Experimental adaptation to marine conditions by a freshwater alga

Abstract

The marine-freshwater boundary has been suggested as one of the most difficult to cross for organisms. Salt is a major ecological factor and provides an unequalled range of ecological opportunity because marine habitats are much more extensive than freshwater habitats, and because salt strongly affects the structure of microbial communities. We exposed experimental populations of the freshwater alga Chlamydomonas reinhardtii to steadily increasing concentrations of salt. About 98% of the lines went extinct. The ones that survived now thrive in growth medium with 36 g⋅L(-1) NaCl, and in seawater. Our results indicate that adaptation to marine conditions proceeded first through genetic assimilation of an inducible response to relatively low salt concentrations that was present in the ancestors, and subsequently by the evolution of an enhanced inducible response to high salt concentrations. These changes appear to have evolved through reversible and irreversible modifications, respectively. The evolution of marine from freshwater lineages is an example that clearly indicates the possibility of studying certain aspects of major ecological transitions in the laboratory.

Sex increases the probability of evolutionary rescue in the presence of a competitor

“…Previous studies have shown that sex can be beneficial when an environment deteriorates in a simple way (Lachapelle & Bell, ; Lachapelle, Bell, & Colegrave, ). Our findings are consistent with these results, given that relative advantage of sexual over asexual populations (in the number of evolutionary rescue events) was 57% in an environment comprising a deteriorating abiotic component.…”

Experimental strategies to assess the biological ramifications of multiple drivers of global ocean change—A review

“…Finally, the way in which drivers change, in addition to intensity and combinations of drivers involved, has the potential to impact evolutionary responses. Rates of environmental change (Collins & de Meaux, ; Lachapelle, Bell, & Colegrave, ), or the presence of environmental fluctuations (Schaum & Collins, ) impact adaptive responses. This is an area where there is a large body of evolutionary theory (Botero, Weissing, Wright, & Rubenstein, ; Collins, de Meaux, & Acquisti, ; Lande, ), which should be exploited to better guide the design of future experiments.…”

Evolution caused by extreme events

“…The rate and duration of environmental change in extreme conditions may be more important than the magnitude of change in determining whether the outcome is extinction, a shift in geographical distribution or local evolution and persistence [20,[26][27][28].…”