Condition dependence of male life span and calling effort in a field cricket

Sexually selected traits are thought to impose survival costs on showy males. Recent empirical work found a negative relationship between male display and survival in a field cricket species (Orthoptera, Gryllidae, Gryllinae) where there is no evidence of a mating bias toward older males. In most species, however, male survival and ornamentation are positively correlated, and older males often have a mating success advantage over younger males. These findings suggest that male quality and survival are positively correlated, but more tests of this hypothesis are needed. We measured the condition dependence of male survival and calling effort in another grylline, Gryllus pennsylvanicus, where older males have previously been shown to have greater mating success. We varied condition by manipulating diet, and measured male life span and calling effort to assess the relative condition dependence of these traits. High- and medium-condition males survived longer than low-condition males, and high-condition males called more than medium- and low-condition males. Differences in calling effort among the condition treatments were not apparent early in life, but emerged as males aged. We discuss possible explanations for the differences between our study and contrasting results such as the previous grylline work.     

A life-history perspective on strategic mating effort in male scorpionflies

In species with high male mating effort, there is a trade-offbetween mating effort spent in a current mating and resourcesleft for future matings. Consequently, to maximize their reproductivesuccess, males have to invest strategically, saving resourcesin matings with low reproductive gain for future, more valuablematings. However, as males age, the expected future reproductivesuccess constantly declines. Thus, the importance of resource rationing may drastically change during a lifetime. Males ofthe scorpionfly Panorpa cognata offer females a costly nuptialgift before copulation, which functions as male mating effort.Resources for the production of these salivary masses are severelylimited for males in poor condition. We found that males investedmore in copulations with high-quality females than in copulationswith low-quality females. However, males ceased to discriminateas they became older. Old males, with a relative small numberof expected future matings, did not invest differentially incopulations with high- versus low-quality females. In copulationswith low-quality females, males invested more in late thanin initial matings, whereas in matings with high-quality females,time of mating had no influence on mating effort. These resultsimply that males adaptively change their resource allocationstrategy during the course of the season. Initial matings seemto be characterized by male prudence; in later matings, malesseem to adopt a more opportunistic mating strategy.     

Paternal effort and its relation to mating success in the European ground squirrel

The necessity for parental care is a driving force for determining mating systems and social organization. The European ground squirrel, Spermophilus citellus, is a polygynous, gregarious species in which male parental behaviour would not be expected. We had observed males digging in litter burrows that were later occupied by females and their offspring. Males never stayed overnight within these burrows. To determine whether this was some kind of paternal effort we tested the following hypotheses: (1) that male burrowing behaviour was directed towards the male's own offspring or towards the pregnant or lactating mother of the male's offspring; (2) that this behaviour had costs in terms of condition, decreased survival or fecundity; and (3) that it benefited offspring condition or survival. All three assumptions were met. Males worked on the litter burrow of their copulatory partners. Thus, this behaviour was directed towards the male's potential offspring. Male burrowing costs were seen in decreased foraging time and increased body mass loss. Offspring benefits were evident in increased mass at natal emergence. We conclude that male digging at litter burrows can be considered as paternal effort. Lastly, we considered the effects of polygyny on this male parental effort by comparing mating effort, mating success and paternal effort. High mating success was associated with high mating effort and low paternal effort. Moderate to low mating success was associated with lower mating effort and higher paternal effort, indicating a trade-off between the two.     

