Prostephanus truncatus mate choice on contact: does pheromone signalling by males affect their mating success?

Prostephanus truncatus is an economically important beetle pest of stored maize and cassava in the tropics. Male beetles signal using an aggregation pheromone that attracts both female and male beetles over large distances. Females preferentially orientate towards the pheromone signals of particular males when given a choice. The influence of pheromone signalling on courtship and mating success was investigated using pheromone biossays and mating trials in both of which a female made a choice between two males. Signalling was manipulated by exposing males to a Female Factor that inhibits pheromone production. The relative attractiveness of males to females based on pheromone bioassays was found not to influence short-range courtship behaviour or mating success.     

Male pipefish prefer dominant over attractive females

Animals may obtain information guiding their choice betweenpotential partners from observing competitive interactionsand displays between them, or from displays directed at thechoosing individual. In the sex-role reversed pipefish Syngnathustyphle females display a temporary ornament (a color pattern)to other females as well as to males. We have previously shown that display of female ornaments per se is attractive to males.Here we show that information from competitive displays canoverride such direct attraction displays as signals in thepartner choice process. In a mate choice experiment, an enclosedmale could choose between two females. On the first experimentalday, females could interact freely, while on the second daythey were isolated from each other. When female-female competitionwas allowed, the ornament display was directed more to theother female than to the male: Time competing, rather thantime courting the male, correlated with ornament display duration.However, ornament display under competition and ornament displayin the absence of competition did not correlate significantly.In fact, females competing more intensively on day one displayedthe ornament less on day two. Furthermore, the ornament displayduring the first, but not the second, day predicted male matechoice on the second day. Thus, males remembered previous informationfrom competitive displays and used it rather than immediateinformation from displays in the absence of female-female competition.We suggest that competitive displays more reliably signal female quality as compared to noncompetitive ones, and that males benefitfrom mating with dominant females.     

Influence of lighting environment on social preferences in sticklebacks from two different photic habitats. II. Shoaling and mate preferences of lab-bred fishes

Different environmental conditions may lead to diverse morphological, behavioral, and physiological adaptations of different populations of the same species. Lighting conditions, for example, vary vastly especially between aquatic habitats, and have been shown to elicit adaptations. The availability of short-wave ultraviolet (UV) light is especially fluctuating, as UV wavelengths are attenuated strongly depending on water properties. The island of North Uist, Scotland, comprises 2 differential habitat types, tea-stained and clear-water lakes, varying considerably in UV transmission. In previous studies, wild-caught 3-spined stickleback Gasterosteus aculeatus populations (3 populations of each habitat type) were tested with respect to their shoaling and mate preferences for fish viewed under UV-present and UV-absent conditions. The results revealed a habitat-dependent preference of UV cues during shoal choice (tea-stained populations: preference for UV-absent condition in tea-stained water; clear-water populations: no preference in clear-water) but an overall preference for UV-present conditions during mate choice. To assess genetic influences on these behavioral patterns, similar experiments were conducted with lab-bred F1-generations of the same stickleback populations that were raised in a common environment (i.e. standardized clear-water conditions). Offspring of sticklebacks from tea-stained lakes tended to prefer shoals viewed under UV-absent conditions (only in tea-stained water), while sticklebacks from clear-water lakes showed a significant preference for the shoal viewed under UV-present conditions in clear-water but not in tea-stained water. Mate-preference experiments demonstrated that females from the tea-stained lakes significantly preferred and females from the clear-water lakes preferred by trend the male viewed under UV-present conditions in the clear-water treatment. The results for both shoaling- and mate-preference tests were largely similar for wild-caught and lab-bred sticklebacks, thus hinting at a genetic basis for the preference patterns.     

Watching sexy displays improves hatching success and offspring growth through maternal allocation

Male attractiveness can have tremendous effects on the fitness of his offspring via good genes, but also via enhanced maternal allocation of resources. Yet the proximate mechanisms influencing differential maternal allocation in relation to male sexiness are poorly known. Here, we studied the importance of visual stimulation for maternal allocation in the Houbara bustard, a vulnerable bird species bred in captivity to support wild populations. Artificial insemination allowed controlling for potential confounding factors, such as a male''s territory quality, social interactions or sperm quality/quantity, probably linked to mate attractiveness. We show that artificially inseminated females stimulated by highly displaying males increased their hatching success, owing to increased fertilization success. The females also increased the allocation of maternal androgens in their eggs, leading to an increase of circulating testosterone and growth rate in chicks. Hence, visual stimulation of the females can promote differential maternal allocation and favour offspring fitness. Our results further suggest that using artificial insemination for species conservation without appropriate stimulation of the breeding females probably has negative impacts on their breeding performance and therefore on population viability.     

