Homosexual behaviour and its longevity cost in females and males of the seed beetle Acanthoscelides obtectus

The level of homosexual behaviour is evaluated in one laboratory population of seed beetle and derived lines selected to reproduce early (E) or late in life (L), where inadvertent selection for either low or high heterosexual activity has been detected. The magnitudes of homosexual interaction, measured as chasing and mounting individuals of the same sex, are estimated over different age classes. These magnitudes are correlated with previously observed levels and patterns of age‐specific variation of heterosexual activity of both sexes in the E and L experimental lines. The results obtained support the perception error hypothesis proposing that a low degree of sexual discrimination is genetically correlated with high sexual activity. The fitness costs of the same‐sex interactions are tested by assessing their effects on longevity. In both sexes, the longevities of homosexual pairs are reduced relative to individually‐housed virgin beetles in both the E and L lines, although homosexual interactions have a more pronounced effect on male survival than on female survival. Although the results obtained suggest that the longevity cost of homosexual interactions can be substantial, this cost is much smaller than the cost of heterosexual interactions.     

Selection on learning performance results in the correlated evolution of sexual dimorphism in life history

The evolution of learning can be constrained by trade‐offs. As male and female life histories often diverge, the relationship between learning and fitness may differ between the sexes. However, because sexes share much of their genome, intersexual genetic correlations can prevent males and females from reaching their sex‐specific optima resulting in intralocus sexual conflict (IaSC). To investigate if IaSC constraints sex‐specific evolution of learning, we selected Caenorhabditis remanei nematode females for increased or decreased olfactory learning performance and measured learning, life span (in mated and virgin worms), reproduction, and locomotory activity in both sexes. Males from downward‐selected female lines had higher locomotory activity and longer virgin life span but sired fewer progeny than males from upward‐selected female lines. In contrast, we found no effect of selection on female reproduction and downward‐selected females showed higher locomotory activity but lived shorter as virgins than upward‐selected females. Strikingly, selection on learning performance led to the reversal of sexual dimorphism in virgin life span. We thus show sex‐specific trade‐offs between learning, reproduction, and life span. Our results support the hypothesis that selection on learning performance can shape the evolution of sexually dimorphic life histories via sex‐specific genetic correlations.     

Increased density and male-male interactions reduce male longevity in the medfly, Ceratitis capitata

We investigated the effect of adult density on male and female longevity and behavioural interactions in a mass-reared strain of the medfly. Male survival decreased significantly, and male-male behavioural interactions increased significantly, with increasing male density (males were kept at 1, 2, 6 and 10 flies per 285 cm²in pots of 5.5 cm in diameter and 12 cm high). No such effects were observed in females over the same density range. This suggests that male survival decreased in response to the deleterious effects of male-male behavioural interactions. At the highest density, courtship wing fanning directed towards other males decreased significantly over time. In addition, as either density or male-biased sex ratio increased, males were increasingly likely to be engaged in courtship wing fanning that was not directed towards females. These results suggest that high adult density may significantly reduce male reproductive success, by decreasing survival and mating success. The results highlight the potentially high survival costs of male-male interactions and indicate differences in the nature of reproductive costs in the two sexes.     

Impact of mating on Anagyrus kamali Moursi (Hym., Encyrtidae) lifetime fecundity, reproductive longevity, progeny emergence and sex ratio

Abstract: The solitary endoparasitoid Anagyrus kamali Moursi (Hym., Encyrtidae) and the Hibiscus mealybug Maconellicoccus hirsutus Green (Hom., Pseudococcidae), were used as a parasite/host model to test the effect of mating on several fitness parameters, i.e. longevity, lifetime fecundity, progeny emergence and sex ratio. At 27 ± 2°C, 8 h light : 16 h dark, mating significantly affected the survival of male parasitoids. Virgin males lived longer (32.2 ± 9.51 days) than mated males (23.9 ± 7.52 days). Female longevity (40.7 ± 16.3 days for virgins and 36.2 ± 10.7 days for mated females) was not affected by mating. The lifetime fecundity of female parasitoids and their oviposition period was not significantly affected by mating. However, the number of hosts parasitized was greater for mated wasps (7.54 ± 4.85 hosts parasitized/day) compared with virgin ones (5.12 ± 2.19 hosts parasitized/day). This resulted in greater progeny production from mated A. kamali females. The progeny of virgin females consisted only of males, whereas the mated ones had a more female‐biased sex ratio. The lowest sex ratio (0.41 M/F ± 0.123) was attained when females had free access to males and were multi‐mated.     

