To court or not to court: reproductive decisions by male fiddler crabs in response to fluctuating food availability

For males, courting and foraging are often behavioral alternatives, which take time and consume energy. When males have a possibility of mating with receptive females, there may be a behavioral trade-off between courtship and feeding; the outcome of which may be affected by male physiological condition and food availability. Although many mathematical models and empirical studies suggest that the expression of male courtship signals are condition-dependent, decisions about courtship and mating strategies in relation to food availability have not attracted much attention. In this study, we tested whether daily changes in food availability affect males’ decisions about whether to court. We conducted experiments with the fiddler crab Uca lactea by providing males with additional food every other day. In food-supplemented enclosures, males did not increase courtship activity on the days when food was supplemented. However, they built more courtship structures (semidomes) and waved more on the days when they were not given additional food. Male size had a strong influence on the number of days the males courted. We also tested whether the frequency of surface mating, as an alternative reproductive tactic, decreased when food was supplemented. Contrary to our expectation, the number of males that exhibited the surface-mating tactic increased when food was supplemented whereas the number of mate-searching females did not change. Our findings in this field study suggest that reproductive decisions by male fiddler crabs are affected by fluctuating food availability and present body condition, and the alternative mating tactic of this species may be more frequently used by males under good condition.     

Mating effort or paternal investment? Incorporation rate and cost of male donations in the wartbiter

Summary Provision of nuptial gifts and incorporation of male-derived substances occurs in several insects. There has been some discussion as to whether these gifts should be regarded as a form of paternal investment or part of mating effort. One assumption of the paternal investment hypothesis is that the donating male is expected to father all, or the majority of, the offspring. The rate of incorporation into developing eggs is therefore assumed to be rapid enough to assure the donating male of paternity of the offspring in which he is investing. Spermatophore production in a paternal investment system is also expected to be costly, since males are providing females with highly nutritious gifts during copulation, thereby increasing female fecundity. Therefore, under conditions of food limitation males are expected to alter either mating frequency or spermatophore size. Experiments on the wartbiter (Decticus verrucivorus), using radioactive isotopes, show that the incorporation rate of male-derived substances is so slow that females become sexually receptive before any material received from the last male have been incorporated into eggs laid by the female. Since sperm mixing occurs in this species and since the label is present in eggs laid up to more than 30 days after mating, males might potentially benefit another male's offspring. The nuptial gift (the spermatophylax) was found, regardless of mating frequency and diet, to have a low protein content. These findings coincide with previous results showing that consumption of the gift had no effect on female fecundity. Instead, wartbiter males keep mating frequency high, are capable of mating every day regardless of food availability, invest the same proportion of the body weight in spermatophore production regardless of size, and produce a spermatophylax that correlates with ampulla size. These results indicate that the nuptial gift mainly functions to increase fertilization success in the wartbiter.     

Forced copulation as a conditional alternative strategy in camel crickets

In the animal kingdom, males typically acquire reproductive access to females through courtship, nuptial gifts, or combat. In many species, small or poor-condition males that are unable to produce an attractive display, proffer an adequate mating gift, or dominate in male–male competition may resort to forced copulation. Forced copulation has been previously demonstrated in the camel cricket Pristoceuthophilus marmoratus and is uniquely facilitated by male hind leg weaponry that functions in both intrasexual competition and sexual coercion. Because male leg armaments are positively allometric, the largest males would seem best equipped to force-copulate, although they might be the most attractive to females, and so least likely to adopt a forced copulation strategy. In order to resolve this potential paradox and determine which males are in fact most likely to force-copulate, we manipulated male body size using diet and performed mating trials. Results showed that (1) male size increased with diet quality, (2) females appear to prefer larger males, and (3) smaller males were more likely to attempt forced copulation. Our results thus suggest that forced copulation is a condition-dependent alternative mating tactic used by small males unattractive to females.     