Sexual swellings in female hamadryas baboons after male take-overs: "deceptive" swellings as a possible female counter-strategy against infanticide

In many primate species, male intanticide is assumed to pose a serious risk for infants, and therefore female counter-strategies are expected. These counter-strategies may include changes in the females' reproductive behavior and physiology, e.g., mating with multiple males and prolonged receptivity. Since the risk of infanticide is particularly high when a new male enters the group or when a male rises in rank, we studied the changes in female reproductive conditions, e.g., post-partum amenorrhea and interbirth intervals, following group take-overs by new males in a captive group of hamadryas baboons (Papio h. hamadryas). Following take-overs, five out of six lactating females immediately developed sexual swellings, thus shortening their post-partum amenorrhea. However, none of these females conceived during the first cycles after the take-over, their reproduction was not accelerated, and four out of five dependent infants survived. Thus, interbirth intervals did not decrease compared to times with no group take-overs. We therefore suggest that these situation-dependent swellings are used by female hamadryas baboons as a counter-strategy to reduce the risk of infanticide, which exists in this species after male take-overs. By offering new males mating opportunities without allowing them to reproduce, females may increase their infants' probability of survival and at the same time avoid the costs of being pregnant and lactating simultaneously.     

The Foraging Costs of Mating Effort in Male Chimpanzees (Pan troglodytes schweinfurthii)

Costs of mating effort can affect the reproductive strategies and lifetime fitness of male primates, but interspecific and interindividual variation in the magnitude and distribution of costs is poorly understood. Male costs have primarily been recognized in seasonally breeding species that experience concentrated periods of mating competition. Here, we examine foraging costs associated with male mating effort in chimpanzees (Pan troglodytes schweinfurthii), a polygynandrous species, in which mating opportunities occur intermittently throughout the year. To quantify male feeding, aggression, and mating, we conducted focal follows on 12 males in a wild community (Kanyawara, Kibale National Park, Uganda) for 11 mo. Males fed less on days when high-value mating opportunities (estrous parous females) were available than on days without any mating opportunities. Reductions in feeding time were related to increased rates of aggression and copulation, indicating that the proximate cause of changes in male foraging was mating effort. Surprisingly, however, there was no relationship between dominance rank and the extent to which feeding time was reduced. High costs of mating effort may reduce the degree of reproductive skew and limit the use of possessive tactics in chimpanzees. We suggest that male bonding in chimpanzees may be favored not only for its benefits but because intragroup competition is so costly. Our results complement the available data on mammals, and primates in particular, by showing that mating effort can have measurable foraging costs even in species, in which breeding is aseasonal and only moderately skewed.     

Evidence for adaptive male mate choice in the fruit fly Drosophila melanogaster

Theory predicts that males will benefit when they bias their mating effort towards females of higher reproductive potential, and that this discrimination will increase as males become more resource limited. We conducted a series of experiments to test these predictions in a laboratory population of the fruitfly, Drosophila melanogaster. In this species, courtship and copulation have significant costs to males, and females vary greatly in fecundity, which is positively associated with body size. When given a simultaneous choice between small and large virgin females, males preferentially mated with larger, more fecund, females. Moreover, after males had recently mated they showed a stronger preference for larger females. These results suggest that male D. melanogaster adaptively allocate their mating effort in response to variation in female quality and provide some of the first support for the theoretical prediction that male stringency in mate choice increases as resources become more limiting.     

Costs of deception and learned resistance in deceptive interactions

The costs that species suffer when deceived are expected to drive learned resistance, although this relationship has seldom been studied experimentally. Flowers that elicit mating behaviour from male insects by mimicking conspecific females provide an ideal system for such investigation. Here, we explore interactions between a sexually deceptive daisy with multiple floral forms that vary in deceptiveness, and the male flies that pollinate it. We show that male pollinators are negatively impacted by the interaction, suffering potential mating costs in terms of their ability and time taken to locate genuine females within deceptive inflorescences. The severity of these costs is determined by the amount of mating behaviour elicited by deceptive inflorescences. However, inexperienced male flies exhibit the ability to learn to discriminate the most deceptive inflorescences as female mimics and subsequently reduce the amount of mating behaviour they exhibit on them with increased exposure. Experienced males, which interact with sexually deceptive forms naturally, exhibit similar patterns of reduced mating behaviour on deceptive inflorescences in multiple populations, indicating that pollinator learning is widespread. As sexually deceptive plants are typically dependent on the elicitation of mating behaviour from male pollinators for pollination, this may result in antagonistic coevolution within these systems.     