Costs and benefits of giant sperm and sperm storage organs in Drosophila melanogaster

In Drosophila, long sperm are favoured in sperm competition based on the length of the female's primary sperm storage organ, the seminal receptacle (SR). This sperm–SR interaction, together with a genetic correlation between the traits, suggests that the coevolution of exaggerated sperm and SR lengths may be driven by Fisherian runaway selection. Here, we explore the costs and benefits of long sperm and SR genotypes, both in the sex that carries them and in the sex that does not. We measured male and female fitness in inbred lines of Drosophila melanogaster derived from four populations previously selected for long sperm, short sperm, long SRs or short SRs. We specifically asked: What are the costs and benefits of long sperm in males and long SRs in females? Furthermore, do genotypes that generate long sperm in males or long SRs in females impose a fitness cost on the opposite sex? Answers to these questions will address whether long sperm are an honest indicator of male fitness, male post‐copulatory success is associated with male precopulatory success, female choice benefits females or is costly, and intragenomic conflict could influence evolution of these traits. We found that both sexes have increased longevity in long sperm and long SR genotypes. Males, but not females, from long SR lines had higher fecundity. Our results suggest that sperm–SR coevolution is facilitated by both increased viability and indirect benefits of long sperm and SRs in both sexes.     

Reproductive strategies of the larval parasitoid Microplitis croceipes

Mate choice may have important consequences for offspring sex ratio and fitness of haplodiploid insects. Mate preference of females of the solitary larval parasitoid Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) for virgin and mated males, and vice versa, and the reproductive consequences (i.e., the sex ratio expressed as the proportion of male offspring) were examined in choice and non‐choice experiments. In addition, the effect of repeated rapid and daily copulation of an individual male on the sex ratio of offspring of the female mates was assessed. Males preferred virgins over mated females, whereas females copulated with a male irrespective of his mating status. In both the rapid and daily copulation assay, females copulating with a male that had copulated five times or more produced a higher sex ratio than females that had copulated with a virgin male. Females that copulated with virgin males once or twice produced a significantly and considerably lower sex ratio than females that first copulated with a sperm‐depleted male followed by a virgin male. This indicates that copulating with a sperm‐depleted male has costs and limits acquisition by the female of sperm from virgin males.     

Sexual attractiveness shared by both sexes mediates same‐sex sexual behaviour in the parasitoid wasp Telenomus triptus

The mating behaviour of a quasi‐gregarious egg parasitoid Telenomus triptus Nixon (Hymenoptera: Platygastridae), which exploits egg masses of a stink bug Piezodorus hybneri (Heteroptera: Pentatomidae), is examined in the laboratory. In this parasitoid wasp, male adults that emerge earlier stay at the natal egg mass and mate with subsequently emerging females. In the present study, a male adult that encounters the emergence of another male always waits for it to egress, and then mounts the newly emerging male. To examine why males of T. triptus show same‐sex sexual behaviour, male adults are presented with a parasitized host egg mass or a freshly killed wasp. Male adults are observed to remain at host egg masses from which only male wasp(s) had emerged. In addition, male adults attempt to copulate with freshly killed young male wasps. It is suggested that newly emerging male wasps are targets of same‐sex sexual behaviour because they possess cues for male sexual behaviour similar to the cues of females. Both the sex and age of freshly killed wasps affect the frequency of the sexual behaviour of male adults: females are more attractive than males, although their attractiveness declines with age. When the mating opportunity is restricted to the natal egg mass, the costs of failing to notice newly emerging female adults should be extremely high. Therefore, males are forced not to discriminate the sex, resulting in same‐sex sexual behaviour.     

Sexual History Affects Mating Behavior and Mate Choice in the Crayfish Orconectes limosus

Because mating entails both costs and potential benefits to both sexes, males and females should be under selection to make optimal choices from among available potential mates. For example, in some cases, individuals may benefit by using information on potential mates' previous sexual histories to make mate choices. In such cases, the form and direction of these benefits may vary both between the sexes and based on the sexual history of the choosing individuals themselves. We investigated the effects of recent previous sexual history on the mate choice and mating behavior of both males and females of the crayfish Orconectes limosus. In one experiment, we found that opposite‐sex dyads comprising crayfish that had both mated 7–8 d previously with other conspecifics were significantly less likely to mate than dyads in which at least one crayfish was unmated. In a second experiment, we found that, when presented with a choice of tethered (but free to move) opposite‐sex conspecifics, only virgin females discriminated between males based on sexual history, showing a preference for virgin males over recently mated males. Mated females, mated males, and virgin males showed no preferences based on the sexual histories of potential mates. We discuss the implications of these inferences in the context of what was previously known about mating behavior and potential sperm limitation in crustaceans and other taxa.     

