Data from: Does gene flow aggravate or alleviate maladaptation to environmental stress in small populations?

Environmental change can expose populations to unfamiliar stressors, and
maladaptive responses to those stressors may result in population declines
or extirpation. Although gene flow is classically viewed as a cause of
maladaptation, small and isolated populations experiencing high levels of
drift and little gene flow may be constrained in their evolutionary
response to environmental change. We provide a case study using the model
Trinidadian guppy system that illustrates the importance of considering
non-adaptive forces (i.e., gene flow and genetic drift) when predicting
(mal)adaptive response to acute stress. We compared population genomic
patterns and acute stress responses of inbred guppy populations from
headwater streams either with or without a recent history of gene flow
from a more diverse mainstem population. Compared to ‘no-gene flow’
analogues, we found that populations with recent gene flow showed higher
genomic variation and increased stress tolerance – but only when exposed
to a stress familiar to the mainstem population (heat shock). All
headwater populations showed similar responses to a familiar stress in
headwater environments (starvation) regardless of gene flow history,
whereas exposure to an entirely unfamiliar stress (copper sulphate) showed
population-level variation unrelated to environment or recent evolutionary
history. Our results suggest that (mal)adaptive responses to acutely
stressful environments are determined in part by recent evolutionary
history and in part by previous exposure. In some cases, gene flow may
provide the variation needed to persist, and eventually adapt, in the face
of novel stress.