Elaborate secondary sexual traits offset the costs that they impose on their bearer by facilitating reproductive benefits, through increased success in intrasexual contests or increased ...attractiveness to choosy mates. Some traits enhance both strategies. Conversely, I show that spotted bowerbirds Chlamydera maculata may face a trade-off. The trait that best predicts their mating success, numbers of Solanum berries exhibited on a bower, also provokes increased intrasexual aggression in the form of bower destructions by neighbouring bower owners, which reduce the quality of the male's bower. At natural berry numbers, levels of mating success in the population are skewed, but levels of destruction do not vary with berry number. When berry numbers are artificially exaggerated, increased levels of destructions occur, but mating success does not increase. When offered excess berries, either to add to the bower or artificially placed on the bower, bower owners preferred to use numbers of berries related to the number that they displayed naturally. This decision is made without direct experience of the attendant changes in destruction or mating success. This indicates that bower owners may assess their own social standing in relation to their neighbours and modulate their display accordingly.
Male
Callinectes sapidus allowed complete recovery of sperm resources and then mated a single time had significantly lower
vas deferens weight than males allowed complete recovery of sperm resources ...but prevented from mating. In laboratory experiments, when a recently mated male (having low sperm volume) competed with a male that had not recently mated (having high sperm volume) for a single pubertal female, the female was just as likely to initiate pairing with the recently mated male as with a male that had not recently mated, despite possible reduction in her fertilization potential. At the end of trials in which stable pair formation occurred, recently mated males were paired significantly more often than males that had not recently mated. The combined effects of the lack of mate choice by females and high mating frequency of some males may result in many females in the population receiving low quantities of sperm.
BACKGROUND: The outcome of male-male competition can be predicted from the relative fighting qualities of the opponents, which often depend on their age. In insects, freshly emerged and still ...sexually inactive males are morphologically indistinct from older, sexually active males. These young inactive males may thus be easy targets for older males if they cannot conceal themselves from their attacks. The ant Cardiocondyla obscurior is characterised by lethal fighting between wingless (“ergatoid”) males. Here, we analyse for how long young males are defenceless after eclosion, and how early adult males can detect the presence of rival males. RESULTS: We found that old ergatoid males consistently won fights against ergatoid males younger than two days. Old males did not differentiate between different types of unpigmented pupae several days before emergence, but had more frequent contact to ready-to-eclose pupae of female sexuals and winged males than of workers and ergatoid males. In rare cases, old ergatoid males displayed alleviated biting of pigmented ergatoid male pupae shortly before adult eclosion, as well as copulation attempts to dark pupae of female sexuals and winged males. Ergatoid male behaviour may be promoted by a closer similarity of the chemical profile of ready-to-eclose pupae to the profile of adults than that of young pupae several days prior to emergence. CONCLUSION: Young ergatoid males of C. obscurior would benefit greatly by hiding their identity from older, resident males, as they are highly vulnerable during the first two days of their adult lives. In contrast to the winged males of the same species, which are able to prevent ergatoid male attacks by chemical female mimicry, young ergatoids do not seem to be able to produce a protective chemical profile. Conflicts in male-male competition between ergatoid males of different age thus seem to be resolved in favour of the older males. This might represent selection at the colony level rather than the individual level.
Orb-weaving spiders of the genus Nephila are notable for their sexual size dimorphism, with dwarf males and giant females. However, less well known is the extreme size polymorphism of males that is ...characteristic of some species. For example, adult male body size in N. edulis varies by an order of magnitude. Previous experiments reveal that male mating behaviour covaries with body size, suggesting the size variation is maintained by opposing pre- and post-insemination sexual selection pressures. Here, we test this idea by allowing males of different sizes to compete directly and simultaneously for access to females. Using the sterile-male technique for paternity assessment, we show that two competing males drawn from the extremes of size variations, split paternity the same way as two males of the same size drawn from the intermediate sizes. The paternity of a large male dropped from 50% to 30% on average if he competed against two instead of one small male. The large male increased his mating frequency when there were more rivals but required a much lower total duration of copulation to achieve the same paternity share. These data are consistent with the idea that opposing pre- and post-insemination selection pressures at least partly explain the variation in male body size.PUBLICATION ABSTRACT
The mbuna cichlids of Lake Malawi are a diverse, monophyletic, and recently derived clade. Sexual selection is thought to have accelerated their rapid diversification, though the mechanism by which ...this has occurred remains unknown. In this study, we examine the effect that male–male interactions have on female preference. We first used a short interaction experiment as a proxy for male dominance. We then measured female preference for (1) a single, isolated male; (2) a group of three, highly ranked males, relative to a group of lower ranked males; and (3) a group of three, mixed-ranked males against a similar group of mixed-rank males. We found that male dominance was highly correlated with male standard length. Female preference for male standard length and for dominance rank was significant in both isolated and group interactions. However, females only showed preference for groups of interacting males when males were segregated by dominance rank, not when groups were composed of both dominant and subordinate males. The results suggest that male–male contests influence female mating decisions. By investigating the rules that dictate the outcomes of such interactions we can elucidate the role that behavior plays in the diversification of this species-rich lineage.