SEX-RATIO MANIPULATION IN RESPONSE TO HOST SIZE BY THE PARASITOID WASP SPALANGIA CAMERONI: A LABORATORY STUDY

The prediction of Charnov et al.'s (1981) host-size model that there should be a negative relationship between host size and wasp sex ratio (proportion sons) was supported for Spalangia cameroni, a solitary parasitoid wasp. The relationship was shown to be a result of offspring sex manipulation by females in response to host size rather than a result of differential mortality of the sexes. A major assumption of the host-size model is that host size has a greater effect on the ultimate reproductive success of emerging female wasps than of males. This assumption was not supported. Host size had a positive effect on the size of both male and female S. cameroni. However, neither host size nor wasp size affected longevity, production of offspring by females, or ability of males to compete for mates. Host size may differentially affect the reproductive success of female and male wasps through effects on other aspects of reproductive success. Tests of the assumptions of offspring sex-ratio manipulation hypotheses are scarce but critical, not only for parasitoid wasps, but also for other organisms.     

Intimate Rendezvous in a Tritrophic Context? Nothing but the Girls for Male Lysiphlebus testaceipes

In insects, mating often occurs after natal dispersal, and hence relies on a coevolved combination of sexual communication and movement allowing mate encounter. Volatile sex pheromones are widespread, generally emitted by females and triggering in‐flight orientation of conspecific males. In parasitoid wasps, unmated females can start laying unfertilized eggs via parthenogenesis so that host patches could serve as sites of rendezvous for mating. Males could therefore use cues associated with host patches to focus their search on females that have successfully found oviposition sites. We hypothesized that in parasitoids exploiting herbivorous hosts, sex pheromones, and herbivore‐induced plant volatiles (HIPV) should act in synergy, triggering male orientation toward ovipositing females. We tested this hypothesis with the aphid parasitoid Lysiphlebus testaceipes. Results from both field and laboratory experiments show that males are strongly attracted to virgin females, but that volatiles from aphid‐infested plants have no effect on male orientation, neither has a cue, nor in interaction with the female sex pheromone. The absence of synergy between sex pheromones and HIPV contrasts with results on other species and raises interesting questions on mating systems and sexual selection in parasitoid wasps.     

The effect of reproductive activity on the longevity of male Drosophila melanogaster is not caused by an acceleration of ageing

Male D. melanogaster kept supplied with virgin females had lower longevity than males kept without access to females. Cessation of reproductive activity by males previously kept with females resulted after a short lag in the same life expectancy as that of flies of the same age which had never had females. Commencement of reproductive activity resulted in life expectancy indistinguishable from that of males of the same age kept with females throughout life. The effect of reproductive activity on longevity is therefore short-term and reversible and not due to an acceleration of ageing. This finding has implications for the way that different theories of the evolution of ageing should be tested.     

Fitness Costs of Sexual Harassment–The Price of Persuasion

Females are often subjected to unwanted mating advances from males. Such advances can be costly to both parties. The short‐term costs of harassment to females have been widely explored in the literature; however, few studies have measured the direct fitness costs. Moreover, male costs are seldom considered. Conventional wisdom would lead us to hypothesise that sexual harassment is costly; thus, when males and females are housed together, harassment should reduce foraging, growth and reproductive output and may disrupt social interactions. This study quantified harassment costs in both sexes by observing behavioural responses and long‐term effects of unsolicited mating in a controlled setting. Sexually mature guppies were subjected to two housing treatments: equal sex ratios or single‐sex groups. The effects of male harassment on males and females were assessed by measuring behaviour, growth rate and the number of offspring produced over a period of 6 mo. Contrary to our expectations, our results indicated no significant differences in foraging and growth rates between mixed‐ and single‐sex shoals for either sex. Moreover, there was no significant difference in fry production between mixed‐ and all‐female shoals. Large males showed higher mortality when housed with females. Both sexes showed a reduction in shoaling when in mixed‐sex groups. Thus, there appear to be few direct costs of harassment for females in natural, mixed‐sex shoals, but males appear to bear significant harassment costs. The study provides insights into reproductive behaviour and life‐history traits.     