Independent effects of male and female density on sexual harassment, female fitness, and male competition for mates in the western mosquitofish Gambusia affinis

Operational sex ratio (the ratio of sexually active males to fertilizable females) has a major influence on male competition for mates and male–female interactions. The contributions of male and female density per se to mating system dynamics, however, are rarely examined, and the fitness consequences are often inferred rather than quantified. Male mosquitofish (Gambusia affinis) compete aggressively and frequently harass females for copulations, a behavior thought to reduce female fitness. Female fitness can also be reduced by increases in female density, which may affect food availability, cannibalism rates, and chemical interactions between females. I manipulated male and female densities of G. affinis to measure their effects on male–male aggression, male harassment toward females, and female fitness. I found that males chased rivals more often and attempted fewer copulations when female density decreased, but surprisingly male density had no significant effect on the frequency of these male behaviors. In contrast, males’ agonistic displays toward other males increased with male density, but display behavior was unaffected by female density. These results suggest that male and female density do not always contribute equally or at all to the patterns of behavior we observe. Female fitness declined as female density increased, the opposite pattern expected if male harassment is costly to females. This suggests that a strong, negative effect of female density overwhelmed any potential costs of male harassment. Sources of female density dependence and the consequences of changes in male and female density to patterns of male behavior are discussed.     

Male size and mating tactic influence proximity to females during sperm competition in bluegill sunfish

Many fishes are characterized by intense sperm competition between males that use alternative mating tactics. In externally fertilizing fishes, males’ proximity to females during spawning can be an important determinant of fertilization success. Here, we assess how mating tactic, body length, speed during streak spawns, and periphery cover affect males’ proximity to females during sperm competition in the externally fertilizing bluegill (Lepomis macrochirus). Bluegill are characterized by three mating tactics referred to as parental, sneaker, and satellite. Parentals are territorial and construct nests, while sneakers use a streaking behavior, and satellites use female mimicry to steal fertilizations from parentals. We show that a small body length is important for sneakers but not for satellites to obtain a close position to the female during spawning. Specifically, smaller sneakers obtain a closer position to females than larger sneakers in part by positioning themselves closer on the periphery of a parental’s nest before streaking but show no difference in the speed at which they streak. The amount of peripheral vegetation around a parental’s nest did not appear to affect proximity of sneakers to females, and there was no relationship between the amount of peripheral vegetation and the frequency of intrusions by either sneakers or satellites. Finally, parentals were farther from the female when a sneaker or satellite intruded than when they spawned alone with the female.     

Allocation of nuptial gifts in tree crickets changes with both male and female diet

Male tree crickets, Oecanthus nigricornis, offer a nuptial gift to females during mating in the form of a secretion from a dorsal metanotal gland. I examined the effects of male and female nutrient limitation on allocation of the gift. Males were fed ¹⁴C radiolabeled amino acids, placed onto high- or low-quality diets and then mated with females also maintained on high- or low-quality diets. Female acquisition of radiolabel increased, and residual radiolabel within the metanotal gland decreased, over time verifying that gift size correlates with duration of courtship feeding. High-diet females produced greater egg numbers and allocated proportionally more of the male-derived amino acids to their ovaries. As predicted, duration of courtship feeding was greater for males on high-quality diets and females on low-quality diets. Amino acid transfer, measured as the proportion of total radiolabel transferred to the female, showed a significant interaction between male and female diet. High-diet females acquired available radiolabel more rapidly from high-diet males, but low-diet females acquired available radiolabel more rapidly from low-diet males. The causes of these differences between feeding duration and nutrient allocation are discussed.     

Fluctuating asymmetry,interspecific aggression and male mating tactics in two species of Japanese scorpionflies

