Mating refusal in Musca domestica: effects of repeated mating and decerebration upon frequency and duration of copulation

The function of prolonged copulations in Enchenopa treehoppers (Hemiptera: Membracidae)

Copulations are very brief in many species, sometimes taking only seconds, but in other species, they can be quite prolonged. Potential explanations for prolonged copulations include time requirements for the transfer of sperm and/or other ejaculate substances. Ejaculate substances could function to regulate female receptivity to subsequent matings, provide nutritional nuptial gifts, or hasten egg oviposition at a potential survival cost to the female. We investigated prolonged copulation in a member of the Enchenopa binotata complex of treehoppers (Hemiptera: Membracidae), in which females rarely remate and copulation can last several hours. We assigned females to treatments in which we interrupted copulation at different times. We also included a control where copulation was not interrupted. We found that females that experienced shorter copulations were more likely to be subsequently receptive to an attractive male. We also found that few females produced offspring when they engaged in short copulations compared to those with longer copulations. We did not find any differences in female survival. Our results support the sperm transfer and receptivity regulation hypotheses. We discuss potential reasons for why these processes should take so long in a species with low female remating.

Postcopulatory Behavior of Tephritid Flies

Mating produces profound changes in the behavior of female flies, such as an increase in oviposition, reduction in sexual receptivity, increase in feeding, and even excretion. Many of these changes are produced by copulation, sperm, and accessory gland products that males transfer to females during mating. Our knowledge on the function of the male ejaculate and its effect on female insects is still incipient. In this article, we review peri- and postcopulatory behaviors in tephritid flies. We address the effects of male copulatory behavior; copula duration; and the male ejaculate, sperm, and accessory gland products on female remating behavior. Many species from these families are pests of economic importance; thus, understanding male mating effects on female behavior contributes to both developing more effective environmentally friendly control methods and furthering our understanding of evolutionary implications of intersexual competition and sexual conflict.

INTERSEXUAL SELECTION IN THE MEDITERRANEAN FRUIT FLY: DOES FEMALE CHOICE ENHANCE FITNESS?

Adaptive hypotheses of female choice predict that females use male courtship displays as an indicator of male quality. A test of whether female choice is adaptive measuring direct and indirect effects of mate choice on females was made using a laboratory population of a lek-mating species, the Mediterranean fruit fly. The nonrandom mating observed in this species is thought to be strongly influenced by female choice. Whether female choice acts to increase fecundity or offspring quality was assessed using two different statistical tests. Multiple regression showed that females generally do not receive direct benefits as a result of mating with males which are successful in copulating with many females. However, in one trial the relationship between male quality and female benefit was nonlinear. Females which mate with males that obtain few matings (<2), and females which mate with males that obtain many matings (>6) enjoy increased fecundity. Mate choice does not, however, appear to enhance offspring quality as father/son correlation and sibling analysis showed no heritable component to male copulatory success.

Control of copula duration and sperm storage by female Queensland fruit flies

Copula duration and sperm storage patterns can directly or indirectly affect fitness of male and female insects. Although both sexes have an interest in the outcome, research has tended to focus on males. To investigate female influences, we compared copula duration and sperm storage of Queensland fruit fly females that were intact, or had been incapacitated through decapitation or abdomen isolation. We found that copulations were far longer when females had been incapacitated, indicating that constraints imposed on copula duration by intact females had been relaxed. Repeatability of copula duration for males was very low regardless of female treatment, and this is also consistent with strong female influence. Number of sperm in the spermathecae was not influenced by female treatment, suggesting that female abdominal ganglia control the transport of sperm to these long-term storage organs. However, more sperm were found in the ventral receptacles of incapacitated females compared to intact females. Overall, results implicate cephalic ganglia in regulation of copula duration and short-term sperm storage in the ventral receptacle and abdominal ganglia in regulation of long-term sperm storage in the spermathecae.

The relative effects of mating status and age on the mating behaviour of female field crickets

Intrinsic factors such as female age and mating status have been found to affect female choosiness. However, as these factors are often confounded in the wild because mated females are usually older individuals, the relative influence of these two factors on female behaviour is unclear. Using a fully factorial design, we tested the relative effects of age and mating status of female field crickets ( Gryllus pennsylvanicus Burmeister, 1838) on both (i) the probability that she would mate and (ii) her latency to mate. We found that virgin females were both more likely to mate and copulated more quickly than mated females, but female age had no significant effect on either the probability of mating or the latency to copulate. These results clearly show that mating status is more important in determining female mating behaviour than age. We suggest that previous work which showed an age effect on female choosiness in virgins alone might be of reduced relevance if most females do not remain unmated for long.

