Female mate assessment and choice behavior affect the frequency of alternative male mating tactics

Explanations for the existence of alternative male mating tacticsfocus primarily on male–male competition. Mating systems,however, are composed of interactions both within and betweenthe sexes, and the role of female behavior in shaping male matingtactics should not be overlooked. By using a dynamic state variablegame model, I examine how female mate assessment and choicebehavior affect the frequency of alternative male mating tactics.When females can accurately assess the quality of males, onlymales with high quality are likely to be chosen as mates, andthus, lower-quality males gain little fitness from courtingfemales. This leads lower-quality males to switch to an alternativemating tactic that attempts to circumvent female mate choice.In contrast, if the abilities of females to accurately assessmales are constrained by assessment costs, imperfect information,or time constraints, or if the pool of available males is smaller,then lower-quality males are increasingly chosen as mates andthey less often use alternative mating tactics. Thus, femalebehavior shapes the frequency of alternative male mating tactics.A consequence of this game between the sexes is that male behavior(i.e., increased alternative mating tactics) decreases the benefitsfemales might otherwise gain from lower assessment costs, clearersignals of male quality, more time to choose a male, and moremales from which to choose a mate.     

No evidence for inbreeding avoidance through postcopulatory mechanisms in the black field cricket, Teleogryllus commodus

Several studies suggest that females mate multiply so that they can preferentially fertilize eggs with the sperm of genetically more compatible males. Unrelated males are expected to be genetically more compatible with a female than her close relatives. We tested whether black field crickets, Teleogryllus commodus, can bias sperm usage toward unrelated males by comparing egg hatching success of females mated to two of their siblings (SS), two sibling males unrelated to the female (NN) or to one unrelated male and a sibling male (NS or SN). Egg hatching success was highly repeatable. Hatching success varied significantly among females of the three mating types (P = 0.011, n = 245 females). The estimated mean hatching success of 36.8% for SS females was significantly less that the 43.4% of NN females, indicating an effect of inbreeding on hatching success. If females preferentially use the sperm of a less closely related male, the hatching success of NS/SN females should be closer to 43.4% than 36.8%. It was, in fact, only 34.9%. This does not differ significantly from the value expected if the two males contributed an equal amount of sperm that was then used randomly. Although polyandry may confer indirect genetic benefits, our results provide no evidence that female T. commodus gain these benefits by biasing paternity toward genetically more compatible males through postcopulatory mechanisms.     

Parasites make male pipefish careless

Parasite-mediated sexual selection is expected to favour the avoidance of matings with infected individuals. However, the extent to which the costs and benefits of discriminating against parasitized mates trade off may depend upon numerous factors. I investigated the effects of sex and infection status on choosiness in sex-role reversed deep-snouted pipefish (Syngnathus typhle L.) that were either artificially infected with the trematode parasite Cryptocotyle sp. or sham-infected. Sham-infected males were significantly more likely to associate with a sham-infected female rather than with a Cryptocotyle-infected female. Infected males failed to discriminate against infected potential partners. Males were choosier the larger they were relative to the females available for choice. Females were not discriminatory, regardless of their infection status. Given an inverse relation between female fecundity and parasite load, choosy unparasitized males may gain enhanced reproductive success from their choice decisions. In contrast, more heavily infected wild-caught males gave birth to slightly fewer, but not smaller offspring than did uninfected or lightly infected males, suggesting only a low direct premium on choosy females. The detrimental effects of parasitism on male choosiness, and the lack of female discrimination against infected males likely have profound repercussions on the strength of sexual selection acting on the two sexes and on the dynamics of host-parasite interactions in this system.     