Summary Fluctuating asymmetry (FA) is defined as small, random deviations from bilateral symmetry in a generally perfect bilaterally symmetrical morphological trait. FA in forewing length affects the outcomes of interspecific contests for food items (dead arthropods) between two species of Japanese scorpionflies, Panorpa nipponensis and P. ochraceopennis, in nature. FA differences between same-sex contestants are more important than either body size or ownership of food in determining the outcomes of interspecific contests; for both sexes, winners statistically significantly more often have relatively low FA. Two condition-dependent mating tactics are used by the males of each species: (a) a male may defend a dead-arthropod nuptial gift, or (b) a male without such an arthropod may wait near a male with one. In both tactics, males release long-distance sex pheromones. Groups of pheromone-releasing males are made up of one male with a nuptial gift and his satellites; the males in a group may be conspecifics or heterospecifics. Males that lose contests for nuptial gifts often become satellites of the contest winners whether or not winners are conspecific. Satellite males have statistically significantly greater FA than males with nuptial gifts in heterospecific male display groups. Satellite males mate infrequently and briefly compared to resource-holding males. Satellites of heterospecific males copulate with conspecific females displaced from nuptial gifts by the resource-holding males of the other species. In both species, the largest and smallest individuals have the greatest FA, and intermediate-sized individuals have the least; this same pattern often occurs in other animals.     

Foraging ability in the scorpionfly <Emphasis Type="Italic">Panorpa vulgaris</Emphasis>: individual differences and heritability

According to indicator models of sexual selection, mates may obtain indirect, i.e. genetic, benefits from choosing partners indicating high overall genetic quality by honest signals. In the scorpionfly Panorpa vulgaris, both sexes show mating preferences on the basis of the condition of the potential partners. Females prefer males that produce nuptial gifts (i.e. salivary secretions) during copulation, while males invest more nuptial gifts in females of high nutritional status. Both characters, males' ability to produce nuptial gifts and high nutritional status of females, are known to be reliable indicators of foraging ability. Thus, besides possible direct benefits, both sexes might also obtain indirect benefits in terms of “good foraging genes” by their choice and thereby increase the fitness of their offspring. A prerequisite for this possibility is the heritability of the respective trait. In the present study, we estimated the repeatability and the heritability of foraging ability. Our results indicate (1) a significant repeatability of individual foraging efficiencies in males and females and (2) a heritable component of this trait by a significant parent–offspring regression. These findings suggest that genetic benefits in terms of increased offspring foraging ability might contribute to selection for mating preferences in both sexes.     

Variation in male courtship costs in butterflies

A cost of mating is common to both sexes but has predominantly been examined in females. In species where males provide resources to females at copulation, male mating costs are expected to be high as nutrient provisioning enhancing female fecundity is assumed to carry costs. In addition, males frequently court females prior to mating, which is known to carry survival costs to both sexes. However, the magnitude and basis of variation in males’ mating costs remains largely unknown. Here, I examine the effect of nutrient provisioning and courtship on male longevity across full-sib families in the paternally investing green-veined white butterfly, Pieris napi. Copulating males suffered a survival cost as did courting males prevented from copulating, indicating the courtship component of mating is costly. Male P. napi release aphrodisiacs during courtship to promote mating, indicating that these compounds may also be costly to produce. Contrary to expectation, nutrient provisioning was not associated with reduced survival relative to males only allowed to court females, although it is possible that this could be masked by the potentially elevated courtship rates of courting males relative to mating males. Families differed in magnitude of reduced male survivorship, indicating a likely genetic basis to variation in costs of courtship and copulation. Male weight was unrelated to longevity and mating success, whereas longevity strongly influenced male mating success, indicating lifespan is an important male fitness trait in this species.     

Female sensory bias may allow honest chemical signaling by male Iberian rock lizards

Some mate choice theories propose that only male signals that are honest and condition-dependent can be stable, while another hypothesis states that males evolve signals that exploit the sensory system of females. However, sensory traps might evolve into honest signals if they are differentially costly for males. We tested whether a pre-existing sensory bias for food chemicals explained chemosensory preferences of female Iberian rock lizards for male scents. We manipulated hunger levels of females and found that food-deprived females had increased chemosensory responses to chemical stimuli from both invertebrate prey and femoral secretions of males, but not to control water. Further tests suggested that cholesta-5,7-dien-3-ol (provitamin D₃), a lipid found in both prey and males’ scent, may be one of the chemicals eliciting these responses. Moreover, hungry females spent more time on scent marks of males that had experimentally increased cholesta-5,7-dien-3-ol than on scent marks of males alone, whereas for control females this effect was not significant. We suggest that preexisting sensory bias for essential nutrients (i.e., provitamin D) may be the origin of similar female responses to male chemicals. However, previous studies have suggested that the allocation of these chemicals to ornaments is costly and only high quality males can afford it. Therefore, preexisting sensory bias for essential nutrients may further allow the evolution and maintenance of honest sexual displays.     