Cholinergic control of synchronized seminal emissions in Drosophila

In many animal species, copulation involves the coordinated release of both sperm and seminal fluid, including substances that change female fertility and postmating behavior. In Drosophila melanogaster, these substances increase female fertility and prevent mating with a second male. By using a PGal4 strain, we targeted together with other cells a dozen cholinergic neurons found only in the male abdominal ganglion (Abg-MAch). Genetic feminization apparently deleted these neurons in males and significantly increased their copulation duration, blocked their fertility in 60% of cases, and only weakly repressed remating in females. Genetic repression of Gal4 activity in all cholinergic neurons completely rescued copulation duration and fertility, and totally prevented remating, indicating that Abg-MAch neurons were functional. The conditional blocking of the synaptic activity of these neurons during copulation induced separate effects on the transfer of the seminal substances involved in fertilization and those involved in remating. These effects were dissociated only when Abg-MAch neurons were feminized, indicating that their presence is required to synchronize the emission of the male substance(s) that changes reproductive behaviors.

Perspective: sexual conflict and sexual selection: chasing away paradigm shifts

Traditional models of sexual selection propose that partner choice increases both average male and average female fitness in a population. Recent theoretical and empirical work, however, has stressed that sexual conflict may be a potent broker of sexual selection. When the fitness interests of males and females diverge, a reproductive strategy that increases the fitness of one sex may decrease the fitness of the other sex. The chase-away hypothesis proposes that sexual conflict promotes sexually antagonistic, rather than mutualistic, coevolution, whereby manipulative reproductive strategies in one sex are counteracted by the evolution of resistance to such strategies in the other sex. In this paper, we consider the criteria necessary to demonstrate the chase-away hypothesis. Specifically, we review sexual conflict with particular emphasis on the chase-away hypothesis; discuss the problems associated with testing the predictions of the chase-away hypothesis and the extent to which these predictions and the predictions of traditional models of sexual selection are mutually exclusive; discuss misconceptions and mismeasures of sexual conflict; and suggest an alternative approach to demonstrate sexual conflict, measure the intensity of sexually antagonistic selection in a population, and elucidate the coevolutionary trajectories of the sexes.

Ultrastructure of the male reproductive accessory glands in the medfly Ceratitis capitata (Diptera: Tephritidae) and preliminary characterization of their secretions

The morphology and the ultrastructure of the male accessory glands and ejaculatory duct of Ceratitis capitata were investigated. There are two types of glands in the reproductive apparatus. The first is a pair of long, mesoderm-derived tubules with binucleate, microvillate secretory cells, which contain smooth endoplasmic reticulum and, in the sexually mature males, enlarged polymorphic mitochondria. The narrow lumen of the gland is filled with dense or sometimes granulated secretion, containing lipids. The second type consists of short ectoderm-derived glands, finger-like or claviform shaped. Despite the different shape of these glands, after a cycle of maturation, their epithelial cells share a large subcuticular cavity filled with electron-transparent secretion. The ejaculatory duct, lined by cuticle, has epithelial cells with a limited involvement in secretory activity. Electrophoretic analysis of accessory gland secretion reveals different protein profiles for long tubular and short glands with bands of 16 and 10kDa in both types of glands. We demonstrate that a large amount of accessory gland secretion is depleted from the glands after 30min of copulation.

Female age and sperm competition: last-male precedence declines as female age increases

Until very recently, most studies of sperm competition have focused on variation in male competitive ability. However, we now know that a number of reproductive traits, including oviposition rate, use of stored sperm and receptivity to mating, vary with female condition. Because females can play an active part in the movement of sperm within their reproductive tract, sperm competition may be influenced by female condition. Existing studies of sperm competition in fruitflies ignore the effects of female condition, using females that are 3-4 days old and in their reproductive prime. But condition will decline as a female senesces. Here, we examine the effect of female age on the outcome of sperm competition in three strains of the fruitfly, Drosophila melanogaster. Previous studies have shown that female age influences preference for mates and male ejaculation strategies. In this study, we find that when males are mated to females that are older than 17 days, last-male sperm precedence decreases significantly. These results could lead to a greater understanding of the physiological mechanisms that regulate the outcome of sperm competition.

