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.     

Impacts of environmental heterogeneity on alternative mating tactics in the threadtail damselfly

Environmental heterogeneity, including variation in the physical environment, may be key to understanding the evolution and maintenance of alternative mating tactics, but its influence is rarely examined. Males of the threadtail damselfly Protoneura amatoria reversibly use two alternative mating tactics (perching vs. hovering) and have previously been found to modulate their use of these tactics in response to variation in both light conditions and the density of ovipositing females. Here, I show that mating success payoffs of the two tactics are differentially influenced by these factors. The payoff of the perching tactic was greater than that of the hovering tactic under low light conditions and at low densities of ovipositing females. The payoff of the hovering tactic was greater under high light conditions and higher densities of ovipositing females. The differential success of the two mating tactics in response to light conditions is discussed in light of flight dynamics, vision, and predation.     

Mating in bighorn sheep: frequent male reproduction via a high-risk “unconventional” tactic

Rocky Mountain bighorn rams use three distinct tactics in competition for mates. Two tactics (tending and blocking) feature defense and cooperative mating over a relatively prolonged consort period (up to 3 days). In the coursing tactic, subordinate rams fight dominants for temporary copulatory access (lasting seconds) to defended ewes. By combining population-wide genetic (microsatellite) exclusion of paternity, behavioral data and a model of bighorn reproductive competition, we estimated that coursing rams fathered 44% of 142 lambs assigned paternity in two natural populations. In one population, the probability of successful defense against coursing was lowest among rams that had many female consorts and held highest dominance rank. Even so, per capita annual male reproductive success was positively associated with social rank in both herds when measured in terms of fall conceptions. The proportion of coursing versus defending ram matings in each population (0.36 and 0.39) was similar to the corresponding fraction of lambs (0.43 and 0.47) fathered by coursing rams, suggesting that sperm competition approximated a fair lottery. Male traits important in gaining social status and obtaining cooperative consorts with ewes were different and potentially in conflict with those needed to defend against (and practise) coursing. Although the concussive weapons (horns) of rams are less dangerous than, for example, the piercing weapons of other bovids, injury from falls and horn blows during coursing brawls may cause death, handicap future mating competition or increase the risk of predation. Coursing is a rare example of an unconventional alternative mating tactic that is high-gain and high-risk. Received: 17 April 1996 / Accepted after revision: 15 March 1997     

Sperm traits in the quacking frog (<Emphasis Type="Italic">Crinia georgiana</Emphasis>), a species with plastic alternative mating tactics

In species where males use alternative reproductive tactics and male phenotypes are confronted with different risks of sperm competition, theory predicts that between-male-type differences in sperm expenditure may evolve. In the frog Crinia georgiana big males can monopolize females, whereas small males often engage in polyandrous matings. Consequently, big males may experience a lower risk of sperm competition than do small males. We tested if the predictions from theoretical models can be applied to the mating system of C. georgiana. Our results showed that small males do not have larger testes relative to their body size compared to their larger counterparts and that the efficiency with which sperm number, size, motility, and longevity are produced by the testes does not differ between small and large males in the predicted way. These results are not in alignment with predictions from a loaded raffle model of sperm competition on sperm expenditure in males with alternative phenotypes. The plasticity in mating tactics used by C. georgiana males and a high intraseasonal variation in male densities may have prevented the evolution of enhanced sperm performance in smaller males. A fair raffle in the sperm competition game played by C. georgiana males could also explain the observed patterns in sperm traits. Future investigations determining the parameters responsible for the deviation from theoretical predictions in this system will test the degree to which current theoretical models can indeed be applied to species with plastic reproductive tactics.     

