overcome the resistance of the female to accepting an extra large ejaculate and that large ejaculates are associated with longer post‐mating sexual refractory periods in the female. This could represent a cost to the female by delaying or preventing her from receiving the genetic benefits of polyandry. At present, it is not clear, however, whether such costs outweigh the potential benefits of nuptial feeding for the female.     

Nuptial Feeding in Insects: Theoretical Models of Male and Female Interests

We present a series of prospective models of nuptial feeding, mainly for insects. The models examine various optimal male and female strategies, but do not include any element of mate choice in which the female chooses males in relation to the gift he provides. We find that the female should use the gift to enhance egg size and/or clutch size when gifts represent a relatively large component of the energy resources for the gametes, or when the gift occurs at a relatively late stage in her reproductive cycle. However, if the female receives a single, relatively small gift during her reproductive cycle, she should show a reduced gametic output at the next oviposition. A literature survey revealed several studies that show increases in egg and clutch sizes following gift donation, but we found no instances in which there was a reduction in gametic output. We also find that if gifts are infrequent, there can be significant sexual conflict over the pattern of allocation of donated resources to future offspring. Male interests will generally be best served by a more immediate use of the resources than will be optimal for the female. This may result in selection for male ability to influence vitellogenesis and/or oviposition. Evidence is available which shows that male-derived substances influence female physiology; this might reflect an outcome towards male interests as a result of an arms race in sexual conflict. Some studies have demonstrated an effect of gift donation on survivorship. We examine models in which gift donation reduces male survival but increases female survival. These suggest that gift donation is most likely to evolve when (1) giving a gift has little effect on male, but a significant effect on female survival, (2) when the male is more likely to father eggs in a later batch, rather than the next batch, and (3) when random mortality is high.     

Courtship Behavior in the Hawaiian Cricket Laupala cerasina: Males Provide Spermless Spermatophores as Nuptial Gifts

The role of sexual selection in the crickets (family Gryllidae) is well known but new forms of courtship behavior continue to be discovered. Here we describe the elaborate mating behavior of the Hawaiian endemic Laupala cerasina (subfamily Trigonidiinae) on the basis of both laboratory and field observations. We found that courtship and mating involve multiple copulations during which repeated spermatophores are transferred. Initial copulations involved the transfer of relatively small ‘microspermatophores’. The final copulation results in the transfer of a considerably larger ‘macrospermatophore’. We tested and rejected the hypothesis that the number of spermatophore transfers results in greater offspring sired by a given male. Matings involving only microspermatophores resulted in no offspring, whereas most matings involving micros and a macrospermatophore, or a macrospermatophore only, produced offspring. A direct examination of the contents of the microspermatophore revealed an absence of sperm, whereas examination of the macrospermatophore revealed the presence of sperm. Given that females consume the spermless microspermatophores, we conclude that the microspermatophores are a form of nuptial feeding of females by males. We discuss possible hypotheses to explain this unusual courtship system.     

Age‐Related Male Reproductive Investment in Courtship Display and Nuptial Gifts in a Moth,Ostrinia scapulalis

Due to a trade‐off between current and future reproduction, costly reproductive investments should be increased towards the end of a lifespan when the probability of reproduction becomes low (terminal investment hypothesis). We investigated age‐related changes in male reproductive investment towards courtship display and the spermatophore in three age classes (young, middle‐aged and old) of a monandrous moth, Ostrinia scapulalis. As predicted, old males had higher mating success than young and middle‐aged males in no‐choice tests. Moreover, two‐choice tests revealed that middle‐aged males had a higher success rate than young males because of their higher courtship frequency rather than any female preference for them. It was found that old males produced a larger spermatophore than young and middle‐aged males, suggesting greater reproductive effort. The protein content of spermatophores also tended to increase with male age. Despite the age‐related variation in spermatophore size and protein content, age did not affect female fecundity or longevity. A decrease in the number of sperm in the older males might counteract the nutritional benefit of larger spermatophores. Alternatively, fitness components other than longevity and fecundity may be influenced by male age.     

