Biology subjects

Michael Jennions

Publications and source records attributed to Michael Jennions.

3 recordsLinked to original sources

bioRxiv2016

Experimental evidence for sexual selection against inbred males when it truly counts

Although there are many correlational studies, unbiased estimates of inbreeding depression only come from experimental studies that create inbred and outbred individuals. Few such studies determine the extent to which inbreeding depression in males is due to natural or sexual selection. Importantly, traits that are closely related to fitness are predicted to be most strongly affected by inbreeding depression, so measuring fitness or key fitness components, rather than phenotypic traits, is necessary to estimate inbreeding depression accurately. Here, we experimentally created inbred and outbred male mosquitofish (Gambusia holbrooki) by mating full-sibs (f=0.25). We show this led to a 23% reduction in genome-wide heterozygosity. Males were then raised on different diets early in life. We then allowed adult males to compete freely for females to test if inbreeding, early diet, and their interaction affect a males share of paternity. Early diet had no effect on paternity, but outbred males sired almost twice as many offspring as inbred males. We also found that males with a relatively long gonopodium (intromittent organ) had greater reproductive success. We demonstrate that inbreeding has important consequences because it negatively affects a key component of male fitness. Given there was no difference in adult mortality this finding can only be due to inbreeding negatively affecting sexually selected traits.

Evolutionary Biology↗

bioRxiv2016

Sexual selection on body size, genitals and heterozygosity: effects of demography and habitat complexity

Environmental variation can maintain genetic variation in sexually selected traits if it affects the strength of directional selection. Specifically, environmental variation in sex-specific mortality will change the operational sex ratio (OSR), which predicts the intensity of mating competition. How the OSR affects selection for specific male traits is poorly understood; and it is unknown how often sexual selection is affected by interactions between the OSR and environmental factors that alter social variables such as mate encounter rates. Here, we experimentally manipulated the OSR and habitat complexity and quantified sexual selection on male mosquitofish (Gambusia holbrooki). In G. holbrooki there is high within-population variation in male size, which may exist because of a tradeoff between the ability to sneak copulate (favouring small males) and monopolize females (favouring large males). The success of each tactic is predicted to depend on the OSR, encounter rates and the ability to stealthily approach conspecifics. We show that, despite greater sharing of paternity under a male-biased OSR, neither the opportunity for selection, nor selection on male traits was affected by the OSR or habitat complexity. Instead, sexual selection consistently favored smaller males with high genetic heterozygosity (using >3000 SNP markers), and a relatively long gonopodium (intromittent organ).

Evolutionary Biology↗

bioRxiv2016

Are sexually selected traits affected by a poor environment early in life?

Conditions experienced early in life can affect key life-history traits. Individuals that experience a poor nutritional environment early in life can reduce potential costs by delaying sexual maturation. The direct costs of delaying maturation are well known (i.e. delayed onset of breeding), but individuals can also face additional costs as adults. Some of these hidden costs accrue due to cryptic morphological and physiological changes. In mosquitofish (Gambusia holbrooki), males with limited food intake early in life delay maturation to eventually reach a similar adult body size to their well-fed counterparts ( catch-up growth). Here we tested whether a poor diet early in life incurs hidden costs due to reduced expression of sexually selected male traits (genital size and ejaculate traits). We found that diet early in life significantly influenced sperm reserves and replenishment rate due to age and development-rate dependent effects. Although catching-up in body size ameliorates some of the costs of a poor start in life for males, our findings suggest that long-term fitness costs might arise because of sexually selection against these males. Our results highlight that fitness costs of a poor start in life can extend into adulthood.

Evolutionary Biology↗