Abstracts (first author)


Dissecting the Bateman gradient: what it really tells us about sex roles

Author(s): Collet J, Dean R, Worley K, Richardson DS, Pizzari T


At the heart of the recent debate on sex roles lies the interpretation of the Bateman gradient, the slope of the regression of reproductive success (number of offspring, T) over mating success (number of mates, M). Typically, males are considered to have a steeper Bateman gradient, thus to undergo stronger sexual selection than females. Recent work challenges this paradigm by questioning the measurement and interpretation of Bateman gradients. In this study we combine an experimental approach with multivariate analyses to resolve the significance of male and female Bateman gradients in the red junglefowl, Gallus gallus. First, the male Bateman gradient is measured by deducing mating success from paternity of the offspring, without accounting for matings that fail to result in fertilisation. We demonstrated that inferring M from offspring parentage leads to a 50% overestimate of the male Bateman gradient compared to a regression using fine-grain mating behaviour. Second, while the male Bateman gradient is concerned with the causal relationship between M and T, we show that variation in other components of male reproductive success, namely female fecundity and paternity share, also cause the Bateman gradient to be overestimated of a further 69%. Finally, there is growing appreciation that female Bateman gradients can be steeper than originally thought. We show that females display a positive Bateman gradient, suggesting that they benefit by mating with multiple males. However, an experimental test shows no evidence that productivity increases with number of mates in females, suggesting that the female Bateman gradient emerges as spurious consequence of males preferentially mating with more fecund females. Our results demonstrate that the mechanisms underpinning Bateman gradients are more complex than currently appreciated, and that understanding the causal relationship of M and T and how it defines sex roles requires an integrated experimental approach.

Abstracts (coauthor)


Phenotypic plasticity requires the breakdown of genetic correlations between the phenotypes expressed in different environments. The same applies to sexual dimorphism, a conceptually related phenomenon where individuals express different phenotypes in response to the genetic environment provided by their sex-determining factors. While sexual dimorphism is ubiquitous, evidence is accumulating that its evolution is often incomplete. Thus, many populations harbour sexually antagonistic variation, alleles that increase the fitness of one sex at the expense of fitness of the other sex. This type of variation is evidence for genetic correlations between males and females constraining the evolution of dimorphism. While sexual antagonism has been documented in a growing range of animal and plant species, we know little about how adaptive conflicts between the sexes are resolved. Here, I present data on a change in the genetic architecture of fitness in laboratory populations of Drosophila melanogaster that is consistent with a resolution of sexual antagonism. We compared two populations that both descend from the outbred laboratory stock LHm in which sexual antagonism has been previously described. The populations have been separated for about 180 generations and maintained under highly standardised rearing conditions. Using estimates of genetic variances and covariances for male and female fitness in the two populations, we can show that the antagonism present in the ancestral LHm population has disappeared in one of the descendant populations. Thus, male and female fitness are no longer genetically correlated, despite the presence of genetic variation for fitness in both sexes and levels of variation at neutral genetic markers that are similar to those in the other population. Using genome-wide genotype data, we are currently investigating the genetic changes associated with this rapid change in the genetic architecture of fitness and resolution of sexual antagonism.


Chairman: Octávio S. Paulo
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XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon


Computational Biology & Population Genomics Group