Chronological vs. Physiological Age as Determinants of Mating Decisions: Studies on Female Choice Over Lifespan in An Acoustic Moth

Life history theory predicts that females may adjust the selectivity expressed in mate choice as they age. Particularly in cases where time is limiting, females are expected to reduce selectivity and thereby avoid losing a terminal mating opportunity. Some evidence for this reduction has been found in vertebrates and long‐lived insects, and several recent findings show that it may also exist in insects with very short adult longevities. Theory also predicts that behavioural adjustments should respond to remaining longevity (physiological age) rather than chronological age, but very little information relevant to this issue exists. We studied age‐related changes in mating behaviour in an acoustic moth species (Achroia grisella; Lepidoptera: Pyralidae) in which females choose males based on the intensity, rhythm and other temporal features of the male song, with the objective of determining whether observed adjustments reflect chronological or physiological age. In accordance with theory, we found that females became less selective in their evaluation of male song rhythm as they aged and that this adjustment was predicted by physiological rather than chronological age. The reduction in selectivity may be due to decreased movement and searching, factors that can prevent a female from perceiving all of the male songs being broadcast locally in a complex environment where the transmission of some songs is blocked in some locations. We did not observe these age‐related effects in a simpler, open environment.     

Sperm Viability in Ram Semen Diluted and Stored in Three Different Extenders

Semen was collected with an artificial vagina from 4 one-year-old rams, in order to study the changes in sperm motility and membrane integrity of spermatozoa split-diluted and stored at 5 °C during 7 days in sodium citrate, Tris, and milk-based extenders, respectively. Sperm motility was assessed subjectively and sperm membrane integrity was determined using the fluorescent probes Calcein-AM and Ethidium homodimer. Representative samples were studied using scanning electron microscopy (SEM). The average incidence of sperm motility decreased over time in all the extenders (p<.001). The incidence of spermatozoa showing progressive motility and intact plasma membrane was significantly higher in semen diluted with sodium citrate than in the other 2 extenders following 4 days of dilution until the end of the study. Evaluation with SEM confirmed the findings obtained with the supra vital fluorescent dyes. The results of the present study indicated that there were no differences between sodium citrate-, Tris- or milk-based extenders when ovine liquid semen was stored at 5 °C during a short period (2 days). However, when semen was stored for longer time, spermatozoa in the sodium citrate-based extender sustained its viability better.     

Possible Female Choice During Copulation in Ozophora baranowskii (Heteroptera: Lygaeidae): Female Behavior, Multiple Copulations, and Sperm Transfer

The remarkable behavior of female Ozophora baranowskii of lightly tapping the male with the hind legs during copulation was studied in relation to multiple copulations, copulation length, and sperm transfer. Multiple copulations did not affect female fecundity, fertility, or longevity. The incidence of tapping was higher in shorter copulations, which did not result in sperm transfer to the female. Female tapping behavior may be a mechanism for choosing between males after copulation has begun.     

Short‐Term Nutritional Limitation Affects Mating Behaviour and Reproductive Output in Dwarf Spiders

Mating decisions can vary considerably depending on individual experience, mate availability and nutritional status. Here, we applied short‐term dietary restrictions to adult female spiders that were well fed during the juvenile stage in an effort to understand whether and how brief periods of food shortage can influence male and female mating decisions and mating behaviour. To assess whether responses vary between closely related species, we conducted the same experiment on the dwarf spiders Oedothorax retusus and O. apicatus. During courtship and mating, males of both species offer secretion to females from glandular tissue in their prosoma. Females were subject to food shortage over a period of 3 wks (‘low‐diet’ treatment, LD) or fed regularly (‘high‐diet’ treatment, HD). We compared courtship probability, mating probability/behaviour, and reproductive output between dietary groups and species. In both Oedothorax species, females in the LD treatment were less likely to mate and more aggressive towards males. Furthermore, LD females produced egg sacs that were significantly lighter than were those of the HD females. Effects of food deprivation on copulation duration, gustatory behaviour and oviposition latency differed between species. Our study shows that short periods of dietary restriction during the adult stage can strongly affect mating behaviour and reproductive output with differences between closely related species.     

Sperm Storage and Use After Multiple Mating in Dinarmus basalis (Hymenoptera: Pteromalidae)

Multiple mating and its effects on the sex ratio in Dinarmus basalis (Hymenoptera: Chalcidoidea, Pteromalidae), an ectoparasitoid of Callosobruchus maculatus (Coleoptera: Bruchidae), were investigated under controlled conditions. Once-mated females suffer a sperm depletion about 21 days after mating and thereafter are constrained to produce only haploid males. On the other hand, three-times-mated females store more sperm in their spermathecae (335 vs 147) and produce daughters during the major part of their reproductive life. Consequently, once-mated females showed a male-biased life time sex ratio (mean = 0.31) as opposed to three-times-mated females (mean = 0.63). Females can copulate only at the beginning of their reproductive life, and multiple mating must occur before egg-laying activity. This behavioral strategy could be an avoidance of consanguinity in a promiscuous environment. This ectoparasitoid species reveals a reproductive strategy which promotes polyandry and a very high sperm efficiency.     