When not to avoid inbreeding

Avoidance of incestuous matings is widely reported across many animal taxa, and the adaptive value of such behavior is explained through inbreeding depression. However, an old and somewhat neglected theoretical result predicts that inbred matings offer another, positive effect on the inclusive fitness of parents: an individual who mates with a relative will help that relative to spread genes identical by descent. This benefit can be substantial, if the additional mating achieved by the relative does not harm his mating success otherwise, and in the context of selfing in plants the phenomenon is well known. Here, we develop a model that derives expected values of inbreeding tolerance, that is, the magnitude of inbreeding depression that is required to make individuals avoid inbreeding, for different animal life histories and parental investment patterns. We also distinguish between simultaneous and sequential mate choice, and show that inbreeding tolerance should often be remarkably high in the latter scenario in particular, although egalitarian parental care will lead to lower tolerance. There is a mismatch between theory and data: the almost complete lack of cases where individuals prefer to mate incestuously is at odds with a large overlap between the predicted range of inbreeding tolerance and estimates of inbreeding depression found in nature. We discuss four different solutions to this enigma, and suggest that inbreeding tolerance, where it is found, should not always be attributed to a simple constraint that has prevented finding any other mate.     

Male size effects on fertilization success: lack of evidence in chinook salmon spawning under experimental conditions

Synopsis Anadromous salmonid females exhibit indicators of mate choice based on male size. Direct benefits to females of mating with larger males have not been identified for semelparous Pacific salmon, Oncorhynchus spp. We tested the null hypothesis that females forced to spawn naturally in a stream channel and artificially (gametes removed manually) with males about half their body mass would experience egg fertilization rates similar to that of females forced to spawn with males of about equal mass. Fertilization rates did not differ significantly between large- and small-male pairs. The fertilization rates were also very similar for eggs deposited naturally and those that we fertilized artificially. Therefore, fertilization success does not appear to be the mechanism responsible for female mate choice based on male size. Benefits of females mating with larger males probably have only indirect (i.e., genetic) benefits to a females offspring, as suggested by previous authors.     

Long-Term Trends in Matrilineal Inbreeding Among the Japanese Macaques of Arashiyama B Troop

In a long-term study of sexual behavior in Japanese macaques, we found that matrilineal inbreeding accounted for 2.9% of the copulations recorded for the Arashiyama B troop during 7 mating seasons between 1968 and 1984. Of the 906 copulatory dyads, 46 (5.1%) occurred among kin. Close matrilineal kin dyads (r = 1/2–1/8, 1.1% of the total of copulatory dyads) strongly avoided matrilineal inbreeding, but for remote kin dyads (r > 1/8, 4.0% of the total) the tendency was weaker in some years. Among the possible determinants of matrilineal inbreeding, we found that it tended to occur among younger and lower-ranking males as an effect of troop demographic changes. There is no significant association between female rank and matrilineal inbreeding. Our results are consistent with the hypothesis that different degrees of kin relatedness are discriminated by individuals with respect to mate choice.     

Growth-related changes in predation behavior in incipient colonies of the ponerine antEctatomma tuberculatum (Olivier)

Summary We traced the development in the laboratory of 18 young colonies of the arboricolous ponerine antEctatomma tuberculatum. Colony foundation is of the partially-claustral type. During the early stages, when the colony is entirely dependent on the queen's behavior, the growth of the colony in terms of number of workers produced over time was relatively predictable. Afterwards, divergence in colony growth in function of the time increases as fast as the number of workers influences the efficiency of colony provisioning.Comparative analysis indicated clear changes in the predation behavior of foundresses and workers as colonies developed. For any stage of colony growth, all individuals provisioned the nest with dead prey or sugar-rich substances in the same way. However, prey hunting involves two different strategies. Foundresses and nanitic workers (originating from colonies with 9–15 workers) foraged actively, catching prey as the result of random encounters. Post-nanitic foragers (originating from colonies with 20–30 workers) and those from nature colonies developed an ambush strategy. Workers in these colonies gained experience at catching and handling prey during a period when they acted as nest guards, and so tended to be more efficient hunters than poorly experienced foundresses or nanitic foragers. The change in strategy was also positively correlated with an increase in the size of workers as the colony matured. A stable maximum in workers size is apparently reached only after the appearance of efficiently hunting foragers, presumably in numbers sufficient to provide adequate quantity and quality of larval food. Such a correlation between worker size and colony growth, assumed general for all ants, has not been demonstrated for Ponerinae before this work.     

Copulatory plugs inhibit the reproductive success of rival males

Ejaculated proteins play important roles in reproductive fitness. In many species, seminal fluid coagulates and forms what has been referred to as a copulatory plug in the female's reproductive tract. In mice, previous work demonstrated that knockout males missing a key seminal fluid protein were unable to form a plug and less successful at siring litters in noncompetitive matings (one female, one male), probably the result of reduced sperm transport or insufficient stimulation of the female. Here, we extend these previous studies to competitive matings (one female, two males) and make two key insights. First, when first males were unable to form a plug, they lost almost all paternity to second males to mate. Thus, the copulatory plugs of second males could not rescue the reduced fertility of first males. Second, we showed that the copulatory plug of first males effectively blocked fertilization by second males, even if first males were vasectomized. Taken together, our experiments demonstrated that first males lost almost all paternity if they never formed a plug. We discuss our results in the context of natural populations, where in spite of the strong effects seen here, pregnant female mice regularly carry litters fertilized by more than one male.