Mating effort and female receptivity: how do male guppies decide when to invest in sex?

Males vary in the degree to which they invest in mating. Several factors can explain this variation, including differences in males’ individual condition and the fact that males allocate their energy depending on the context they face in each mating attempt. Particularly, female quality affects male reproductive success. Here, we studied whether male guppies (Poecilia reticulata) strategically allocated more mating effort, in terms of mating behaviour and male–male competition, when they were matched with a receptive (R) female than a non-receptive one. In accordance with our prediction, we found that males increased their mating behaviour when they were with a receptive female. Even though male guppies can inseminate non-receptive females, we only found high levels of courtship between males that were with a receptive female rather than a non-receptive one. Although there was little affect of female receptivity on male–male competition, we found that males chased and interrupted courtships more with receptive females than with non-receptive females regardless of odour. Finally, we also studied whether the sexual pheromone produced by receptive female guppies is a cue that males use in order to increase their mating effort. We found that males were more attracted to a female when they perceived the sexual pheromone, but only increased their mating and aggressive behaviours when females showed receptive behaviour. This strategic increase in mating effort could result in higher male reproductive success because mating attempts towards receptive females are likely to be less costly and males could have a greater probability of fertilisation.     

The evolution of empty nuptial gifts in a dance fly, Empis snoddyi (Diptera: Empididae): bigger isn't always better

Adaptive female choice is thought to have led to the evolution of nutritionally valuable nuptial gifts in many insect species. However, in several dance fly species, males offer and females accept “empty gifts” with no nutritional value. In the species studied here, Empis snoddyi Steyskal, males produce empty balloons comprised of hundreds of silk bubbles and form mating swarms that females approach to investigate males. Males within the swarm engage in agonistic interactions. The empty balloon has been hypothesized to be an indicator of male condition such that males with larger balloons are predicted to have higher mating success and be more successful in male-male interactions than males with smaller balloons. We examined the role of male body size and balloon size in the context of intersexual and intrasexual selection. We found that neither male body size nor balloon size affected the outcome of pairwise male-male interactions. Using multiple-regression techniques, we found significant linear selection for increasing male body size and decreasing balloon size associated with mating success, a surprising result given a positive relationship between male body size and balloon size. A visualization of selection showed the highest peak of male mating success for larger males with intermediate-size balloons. These results can be explained by a trade-off between long-range attraction of females using large balloons and close-range attraction of females via improved flying efficiency associated with smaller balloons. Both male body size and balloon size are important components in determining male mating success; however, the empty balloon does not appear to play a typical role as a sexually selected ornament. Received: 29 December 1997 / Accepted after revision: 7 October 1998     

Female tactics to reduce sexual harassment in the Sumatran orangutan (Pongo pygmaeus abelii)

Orangutan males demonstrate intrasexual dimorphism with corresponding alternative mating strategies. Sexual harassment is the predominant feature of the mating strategy that subadult males pursue. This study investigated the countertactics that females employ to reduce sexual harassment by subadult males. I observed 207 copulations during more than 9,000 h of focal follows of wild Sumatran orangutans at the Suaq Balimbing Research Station over a 23-month period. Rates of copulations initiated by subadult males increased during months of high fruit abundance, and most mating attempts were directed toward females with weaned infants. Simultaneous harassment by multiple subadult males increased significantly during months of high fruit abundance, and nearly all adult female-adult male consortships occurred during periods of high fruit abundance. Females who maintained spatial association with adult males, either via consortship or by nonmating temporary parties, received lower rates of harassment, as measured by the success rate of subadult male mating attempts. Adult female-adult male parties did not always result in mating between the associating dyad. Female initiation of protective services by adult males is one social tactic that female orangutans employ to reduce sexual harassment. Females therefore receive direct services from adult males, which may be one factor that influences female mate choice in Sumatran orangutans.     