Female rock shrimp<Emphasis Type="Italic"> Rhynchocinetes typus</Emphasis> mate in rapid succession up a male dominance hierarchy

The dynamics of male-male competition for mates and patterns of female choice depend critically on the social environment. We released newly molted sexually receptive females of the rock shrimp Rhynchocinetes typus in the field and recorded their interactions with males. In the dense aggregations in which these shrimp live, most females were encountered and seized by males within 2 min. Usually, females were first seized by subordinate males, and subsequently taken over by the dominant males. Many females (17 out of 23) had multiple mates during the 10-min observation period, and most of them received spermatophores from multiple males. Males used different mating tactics in accordance with their dominance status: subordinate males often used the sneaking tactic, seizing the female and immediately transferring spermatophores. In contrast, all dominant males used the primary mating tactic; they seized and stimulated the female before transferring spermatophores. Results from previous studies had indicated that females may reduce the fertilization chances of subordinate males by delaying spawning and removing spermatophores. We suggest that this capability in combination with the observed rapid mate succession may enable females to exploit male contest behaviors.Communicated by P. Backwell     

Sex in the dark: determinants and consequences of mixed male mating tactics in<Emphasis Type="Italic"> Microcebus murinus</Emphasis>, a small solitary nocturnal primate

In mammals with solitary females, the potential for males to monopolize matings is relatively low, and scramble competition polygyny is presumed to be the predominant mating system. However, combinations of male traits and mating tactics within this type of polygyny have been described. The main aim of our study was to identify the relative importance of, and interactions among, potential determinants of contrasting male reproductive tactics, and to determine their consequences for male reproductive success in a small solitary nocturnal Malagasy primate, the gray mouse lemur (Microcebus murinus). We studied their mating behavior over three consecutive annual mating seasons. In addition, we determined the genetic relationships among more than 300 study animals to quantify the reproductive success of individual males. We found that, with a given relatively low overall monopolization potential, successful male mouse lemurs roamed extensively in search of mates, had superior finding ability and mated as early as possible. However, contest competition was important too, as temporary monopolization was also possible. Males exhibited different mating tactics, and heavier males had a higher reproductive success, although most litters had mixed paternities. Switching between tactics depended on short-term local variation in monopolization potential determined by a pronounced dynamic in fertilization probability, number of alternative mating opportunities, and the operational sex ratio. This study also revealed that the dynamics of these determinants, as well as the mutual interactions between them, necessitate a detailed knowledge of the mating behavior of a species to infer the impact of determinants of alternative mating tactics.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by S. AlbertsThis revised version was published online in August 2004 with corrections to Figure 2.     

Alternative mating tactics in dimorphic males of the harvestman <Emphasis Type="Italic">Longiperna concolor</Emphasis> (Arachnida: Opiliones)

Intense male–male competition for females may drive the evolution of male morphological dimorphism, which is frequently associated with alternative mating tactics. Using modern techniques for the detection of discontinuous allometries, we describe male dimorphism in the Neotropical harvestman Longiperna concolor, the males of which use their elongated, sexually dimorphic legs IV in fights for the possession of territories where females lay eggs. We also tested three predictions related to the existence of alternative mating tactics: (1) if individuals with relatively longer legs IV (majors) are more likely to monopolize access to reproductive resources, they are expected to remain close to stable groups of females more than individuals with relatively shorter legs IV (minors) do; (2) if minors achieve fertilization by moving between territories, they are expected to be less faithful to specific sites; and (3) majors should be observed in aggressive interactions more often. We individually marked all the individuals from a population of Longiperna during the reproductive season and recorded the location of each sighting for males and females as well as the identity of males involved in fights. Majors were more likely to have harems, and large majors were even more likely to do so. Majors were more philopatric and all males involved in fights belonged to this morph. These results strongly suggest that the mating tactic of the majors is based on resource defense whereas that of the minors probably relies on sneaking into the territories of the majors and furtively copulating with females.     

Operational sex ratio and alternative reproductive behaviours in the European bitterling,<Emphasis Type="Italic"> Rhodeus sericeus</Emphasis>

We investigated the effects of male population density and male-biased operational sex ratio (OSR) with constant and limited resource density on male mating tactics shown by a freshwater fish, the European bitterling, Rhodeus sericeus. This species spawns inside living unionid mussels. Large males defended territories and were aggressive towards conspecifics under equal sex ratios. They also monopolised pair spawnings with females, releasing 98% of all sperm clouds during mating. However, the mating tactic changed at high male density where large males ceased to be territorial and instead competed with groups of smaller males to release sperm when females spawned. Large, medium and small males now obtained 61%, 33%, and 6% of sperm releases respectively, thereby reducing the opportunity for sexual selection by half. Females spawned at equal rates in the two densities of males, despite lower courtship at high density. These results run counter to the usual expectation that an increasingly male-biased OSR should lead to higher variance in male mating success. Instead, the use of alternative reproductive behaviours by males can lead to lower resource competition and mating variance at high male densities.     

