SEXUAL TRAITS ARE SENSITIVE TO GENETIC STRESS AND PREDICT EXTINCTION RISK IN THE STALK‐EYED FLY,DIASEMOPSIS MEIGENII

Abstract

The handicap principle predicts that sexual traits are more susceptible to inbreeding depression than nonsexual traits. However, this hypothesis has received little testing and results are inconsistent. We used 11 generations of full-sibling mating to test the effect of inbreeding on sexual and nonsexual traits in the stalk-eyed fly Diasemopsis meigenii. Consistent with the theoretical predictions, the male sexual trait (eyespan) decreased more than nonsexual traits (female eyespan and male wing length), even after controlling for body size variation. In addition, male eyespan was a reliable predictor of line extinction, unlike other nonsexual traits. After 11 generations, inbred lines were crossed to generate inbred and outbred families. All morphological traits were larger in outbred individuals than inbred individuals. This heterosis was greater in male eyespan than in male wing length, but not female eyespan. The elevated response in male eyespan to genetic stress mirrored the result found using environmental stress during larval development and suggests that common mechanisms underlie the patterns observed. Overall, these results support the hypothesis that male sexual traits suffer more from inbreeding depression than nonsexual traits and are in line with predictions based on the handicap principle.

The nutritionally responsive transcriptome of the polyphenic beetle Onthophagus taurus and the importance of sexual dimorphism and body region

“…Morphological data across a wide range of taxa generally corroborate these predictions (e.g. birds: [34,35]; flies: [30,36]; beetles: [37]; fish: [38]; crustaceans: [39]), and at least one study on fruit flies has been able to demonstrated that high-condition populations are more sexually dimorphic in transcription than low-condition populations [40]. However, more precise knowledge of the transcriptomic underpinnings of condition-dependence is lacking [24].…”

Ejaculate investment and attractiveness in the stalk‐eyed fly, Diasemopsis meigenii

“…Eyespan is sexually dimorphic, with males having more widely displaced eyes than females (Baker and Wilkinson 2001) and is subject to sexual selection through female choice for large male ornamentation (Burkhardt and de la Motte 1988; Wilkinson et al 1998; Cotton et al 2006). Male eyespan is a highly condition-dependent trait in D. meigenii (Bellamy et al 2013) and other stalk-eyed fly species (David et al 1998; Bjorksten et al 2001; Cotton et al 2004). In the related stalk-eyed fly species Teleopsis dalmanni , eyespan is a reliable indicator of the size of male internal reproductive organs (Rogers et al 2008; Cotton et al 2010).…”

Limits to environmental masking of genetic quality in sexual signals

“…A suite of 105 inbred lines were founded from a stock of Diasemopsis meigenii (Bellamy et al, ), an African stalk‐eyed fly, derived from flies collected in South Africa by S. Hilger in 2000. After 11 generations of full‐sib mating ( f ~ 0.908), the extant lines were bred in cage culture (~200 flies/cage).…”

“…Eggs were collected from each line, and larvae were raised on excess puréed sweet corn. At eclosion, offspring were placed in large cages, separated by sex (~2 weeks), raised until sexual maturity (~10 weeks) and kept under standard conditions (Bellamy et al, ).…”

“…This allowed us to compare low genetic quality, highly homozygous “incross” lines with high genetic quality, highly heterozygous “outcross” lines. We used incross and outcross lines not to study the effect of inbreeding per se, but because previous work unambiguously shows that they correspond to low and high genetic quality classes (Bellamy et al, ), since a suite of traits (thorax, wing and eyespan) in both sexes are reduced among incross lines (Bellamy et al, ). The large number of independent crosses within or between lines allows us to capture the contribution of genetic variation in the sexual ornament among low and high genetic quality classes.…”