10 research outputs found
The genetics of maternal care: Direct and indirect genetic effects on phenotype in the dung beetle Onthophagus taurus
While theoretical models of the evolution of parental care are based on the assumption of underlying genetic variance, surprisingly few quantitative genetic studies of this life-history trait exist. Estimation of the degree of genetic variance in parental care is important because it can be a significant source of maternal effects, which, if genetically based, represent indirect genetic effects. A major prediction of indirect genetic effect theory is that traits without heritable variation can evolve because of the heritable environmental variation that indirect genetic effects provide. In the dung beetle, Onthophagus taurus, females provide care to offspring by provisioning a brood mass. The size of the brood mass has pronounced effects on offspring phenotype. Using a half-sib breeding design we show that the weight of the brood mass females produce exhibits significant levels of additive genetic variance due to sires. However, variance caused by dams is considerably larger, demonstrating that maternal effects are also important. Body size exhibited low additive genetic variance. However, body size exerts a strong maternal influence on the weight of brood masses produced, accounting for 22% of the nongenetic variance in offspring body size. Maternal body size also influenced the number of offspring produced but there was no genetic variance for this trait. Offspring body size and brood mass weight exhibited positive genetic and phenotypic correlations. We conclude that both indirect genetic effects, via maternal care, and nongenetic maternal effects, via female size, play important roles in the evolution of phenotype in this species
Environment-dependent use of mate choice cues in sticklebacks
Human-induced environmental changes alter terrestrial and aquatic ecosystems worldwide. This influences also evolutionary processes, such as sexual selection, by constraining mate choice and mate competition. Organisms often use multiple cues in mate choice, with different cues indicating the same or different benefits. Because the assessment and information content of cues can vary with environmental conditions, changes in the environment could alter mate choice. Here we determined if increased phytoplankton turbidity influences the relative use of olfactory and visual cues in mate choice in the three-spined stickleback Gasterosteus aculeatus. In a mate choice experiment, we found that females relied more on visual than olfactory cues in clear water. However, in turbid water, the pattern was the opposite with olfactory cues being more important than visual cues. Interestingly, mate preferences based on visual and olfactory cues did not agree, which suggests that human-induced environmental change could shift mate choice. This could influence the direction and target of sexual selection and have further consequences for the viability of the population under the new conditions. Copyright 2009, Oxford University Press.
Experimental analysis of sperm competition mechanisms in a wild bird population
Recent work on wild birds has revealed the importance of sperm competition as a source of sexual selection, but behavioral and paternity studies have previously provided only indirect evidence for mechanisms of sperm competition in wild birds. In a field study of collared flycatchers Ficedula albicollis we used a previously uncharacterized method to determine the frequency and timing of extra-pair inseminations. By counting the number of sperm trapped on the perivitelline layer of eggs, we determined the timing of inseminations and estimated, on a day-to-day basis, the amount of sperm females stored. Our results showed that female collared flycatchers preferentially engaged in extra-pair copulations when mated to an unattractive male with a small white forehead patch. These copulations were timed for the middle part of their fertile period, at least 2 days after the last within-pair insemination. Although the mean number of extra-pair insemination events was only 1.33 per cuckolding female, the ratio between the number of sperm from extra-pair and pair inseminations was at least 5 to 1. Thus a single, well timed extra-pair insemination caused by female behavior could greatly bias fertilization probability in favor of an attractive extra-pair male. Our results suggest a possible behavioral mechanism for female control of sperm competition