Male and female secondary sexual traits show different patterns of quantitative genetic and environmental variation in the horned beetle Onthophagus sagittarius.

The expression of secondary sexual traits in females has often been attributed to a correlated response to selection on male traits. In rare cases, females have secondary sexual traits that are not homologous structures to secondary sexual traits in males and are thus less likely to have evolved in females because of correlated selection. In this study, we used the dung beetle Onthophagus sagittarius, a species with sex-specific horns, to examine the environmental and quantitative genetic control of horn expression in males and females. Offspring subjected to different brood mass manipulations (dung addition/removal) were found to differ significantly in body size. Brood mass manipulation also had a significant effect on the length of male horns; however, female horn length was found to be relatively impervious to the treatment, showing stronger patterns of additive genetic variance than males. We found no correlations between horn expression in males and females. We therefore conclude that the horns of O. sagittarius females are unlikely to result from genetic correlations between males and females. Rather, our data suggest that they may be under independent genetic control.

Watson NL ，Simmons LW 《-》

No fecundity cost of female secondary sexual trait expression in the horned beetle Onthophagus sagittarius.

Typically males bear the products of sexual selection in the form of ornaments and/or weapons used to compete for and attract females. Secondary sexual traits in females have been thought of as the product of correlated responses to sexual selection on males. However, there is increasing phylogenetic evidence that female secondary sexual traits can arise independently of selection on males, and may be subject to sexual selection. Theoretical models of the evolution of female ornamentation via male mate choice have assumed that females suffer a cost of ornament expression via reduced fecundity, and hence female ornaments are less likely to evolve than male ornaments. In the dung beetle Onthophagus sagittarius, there has been an independent evolutionary origin of horns in females that are qualitatively different from the horns produced by males. We use this system as a model to examine the costs of horn expression for females within a life-history context. We identified a longevity cost of reproduction for females that was independent of horn expression. Large females lived longer, and after controlling for lifespan, had a higher lifetime fecundity, and invested more heavily in maternal provisioning than did small females. We found no evidence of a cost to females of investment in horns. Rather, the rate of increase in fecundity and horn expression with body size were equal, so that absolute horn size provides an accurate indicator of body size and maternal quality. The effects we observe were independent of female contest competition and/or male mate choice, which were excluded in our experimental protocol. However, we speculate on the potential functional contributions female horns might make to female fitness.

Simmons LW ，Emlen DJ 《-》

Males influence maternal effects that promote sexual selection: a quantitative genetic experiment with dung beetles Onthophagus taurus.

Kotiaho JS ，Simmons LW ，Hunt J ，Tomkins JL ... -  《AMERICAN NATURALIST》

The genetics of primary and secondary sexual character trade-offs in a horned beetle.

When structures compete for shared resources, this may lead to acquisition and allocation trade-offs so that the enlargement of one structure occurs at the expense of another. Among the studies of morphological trade-offs, their importance has been demonstrated primarily through experimental manipulations and comparative analyses. Relatively, a few studies have investigated the underlying genetic basis of phenotypic patterns. Here, we use a half-sibling breeding design to determine the genetic underpinnings of the phenotypic trade-off between head horns and the male copulatory organ or aedeagus that has been found in the dung beetle Onthophagus taurus. Instead of the predicted negative genetic covariance among characters that trade-off, we find positive genetic covariance between absolute horn and aedeagus length and zero genetic covariance between relative horn and aedeagus length. Therefore, although the genetic covariance between absolute horn and aedeagus length would constrain the independent evolution of primary and secondary sexual characters in this population, there was no evidence of a trade-off. We discuss alternative hypotheses for the observed patterns of genetic correlation between traits that compete for resources and the implications that these have for selection and the evolution of such traits.

House CM ，Simmons LW 《-》

Pupal remodeling and the development and evolution of sexual dimorphism in horned beetles.

Moczek AP 《-》