Male–male competition and alternative male mating tactics influence female behavior and fertility in Japanese medaka (Oryzias latipes)

Intense male–male competition driven by high male density during mating can result in the evolution of alternative mating tactics that increase male fertilization success. The effects of alternative male mating tactics on females can range from increased fertilization and genetic benefits to decreased fertilization and loss of paternal care. However, the influence of male competitive behavior and alternative mating tactics on female behavior and reproductive success has seldom been addressed. In this work, I investigated the occurrence of alternative male mating tactics and their potential influence on female behavior and fertilization success in Japanese medaka (Oryzias latipes). Groups of one, two, or four males competed for access to a female in a repeated-measures experiment. Male density had a significant influence on female reproductive output as a result of a change in competitive mode from contest to scramble competition that coincided with more disruption during mating when more than one male attempted to mate. By contrast, sneaking during mating was beneficial to males, as more than one male sired offspring in most spawnings involving sneaker males. These results suggest that there may be conflict between males and females over mating, such that females are detrimentally affected by the occurrence of alternative mating tactics, whereas males may benefit from sneak mating. The occurrence of conflict between the sexes can be related to ecological factors, such as male density, which cause behavioral change in both males and females.     

Sex,food and conflicts: nutrition dependent nuptial feeding and pre-mating struggles in scorpionflies

Female and male reproductive interests often differ. In species in which matings are accompanied by a transfer of resources valuable for both participants, such as nuptial prey gifts, conflicts may readily occur. Scorpionflies may use alternative mating tactics. One is to offer a prey item (dead arthropod) to females in exchange for mating. This prey gift tactic includes a conflict because a male must decide on whether to offer the gift rather than to fight the female and consume the gift. The outcome may depend on the nutritional status of both males and females. Males may be more willing to give if they themselves are satiated and the condition of the females may influence the payoff from the males’ investment. Similarly, females may be more willing to accept food gifts if they are in poor nutritional condition. In this study of the scorpionfly Panorpa cognata, I experimentally manipulated the feeding history of both males and females. I observed the outcome of the direct interactions that followed when males that were holding prey were approached by females. I found that well-fed males offered the food gift sooner than males in poor nutritional condition that fed extensively on the food item before offering. Female condition had no significant influence on whether prey items were offered by males or accepted by females. I also found that well-fed males rarely searched for prey to pursue the prey gift tactic in courtship. Thus, the prey tactic does not seem to be the males’ first option.     

Family-related differences in social foraging tactic use in the zebra finch (Taeniopygia guttata)

When animals forage in groups, they can search for food themselves (producer tactic), or they can search for opportunities to exploit the food discoveries of others (scrounger tactic). Both theoretical and empirical work have shown that group-level use of these alternative tactics is influenced by environmental conditions including group size and food distribution, and individual tactic use can be influenced by several measures of individual state, including body condition. Because body condition has been shown to be heritable for various species, social foraging tactics may also be heritable. We looked for evidence of heritability in social foraging tactic use in the zebra finch (Taeniopygia guttata) by testing whether: (1) natural variation in body condition correlates with tactic use, (2) there are family-related differences in body condition, and (3) there are family-related differences in observed tactic use. Tactic use in the zebra finch was significantly related to body condition; individuals with lower body condition scores had a significantly higher use of the scrounger tactic as predicted from variance-sensitive producer–scrounger models. Body-condition scores differed significantly between families, suggesting that this aspect of individual state may have a heritable component. Finally, we recorded significant family-related differences in the use of producer and scrounger alternatives. These results are consistent with heritability in observed tactic use resulting from an inheritance of individual state, in this case body condition, which itself influences tactic use. Understanding how and why individuals differ in their use of alternative tactics is fundamental as it may provide important insights into inter-individual variation in fitness.     

