I predicted exploration and activity would not influence habituation, as they are not conceptually related to threatening situations (Réale et al., 2007). This was, overall, supported by my findings, as exploration and activity had no significant effect on habituation. These traits could reasonably be hypothesised to have some influence on habituation if they affected the risk-taking of crickets in an indirect way, such as if active crickets were less likely to stay still for multiple extended periods of time (for example, due to them requiring a stronger stimulus than less active crickets to motivate immobility). There was some evidence for this, as, in female crickets, there was a tendency for more active crickets to habituate more readily to the threatening stimuli. In the field of animal personality, it has not been easy to devise tests that distinctly measure only one personality trait (Réale et al., 2007; Carter et al., 2013). These results suggest that activity can have an impact in a risk-taking context, when the response measured is clearly connected to locomotion, like freezing. 

 

Exploration had no impact on habituation, suggesting that the novelty of the situation was overpowered by the threat, and had no effect on the crickets’ behaviour. This is interesting as the relationship between antipredator behaviour and responses to novelty is not clear (e.g. Carter et al., 2012). However, I found no significant correlation between boldness and exploration. This suggests that exploration and boldness in crickets were appropriately separated and measured by our assays, and these methods can be reliably used in further work on personality.

 

I predicted that bold individuals would more readily habituate to simulated predator attacks. This was based on the fact that boldness may be connected to the tendency to habituate to a threatening stimulus, such as a predator attack, as boldness is the willingness to take risks (Réale et al., 2007). Indeed, this is what I found for male crickets. Habituation to risky stimuli could, thus, be considered part of boldness, and both the shelter emergence test and the habituation test may measure the same underlying trait. However, there was no connection between boldness and habituation in females. Therefore, either habituation to risky stimuli is not exactly the same trait as measured in the shelter emergence test, or there is a sex difference in what constitutes boldness in these tests. Because boldness and habituation are easily connected on the conceptual level, it is unlikely they represent completely separate traits. Males and females may differ in the neurological mechanisms underlying risk-taking, and how they adapt to ecological variation. This could result in males and females behaving similarly in a test measuring boldness in one instant (shelter emergence test) but differently in a test measuring boldness over time (threatening stimulus test).

 

The difference between bold male and bold female crickets may reflect subtle sex differences in the potential gains of risk-taking in the shelter emergence test and the habituation test, as even a bold individual should not be expected to take risks for no potential reward. Access to mates is potentially more valuable to males than females (Bateman, 1948; Janicke et al., 2016), so bold females may take risks primarily to gain resources, while bold males also take risks to find mates. In the shelter emergence test, crickets had to walk out of shelter into an open area, which was not visible to the cricket before emerging, and, therefore, might contain food. In the habituation test, crickets were allowed to explore the arena for 1 minute before the first simulated attack and may have determined that there was no food in the arena. In addition to the test cricket, other crickets were present in the room throughout testing and chirping sounds (produced by males to attract females (Horch et al., 2017)) were virtually always audible. Bold male crickets may have been encouraged to take risks and move around by the perceived proximity of female crickets and male competitors, while bold female crickets may perceived no potential reward for taking risks in the same situation. Antipredator behaviour sex differences, in which females value food more than males, have been observed before (Post & Götmark, 2006; Vesakoski et al., 2008; Powolny et al., 2014). By incorporating the option of access to resources into experiments looking at habituation to risky stimuli, we may develop a more complete understanding of the sex differences I found here. In addition, variation in sociability (the individual's response to the presence of absence of conspecifics (Réale et al., 2007)) could explain some of the variation in how individuals behaved in the threatening stimulus test, as crickets in the test are alone in a threatening situation and can hear other crickets nearby. Differences in how the physical absence and auditory presence of conspecifics is preceived by crickets could have had effects on their responses to the threats. Currently, sociability has not been studied in crickets and it is not known if they possess individual differences in this trait.

 

Predator personality and behaviour is an important factor shaping predator-prey interactions, and, thus, whole communities (Toscano & Griffen, 2014; Chang et al., 2017; Start & Gilbert, 2017). Based on my results, I can hypothesise that variation in predator behaviour is relevant to the variation in prey responses to attacks. Sensitisation-prone crickets are well-prepared for a persistent predator that stays nearby and might attack again, while habituation-prone crickets are prepared for a predator that gives up and moves on easily (or easily allows a fleeing cricket to escape). Whether crickets habituate or become sensitised, could affect what type of predators predate on them (as with mudcrabs ( Panopeus herbstii) and their different predators (Belgrad & Griffen, 2016)), and could also predict how crickets respond to new predators or are able to exploit new resources. Notably, non-native, migrant populations tend to be better at utilising novel resources, but worse at evading novel predators compared to the native populations, that are familiar with the predators. This has to do with boldness-biases in the individuals that found migrant populations (reviewed by Carlsson et al., 2009 (multiple taxa); Chapple et al., 2012 (multiple taxa); Juette et al., 2014 (freshwater fish)). I hypothesise that being prone to habituation could be one of the mechanisms by which non-native individuals take advantage of resources, at the expense of the more sensitisation-prone native individuals, and by which they are also more easily attacked by native predators.

 

In conclusion, I found that the way personality variation affected responses of individuals to repeated simulated predator threats, depended not only on the personality measure in focus, but also on sex. For boldness, crickets varied in how they responded to repeated simulated predator attacks, and in male crickets, bold individuals were more likely to habituate to the attacks. This could be because males had more to gain by taking risks while being under threat, and future work should test this hypothesis. In general, future studies on animal personality must take into account that there may be sex differences in potential costs and benefits of risk-taking in different situations. Differences in tendency to habituate are likely to be important for predator-prey relationships, with potential implications for intraspecific competition.

 

Acknowledgments

 

I want to thank my supervisor Hanne Løvlie for her help and support and my examiner Carlos Guerrero-Bosagna for his help. I want to thank Susana Garcia Dominguez, Laura Garnham, Kristoffer Lundgren, Clara Gómez Dunlop, and Rob Boddington for their help with testing and improving the thesis.