Mutation and sexual selection: a test using barn swallows from Chernobyl

Abstract Secondary sexual characters have been hypothesized to be particularly susceptible to the deleterious effects of mutation because the expression of such characters is usually influenced by many more metabolic pathways than are ordinary morphological characters. We tested this hypothesis using the elevated mutation rates in the barn swallow ( Hirundo rustica ) of the Chernobyl region of Ukraine as a model system. A great deal is known about the relative importance of different characters for male mating success in this species. The importance of phenotypic characters for male mating success was quantified based on a long-term study of a Danish breeding population, by expressing phenotypic differences between mated and unmated males as the difference between log-transformed mean values. For field samples from Ukraine we likewise expressed the difference in male phenotype between individuals living in a relatively uncontaminated area and individuals from the Chernobyl region as the difference between log-transformed mean values. The standardized difference in male phenotype between the two regions in Ukraine for the 41 different characters was strongly positively correlated with the standardized difference in male phenotype between mated and unmated males from Denmark. The standardized difference in male phenotype between the two regions in Ukraine was significantly positively associated with sexual size dimorphism. However, the standardized difference in male phenotype between mated and unmated males was a much better predictor of standardized difference in male phenotype between the two regions in Ukraine than was the standardized difference in sexual size dimorphism, expressed as the difference between log-transformed mean values for males and females. These findings are consistent with the hypothesis that traits most important for sexual selection are particularly susceptible to the effects of deleterious mutations.     

Reproductive and subsocial behaviour in the ovoviviparous leaf beetle Gonioctena sibirica (Coleoptera: Chrysomelidae)

Abstract.

• 1 In the spring, females of the leaf beetle Gonioctena sibirica deposited larvae on the ventral surface of growing young leaves situated on the apical position of shoots of the willow Salix bakko.
• 2 The parent females remained with the larvae usually on the underside of the basal part of leaves, facing toward the base of shoots. When other arthropods approached, the females temporarily moved towards these intruders, showing aggressive behaviour such as swinging the body or stamping the legs. Many females remained with their larvae until the larvae grew into the final (fourth) instar. No female produced an additional brood in the field.
• 3 Broods from which parent females were experimentally removed suffered higher mortality than those in which females were left intact. Arthropods such as spiders and ants were observed preying on the larvae. In contrast, the survivorship of broods from which females were removed and intruders were excluded with a sticky substance applied to the base of twigs was not different from that of control broods. These results demonstrate that the main mortality factor of offspring is pedestrian arthropod predators and females physically repel the predators.
• 4 Potentially alternative reproductive strategies, such as producing a large number of offspring by iteroparity and/or larger brood(s) with less or no care, seem to be inhibited in G.sibirica by larval dependence on growing young leaves which are temporally limited and by ovoviviparity which may have limited brood size.

     

Sex differences in the drivers of reproductive skew in a cooperative breeder

Many cooperatively breeding societies are characterized by high reproductive skew, such that some socially dominant individuals breed, while socially subordinate individuals provide help. Inbreeding avoidance serves as a source of reproductive skew in many high‐skew societies, but few empirical studies have examined sources of skew operating alongside inbreeding avoidance or compared individual attempts to reproduce (reproductive competition) with individual reproductive success. Here, we use long‐term genetic and observational data to examine factors affecting reproductive skew in the high‐skew cooperatively breeding southern pied babbler (Turdoides bicolor). When subordinates can breed, skew remains high, suggesting factors additional to inbreeding avoidance drive skew. Subordinate females are more likely to compete to breed when older or when ecological constraints on dispersal are high, but heavy subordinate females are more likely to successfully breed. Subordinate males are more likely to compete when they are older, during high ecological constraints, or when they are related to the dominant male, but only the presence of within‐group unrelated subordinate females predicts subordinate male breeding success. Reproductive skew is not driven by reproductive effort, but by forces such as intrinsic physical limitations and intrasexual conflict (for females) or female mate choice, male mate‐guarding and potentially reproductive restraint (for males). Ecological conditions or “outside options” affect the occurrence of reproductive conflict, supporting predictions of recent synthetic skew models. Inbreeding avoidance together with competition for access to reproduction may generate high skew in animal societies, and disparate processes may be operating to maintain male vs. female reproductive skew in the same species.     

Patterns of fluctuating asymmetry in sexual ornaments predict female choice

Extravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U-shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U-shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes.