The relative contributions of the X chromosome and autosomes to local adaptation

Authors: Clémentine Lasne, Carla M Sgrò, and Tim Connallon

Published in: Genetics, volume 205, issue 4 (April 2017)

Abstract

Models of sex chromosome and autosome evolution yield key predictions about the genomic basis of adaptive divergence, and such models have been important in guiding empirical research in comparative genomics and studies of speciation.

In addition to the adaptive differentiation that occurs between species over time, selection also favors genetic divergence across geographic space, with subpopulations of single species evolving conspicuous differences in traits involved in adaptation to local environmental conditions. The potential contribution of sex chromosomes (the X or Z) to local adaptation remains unclear, as we currently lack theory that directly links spatial variation in selection to local adaptation of X-linked and autosomal genes.

Here, we develop population genetic models that explicitly consider the effects of genetic dominance, effective population size, and sex-specific migration and selection, on the relative contributions of X-linked and autosomal genes to local adaptation.

We show that X-linked genes should nearly always disproportionately contribute to local adaptation in the presence of gene flow. We also show that considerations of dominance and effective population size — which play pivotal roles in the theory of faster-X adaptation between species — have surprisingly little influence on the relative contribution of the X chromosome to local adaptation. Instead, sex-biased migration is the primary mediator of the strength of spatial large-X effects.

Our results yield novel predictions about the role of sex chromosomes in local adaptation. We outline empirical approaches in evolutionary quantitative genetics and genomics that could build upon this new theory.

Citation

Lasne C, Sgrò CM, Connallon T (2017) The relative contributions of the X chromosome and autosomes to local adaptation. Genetics, PDF DOI

Revealing hidden evolutionary capacity to cope with global change

Authors: Evatt Chirgwin, Keyne Monro, Carla M Sgrò and Dustin J Marshall

Published in: Global Change Biology, volume 21, issue 9 (September 2015)

Abstract

The extent to which global change will impact the long-term persistence of species depends on their evolutionary potential to adapt to future conditions.

While the number of studies that estimate the standing levels of adaptive genetic variation in populations under predicted global change scenarios is growing all the time, few studies have considered multiple environments simultaneously and even fewer have considered evolutionary potential in multi- variate context.

Because conditions will not be constant, adaptation to climate change is fundamentally a multivariate process so viewing genetic variances and covariances over multivariate space will always be more informative than relying on bivariate genetic correlations between traits. A multivariate approach to understanding the evolutionary capacity to cope with global change is necessary to avoid misestimating adaptive genetic variation in the dimensions in which selection will act.

We assessed the evolutionary capacity of the larval stage of the marine polychaete Galeolaria caespitosa to adapt to warmer water temperatures. Galeolaria is an important habitat-forming species in Australia, and its earlier life-history stages tend to be more susceptible to stress. We used a powerful quantitative genetics design that assessed the impacts of three temperatures on subsequent survival across over 30,000 embryos across 204 unique families.

We found adaptive genetic variation in the two cooler temperatures in our study, but none in the warmest temperature. Based on these results, we would have concluded that this species has very little capacity to evolve to the warmest temperature. However, when we explored genetic variation in multivariate space, we found evidence that larval survival has the potential to evolve even in the warmest temperatures via correlated responses to selection across thermal environments.

Future studies should take a multivariate approach to estimating evolutionary capacity to cope with global change lest they misestimate a species’ true adaptive potential.

Citation

Chirgwin E, Monro K, Sgrò CM, Marshall DJ (2015) Revealing hidden evolutionary capacity to cope with global change. Global Change Biology, 21: 3356–3366. PDF DOI

Is adaptation to climate change really constrained in niche specialists?

Authors: Belinda van Heerwaarden and Carla M Sgrò

Published in: Proceedings of the Royal Society B, volume 281, number 1790 (September 2014)

Abstract

Species with restricted distributions make up the vast majority of biodiversity.

Recent evidence suggests that Drosophila species with restricted tropical distributions lack genetic variation in the key trait of desiccation resistance. It has therefore been predicted that tropically restricted species will be limited in their evolutionary response to future climatic changes and will face higher risks of extinction. However, these assessments have been made using extreme levels of desiccation stress (less than 10% relative humidity (RH)) that extend well beyond the changes projected for the wet tropics under climate change scenarios over the next 30 years.

Here, we show that significant evolutionary responses to less extreme (35% RH) but more ecologically realistic levels of climatic change and desiccation stress are in fact possible in two species of rainforest restricted Drosophila. Evolution may indeed be an important means by which sensitive rainforest-restricted species are able to mitigate the effects of climate change.

Citation

van Heerwaarden, B Sgrò CM (2014) Is adaptation to climate change really constrained in niche specialists? Proceedings of the Royal Society B 280(1790) PDF DOI