Male mate choice favors more colorful females in the gift-giving cabbage butterfly

While the phenomenon of male mate choice has attracted considerable attention in the last two decades, whether this sexual selection mechanism could drive the evolution of female ornaments remains poorly understood. Here, we used experimental manipulation of female wing coloration to investigate male mate choice in Pieris rapae, a gift-giving butterfly. Further, we tested whether males’ nutritional status influenced their mating preferences by subjecting larvae to short periods of starvation. We found that males showed significantly more mating approaches toward control females with more colorful wings (higher pteridine content), and that this preference was strongest in low-nutrition males. Additionally, a study of field-collected females revealed that pteridine-based wing coloration was positively correlated with female egg load, which suggests such ornaments may signal female quality. Pteridine-based ornaments are widespread in nature, however their potential as honest signals in male mate choice remains largely unexplored. This work furthers our understanding of how male mate choice and female ornamentation may evolve in species whose mating systems include nutritional nuptial gifts.     

Rhythmic male reproductive behavior controls timing of courtship and mating in Laupala cerasina

In many organisms, mating behavior occurs at a particular time of day, which may be important for avoiding mate competition or interspecific mating. Crickets of the Hawaiian genus Laupala exhibit an unusually protracted courtship in which males produce a series of nuptial gifts prior to the species-typical time of mating. Mating time is one of several rhythmic behaviors that have diverged among closely related Laupala species, which exhibit an extremely high speciation rate. Mating rhythm may reflect direct selection on male and/or female sexual receptivity or the pleiotropic consequence of selection on other rhythmic behaviors. To examine the role of sexual rhythmicity in Laupala cerasina, we characterized the time boundaries or “circadian gate” of courtship and mating, as well as female phonotactic response to male song. We also examined which sex is responsible for mating rhythmicity by phase-shifting males relative to the female photophase. Our results demonstrate that mating behavior is gated by the end of the light phase. Time limits to female mating receptivity were not observed and thus male rhythm alone appears to be responsible for the timing of mating. Furthermore, when courtship is initiated later in the day, males produce fewer nuptial gifts and increase nuptial gift production rate while delaying mating, suggesting that the number of gifts a female receives is important to male reproductive success.     

Bushcricket song as a clue for spermatophore size?

Bushcricket males of Poecilimon zimmeri transfer large and protein-rich spermatophores during mating, which females directly ingest. There is correlational evidence that heavier males transfer larger nuptial gifts. In no-choice mating trials, females mated randomly with respect to male’s body weight. In contrast, in two-choice mating trials, female bushcrickets exhibit clear choice for the heavier male. This heavier male advantage was also found in pre-mating choice during phonotaxis. With manipulated mute males, females mated at random with regard to body weight of the competitors. The number of physical encounters between a female and males was low in all tests with a single male (no choice) and greater in choice-tests with two competing males. The latencies to mate also differed significantly between treatments. The time mating pairs spent in precopula was short in experiments where the males could hear rivals and significantly longer in all other tests using either a single male or mute males. Thus, acoustic signalling in male bushcrickets seems to signal male body weight. A preference for heavier males may reflect a female’s preference for a larger spermatophore and therefore a greater direct benefit.     

Seasonal variation in male-female competition,cooperation and selfish hoarding in a monogamous songbird