Polyandry and enhanced reproductive success in the harlequin-beetle-riding pseudoscorpion

The growing molecular evidence that females of many species mate with several males calls for a critical reassessment of the selective forces which act to shape female mating tactics. In natural populations of the harlequin-beetle-riding pseudoscorpion, Cordylochernes scorpioides, females are polyandrous and typically produce mixed-paternity broods. Laboratory behavioral analyses and breeding experiments indicate that polyandry in this pseudoscorpion is an active strategy which increases female reproductive success. Females restricted to mating with a single male experienced a higher rate of embryo failure and produced significantly fewer offspring than either females mated to more than one male in the laboratory or females naturally inseminated in the field. Forced copulation, insufficient sperm from a single mating, male nutrient donations and variation in inherent male genetic quality cannot explain the greater number of nymphs hatched by polyandrous females in this study. Evidence suggests that, by mating with several males, C. scorpioides females may exploit postcopulatory mechanisms for reducing the risk and/or cost of embryo failure resulting from fertilization by genetically incompatible sperm. Received: 5 May 1996 / Accepted after revision: 16 October 1996     

Food abundance affects energy intake and reproduction in frugivorous female Assamese macaques

In most mammals, female fertility and reproduction are strongly influenced by nutritional status and, therefore, by foraging conditions. Here, we investigate the relationship between food resources, feeding competition, energy intake and reproduction in a group of wild female Assamese macaques (Macaca assamensis) in northeastern Thailand. Over 2,100 h of data on feeding behaviour, energy intake and activity budgets were combined with data on resource characteristics, female reproduction and physical condition. We found that an increase in food availability had a positive effect on female energy intake and conception rates. In addition, it appeared that females incurred energetic costs during lactation and that females with a better physical condition during the mating season were more likely to conceive. The annual birth season occurred a few months before the annual peak in food availability, causing peak lactation to coincide with a period of high food availability. This suggests that females use the increased food abundance to compensate for the energetic costs of lactation. Neither energy intake rates nor activity budgets were influenced by female dominance rank, even during periods when the levels of contest competition were predicted to be high. In line with this, we found no evidence for rank-related differences in reproduction. The apparently limited influence of feeding competition in female Assamese macaques adds to the debate on the extent to which patterns in feeding competition and fitness can reliably be predicted based on ecological conditions. We suggest that this may partially be resolved by including potential competition-reducing mechanisms into the predictive framework.     

Differences in abalone growth and morphology between locations with high and low food availability: morphologically fixed or plastic traits?

Many species of sedentary marine invertebrates exhibit large spatial variation in their morphology, which allow them to occupy a broad geographic distribution and range of environmental conditions. However, the detection of differences in morphology amongst variable environments cannot determine whether these differences represent a plastic response to the local environment, or whether morphology is genetically fixed. We used a reciprocal transplant experiment to test whether ‘stunted’ blacklip abalone (Haliotis rubra) are the result of a plastic response to the environment or fixed genetic trait. Furthermore, we related environmental factors, that affect food availability (density of abalone, water movement, algal cover and reef topography), to differences in growth and morphology. Morphological plasticity was confirmed as the mechanism causing morphological variation in H. rubra. Individuals transplanted to sites with ‘non-stunted’ H. rubra grew significantly faster when compared to stunted controls, whilst individuals transplanted to stunted sites grew significantly slower compared to non-stunted controls. The growth response was greater for individuals transplanted from ‘non-stunted’ to ‘stunted’ sites, suggesting that the environmental stressors in morphologically ‘stunted’ habitat are stronger compared to locations of faster growing morphology. We propose that these differences are related to resource availability whereby low algal cover and topographic simplicity results in stunted populations, whereas high algal abundance and topographic complexity results in non-stunted populations.     