Male accessory gland secretions: modulators of female reproductive physiology and behavior

Secretions of male accessory glands contain a variety of bioactive molecules. When transferred during mating, these molecules exert wide-ranging effects on female reproductive activity and they improve the male's chances of siring a significant proportion of the female's offspring. The accessory gland secretions may affect virtually all aspects of the female's reproductive activity. The secretions may render her unwilling or unable to remate for some time, facilitating sperm storage and ensuring that any eggs laid will be fertilized by that male's sperm. They may stimulate an increase in the number and rate of development of eggs and modulate ovulation and/or oviposition. Antimicrobial agents in the secretions ensure that the female reproductive tract is a hospitable environment during sperm transfer. In a few species the secretions include noxious chemicals. These are sequestered by developing eggs that are thereby protected from predators and pathogens when laid.

Sperm competitive ability and genetic relatedness in Drosophila melanogaster: similarity breeds contempt

Offspring of close relatives often suffer severe fitness consequences. Previous studies have demonstrated that females, when given a choice, will choose to avoid mating with closely related males. But where opportunities for mate choice are limited or kin recognition is absent, precopulatory mechanisms may not work. In this case, either sex could reduce the risks of inbreeding through mechanisms that occur during or after copulation. During mating, males or females could commit fewer gametes when mating with a close relative. After mating, females could offset the effects of mating with a closely related male through cryptic choice. Few prior studies of sperm competition have examined the effect of genetic similarity, however, and what studies do exist have yielded equivocal results. In an effort to resolve this issue, we measured the outcome of sperm competition when female Drosophila melanogaster were mated to males of four different degrees of genetic relatedness and then to a standardized competitor. We provide the strongest evidence to date that sperm competitive ability is negatively correlated with relatedness, even after controlling for inbreeding depression.

Genetic divergence of the seminal signal-receptor system in houseflies: the footprints of sexually antagonistic coevolution?

To understand fully the significance of cryptic female choice, we need to focus on each of those postmating processes in females which create variance in fitness among males. Earlier studies have focused almost exclusively on the proportion of a female's eggs fertilized by different males (sperm precedence). Yet, variance in male postmating reproductive success may also arise from differences in ability to stimulate female oviposition and to delay female remating. Here, we present a series of reciprocal mating experiments among genetically differentiated wild-type strains of the housefly Musca domestica. We compared the effects of male and female genotype on oviposition and remating by females. The genotype of each sex affected both female oviposition and remating rates, demonstrating that the signal-receptor system involved has indeed diverged among these strains. Further, there was a significant interaction between the effects of male and female genotype on oviposition rate. We discuss ways in which the pattern of such interactions provides insights into the coevolutionary mechanism involved. Females in our experiments generally exhibited the weakest, rather than the strongest, response to males with which they are coevolved. These results support the hypothesis that coevolution of male seminal signals and female receptors is sexually antagonistic.

Drosophila seminal fluid proteins enter the circulatory system of the mated female fly by crossing the posterior vaginal wall

Seminal fluid proteins from males of many insect species affect the behavior and physiology of their mates. In some cases, these effects result from entry of the proteins into the female's circulatory system. In the fruit fly Drosophila melanogaster, some seminal fluid proteins enter the female's circulatory system after transfer from the male while others remain confined within the reproductive tract. To address where and how seminal fluid proteins enter the hemolymph of the mated female, we compared the kinetics of transfer and localization in mated females of two seminal fluid proteins that enter the hemolymph (Acp26Aa and Acp62F) and one that does not (Acp36DE). We also generated transgenic flies that produce Acp26Aa tagged with Aequorea victoria green fluorescent protein (GFP) to monitor its transfer in vivo. We report that Acps enter the female circulatory system from the posterior vagina immediately after insemination. The ability of Acps to enter the female hemolymph correlates with their ability to cross the intima that lines the posterior vagina. The ventral posterior vagina is structurally unlike other parts of the female reproductive tract in that it lacks muscles. We hypothesize that it has higher permeability thus affording access to the female's circulatory system.

Ectopic expression of sex peptide alters reproductive behavior of female D. melanogaster

Sex peptide, a secreted component of the male accessory glands, has been shown to induce behavioral and physiological changes in mated Drosophila. We transformed flies with a hybrid gene containing an hsp70 promoter fused to a cDNA encoding sex peptide. Heat-induced ectopic expression of the peptide in transgenic virgin females altered their reproductive behavior, in the presence of courting males, to that observed in mated females. This demonstrates that the peptide is functional as expected. Time course studies revealed that the behavioral change appeared earlier than the stimulated ovulation. We have also introduced a modified sex peptide gene that is driven by the yp1 enhancer, conferring expression in adult females, and shown that these flies refuse mating constitutively in the presence of courting males and lay unfertilized eggs at the rate of mated females.