Résumé
Evolutionary Rescue (ER) occurs when populations, which have declined due
to rapid environmental change, recover through genetic adaptation. The
success of this process and the evolutionary trajectory of the population
strongly depend on the rate of environmental change. Here we investigated
how different rates of temperature increase (from 23°C to 32°C) affect
population persistence and evolutionary change in experimental microcosms
of the protozoan Paramecium caudatum. Consistent with theory on ER, we
found that those populations experiencing the slowest rate of temperature
increase were the least likely to become extinct and tended to be the best
adapted to the new temperature environment. All high-temperature
populations were more tolerant to severe heat stress (35°C, 37°C),
indicating a common mechanism of heat protection. High-temperature
populations also had superior growth rates at optimum temperatures,
leading to the absence of a pattern of local adaptation to control (23°C)
and high-temperature (32°C) environments. However, high-temperature
populations had reduced growth at low temperatures (5-9°C), causing a
shift in the temperature niche. In part, the observed evolutionary change
can be explained by selection from standing variation. Using mitochondrial
markers, we found complete divergence between control and high-temperature
populations in the frequencies of six initial founder genotypes. Our
results confirm basic predictions of ER and illustrate how adaptation to
an extreme local environment can produce positive as well as negative
correlated responses to selection over the entire range of the ecological
niche.