Male-male interference competition decreases spawning rate in the European bitterling (<Emphasis Type="Italic">Rhodeus sericeus</Emphasis>)

We investigated the consequences of male-male interference competition associated with alternative male mating tactics in a freshwater fish, the European bitterling (Rhodeus sericeus). Male bitterling defend territories around living mussels and attract females to lay their eggs in the gill cavities of mussels. We experimentally manipulated spawning-site abundance and male density at two spatial scales. We showed that the total number of eggs spawned by females was constrained by the number of mussels available for oviposition. The effect was mediated by behavioral interactions among competing males because of variation in the Operational Sex Ratio (OSR) in close proximity to a mussel and not by a direct limitation in mussel capacity to accommodate the eggs. Both total and local male densities affected spawning behavior, and interacted in their effect on female spawning rate. Territorial male aggression caused courtship interruptions that prolonged the time until successful spawning and increased with male density. However, territoriality broke down at the highest male density, with a consequent stabilizing effect on spawning rate.Communicated by J. Krause     

Quantifying male attractiveness and mating behaviour through phenotypic size manipulation in the Trinidadian guppy, Poecilia reticulata

Although many studies have examined the effects of male size on attractiveness and mating behaviour, few have taken genetic background into consideration. Phenotypic manipulation permits the experimental adjustment of morphological traits while keeping genetic background constant. Here, male guppies, Poecilia reticulata, an ideal model for this type of manipulation, were raised at different temperatures to produce sibling pairs that differed in size. These were then used to investigate male mating behaviour and male attractiveness, assessed through female mate choice, in relation to this size dimorphism. Further, male–male competition, which is intrinsic to male mating behaviour, is also likely to be affected by their size. Through the use of repeated measures analyses we demonstrate that females significantly prefer larger males and male size and competition significantly affect several aspects of male mating behaviour. Larger siblings perform more sneaky mating attempts and spend more time chasing females. The frequencies of both these behaviours increase with competition. While display frequency is unaffected by male size and competition, display duration and the amount of time spent attending females are reduced in the presence of competitors. This study highlights the use of phenotypic manipulation as a valuable tool for investigating behavioural interactions and confirms that both male size and competition are significant factors in the guppy mating system.     

Frequency-dependent male mate harassment and intra-specific variation in its avoidance by females of the damselfly Ischnura elegans

We focused on male harassment on different female color morphs of the damselfly Ischnura elegans and on variation in morph-specific mating avoidance tactics by females. In I. elegans, one of the female morphs is colored like the conspecific male (andromorphs) while the other morphs are not (gynomorphs). Our first goal was to quantify morph-specific male mating attempts, hence male harassment, in populations with manipulated population parameters (densities, sex ratios, and proportion of andromorphs). Second, we examined the female's perspective by looking for potential differences in morph-specific mating avoidance tactics and success of those tactics in a natural population. Differences in population conditions did influence the number of male mating attempts per morph. The less frequent female morph was always subject to fewer mating attempts, which contradicts earlier hypotheses on mimicry, but supports those that assume that males learn to recognize female morphs. Gynomorphs occupy less open habitat and often fly away when a male approaches, while andromorphs use more open habitat, do not fly large distances and directly face approaching males. Female morphs did not differ in the proportion of successful mating-avoidance attempts. Our results suggest that the maintenance of the color polymorphism is most probably the result of interactive selective forces depending on variation in all population conditions, instead of solely density- or frequency-dependent selection within populations.     

Mating behavior of <Emphasis Type="Italic">Abdopus aculeatus</Emphasis> (d’Orbigny 1834) (Cephalopoda: Octopodidae) in the wild