Cost of reproduction in male medflies: The primacy of sexual courting in extreme longevity reduction

In polygynous insect species, male reproductive success is directly related to lifetime mating success. However, the costs for males of sexual activities such as courting, signaling, and mating are largely unknown. We studied the cost of sexual activities in male Mediterranean fruit flies, Ceratitis capitata (Tephritidae), a polygynous lekking species, by keeping cohorts of individual male flies under relaxed crowding conditions in the laboratory. We used 5 cohorts among which individuals differed in their opportunities to interact with con-specifics and recorded life span, and in one treatment, mating rate. We found that males kept singly lived more than twice as long as males that interacted intensively with mature virgin females, while male-male interactions caused a smaller reduction in longevity. Because longevity of males that could court but not mate was not significantly different from those that could court and mate, we conclude that courting (not mating) was responsible for the observed longevity reduction. Moreover, we detected high variability in male mating success, when 5 virgin females were offered daily. In contrast to the cohort level, individual males that mated at a high rate lived relatively long, thus indicating heterogeneity in quality or sexual strategy among males.     

Offspring sex ratio and development are determined by copulation activity in Echinothrips americanus MORGAN 1913 (Thysanoptera: Thripidae)

The costs of parthenogenetic reproduction are more or less unknown in thrips. However, IPM strategies require an understanding of temporal and spatial life‐history variations and sex ratios. Hence, different circumstances with regard to mating and sperm storage, and their effects on the life history of the adults and progeny, were tested in Echinothrips americanus. Different conditions were investigated: (1) one female and one male with permanent access to each other, (2) one female and one male with limited access to each other, (3) one virgin male only, (4) one virgin female only and (5) two virgin females permanently associated. Mating or not mating has a significant effect on the longevity of females and males, and on female fecundity. As a result of tested condition (2), limited access has a positive effect on longevity of a male. On the other hand, permanent access (1) or no access to a female (3) leads to shorter longevity of a male. For a female with permanent access to a male (1), longevity and oviposition rate are reduced. In addition, test conditions of parents have a significant effect on developmental time of the offspring and their sex ratio. Compared to a female under condition (1), a female with limited access to a male (2) delivers offspring with a more male‐biased sex ratio, independent of the period of time after last male access. Concerning the time for development of the offspring, females under condition (2) and under condition (4) deliver an F1 generation with a shorter developmental time than those under condition (1). Therefore, E. americanus seems to have a feedback system, that is offspring in low male‐biased populations develop faster and generate an adapted sex ratio. Hence, the assumption of a lower infestation risk in arrhenotokous than in thelytokous parthenogenesis should be reconsidered.     

Persistent courtship reduces male and female longevity in captive tsetse flies Glossina morsitans morsitans Westwood (Diptera: Glossinidae)

Where males can increase their mating success by harassing femalesuntil they accept copulation, harassing tactics can be expectedto evolve to a point where they have costs to the longevityof both sexes. By experimentally manipulating the sex ratioin captive groups of tsetse flies Glossina morsitans morsitans,we demonstrated that the longevity of females declines wheresex ratios are biased toward males, while the longevity of malesdeclines where the sex ratio is biased toward females. Neitherirradiation of males nor prevention of copulation by blockingor damaging the external male genitalia increased the longevityof females caged with them, suggesting that female longevitywas reduced by the physical aspects of male harassment ratherthan by components of the ejaculate     

Single and multiple mating reduces longevity of female dumpling squid (Euprymna tasmanica)

For many species, mating is a necessary yet costly activity. The costs involved can have an important influence on the evolution of life histories and senescence. Females of many species mate multiply, and this behaviour can inflict a longevity cost. Most studies investigating the effects of multiple mating on female survival have been conducted on insects, and the effects in other taxa are largely unknown. We investigate the effects of both a single mating and a second mating on longevity in female dumpling squid (Euprymna tasmanica), a species in which both sexes mate multiply. Through comparing the longevity of virgin, once‐mated and twice‐mated females, we found that a single mating reduced female life span by 15 days on average. A second mating resulted in an additional 8 day (on average) longevity cost, despite no difference in total clutch mass, number of clutches, single egg mass or number of eggs per clutch between once‐mated and twice‐mated females. This demonstrates a cost to multiple mating which may be independent of the cost of egg production. Furthermore, total clutch mass and female life span were positively correlated, whereas female life span decreased with increasing average water temperature. The presence of an additive effect of reproduction on longevity suggests that multiple mating in cephalopods may have benefits that outweigh these costs, or that there is a conflict in optimal mating frequency between males and females.     

