Search results for "Operational sex ratio"
showing 6 items of 6 documents
Sperm depletion, male mating behaviour and reproductive ‘time-out' in Gammarus pulex (Crustacea, Amphipoda).
2009
6 pages; International audience; In Gammarus pulex, male–male competition is generally intense because the operational sex ratio (OSR) is strongly biased towards males; however, studies have shown possible fluctuation in this intrasexual competition, which could be caused by sperm depletion, a phenomenon recently found in gammarids. Sperm depletion may also affect male mating behaviour. We therefore tested the influence of sperm depletion on the OSR in G. pulex. Two sets of experiments were conducted: first, to find out the number of sperm in the testis before and after mating events (sperm depletion), and second, to test the implications of sperm depletion for the mating behaviour of male …
High maternal species density mediates unidirectional heterospecific matings inCalopteryxdamselflies
2012
Hybridization is a well-known phenomenon, but there are still relatively few studies addressing the question of reproductive isolation between related sympatric animal species with largely overlapping ranges. Population density, relative abundance, and operational sex ratio (OSR) are among the factors known to have an influence on the frequency of heterospecific matings in sympatric populations. Here we had two aims. First, we used microsatellite markers and field observations to study the frequency of hybrids, and backcrosses, and the rate of heterospecific matings between two sympatric damselfly species Calopteryx splendens (Harris, 1780) and Calopteryx virgo (Linne, 1758). Second, we inv…
Coevolution of parental investment and sexually selected traits drives sex-role divergence
2016
Sex-role evolution theory attempts to explain the origin and direction of male–female differences. A fundamental question is why anisogamy, the difference in gamete size that defines the sexes, has repeatedly led to large differences in subsequent parental care. Here we construct models to confirm predictions that individuals benefit less from caring when they face stronger sexual selection and/or lower certainty of parentage. However, we overturn the widely cited claim that a negative feedback between the operational sex ratio and the opportunity cost of care selects for egalitarian sex roles. We further argue that our model does not predict any effect of the adult sex ratio (ASR) that is …
Quantitative measure of sexual selection with respect to the operational sex ratio: a comparison of selection indices
2006
Despite numerous indices proposed to predict the evolution of mating systems, a unified measure of sexual selection has remained elusive. Three previous studies have compared indices of sexual selection under laboratory conditions. Here, we use a genetic study to compare the most widely used measures of sexual selection in natural populations. We explored the mating and reproductive successes of male and female bank voles,Clethrionomys glareolus, across manipulated operational sex ratios (OSRs) by genotyping all adult and pup bank voles on 13 islands using six microsatellite loci. We used Bateman's principles (IsandIand Bateman gradients) and selection coefficients (s′ andβ′) to evaluate, f…
The operational sex ratio of the sea urchin Paracentrotus lividus populations: the case of the Mediterranean marine protected area of Ustica Island (…
2009
We investigated, with a series of field and laboratory observations, the possible effect of the starfish Marthasteria glacialis predation on the operational sex ratio (OSR), i.e. the number of sexually mature males divided by the total number of sexually mature adults of both sexes at any one time, of the edible sea urchin Paracentrotus lividus. The OSR was estimated three times during the sea urchin summer spawning period (July 2004, June 2005 and July 2006) on barren substrates of Ustica Island Marine Protected Area (Southern Tyrrhenian Sea, Italy). Four sites were selected: two characterized by high M. glacialis density (take zone C) and two controls with low starfish density (no-take zo…
Operational sex ratio and resource defence as predictors of the mating system in European bitterling
2003
Operational sex ratio (OSR), the ratio of sexually active males to fertilizable females in a population, plays a central role in the theory of mating systems by predicting that the intensity of male–male competition and the degree of sexual selection increases as the OSR becomes increasingly male biased. At high values of OSR, however, resource defence theory predicts the breakdown of territoriality and a shift towards scramble competition with a decrease in sexual selection. The direction that correlations between OSR and resource competition and variance in mating success will take depends on the biology of the species of interest. We investigated the effects of male population density an…