The mating system of Abdopus aculeatus incorporates sneaker matings, mate guarding, sex-specific body patterns, frequent copulations, and male–male competition for mates, making it more similar to that of aggregating decapod cephalopods than any previously known octopus social system. Large male–female A. aculeatus occupy ‘Adjacent’ (G_A) dens and copulate frequently in mate-guarding situations over successive days. Nearby individuals copulate in ‘Temporary guarding’ (G_T) and ‘Transient’ (T; non-guarding) situations, the latter of which can involve ‘Sneaker’ (S) mating. In a focal animal study of these octopuses in the wild (Sulawesi, Indonesia) we addressed the hypotheses that they demonstrate: (1) precopulatory mate choice, (2) differential copulation rates by individuals employing different mating tactics, and (3) distant sex identification. We quantified daily copulation rates of A. aculeatus of reproductive size as well as aspects of copulation duration, display, mate-competition, and mate rejection. Mating tactic correlated with daily copulation rates. ♂G_A spent significantly more time copulating than did ♂T, while ♀G_A spent more than twice as much time per day in copula than did other females. Sneaker copulations lasted longer than those by males adopting other tactics. Mate-guarding was an effective and important tactic used by males to temporarily monopolize mating with apparently non-selective females. Males demonstrated clear pre-copulatory mate choice by guarding and mating repeatedly with large females (typically ♀G_A). While foraging alone away from the den, ♂G procured ‘Transient’ copulations with unguarded females. However, mate-guarding reduced the amount of time ♂G were alone and may impede their ability to seek out new mates. Low-copulation rates by ♀T, the smallest female tactic on average, may reflect this trade-off between mate preference and mate-searching by males, or non-receptivity of some females. A male-typical body pattern (black and white stripes) appeared to facilitate distant sex identification. Although mating and aggression were often initiated before contact between individuals, same-sex copulations and intense male–female aggression were rare. By contrast frequent male–female copulations and intense male–male aggression were consistent behavioral components of mating in A. aculeatus at these sites. Because the behavioral and ecological characters conducive to this complex system are not exclusive to A. aculeatus, it is possible that other octopuses exhibit some or all of these behaviors. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Polyandrous mating in treetops: how male competition and female choice interact to determine an unusual carnivore mating system

The diversity of mammalian mating systems is primarily shaped by sex-specific reproductive strategies. In the present study, we explored determinants and consequences of a unique mating system exhibited by fossas (Cryptoprocta ferox), the largest Malagasy carnivore, where females mate polyandrously on traditional mating trees, and males exhibit intrasexual size dimorphism. Males face both contest and scramble competition, and inter-sexual size dimorphism can be pronounced, but its magnitude depends on the male morph. Using a continuous behavioral observation of six estrous females over 4 years, we investigated correlates of male contest competition and female choice based on 316 copulations. Furthermore, we assessed correlates of male scramble competition based on testes size and movement data obtained from GPS tracking. We found that females dominated males regardless of their smaller size and that females actively solicited copulations. Heavy males had highest mating success during the female’s peak mating activity, but were discriminated against afterwards. Female choice and male–male competition thus converged to generate a mating advantage for heavier males. Our results suggest that females actively seek polyandrous matings, presumably for indirect genetic benefits. Since body mass is the major determinant of male mating success and is at the same time dependent on the degree of sociality and associated hunting mode of the respective male morph, a male’s feeding ecology is likely to influence its reproductive tactic. A combination of benefits from female polyandry and the consequences of different subsistence strategies may thus ultimately explain this unusual mating system.     

Alternative mating tactics in the Italian treefrog, <Emphasis Type="Italic">Hyla intermedia</Emphasis>

As in many lekking anurans, Italian treefrog males use two mating tactics: they can attract females by calling vigorously or be satellites, that is, they can remain silent in proximity of a calling male and try to intercept females attracted by their neighbour. We investigated the factors that affected the expression of this mating tactic. Consistent with the conditional mating tactic hypothesis, satellites were smaller than average and smaller than their parasitised calling males. They spent a larger-than-average number of nights at the breeding site, where most of them were also observed calling. Moreover, satellites showed lower call rates and lower mating success than those of males they parasitise but not lower than those of males they did not parasitise. Overall, these results, together with those derived from the analyses of the seasonal and spatial distribution of males, provide evidence for a non-random association between satellites and calling males and are consistent with the hypothesis that satellites have spectral and temporal acoustic preferences that parallel those of females. By adopting the less-successful satellite mating tactic, competitively inferior males can nevertheless maximise their potential reproductive fitness by sexually parasitising the most attractive chorusing males.