Phenotypic data for: Does size-selective harvesting erode adaptive potential to thermal stress?

Overharvesting is a serious threat to many fish populations. High
mortality and directional selection on body size can cause evolutionary
change in exploited populations, via selection for a specific phenotype
and a potential reduction in phenotypic diversity. Whether the loss of
phenotypic diversity that accompanies directional selection impairs
response to environmental stress is not known. To address this question,
we exposed three zebrafish selection lines to thermal stress. Two lines
had experienced directional selection for (1) large and (2) small body
size, and one was (3) subject to random removal of individuals with
respect to body size (i.e. line with no directional selection). Selection
lines were exposed to three temperatures (elevated, 34°C; ambient, 28°C;
low, 22°C) to determine the response to an environmental stressor (thermal
stress). We assessed differences among selection lines in their life
history (growth and reproduction), physiological traits (metabolic rate
and critical thermal max), and behaviour (activity and feeding behaviour)
when reared at different temperatures. Lines experiencing directional
selection (i.e., size selected) showed reduced growth rate and a shift in
average phenotype in response to lower or elevated thermal stress compared
with fish from the random-selected line. Our data indicate that
populations exposed to directional selection can have a more limited
capacity to respond to thermal stress compared with fish that experience a
comparable reduction in population size (but without directional
selection). Future studies should aim to understand the impacts of
environmental stressors on natural fish stocks.