Condition Dependence of Sexual Ornament Size and Variation in the Stalk-Eyed Fly Cyrtodiopsis Dalmanni (Diptera: Diopsidae)

Abstract

We used the stalk-eyed fly Cyrtodiopsis dalmanni to examine predictions made by condition-dependent handicap models of sexual selection. Condition was experimentally varied by manipulation of larval food availability. Cyrtodiopsis dalmanni is a highly dimorphic species exhibiting strong sexual selection, and the male sexual ornament (exaggerated eyespan) showed strong condition-dependent expression relative to the homologous trait in females and nonsexual traits. Male eyespan also showed a great increase in standardized variance under stress, unlike nonsexual traits. The inflated variance of the male ornament was primarily attributable to condition-dependent (but body-size-independent) increase in variance. Thus, evaluation of male eyespan allows females to gain additional information about male condition over and above that given by body size. These findings accord well with condition-dependent handicap models of sexual selection.

Sexual Selection, Genetic Architecture, and the Condition Dependence of Body Shape in the Sexually Dimorphic Fly Prochyliza Xanthostoma (Piophilidae)

“…A fruitful approach to the study of condition dependence is the comparison of traits with different functions within a single species (e.g., Møller and Petrie 2002;Møller and Mousseau 2003;Cotton et al 2004b). Unfortunately, most such studies have contrasted a single sexually selected trait with a single control trait (see Cotton et al 2004a).…”

“…Because diet quality is likely to represent an important source of variation in condition among individuals in the wild, diet manipulation is an effective method of investigating the effects of an environmental factor affecting condition (Emlen 1997;Cotton et al 2004a). However, if we seek to understand how reaction norms are shaped by sexual selection, it is important to employ treatments that fall within the range of environments experienced in the wild by individuals that survive to adulthood (Cotton et al 2004b).…”

“…However, if we seek to understand how reaction norms are shaped by sexual selection, it is important to employ treatments that fall within the range of environments experienced in the wild by individuals that survive to adulthood (Cotton et al 2004b). Thus, relatively subtle manipulations may provide more relevant insights than extreme contrasts that can only be achieved under laboratory conditions.…”

“…In contrast, relative trait sizes may exhibit negative genetic or phenotypic correlations, making it easier to interpret variation in body shape. Indeed, condition dependence of morphology is conventionally defined in terms of condition effects on body shape, with sexual traits expected to increase faster than nonsexual traits in relation to body size as condition increases (see Cotton et al 2004a). Estimating the condition dependence of relative trait sizes also makes it possible to determine which traits, if any, signal condition more reliably than body size.…”

Fear, food and sexual ornamentation: plasticity of colour development in Trinidadian guppies

“…As such, females can use male ornamentation to assess variation in male condition or quality during mate choice, given that only males in high condition can afford the cost of extreme ornamentation ( [15][16][17][18][19], but see Cotton et al [20]). Thus, variation in the developmental environment can not only impact the expression of sexually selected traits, with high condition males exhibiting more exaggerated ornaments [21][22][23][24][25][26][27], but also determine a male's probability of mating [21,28].…”