Crickets increase sexual signalling and sperm protection but live shorter in the presence of rivals

The sociosexual environment animals experience through their life can shape the evolution of key life history traits, including longevity. Male–male competition, for instance, may influence the resources allocated to traits involved in male reproductive success. Here, I test whether lifelong exposure to a competitor male influences male investment in pre‐ and post‐copulatory sexual traits (calling effort and sperm quality) and how this affected the oxidative status and longevity of male field crickets (Gryllus bimaculatus). As expected, the visual exposure to a mating competitor promoted a higher calling effort in the male crickets but resulted in a decline in the haemolymph antioxidant content. The haemolymph antioxidant content negatively covaried with the antioxidant content of the sperm but interestingly, only when the males were exposed to a competitor. This suggests that when mating competition is high, males may prioritize sperm antioxidant protection against somatic maintenance. Finally, I provide evidence that male–male competition imposes additional costs to reproduction, as males exposed to a mating competitor lost a significant proportion of body antioxidant defences and body mass over time and in long term, had a reduced lifespan. Overall, this study strongly suggests that intrasexual competition may impose additional oxidative costs during reproduction for males, with negative consequences on lifespan. Moreover, the results highlight the role of oxidative stress as a physiological mechanism underlying the trade‐off between reproduction‐longevity and through which sexual selection may contribute to the evolution of senescence patterns.     

Foraging time of rutting bighorn rams varies with individual behavior, not mating tactic

Mate guarding is the primary mating tactic used by dominantmales of many species of ungulates. Guarding males are thoughtto forage less during the rut than do nonguarding males, possiblyleading to greater fitness costs. I observed bighorn rams foragingduring the pre-rut and the rut. I compared how coursing (analternative mating tactic) and tending (a form of mate guarding)affected the foraging behavior of bighorn rams over the rut,to test whether foraging was more constrained by mate guardingthan by coursing. All adult males spent less time feeding duringthe rut compared with the pre-rut. The decrease in time spentfeeding, however, was independent of mating tactic. Contraryto expectation, individual rams observed both coursing and tendingspent less time foraging when coursing than when tending. Foryoung rams, the time spent in rutting activities was correlatedwith individual pre-rut mass, indicating that males either modifytheir behavior according to available metabolic reserves oradjust the energy devoted to rutting activities to the levelof expected benefits. Mate guarding does not appear to constrainforaging more than coursing. The costs of male reproductivebehavior may depend more upon individual effort than on theparticular tactic adopted.     

The Starling Mating System as an Outcome of the Sexual Conflict

Many bird species demonstrate a variable mating system, with some males being monogamously mated and other males able to attract more than one mate. This variation in avian mating systems is often explained in terms of potential costs of sharing breeding partners and compensation for such costs. However, whenever there is a difference in the optimal mating system for males and females, a sexual conflict over the number of partners is expected. This paper contains a verbal model of how a conflict between male and female European starlings (Sturnus vulgaris),resulting from the fitness consequences of different mating systems for males and females differing over time, determines the mating system. We demonstrate that males and females have contrasting fitness interests regarding mating system, such that males gain from attracting additional mates whereas already mated females pay a cost in terms of reduced reproductive success if males are successful in attracting more mates. We demonstrate how this can be traced to the rules by which males allocate non-sharable care between different broods. Furthermore, we demonstrate that there exist male and female conflict behaviours with the potential to affect the mating system. For example, aggression from already mated females towards prospecting females can limit male mating success and males can circumvent this by spacing the nest-sites they defend. The realised mating system will emerge as a consequence of both the fitness value of the different mating systems for males and females, and the costs for males and females of intersexual competition. We discuss how this model can be developed and critically evaluated in the future.     

