摘要: Copulatory plugs (CP) are substances produced during copulation that block the genital openings of the female. In several species of Nematoda, males produce CP that are thought to impede female remating and thus sperm competition. The relatively large size of the CP in several nematodes, and its evolutionary loss in self-fertilizing populations of Caenorhabditis elegans, suggests that CP are costly to produce. If CP production is costly, the application of basic concepts of strategic ejaculation theory suggests a modulated allocation of CP in response to sperm competition risk. This hypothesis led us to predict that males perceiving a higher risk of sperm competition will produce larger CP. We tested these ideas with the entomopathogenic, gonochoristic nematode Rhabditis regina. Our first experiment provides evidence suggesting that production of CP is costly, because the size of CP is negatively affected by stressful conditions (high population density, small male adult size, and suboptimal food type). The results of our second experiment support the prediction that males adjust the size of CP to sperm competition risk: the average size of CP increased as the number of males competing for one female increased. Overall, our study supports the idea that in R. regina the production of CP is costly for males and that the size of the CP produced is influenced by sperm competition risk.

摘要: Ecological variation in resources can influence the distribution and encounter rates of potential mates and competitors and, consequently, the opportunity for sexual selection. Factors that influence the likelihood that females mate multiply could also affect the potential for sperm competition. In Wellington tree weta (Hemideina crassidens, plural weta), the size of tree cavities (called galleries) used as refuges affects weta distribution and thus the opportunity for sexual selection and selection on male weaponry size. We examined the predicted effects of gallery size and male weaponry size on the potential for sperm competition. We asked if gallery size influenced the potential for multiple mating by females and potential for sperm competition, if male weaponry size was associated with relative expected sperm competition intensity (SCI), and if estimated male mating success was correlated with potential SCI. To quantify relative competitive environments of males, we created and analyzed networks of potential competitors based on which males could have mated with the same females. We found that small galleries had higher potential for female multiple mating and higher potential for sperm competition. Size of male weaponry was not associated with expected relative SCI. Regardless of gallery size, males with more potential mates were expected to face lower expected relative sperm competition. Thus, in this system, variation in the size of available refuges is likely to influence the potential for sperm competition, in a way that we might expect to increase variation in overall reproductive success.

摘要: Angle dependent colors, such as iridescence, are produced by structures present on flower petals changing their visual appearance. These colors have been proposed to act as signals for plant-insect communication. However, there is a paucity of behavioral data to allow for interpretations of how to classify these colors either as a signal or a cue when considering the natural conditions under which pollination occurs. We sampled flowers from 6 plant species across various viewpoints looking for changes in the visual appearance of the petals. Spectral characteristics were measured with different instruments to simulate both the spectral and spatial characteristics of honeybee's vision. We show the presence of color patches produced by angle dependent effects on the petals and the calyx of various species; however, the appearance of the angle dependent color patches significantly varies with viewpoint and would only be resolved by the insect eye at close distances. Behavior experiments with honeybees revealed that pollinators did not use angle dependent colors to drive behavior when presented with novel flower presentations. Results show that angle dependent colors do not comply with the requirements of a signal for plant-pollinator communication since the information transmitted by these colors would be unreliable for potential, free-flying pollination vectors. We thus classify angle dependent colors produced by micro-and ultra-structures as being a cue (a feature which has not evolved for communication), and observe no evidence supporting claims of these angle dependent colors having evolved as visual signal.

摘要: Turn-taking is a common feature in human speech, and is also seen in the communication of other primate species. However, evidence of turn-taking in vocal exchanges within a short time frame is still scarce in nonhuman primates. This study investigated whether dynamic adjustment during turn-taking in short calls exists in Japanese macaques Macaca fuscata. We observed exchanges of short calls such as grunts, girneys, and short, low coos during social interactions in a free-ranging group of Japanese macaques. We found that the median gap between the turns of two callers was 250 ms. Call intervals varied among individuals, suggesting that call intervals were not fixed among individuals. Solo call intervals were shorter than call intervals interrupted by responses from partners (i.e., exchanges) and longer than those between the partner's reply and the reply to that call, indicating that the monkeys did not just repeat calls at certain intervals irrespective of the social situation. The differences in call intervals during exchanged and solo call sequences were explained by the response interval of the partner, suggesting an adjustment of call timing according to the tempo of the partner's call utterance. These findings suggest that monkeys display dynamic temporal adjustment in a short time window, which is comparable with turn-taking in human speech.

摘要: There is increasing interest in flies as potentially important pollinators. Flies are known to have a complex visual system, including 4 spectral classes of photoreceptors that contribute to the perception of color. Our current understanding of how color signals are perceived by flies is based on data for the blowfly Lucilia sp., which after being conditioned to rewarded monochromatic light stimuli, showed evidence of a categorical color visual system. The resulting opponent fly color space has 4 distinct categories, and has been used to interpret how some fly pollinators may perceive flower colors. However, formal proof that flower flies (Syrphidae) only use a simple, categorical color process remains outstanding. In free-flying experiments, we tested the hoverfly Eristalis tenax, a Batesian mimic of the honeybee, that receives its nutrition by visiting flowers. Using a range of broadband similar-dissimilar color stimuli previously used to test color perception in pollinating hymenopteran species, we evaluated if there are steep changes in behavioral choices with continuously increasing color differences as might be expected by categorical color processing. Our data revealed that color choices by the hoverfly are mediated by a continuous monotonic function. Thus, these flies did not use a categorical processing, but showed evidence of a color discrimination function similar to that observed in several bee species. We therefore empirically provide data for the minimum color distance that can be discriminated by hoverflies in fly color space, enabling an improved understanding of plant-pollinator interactions with a non-model insect species.