Signalling and Sexual Conflict: Female Spiders Use Stridulation to Inform Males of Sexual Receptivity

The use of acoustic signals by males during courtship and mating is well known. Nevertheless, their association with female unwillingness to mate is much less studied. In spiders, stridulation during sexual interactions is relatively common in some groups, but mainly restricted to males. In the pholcid spider Holocnemus pluchei, both sexes have stridulatory organs. The aims of the present work were (1) to establish whether female stridulation occurs during intra‐ and inter‐sexual interactions, (2) to determine whether female reproductive status affects the likelihood that she will stridulate and (3) to determine whether female stridulation is influenced by male sexual behaviour. We found that female stridulation usually occurs both during intrasexual interactions and, most frequently, during intersexual interactions. Females with more previous matings stridulated more frequently. Stridulation intensity was higher in females that did not accept new copulations compared with those that copulated. Female stridulation did not vary in elaborated and non‐elaborated courtship. Thus, females use stridulation to communicate levels of sexual receptivity. It is also possible that females use stridulation to indirectly assess male ability to persist and persuade.     

Condition-Dependent Effects of Mating on Longevity and Fecundity of Female Medflies: The Interplay between Nutrition and Age of Mating

Background

In various species mating exerts direct and indirect effects on female demographic traits ranging from life span shortening to behavioural shifts. A wealth of data regarding effects of nutrition on longevity and reproduction output also exists. Nonetheless, little is known regarding the interaction between the age of mating and nutrition on female fitness.

Methodology

We studied, the effects of protein deprivation and age of mating on female fitness traits, using a wild population of the Mediterranean fruit fly (medfly). We tested the hypotheses that (a) protein availability increases female lifespan and fecundity, (b) female longevity and egg production are independent of mating and the age of mating, and (c) female mating behaviour is independent of their age and nutritional status. Thus, we recorded the mating success and the copulation characteristics, as well as the egg production and survival of females mated at young or at old age and fed a full or a protein-deprived diet.

Results

Mating boosts egg production and reduces longevity of protein-fed females. On the contrary, mating increases the longevity of protein-deprived females. Mortality responses (negative or positive) to mating are expressed after a long lag phase. Old females are more receptive and less selective than young females regardless of the food regime.

Conclusions

Our findings suggest that condition (nutritional status and age) defines the positive or negative output of mating in female medflies. These results contribute towards understanding the effects of mating, aging, resource allocation and their interactions on survival and female reproduction.     

Male Demography,Female Mating Behavior,and Infanticide in Wild Patas Monkeys (Erythrocebus patas)

Infanticide by males has been hypothesized to be a naturally selected behavioral strategy that increases the infanticidal male's reproductive success. The sexual selection hypothesis has been challenged via alternative, nonadaptive hypotheses that dispute its empirical and theoretical bases. Two of the most widely recognized alternatives are the social pathology hypothesis, in which infanticide results from overcrowding or recent human disturbance, and the generalized aggression hypothesis, in which infanticide is an epiphenomenon of increased male aggression. We report the first case of infanticide in wild, seasonally breeding patas monkeys (Erythrocebus patas) living at a low population density in a stable habitat, conditions which do not support the social pathology hypothesis. Its exceptional occurrence is consistent with the sexual selection hypothesis: over a 7-year period the infanticidal male was the only one of 13 resident males that was not present during the actual conception season but was present during the following birth season. Also consistent with this hypothesis, mothers were differentially targeted for male aggression, which increased sevenfold during the days surrounding the infanticide and then decreased to baseline levels after the infanticide. Aggression targeted at mothers does not support the generalized aggression hypothesis. As predicted by the sexual selection hypothesis, females began soliciting mating immediately after the infanticide, despite its occurrence in the nonconceptive season.     