Strategic male mating effort and cryptic male choice in a scorpionfly

In animal species with high male mating effort, males often find themselves in a dilemma: by increasing their mating effort, the gain from each copulation increases but simultaneously reduces available resources and, thus, the opportunity for future copulations. Therefore, we expect males to spend less reproductive resources on matings that provide low reproductive potential, thereby saving resources for future copulations, possibly with high-quality females, a sort of cryptic male choice. However, the strength of the trade-off between investment in a current mating and resources available for future matings must not be the same for all males. Males with relatively high mating costs should allocate their limited resources more cautiously than males with more plentiful resources. Here, we examine this prediction in the scorpionfly Panorpa cognata. Prior to copulation, males produce a large salivary mass on which females feed during copulation. We show that the production of larger salivary masses leads to longer copulations. Moreover, the size of the salivary gland and salivary mass increases with increasing male condition. However, males in poor condition make a relatively higher mating investment than males in good condition. We therefore expect male condition to influence cryptic male choice. In accordance with our hypothesis, only males in poor condition choose cryptically, producing larger salivary masses in copulations with females of high fecundity.     

Age- and density-dependent reproductive effort in male red deer

Reproductive effort in female ungulates originates from gestation and lactation and has been studied extensively; however, no comparable studies of reproductive effort in males (due to fighting for access to mates) have, to our knowledge, previously been reported. Here, we report on weight loss of male red deer during the annual mating season--a direct measure of male reproductive effort (or somatic reproductive costs). The 'terminal investment' hypothesis predicts that reproductive effort should increase with age, given that costs remain stable. We also propose the 'mating strategy-effort' hypothesis, which predicts that reproductive effort peaks in prime-aged males, since they are most often the harem holders. Consistent with the mating strategy-effort hypothesis, relative weight loss during the rutting season peaked at prime age and was lower in younger and senescent males. Weight loss during the rut was relatively smaller as density increased and more so for older males. This is probably primarily due to males (particularly senescent males) starting their rut in poorer condition at high density. The pattern of reproductive effort in males with regard to age and density therefore differs markedly from the pattern reported for females.     

Repeated matings offset costs of reproduction in female crickets

Summary Courtship food gifts can be a significant source of nutrition to females and costly for males to produce; hence, costs of reproduction should be reduced for multiple-mating females and increased for multiplemating males in a gift-giving species. We tested this hypothesis by experimentally manipulating mating opportunities of males and females of two cricket species,Gryllodes sigillatus, a gift-giving species andGryllus veletis, a non-gift-giving species. Females of both species consume the externally attached spermatophore after mating, but inG. sigillatus, the sperm-containing ampulla is accompanied by a large gelatinous spermatophylax. In both species, survival of mated females given limited access to males was reduced relative to virgin females, thus suggesting a cost of reproduction to females. However, females given unlimited mating opportunities lived as long as virgins and also produced significantly more offspring than limited-access females. These results suggest that benefits of repeated matings, particularly those arising through spermatophore consumption, offset costs of reproduction in females. Lack of a treatment by species interaction suggests that females of both species derive nutritional benefits through spermatophore consumption, and that any additional advantage to the consumption of the spermatophylax inG. sigillatus is offset by more frequent mating byG. veletis females. In contrast to females, varying mating opportunities had no effect on male survival, suggesting that mating effort is not very costly to males. Male survival increased linearly with body mass but only when males were food-deprived, suggesting that larger males possess greater initial energy reserves to sustain their longevity when food-stressed.     