For several decades, behavioral ecologists have studied the effects of the environment on the behavior of individuals; but only fairly recently they have started to ask the reverse question: how do ...the behavioral strategies of individuals affect the composition and dynamics of populations and communities? Although intuitively obvious, this feedback from individual to higher levels is difficult to demonstrate, except in systems with exceptionally fast and marked responses of the populations to the behavior of its members. Such a system exists in sperm-dependent species. In European water frogs, for instance, successful reproduction of a hybrid species (R. esculenta, genotype LR) requires mating with one of its parental species (R. lessonae, genotype LL), except in the rare cases where hybrids are triploid. The sexual host LL, however, should avoid matings with the sexual parasite LR, because the resulting LR offspring will eliminate the L genome from their germ line. In this study we investigate how this conflict is solved. Since water frog hybrids come in both sexes, rather than as females only like in other sperm-dependent systems, we performed the tests with both females and males. One individual was given a choice between two individuals of the opposite sex, one an LL and the other an LR. In both species, females showed the predicted preference for LL males, whereas males did not discriminate between LL and LR females. On the individual level, we interpret the sex difference in choosiness by the lower costs from mating with the wrong species (LR) and the higher benefits from mating with large individuals in males than in females. In “normal” species, male preference for large (i.e. more fecund) females is advantageous, but in this system such a choice can result in mating with the larger LR females. With respect to the structure and dynamics of mixed populations, we discuss that the observed female preference is consistent with the higher mating success of LL males found in nature. Hence, mate female choice is a strong candidate for a mechanism promoting coexistence of the sperm-dependent hybrid and its sexual host. This confirms predictions from previous theoretical models.
It is becoming increasingly clear that mate preferences are not static, but can vary as a function of ecological conditions and the state of the choosing individual. This applies not only to females, ...the sex that has usually been the subject in research on mate preferences, but also to males. Under certain conditions, males should be selective in their choice of breeding partner. In the two-spotted goby, Gobiusculus flavescens, a small marine fish, breeding females develop conspicuous yellow-orange bellies, which they actively display to males during courtship. We have recently shown that males prefer more colourful females as mates. In this study, we test if the size of a male affects his preference for colourful females. Using three-compartment mate-choice aquaria, we recorded the interest shown by a male in two females differing in coloration but similar in size. Large and small males were equally eager to court females, but only large males showed a greater interest in the more colourful females. We suggest that small males are unselective because they usually obtain few mating opportunities, as a result of being unsuccessful in mate attraction or male contest competition. This study provides the first demonstration that the size of a male affects his preference for female colour.
Hybridization is a widespread phenomenon in many vertebrate groups. Prezygotic isolating mechanisms, probably caused by selection against hybrids with reduced fitness, reduce the likelihood of such ...events. Although hybrid-reduced fitness relatively to parental species is common, hybridization can also be beneficial, and hybrids sometimes outperform the pure species type. In this study, we examined two potential processes, Hubbs's principle and male-male competition, which could enhance hybridization in the waterfrog complex and thus explain the proportion of heterospecific pairs collected in a natural pond. Firstly, by collecting 791 frogs in the field to study pair and chorus composition, we showed that in a mixed Rana lessonae-Rana esculenta population, the scarcity of hybrid R. esculenta males did not account for the proportion of heterospecific pairs: indeed, when examining pairing composition in six different choruses, we found that hybrid males were always under-represented and that R. esculenta females were found paired with R. lessonae males. Secondly, we investigated experimentally whether or nor male-male competition mechanism could explain pair formation in waterfrogs. Our mating speed experiment highlights mechanisms that could explain heterospecific pairs in a context of promiscuous mating where scramble competition was intense. To measure the rapidity with which a male grasps a female, we placed males in a grid cage with a female, and the dynamics of pair formation was monitored. R. esculenta males showed a lower pairing success than R. lessonae males as a smaller proportion of them amplexed females, and more time was needed for them to get amplexed. Thus, a less adaptative mechanism than female mate choice may also explain the mating pattern observed in waterfrog species.
The effect of host size on male fitness was tested in the parasitoid wasp
Dinarmus basalis (Hymenoptera, Pteromalidae) using hosts of different fresh weight. Fitness was measured as the sperm stock ...in seminal vesicles, and the ability to access females in single or competition situations. Both body size and sperm in seminal vesicles increased with host fresh weight. Males from small hosts had a reduced size and sperm stock compared to those from larger hosts. In single situations, males from both small and large hosts had similar reproductive capacities, whereas in multiple mating or competition situations, males from small hosts were at a disadvantage, inseminating fewer females and copulating less frequently. However, females did not appear to choose between males, and no effect on sperm stored in the spermatheca was observed. Being small does not prevent a
D. basalis male mating and producing progeny in single situations, although more offspring could be expected from larger males because of their better competitive abilities.
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