Genetic assimilation—the evolutionary process by which an environmentally induced phenotype is made constitutive—represents a fundamental concept in evolutionary biology. Thought to reflect adaptive phenotypic plasticity, matricidal hatching in nematodes is triggered by maternal nutrient deprivation to allow for protection or resource provisioning of offspring. Here, we report natural Caenorhabditis elegans populations harboring genetic variants expressing a derived state of near-constitutive matricidal hatching. These variants exhibit a single amino acid change (V530L) in KCNL-1, a small-conductance calcium-activated potassium channel subunit. This gain-of-function mutation causes matricidal hatching by strongly reducing the sensitivity to environmental stimuli triggering egg-laying. We show that reestablishing the canonical KCNL-1 protein in matricidal isolates is sufficient to restore canonical egg-laying. While highly deleterious in constant food environments, KCNL-1 V530L is maintained under fluctuating resource availability. A single point mutation can therefore underlie the genetic assimilation—by either genetic drift or selection—of an ancestrally plastic trait.
KAUST Repository Item: Exported on 2021-02-05
Acknowledgements: For helpful discussions and pointing out the curious phenotype of JU751, we would like to thank M.-A. Félix. For help with experimental work and data analysis, we thank B. Billard, S. Fausett, N. Poullet, G. Bouzouida, N. Schwartz-Tamoglia, N. Callemeyn-Torre, J.-A. Lepesant, R. Salle, J. Costa, and F. Mallard. For advice and helpful comments on previous versions of the manuscript, we thank E. Abouheif, L. Noble, and three anonymous reviewers. Strains and materials were provided by M.-A. Félix, the C. elegans Natural Diversity Resource (CeNDR), and the Caenorhabditis Genetics Center (CGC), which is funded by NIH Office of Research Infrastructure Programs (P40 OD010440).