Determinants of Pair‐Living in Red‐Tailed Sportive Lemurs (Lepilemur ruficaudatus)

Pair‐living and a monogamous mating strategy are rare and theoretically unexpected among mammals. Nevertheless, about 10% of primate species exhibit such a social system, which is difficult to explain in the absence of paternal care. In this study, we investigated the two major hypotheses proposed to explain the evolution of monogamy in mammals, the female defence hypothesis (FDH) and the resource defence hypothesis (RDH), in red‐tailed sportive lemurs (Lepilemur ruficaudatus), a nocturnal primate from Madagascar. We analysed behavioural data from eight male–female pairs collected during a 24‐mo field study to illuminate the determinants of pair‐living in this species. Male and female L. ruficaudatus were found to live in dispersed pairs, which are characterised by low cohesion and low encounter rates within a common home range. Social interactions between pair partners were mainly agonistic and characterised by a complete absence of affiliative interactions – body contact was only observed during mating. During the short annual mating season, males exhibited elevated levels of aggression towards mates, as well as extensive mate guarding and increased locomotor activity. In addition, males were exclusively responsible for the maintenance of proximity between pair partners during this period, and they defended their territories against neighbouring males but not against females. Together, these results point towards the importance of female defence in explaining pair‐living in L. ruficaudatus. We discuss the spatial and temporal distribution of receptive females in relation to the female defence strategies of males and suggest possible costs that prevent male red‐tailed sportive lemurs from defending more than one female.     

The Effects of Perceived Mating Opportunities on Patterns of Reproductive Investment by Male Guppies

Males pay considerable reproductive costs in acquiring mates (precopulatory sexual selection) and in producing ejaculates that are effective at fertilising eggs in the presence of competing ejaculates (postcopulatory sexual selection). Given these costs, males must balance their reproductive investment in a given mating to optimise their future reproductive potential. Males are therefore expected to invest in reproduction prudently according to the likelihood of obtaining future matings. In this study we tested this prediction by determining whether male reproductive investment varies with expected future mating opportunities, which were experimentally manipulated by visually exposing male guppies (Poecilia reticulata) to high or low numbers of females in the absence of competing males. Our experiment did not reveal consistent effects of perceived future mating opportunity on either precopulatory (male mate choice and mating behaviour) or postcopulatory (sperm quality and quantity) investment. However, we did find that male size and female availability interacted to influence mating behaviour; large males visually deprived of females during the treatment phase became more choosy and showed greater interest in their preferred female than those given continuous visual access to females. Overall, our results suggest males tailor pre- rather than postcopulatory traits according to local female availability, but critically, these effects depend on male size.     

Paternal investment directly affects female reproductive effort in an insect

Female reproductive effort can be influenced by the quality of her mate. In some species, females increase their reproductive effort by differentially allocating resources after mating with high-quality males. Examination of female reproductive effort in relation to male quality has implications for estimating the evolvability of traits and for sexual-selection models. Accurate quantification of reproductive investment is not possible in many species. Butterflies are an exception, as most nectar-feeding species emerge with almost intact reproductive resources, and in some species males provide nutrients at mating that enhance female fecundity. By manipulating male donations and using radioactive isotopes, we quantified the effect of variation in nutrient provisioning on female reproductive effort in two butterfly species. In the greenveined white butterfly, Pieris napi, females increased their reproductive effort after receiving large male donations. By contrast, in the speckled wood, Pararge aegeria, where males do not provide nutrients, female reproductive effort was independent of male ejaculate. Increased reproductive effort in Pieris napi resulted from the production of more eggs, rather than from investing more resources per egg. In this species donating ability is heritable; hence females laying more eggs after mating with high-donating males benefit both through higher fecundity and through the production of high-donating sons.     

Mating status, immune defence, and multi-parasite burden in the damselfly Coenagrion armatum

Immunity and reproductive effort are both physiologically costly and often a trade-off between these functions has been shown. In studies with damselflies, parasite load has been associated with fitness costs, such as reductions in mating success, male condition, and survival. Although each individual may be simultaneously infected by various parasite species, most studies have concentrated on the effects of a single parasite taxon. We examined natural ecto- and endoparasite infection levels in male Coenagrion armatum (Charpentier) (Odonata: Coenagrionidae) damselflies in relation to their mating status, fat reserves, and ability to further mount an immune response, measured as encapsulation of an experimentally introduced foreign object. Encapsulation response was lower for mated (paired) males than for single males and declined with increasing water mite abundance. Mated males had fewer water mites than single males. Male weight or fat reserves did not explain variation in encapsulation response. The number of gregarine gut parasites was not related to the level of encapsulation response and did not differ between mated and single males. However, there was a negative correlation between mite abundance and gregarine load. Our data suggest that current mite infection may compromise a male's resistance against further infections by pathogens and parasites, and there may be a trade-off between reproductive effort and encapsulation response in male C. armatum .     

