Abstract
Hybridization may increase the probability of adaptation to extreme stresses. This advantage could be caused by an increased genome plasticity in hybrids, which could accelerate the search for adaptive mutations. High ultraviolet (UV) radiation is a particular challenge in terms of adaptation because it affects the viability of organisms by directly damaging DNA, while also challenging future generations by increasing mutation rate. Here we test whether hybridization accelerates adaptive evolution in response to DNA damage, using yeast as a model. We exposed 180 populations of hybrids between species (Saccharomyces cerevisiae and Saccharomyces paradoxus) and their parental strains to UV mimetic and control conditions for approximately 100 generations. Although we found that adaptation occurs in both hybrids and parents, hybrids achieved a lower rate of adaptation, contrary to our expectations. Adaptation to DNA damage conditions comes with a large and similar cost for parents and hybrids, suggesting that this cost is not responsible for the lower adaptability of hybrids. We suggest that the lower adaptive potential of hybrids in this condition may result from the interaction between DNA damage and the inherent genetic instability of hybrids.
Highlights
Heterogeneous environments constantly challenge organisms by changing which phenotypes are optimal
Experimental Evolution We tested whether yeast hybrids would adapt faster than parental species to DNA stress conditions
We carried out an experiment with 90 independent populations of two parental species (S. cerevisiae and S. paradoxus) and their F1 diploid hybrid
Summary
Heterogeneous environments constantly challenge organisms by changing which phenotypes are optimal. Prime examples include Darwin finches, which benefited from hybridization during adaptation to the adverse climatic conditions caused by the exceptionally severe El Niño event (Grant & Grant, 1996) Another example is increased invasiveness of plant species (Schierenbeck & Ellstrand, 2009). Rise in sea level is associated with recurrent hybridization between native species and invasive ones of the Spartina genus in coastal marshes (Gallego-Tévar et al, 2018, 2019) In such cases, hybridization may facilitate adaptation through genomic admixture and its associated increase in phenotypic diversity, which could be critical in extreme environments (Grant & Grant, 1996; Heil et al, 2017; Lexer et al, 2003; Martin et al, 2006). Hybrids often show phenotypes outside of the range observed in parental species because of transgressive segregation or heterosis, and these phenotypes may be adaptive (Landry et al, 2007; Nolte & Sheets, 2005; Rieseberg et al, 1999; Vega & Frey, 1980)
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