Male Dominance Rank,Female Mate Choice and Male Mating and Reproductive Success in Captive Chimpanzees

Mating and consequently reproductive success in male vertebrates are predominantly determined by intermale competition and female mate choice. Their relative importance however, is still poorly understood. We investigated the interrelationship between male dominance rank — a formal indicator of male competitive ability — female mate choice, and male mating success in a multimale-multifemale group of captive chimpanzees. In addition, we examined the relationship between male dominance rank and reproductive success determined by genetic paternity analysis over a 13-yr period in the same captive population. We related the frequencies of sociosexual behaviors to the female anogenital swelling stage and female fertile phase as determined by urinary and fecal progestogen analysis. Rates of behaviors in both sexes increased with increasing intensity of female swelling, but they were not influenced by the timing of the fertile phase. Male mating success was clearly related to male dominance rank, with high-ranking males performing the overwhelming majority of copulations. This was mainly due to both rank-related rates of male soliciting behavior and intermale aggressiveness during the period of well-developed female anogenital swelling. Although females solicited copulations mainly from the high-ranking males and thus expressed a mate choice based on rank, their overall contribution in initiating copulations and thus influencing male mating success was low. The data on paternity from the population, which always contained 4 adult males, revealed that -males sired the majority (65%) of offspring. We conclude, that male dominance rank is an important determinant of male mating and reproductive success in captive (and presumably wild) chimpanzees and that female mate choice is of minor importance in modulating male reproductive outcome.     

Female Mate Preference and Male Mating Success of Ayu Fish,Plecoglossus altivelis (Osmeridae) under a Promiscuous Mating System

The ayu, Plecoglossus altivelis, is known to show wide variation in adult body size. We examined the spawning behavior in experimental spawning groups of fish in which male body size varied. Males never competed with each other for females or spawning site, while females spawned repeatedly, 17–97 times depending on body size, with previous or novel males. Males exhausted their sperm after a single mating episode, on average, regardless of body size. Moreover, repeated sperm production apparently reduced the residual lifespan. Females preferred mating simultaneously with more than one male and allowed males of body size similar to their own to mate more frequently. Thus the largest male within a spawning group was not always the most successful at mating, but mating success of any given male appears to depend upon body size distribution of females within the population. Female mate preference has apparently evolved to ensure complete fertilization under circumstances where males have been selected to economize sperm output during any one mating episode.     

Sperm Storage in the Yellow Dung Fly Scathophaga stercoraria: Identifying the Sperm of Competing Males in Separate Female Spermathecae

We examined the effects of male and female behaviour and morphology on the process of sperm storage in the yellow dung fly Scathophaga (Scatophaga) stercoraria. The larger of two males was more successful in transferring sperm to females' spermathecae the greater the difference in weight to his smaller competitor, as expected from previous studies by other authors. Sperm length, which is not correlated to body size, affected sperm access to the spermathecae, the female storage organs; longer sperm were more likely to be found in the spermathecae. A female typically had a singlet spermatheca and two spermathecae arranged as a pair, a doublet. However, there was variation from this pattern, which influenced the pattern of sperm storage. We measured the proportion of sperm from two competing males in females' singlet and doublet spermathecae. When the larger male's sperm were longer than his competitor's, they were more often in a female's singlet when he was her first mate and equally likely to be in the singlet or doublet when he was her second mate. When the larger male's sperm were shorter than his competitor's, the pattern was more complicated, principally because his sperm were not as successful at entering the female's doublet when he was her second mate. Counts of sperm, made using the same experimental procedure, showed that these effects were due to greater numbers of sperm entering the females' doublets when the larger male mated second. Sperm length was thus the factor with the largest single influence on the pattern of sperm storage. However, our most important result is that it was the interactions between male and female characters that were significant. Males mostly determine the early, especially precopulatory, events and females strongly influence the later ones.     

Male and Female Mate-Choice Decisions by Evarcha culicivora, An East African Jumping Spider

There has been a considerable recent interest in the criteria by which animals choose mates and in the extent to which mating systems tend to be based on mutual mate choice. In this study, we consider Evarcha culicivora, a salticid spider from East Africa. This species has some unusual characteristics, including active display by females as well as males, males that kill females more frequently than females kill males and wide intrasexual variation in body size. For females, larger males are especially dangerous. Here, we demonstrate, using two experimental designs (live‐mate choice and mount choice), that virgin males, virgin females and previously mated males prefer larger opposite‐sex individuals as potential mates, but mated females prefer smaller, safer males as potential mates.