Direct and indirect fitness consequences of female choice in a crustacean

Understanding the evolution and maintenance of female mate choice requires information on both the benefits (the sum of direct and indirect benefits) and costs of selective mating. In this study, I assessed the fitness consequences of female mate choice in a freshwater crustacean. In Hyalella amphipods, males attempt to form precopulatory pairs with females. Large males, bearing large posterior gnathopods, tend to be over-represented in precopulatory pairs. I show that females receive both direct (reduced risk of predation while paired) and indirect (sexy sons) benefits from mating with these males. Furthermore, the behavioral mechanisms used to filter male phenotypes carry no detectable energetic cost for females. Thus, females that choose males with successful phenotypes are expected to have higher Darwinian fitness than females that mate at random. This study shows that direct and indirect selection act together to favor large male size, which explains the sexual size dimorphism and size-based mating biases observed in this species.     

Application of paternity discrimination by DNA polymorphism to the analysis of the social behavior of primates

Paternity in many primate species cannot be established reliably on behavioral grounds. For instance, Japanese macaques (Macaca fuscata) have a multi-male group structure and promiscuous mating patterns. On the other hand, accurate evaluation of male reproductive success is needed to analyze primate behavior. DNA finger-printing techniques were applied to 2 captive groups of Japanese macaques in the Primate Research Institute of Kyoto University for identification of paternity. Also, mating behavior of a captive group was observed in order to compare the reproductive success of each male with that expected on the basis of his observed mating activity. The number of offspring of full adult males was not related to their social rank although the number of copulations with ejaculation was highly correlated with their social rank. Monitoring of the female sexual cycles from the plasma profiles of gonadotropins and ovarian hormones suggested that males could not choose females at days of ovulation. The results of two-free-ranging wild troops, like those of the captive groups, indicated that high-ranking males could not monopolize the paternity of offspring. The results of paternity discrimination in Japanese macaques were compared with results from patas monkeys (Erythrocebus patas) in a discussion of social structure and male reproductive success. Some aspects of polymorphism detection techniques are also discussed.     

Physiological costs enforce the honesty of lek display in the black grouse (Tetrao tetrix)

Females may use condition-dependent sexual traits as reliable cues of male “quality” if the costs of the expression of such traits vary with male “quality”, and if there is positive genetic correlation between male traits and condition. However, there are multiple ways of measuring the changes in body condition which reflect physiological costs meaning that the multifaceted nature of the physiological costs associated with the expression of sexual traits has rarely been thoroughly examined. In the lekking black grouse (Tetrao tetrix), mating success is highly skewed towards males defending central territories and having high survival rates to the following year, but the mechanisms underpinning such superior performance remain unclear. In this study, we quantified the changes in five measures of body condition before and after the mating season and related these changes to male lek performance (fighting rate, territory centrality and mating success) to understand the physiological costs of male reproductive effort. Between the two capture sessions, male body mass decreased significantly, blood parasite counts and plasma carotenoid concentration increased substantially while the total immunoglobulin concentration tended to increase. There was no overall impairment of individual body condition as the changes in the five measures of body condition were unrelated. Male fighting rate was unrelated to changes in the condition measures but males losing more body mass defended central territories and had high mating success. Therefore, females preferring central, dominant males may select males better able to afford the energetic costs of lek performance thereby effectively enforcing the honesty of male display.