Warming temperatures associated with climate change and urbanization affect both terrestrial
and aquatic populations with freshwater fish being especially vulnerable. As fish
rely on water temperature to regulate their body temperature, elevated temperatures
can alter physiology and in turn behavioral and cognitive skills. We examined whether
reproduction, physiology, behavior, and cognitive skills were altered by exposure
to elevated water temperatures during one reproductive cycle in the live-bearing fish,
Gambusia affinis. We found that within four days of exposure to a higher temperature
(31 degrees C), females were more likely to drop underdeveloped offspring than females
maintained at 25 degrees C. However, females did not show a change in cortisol release
rates over time or altered fecundity and reproductive allotment, despite increased
growth at the higher temperature. But in the heat treatment fish that started the
experiment with higher baseline cortisol dropped their offspring sooner than fish
with lower cortisol release rates. We used a detour test to explore behavior and cognitive
skills at three time points after exposure to the heat treatments: early, midway,
and at the end (day 7, 20 and 34). We found that on day 7, females were less likely
to exit the starting chamber when maintained at 31 degrees C but did not differ in
their time to exit the starting chamber or in their motivation (reach the clear barrier).
Similarly, females did not differ in their time to swim around the barrier to reach
a female fish reward (solving skill). Nonetheless, we found a link between behavior
and cognition, where females who were slower to exit the start chamber got around
the barrier faster, indicating that they learned from prior experience. Together our
results indicate that G. affinis is initially affected by elevated water temperatures
but may partially cope with higher temperatures by not altering their hypothalamus-interrenal
axis (baseline cortisol), and at the same time this might act to buffer their young.
Acclimation may reduce costs for this species and potentially explain why they are
successful invaders and tolerant species despite climate change.
