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Glossary Critical thermal limits (CTL): CTLs are a suite of commonly used measures of the maximum and minimum temperatures at which organisms can viably function. Individuals are exposed to either static stressful temperatures or gradually ramping temperatures and observed for physiological failure; e.g., uncoordinated movement, heat coma, or death [1]. Typically, either the duration of exposure or the temperature at which loss of viability is observed is recorded as the thermal limit. Fecundity: The total number of offspring an individual can produce across a set interval or lifetime. Fertility: The ability of an organism to produce viable offspring. Fertility can be measured in a number of ways but always reaches its lower limit when conditions prevent an individual from producing any offspring (i.e. sterility). Hardening: Increased thermal tolerance shown by organisms after a short period of exposure to a stressful but non-lethal temperature within the same life stage. Hardening tests are one component of a species plastic response when exposed to stressful temperatures [2]. Sterility: Describes an individual that cannot produce any offspring over a defined period, and thus is synonymous with complete infertility. Thermal fertility limits (TFL): Outlined here for the first time, TFLs refer to a level and duration of thermal stress that renders individuals unable to reproduce. For populations and species this can be defined as the temperature at which a given proportion of individuals are qualitatively sterile and it includes both higher (TFMAX) and lower (TFMIN) thermal stress

Abstract. Traditional models of sexual selection propose that partner choice increases both average male and average female fitness in a population. Recent theoretical and empirical work, however, has stressed that sexual conflict may be a potent broker of sexual selection. When the fitness interests of males and females diverge, a reproductive strategy that increases the fitness of one sex may decrease the fitness of the other sex. The chase-away hypothesis proposes that sexual conflict promotes sexually antagonistic, rather than mutualistic, coevolution, whereby manipulative reproductive strategies in one sex are counteracted by the evolution of resistance to such strategies in the other sex. In this paper, we consider the criteria necessary to demonstrate the chase-away hypothesis. Specifically, we review sexual conflict with particular emphasis on the chase-away hypothesis; discuss the problems associated with testing the predictions of the chase-away hypothesis and the extent to which these predictions and the predictions of traditional models of sexual selection are mutually exclusive; discuss misconceptions and mismeasures of sexual conflict; and suggest an alternative approach to demonstrate sexual conflict, measure the intensity of sexually antagonistic selection in a population, and elucidate the coevolutionary trajectories of the sexes.

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Sexual conflict over reproduction can occur between males and females. In several naturally promiscuous insect species, experimental evolution studies that have enforced monogamy found evidence for sexual conflict. Here, we subjected the naturally promiscuous, sperm-heteromorphic fruit fly Drosophila pseudoobscura to enforced monogamy, standard levels of promiscuity, and elevated opportunities for promiscuity in four replicate lines. We examined the effect of male and female selection history and the proximate effect of variation in male density on female fitness parameters. We found that male density rather than male selection history explained a greater degree of female fecundity, egg hatching success, and productivity. Additionally, females selected under elevated promiscuity had greater fecundity and hatching success than did enforced monogamy females. Selection line males do not differ in their capacity to coerce females to remate, suggesting no divergence in precopulatory manipulative ability. However, these males did vary in their ability to suppress female remating, suggesting postcopulatory manipulation. These results indicate that sexual conflict can be manifested through both the proximate effects of male density and the historical levels of sexual selection and that the sexes respond differentially to these factors and further stress the multifarious channels of sexual communication that contribute to fitness.