Behavioural Thermoregulation and Escape Behaviour: Investigating the Thermal Biology of Round Gobies

Abstract

The invasive round goby (Neogobius melanostomus) has successfully colonized all of the Great Lakes since its discovery in the region in 1991, yet little is known about its thermal biology. The focus of this thesis was to examine the effect of acclimation to unseasonably warm temperatures on round goby behavioural thermoregulation, as well as behavioural and physiological performance during escapes with warm acute temperatures. Juvenile gobies were acclimated to either 21°C or 24°C for each set of experiments. I first examined goby thermal preference in a shuttlebox through their ability to escape from unfavourable temperatures. I found that escape temperatures were plastic following acclimation to a rise in 3°C rise in temperature (+3°C) and associated positively with acclimation temperature, even though gobies showed slightly lower-than-expected average escape temperatures in each acclimation treatment. Interestingly, acclimation to +3°C leads to lower exploratory behaviour in warm waters and lower overall activity levels during behavioural thermoregulation. In risky situations involving threat of predation, exploratory behaviour is often linked to boldness. Next I investigated exploratory swimming through two behavioural traits: ability to voluntarily enter a tunnel and subsequent swimming activity while being chased in a detour task. Detour tasks require a fish to swim down a narrow space and then detour to the left or right as they approach a barrier. A strong correlation between behavioural traits suggests the two behavioural traits are a good measure of risky swimming behaviour. With respect to the impact of warm acute temperatures, I observed an increase in strength of risky swimming behaviour following a rise in acute temperature of 6°C (+6°C). Finally, I examined burst swimming performance (C- and S-starts) during the detour task. While there was no observed effect of warm acute temperatures on most C- and S-start performance measures, there was a significant increase in S-start time to maximum velocity at +6°C. Along with the observed plasticity in strength of risky swimming behaviour, my findings showed that acclimation to +3°C shifted physiological performance of escapes. My findings provide a greater understanding of round goby physiological and behavioural functioning during short- and long-term rises in temperature.