Bayesian analysis of additive epistasis arising from new mutations in mice

Evolution of Reproductive Efficiency in Caenorhabditis elegans Under Obligatory Outcrossing

Radical shifts in reproductive systems result in radical changes in selective pressures acting on reproductive traits. Nematode Caenorhabditis elegans constitutes one of rare model systems where such shifts can be experimentally induced, providing an opportunity for studying the evolution of reproductive phenotypes in real time. Evolutionary history of predominantly selfing reproduction in has led to degeneration of traits involved outcrossing, making it inefficient. Here, we introduced obligatory outcrossing into isogenic lines of C. elegans and allowed replicate populations to evolve under the new reproductive system. We predicted that they should evolve higher outcrossing efficiency, leading to increased fitness relative to unevolved ancestors. To test this prediction, we assayed fitness of both ancestral and evolved outcrossing populations. To control for the potentially confounding effect of adaptation to laboratory conditions, we also assayed populations with wild-type (selfing) reproductive system. In five experimental blocks, we measured competitive fitness of 12 evolved populations (6 outcrossing, 6 selfing) after ca. 95 generations of evolution, along with their respective ancestors. On average, we found that fitness increased by 0.72 SD (± 0.3 CI) in outcrossing and by 0.52 (± 0.35 CI) in selfing populations, suggesting further adaptation to laboratory conditions in both types. Contrary to predictions, fitness increase was not significantly higher in outcrossing populations, suggesting no detectable adaptation to the changed reproductive system. Importantly, the results for individual populations varied strongly between experimental blocks, in some cases even differing in effect direction. This emphasises the importance of experimental replication in avoiding reporting false findings.

"Conversion" of epistatic into additive genetic variance in finite populations and possible impact on long-term selection response

The role of epistasis in understanding the genetic architecture and variation of quantitative traits and its role, if any, in artificial selection and livestock improvement more generally has a long and sometimes controversial history. Its presence has been clearly demonstrated in, for example, laboratory experiments, but the amount of variation it contributes is likely to be small in outbred populations. In a finite population, although additive x additive epistatic variance is lost by genetic drift, it also contributes by conversion to additive variance through drift sampling and therefore has a potential indirect role in medium and long-term selection response, with superficial similarity to and hard to distinguish from mutation. Whilst predictions of response require knowledge of genetic parameters, an infinitesimal model provides some analytic results. Otherwise there is little quantitative information relevant to animal populations on which to judge this potential role of epistasis and reach firm conclusions.

Is Continued Genetic Improvement of Livestock Sustainable?

Large genetic improvements in the quantitative traits of growth, production, and efficiency of farmed livestock have been made over recent decades, and by introduction of genomic technology these are being enhanced. Such continued improvement requires that there be available variation to utilize. The evidence is that little variation has been lost and such rates are indeed sustainable in the future.