Evolutionary Rescue of a Species in a Deteriorating Environment
Lachapelle, J. and Bell, G. 2012. Evolutionary rescue of sexual and asexual populations in a deteriorating environment. Evolution 66: 3508-3518.
Lachapelle and Bell tested this theory by comparing populations of Chlamydomonas reinhardtii - which originally differed in (1) their expression of sexuality and (2) their initial amount of genetic diversity - in a laboratory study where selected lines of the species were serially propagated in watery environments, and where the level of stress caused by periodic salt additions gradually increased over time, as the aquatic environments were transformed from a freshwater state to fully marine salinity conditions.
Based on their analysis, "in the long term," in the words of the two Canadian researchers, "the combination of high diversity and obligate sexuality was most effective in supporting evolutionary rescue," such that "most of the adaptation to high-salt environments in the obligate sexual-high diversity lines [italics added] had occurred by midway through the experiment, indicating that positive genetic correlations of adaptation to lethal stress with adaptation to sub-lethal stress greatly increased the probability of evolutionary rescue."
The take-home message of Lachapelle and Bell's experimental work, as they describe it, is that "the evolutionary rescue events observed in this study provide evidence that major shifts in ways of life can arise within short time frames through the action of natural selection in sexual populations."