Both sexes suffer increased parasitism and reduced energy storage as costs of reproduction in the brown anole,Anolis sagrei

Sexual selection theory proposes that males suffer reduced immune function and increased parasitism as costs of expressing sexual signals. Life‐history theory proposes that females suffer the same costs because of inherent trade‐offs between reproduction and self‐maintenance. Mechanistically, each theory invokes an energetic trade‐off, although few experiments have directly compared these costs of reproduction between the sexes as a result of fundamental sex differences in the nature of reproductive investment and a tendency for each theory to focus on a single sex. To test whether males and females experience comparable costs of reproduction in terms of energetics, immune function, and parasitism, we used gonadectomy to eliminate most aspects of reproductive investment in wild brown anole lizards (Anolis sagrei) of both sexes. We compared these nonreproductive males and females with intact, reproductive controls with respect to stored energy (fat bodies), immune function (swelling response to phytohemagglutinin), and the prevalence and intensity of infection by four types of parasite (gastric nematodes, intestinal nematodes, faecal coccidia, and ectoparasitic mites). Gonadectomized anoles experienced dramatic increases in fat storage that were accompanied by decreases in the prevalence of intestinal nematodes and in the intensity of coccidia infection. These costs of reproduction were comparable between males and females, although neither sex exhibited the predicted increase in immune function after gonadectomy. Our results suggest that, despite fundamental sex differences in the nature of reproductive investment, both male and female anoles experience similar costs of reproduction with respect to energy storage and some aspects of parasitism.     

Post-Mating Interactions and Their Effects on Fitness of Female and Male Echinothrips americanus (Thysanoptera: Thripidae), a New Insect Pest in China

Post-mating, sexual interactions of opposite sexes differ considerably in different organisms. Post-mating interactions such as re-mating behavior and male harassment can affect the fitness of both sexes. Echinothrips americanus is a new insect pest in Mainland China, and little is known about its post-mating interactions. In this study, we observed re-mating frequency and male harassment frequency and their effects on fitness parameters and offspring sex ratios of E. americanus females. Furthermore, we tested the impact of mating and post-mating interactions on fitness parameters of males. Our results revealed that the re-mating frequency in female adults was extremely low during a 30-day period. However, post-mating interactions between females and males, consisting mainly of male harassment and female resistance, did occur and significantly reduced female longevity and fecundity. Interestingly, increased access to males did not affect the ratio of female offspring. For males, mating dramatically reduced their longevity. However, post-mating interactions with females had no effects on the longevity of mated males. These results enrich our basic knowledge about female and male mating and post-mating behaviors in this species and provide important information about factors that may influence population regulation of this important pest species.     

Males Benefit from Mating with Outbred Females in Drosophila littoralis: Male Choice for Female Genetic Quality?

The evolution and expression of mate choice behaviour in either sex depends on the sex‐specific combination of mating costs, benefits of choice and constraints on choice. If the benefits of choice are larger for one sex, we would expect that sex to be choosier, assuming that the mating costs and constraints on choice are equal between sexes. Because deliberate inbreeding is a powerful genetic method for experimental manipulation of the quality of study organisms, we tested the effects of both male and female inbreeding on egg and offspring production in Drosophila littoralis. Female inbreeding significantly reduced offspring production (mostly due to lower egg‐to‐adult viability), whereas male inbreeding did not affect offspring production (despite a slight effect of paternal inbreeding on egg‐to‐adult viability). As inbreeding depressed female quality more than male quality, the benefits of mate choice were larger for males than for females. In mate choice experiments, inbreeding did not affect male mating success (measured as a probability to be accepted as a mate in a large group), suggesting that females did not discriminate among inbred and outbred males. In contrast, female mating success was affected by inbreeding, with outbred females having higher mating success than inbred females. This result was not explained by lower activity of inbred females. Our results show that D. littoralis males benefit from mating with outbred females of high genetic quality and suggest adaptive male mate choice for female genetic quality in this species. Thus, patterns of mating success in mate choice trials mirrored the benefits of choice: the sex that benefited more from choice (i.e. males) was more choosy.