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Costs of sexual traits are of central importance to the theory of sexual selection. To qualify as a cost in line with theoretical models, empirical studies must demonstrate that sexual traits cause negative effects on one component of fitness of the trait bearer. Moreover, it must be demonstrated that the costs are differential such that negative effects on fitness are more severe for individuals in poor condition than for individuals in good condition. However, in the current literature, there is confusion over what qualifies as a cost, and costs are often anticipated based on findings of increased expenditure. Consequently, it seems that the generally accepted notion that sexual traits are costly is in fact based almost exclusively on indirect evidence and that direct empirical evidence is very scarce.

Understanding the ultimate causes of population declines and extinction is vital in our quest to stop the currently rampant biodiversity loss. Comparison of ecological characteristics between threatened and nonthreatened species may reveal these ultimate causes. Here, we report an analysis of ecological characteristics of 23 threatened and 72 nonthreatened butterfly species. Our analysis reveals that threatened butterflies are characterized by narrow niche breadth, restricted resource distribution, poor dispersal ability, and short flight period. Based on the characteristics, we constructed an ecological extinction risk rank and predicted which of the currently nonthreatened species are at the highest risk of extinction. Our analysis reveals that two species currently classified as nonthreatened are, in fact, at high risk of extinction, and that the status of a further five species should be reconsidered.conservation biology ͉ threatened species ͉ biodiversity ͉ Lepidoptera ͉ World Conservation Union Red List

Genetic benefits in the shape of 'good genes' have been invoked to explain costly female choice in the absence of direct fitness benefits. Little genetic variance in fitness traits is expected, however, because directional selection tends to drive beneficial alleles to fixation. There seems to be little potential, therefore, for female choice to result in genetic benefits, giving rise to the 'lek paradox'. Nevertheless, evidence shows that genetic variance persists despite directional selection and genetic benefits of female choice are frequently reported. A theoretical solution to the lek paradox has been proposed on the basis of two assumptions: that traits are condition-dependent, and that condition shows high genetic variance. The observed genetic variability in sexual traits will be accounted for, because a proportion of the genetic variance in condition will be captured and expressed in the trait. Here we report results from experiments showing that male courtship rate in the dung beetle Onthophagus taurus is a condition-dependent trait that is preferred by females. More importantly, male condition has high genetic variance and is genetically correlated with courtship rate. Our results thereby represent a significant step towards a resolution of the lek paradox.

Sperm competition is widely recognized as a potent force in evolution, influencing male behavior, morphology, and physiology. Recent game theory analyses have examined how sperm competition can influence the evolution of ejaculate expenditure by males and the morphology of sperm contained within ejaculates. Theoretical analyses rest on the assumption that there is sufficient genetic variance in traits important in sperm competition to allow evolving populations to move to the evolutionarily stable equilibrium. Moreover, patterns of genotypic variation can provide valuable insight into the nature of selection currently acting on traits. However, our knowledge of genetic variance underlying traits important in sperm competition is limited. Here we examine patterns of phenotypic and genotypic variation in four sperm competition traits in the dung beetle Onthophagus taurus. Testis weight, ejaculate volume, and copula duration were found to have high coefficients of additive genetic variation (CV(A)S), which is characteristic of fitness traits and traits subject to sexual selection. Heritabilities were high, and there was some evidence for Y-linked inheritance in testis weight. In contrast, sperm length had a low CV(A), which is characteristic of traits subject to stabilizing selection. Nevertheless, there was little residual variance so that the heritability of sperm length exceeded 1.0. Such a pattern is consistent with Y-linked inheritance in sperm length. Interestingly, we found that testis weight and sperm length were genetically correlated with heritable male condition. This finding holds important implications for potential indirect benefits associated with the evolution of polyandry.

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Summary 1.Pheromones are chemical signals that function not only as mate attractors, but may also relay important information to prospective mates. In order for the information to be reliable, the signal must be costly to produce and this is likely to result in condition dependent expression of the signal. 2. We present results from two experiments on the grain beetle Tenebrio molitor examining phenotypic condition dependence of pheromones and patterns of female preference for pheromones. We also analysed condition dependence of two measures of immunocompetence: encapsulation response and phenoloxidase activity. 3. By manipulating the nutritional condition of the males we found that the attractiveness of the male pheromones to virgin females was condition-dependent, indicating that the production of the pheromones is affected by the condition of the male. We also found that the phenoloxidase activity of the males was affected by the nutritional condition of the male but that encapsulation rate was not. 4. Our results show that pheromones are condition-dependent signals, the quantity of which females use in their mate choice.

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