Understanding what makes a lizard invasive: the role of behaviour and cognition

The world has been changing at an unprecedented rate due to the 'progress' of human society. Globalization has changed our way of living, and it translates into severe negative effects on our ecosystems. Additionally, globalization also demands more connections and transport, creating frequent and dynamic networks worldwide, of both people and cargo. This can lead to the movement of thousands of species outside their native range, and biological invasions are now a contemporary global problem. While most invasions end in failure, some manage to successfully take hold and adapt to new locations. What determines a species' invasive success is of great interest and importance for conservation efforts. Behaviour is believed to play a key role in the success of invasive species, although the mechanisms are still unclear, especially for unintentional invasions. Members of the lizard genus Podarcis show high variability in their invasive potential and are thus a well-suited model for studying the role of behaviour during biological invasions. The Italian wall lizard, Podarcis sicula, is a globally invasive species that hitchhikes on transportation of people or cargo, and does well in novel environments. In addition to behaviour, there is mounting evidence that cognition may also be a determining factor for invasion success. The aim of my thesis is to understand the role of behaviour and cognition in determining what makes P. sicula such a good invader. I used animals from an introduced population in Lisbon (Portugal) to examine behavioural traits that might be linked to a species' invasive success. My original contribution to knowledge is uncovering the potential role of behavioural flexibility, social learning ability, behavioural traits, and competition in the invasion process. Although I focused on the invasive lizard P. sicula, my study highlights the potential role of behaviour and cognition in invasions more broadly. My thesis has thus 4 chapters written as stand-alone publications that deal with different behavioural components. I predicted that P. sicula would have greater levels of behavioural flexibility than congeneric non-invasive species - P. bocagei and P. carbonelli. The ability to reverse a previously learnt discrimination can be indicative of behavioural flexibility. I used a discrimination task and a reversal and quantified the number of errors and overall learning ability of all three species (chapter I). The invasive species had relatively less difficulty than the non-invasive species to reverse the task. Also, I found different cognitive ability between the invasive species and the two non-invasive species (P. bocagei and P. carbonelli had a more similar learning pattern between them). Chapter II dealt with the ability of P. sicula to obtain relevant social information to solve a task, from other P. sicula, or from a different species they had never encountered in nature (P. bocagei). The role of heterospecific learning in biological invasions has never been studied before. Remarkably, this invasive species learnt equally well from individuals of the same or different species. In chapter III, I used a sympatric congeneric species, P. virescens, native to the study site, to compare personality traits likely related to invasive success. I measured exploratory behaviour of lizards in a novel arena (activity and shelters visited); boldness (latency to emerge from a suboptimal shelter, after being scared into it); and neophobia (minimum distance between a lizard and a novel object placed in the arena). I found the invasive P. sicula to be more exploratory, neophilic, and bolder than the sympatric native species. Additionally, while the native species showed high repeatability in its behaviours and had all traits correlated, the invasive species was much less consistent and showed no correlation between traits. Finally, since the sympatric P. virescens has likely been displaced from gardens where P. sicula is found, interspecific competition could be an important factor governing their success as an invader. I thus assessed the mechanisms P. sicula might use to outcompete the sympatric P. virescens in this location (chapter IV). I established mixed groups of both species and scored several behaviours linked to competitive ability. Although I predicted competitive interference (e.g. the invasive species with more aggressive behaviours), I actually found evidence for competitive exploitation (e.g. the invasive species being more efficient at exploiting resources). Collectively, my thesis shows differences in cognitive skills between invasive and non-invasive Podarcis, and that the invasive P. sicula is able to socially learn from the same and different species. Also, P. sicula has behavioural traits (e.g. boldness and foraging efficiency) that can be linked to its invasive success. The results from these chapters highlight the potential importance of behaviour in biological invasions, and give insight into why this lizard species is such a successful invader, and into what impact it might have on native species. This work will hopefully contribute to a better understanding of the behavioural basis of invasions, and ultimately assist conservation efforts.