The evolution of temperature tolerance and invasiveness in a fluctuating thermal environment

The consequences of the climate change on species are still uncertain, despite of intensive research. Currently, rising temperature is not the only concern, since the climate change scenarios also predict increases in the amount of disturbances, such as storms, floods, and thermal fluctuations. Disturbances have also been shown to affect species’ evolution, for example by selecting for traits that are advantageous in fluctuating environments but are also facilitating invasiveness. In this thesis, I study the consequences of evolving in a fluctuating thermal environment by utilizing bacterial microcosms. First I tested the effects of fluctuating vs. constant temperature on the evolution of temperature tolerance, both in one-species setting (I) and with multiple species (II). Then I studied how pre-adaptations to fluctuating vs. constant temperature, together with environmental conditions, affect invasion success (III). Additionally I also tested the effects of propagule pressure and genetic diversity on invasion success (IV). The results of the studies I and II show that constant and fluctuating thermal environments require different kinds of adaptations, as measurements taken in constant environments (traditional tolerance curve approach) did not reveal the adaptations to fluctuating environment. In study III, I found that fluctuations during invasion as well as pre-adaptations to fluctuating environment increased the invasion success of the invader. However, in study IV, I did not find any clear evidence that high propagule pressure or high genetic variance would have increased invasion success. To conclude, the results in this thesis demonstrate that adaptations that aid species to cope with disturbed environments can also lead to increased invasiveness. Furthermore, these adaptations might not be detectable using traditional measurement methods, which could, in the worst case, lead to incorrect conclusions and management actions, when considering climate-change driven extinction risks, or the effects of invasive species on natural environments.