The evolution of risk-taking behaviour during a post-Pleistocene radiation of Bahamas mosquitofish (Gambusia hubbsi)

Abstract

Risk-taking behaviours are essential for animals’ survival and are often referred to as variation along the bold-shy continuum in animal personality research. Predation risk is a fundamental driver shaping individuals’ behaviours, and sex often plays an underlaying role in behavioural variation between individuals as well. Home to a post-Pleistocene radiation of Bahamas mosquitofish, Bahamian blue hole ecosystems have created an ideal natural setting for testing the effect of predation risk on variation in female and male risk-taking behaviours. This is because of low covariation between the presence or absence of predatory fish and other environmental factors. Using common garden experiments, I tested for genetically based differences in risk-taking (boldness) behaviours across predation regimes with laboratory-reared Bahamas mosquitofish. I also assessed the repeatability of boldness behaviours. I found that whether Bahamas mosquitofish originated from sites with predators present or absent did not affect the risk-taking behaviours in a general way, because only females displayed a behavioural divergence in boldness between different predation regimes. Moreover, males were found to be bolder than females in general, and I found that boldness was correlated with the level of aggression into a behavioural syndrome. Finally, I found that the level of behavioural repeatability was similar both across predation regimes and sexes. My data add to our understanding on how important ecological agents of selection may shape behavioural variation and correlations in animal populations and highlights the importance of considering sex-specific differences.

Popular Abstract

Do predators affect risk-taking behaviours in fish?

Just like humans, other animals may also have a “personality”, by behaving consistently in certain situations. Animal personality traits are often divided into five main categories: shyness-boldness, sociability, exploration-avoidance, aggressiveness and activity level. Among those five personalities, shyness-boldness has been mostly studied because it relates to obtaining resources and mating opportunities, while also affecting survival in the wild. Bold individuals are more risk-prone compared with shy individuals, especially when potential danger is lurking. Moreover, some behaviours may often be linked to each other. For example, bolder individuals may also at the same time be more explorative and more aggressive. Exposure to predators and a given animal’s sex may also affect individuals’ risk-taking behaviours. On the Bahamas, old vertical caves filled with water, for approximately 10 000 years ago, are today known as Bahamian blue holes. The unique environments provide a perfect natural setting to study the influence predators have on fish behaviours.

I explored the risk-taking behaviours on the offspring of wild Bahamas mosquitofish raised in standard laboratory conditions, because measuring behaviours on animals from the wild may include environmental effects in addition to underlaying genetically-based behaviours. Hence, I raised all my fish in the same environment, in an experimental design known as “common garden”. This will serve to minimize any environmental effects on the behaviours. I measured fish behavioural responses after I chased them with a dip-net, to simulate a risky situation, for example a predator attack. I collected seven risk-related behaviours to compare risk-taking levels in fish from many perspectives. Also, I conducted the same tests during two consecutive days to test if the behaviours are repeatable, that is if different fish individuals show the same behavioural response across time. Moreover, I tested if boldness relates to other traits (i.e., colour and aggression) to investigate if there is some relationship between boldness and other important characteristics. This is because boldness may influence other behaviours or traits to form a group of features allowing for better adaptation to specific environments.

I found that there is no general difference in boldness between fish originating from sites with predators present or absent, because male fish did not show differences, but females displayed behavioural divergence between predation regimes. Hence, the effect was sex-specific. This suggests that females are more responsive than males towards the effect from predators. Moreover, males were generally more risk-prone than females. I also found that boldness is positively correlated to the level of aggression, but not with colouration. In other words, bolder fish would also be more aggressive towards other fish, while there is no relationship between boldness and colour features. Finally, the risk-taking behaviours were moderately repeatable in all fish. This suggests that a risk-taking “personality” indeed exists in Bahamas mosquitofish.

Predation appears to play a different role in influencing risk-taking behaviours between male and female fish. Thus, it is important to understand such ecological agents of selection because these agents may shape behaviours and correlations among behaviours and other traits in animal populations. Moreover, it appears to be essential to consider male and female behaviours separately when comparing behaviours across ecological gradients. Improvement of understanding of populational differences in this unique system may help to uncover key ecological and evolutionary processes, such as the formation of new species.

Master’s Degree Project in Biology 45 credits, 2021
Department of Biology, Lund University

Advisor: Kaj Hulthén
Aquatic Ecology/Department of Biology

• author: Liu, Runzhe
• supervisor: Kaj Hulthén
• organization: Degree Projects in Biology
• course: BION02 20201
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9059660
• date added to LUP: 2021-06-29 11:03:34
• date last changed: 2021-06-29 11:03:34