Both cooperation and conflict between the sexes are commonplace in monogamous mating systems. However, little is known about how cooperation and competition varies seasonally in monogamous species that maintain permanent territories. We presented territorial pairs of male and female New Zealand robins (Petroica australis) with a large supply of insect prey at monthly intervals for 2 years. Behavioural observations after food presentation were then made to quantify seasonal and sexual differences in aggressive interactions over prey, prey acquisition rates, mate provisioning, offspring provisioning, selfish food hoarding and cache retrieval. Data were used to evaluate sex-specific behavioural strategies of mediating competition for food. Results showed that males aggressively excluded females from experimental food sources year-round. Females only accessed food sources when males left them unattended. Consequently, females acquired fewer prey than males. After controlling for differences in prey acquisition, both sexes consumed similar amounts of prey in the non-breeding season. Even though males aggressively excluded females from accessing food sources directly, males fed large amounts of prey to females during the breeding season. Both sexes provisioned young at similar rates. Males cached less prey than females in the breeding season but more prey than females in the non-breeding season. Females showed similar caching intensities year-round. Although males tried to defend their hoards, females frequently retrieved male-made caches. Overall, results showed that although New Zealand robins cooperate to raise offspring during the breeding season, conflict between the sexes occurs year-round. Males and females display different behavioural strategies to gain access to experimental food sources, which appear to lessen male–female competition for food and evenly distribute food resources between the sexes.     

Female seed beetles, <Emphasis Type="Italic">Callosobruchus maculatus,</Emphasis> remate for male-supplied water rather than ejaculate nutrition

Female seed beetles, Callosobruchus maculatus, mate multiply even though association with males and copulations carry costs, such as injury to the genital tract. Multiple mating (polyandry) may, however, offset these costs through the acquisition of food and water, two material benefits hypothesized to be obtained from the large ejaculates produced by males. The material benefits hypothesis can be tested by increasing female access to nutrients and water, with the prediction that female mating frequency will decrease as copulation is no longer required to derive these materials. Females were given water, 5% sugar–water or baker’s yeast, and were compared with females deprived of these. We presented females with virgin males daily for 8 days and recorded female mating frequency, survivorship, and fecundity. Females provided with water and sugar–water decreased mating frequency. Thus, water, rather than nutrients in the ejaculate, appears to be important to females of this species. In addition, both life span and fecundity were extended for females in the sugar–water and water treatments. Since water is scarce in the arid environment in which this species is found, we conclude that polyandry provides material benefits to females that may offset some of the costs of associating with males.     

Female encounter rates and fighting costs of males are associated with lek size in Drosophila mycetophaga

Male costs and benefits associated with male display size in field populations of an Australian lekking Drosophila species were examined. Results suggested that male mating success increased with display size, since matings appeared to be more common in large displays, and since the probability of males encountering a female increased as displays contained more males. Female encounter probabilities did not increase once about 20 males or more were present on a display. Male size and fighting costs tended to increase with display size. The distribution of males among displays did not follow the ideal free distribution in the sense that each male did not have equal mating opportunity per unit time. Deviation from an ideal free distribution may have been due to female preference for mating in aggregations rather than with solitary males, since in a field experiment females were more willing for mating in an aggregation of five males than with solitary males. Received: 22 May 1997 / Accepted after revision: 1 November 1997     

Reproductive trade-offs from mating with a successful male: the case of the tephritid fly Anastrepha obliqua

In lekking species, females may become sperm-limited when mating with sexually successful males, and this may be exacerbated by a poor male diet. Polygynous males may also be limited by the amount of accessory gland products (AGPs) they can transmit to females, which in turn may influence the females’ refractory period and longevity. Here, we tested the effect of male mating history, larval and adult diet on copula duration, mating intervals, female fecundity, fertilisation success, life span and likelihood to remate using sexually successful males of the lekking tephritid fly Anastrepha obliqua. Flies originated from either a native or exotic host fruit and were protein-fed or deprived. Male diet and larval host influenced copula duration, while the time elapsed between matings was affected by the interaction of mating order and male adult diet. Female fecundity was not influenced by female position in mating order or protein inclusion into the male diet. However, mating order and male larval diet influenced female fertilisation success. Importantly, as males mated successively they were less able to induce a refractory period on females, as the last females to mate with a male were more likely to remate and had slightly longer life spans than the first females to mate with males. These results might be attributed to a decrease in male AGPs with increasing male mating frequency. We discuss the role of conditional expression of male mating frequency with respect to A. obliqua’s life history, the trade-off that females face when mating with a successful male, the effect of larval diet on adult sexual performance and the possibility for sexual conflict to occur due to high male mating rates and fitness costs to females.