Perch in a heated ecosystem reveal how climate change can shape fish evolution

Jingyao Niu has used data collected over the course of the past four decades, and compared perch from an artificially warmed ecosystem with those from a neighbouring non-warmed ecosystem. Her studies show that the “heated” perch reached sexual maturity at a smaller size. After more generations of heat exposure, perch reached maturity at an even smaller size. This suggests that there might have been an evolutionary adaptation in the life history of fish to ecosystem warming.

− When it comes to adaptive evolution – maximizing one's own reproductive success – there is often trade-offs among life-history traits in fish. For example, it can be a fitness advantage to reach sexual maturity at a smaller size in warm conditions. This is because a smaller body has in general less heat loss, spends less energy in growth and thus can devote more energy to reproduction. Being able to reproduce as early as possible also increase the chance of reproducing when the environment is unstable or hostile, explains Jingyao Niu.

She also compared DNA between perch from the warmed- and non-warmed-ecosystem, extracted from older bone and fresh muscle samples collected over the four decades of warming. The results indicate that the perch in the warmed area have changed genetically in response to living in the higher temperatures.

Jingyao Niu also conducted a field experiment where she hatched larvae from perch eggs collected from the warmed and non-warmed areas, and placed them in tanks separately with zooplankton and phytoplankton. The results showed that the larvae from the warmed area may have developed adaptations in their foraging behaviour, as they ate fewer zooplankton, but larger, than the larvae from the non-warmed area.

− This is important because it shows how the effects of climate change at one trophic level in the ecosystem can have effects cascade down to another level via species interactions, says Jingyao Niu.

Her thesis clarifies that ecosystem-scale warming can drive evolutionary changes in fish, and that these changes, in turn, can affect ecosystems.

− My research shows the importance of considering evolutionary processes along with ecological factors when evaluating the effects of climate change, as I am not studying only the effects of increase in temperature per se, but, most importantly, the effects of a warmed up ecosystem, says Jingyao Niu.

Read the thesis Ecological and evolutionary consequences of ecosystem warming in fish