Responses to threat in a freshwater invader: longitudinal data reveal personality, habituation, and robustness to changing water temperatures in the "killer shrimp" Dikerogammarus villosus (Crustacea: Amphipoda)

Changes in the anxiety-like and fearful behavior of shrimp following daily threatening experiences

Behavioral variation in animals is often influenced by experience. Previous studies have found that daily threatening experiences can enhance fear- and anxiety-like behaviors in some vertebrates. However, it is unclear whether the change in fear/anxiety behavior occurs in invertebrates. The present study investigated whether fear/anxiety behavior could be affected by a net-chasing treatment in two shrimp species (Neocaridina denticulata ssp. and Palaemon pacificus). The net-chasing treatment was repeated for 8 days to simulate daily predator experiences, and behavioral tests (open-field, shelter-seeking, and escape-response tests) were conducted on the day following the last day of treatment. Net-chased N. denticulata ssp. displayed a tendency to remain near a wall compared with the control in the open-field test, whereas net-chased P. pacificus shrimps demonstrated greater escape behavior compared with the control in the escape-response test. These results suggest that fear/anxiety behavior for both shrimp species can be affected by the net-chasing treatment, although the pattern of behavioral change differed between the two species. The findings suggest that daily threatening experiences change the behavior of shrimp and cause them to select a regular avoidance strategy when they encounter risks and unknown situations.

To hide or to feed: an evaluation of personality traits in the sand bubbler crab, Dotilla wichmanni, when responding to environmental interference

Behaviour plays a crucial role in a species' ability to cope with environmental challenges. However, this ability may be affected by repeatable individual differences in behaviour, a pattern described as animal personality. The consideration of animal personality is therefore essential when understanding how a species copes with its environmental stressors. For sand bubbler crabs, feeding is often disrupted by environmental interference, in the forms of predatory events and human recreational activities. How these crabs deal with such disruption is, however, not well documented. Here, we characterised the foraging and risk-taking behaviours of Dotilla wichmanni when responding to induced disruption. Whether these are personality traits and if they form part of a behavioural syndrome were also examined. We quantify both behaviours by taking four measures (two per behaviour). All behavioural measures were consistently different among individuals, suggesting that D. wichmanni exhibits personality. Results further suggest that they could cope with some environmental interference, although this is limited. Crabs did not vary the time spent hiding in burrows with each repeated disruption nor did behavioural plasticity differ between individuals. Notwithstanding these, the absence of support for a foraging-risk propensity behavioural syndrome points to possible complexity in the crabs' coping ability.

Personality traits influence contest outcome, and vice versa, in a territorial butterfly

Holding a territory is often crucial in order to acquire key resources, including mating partners. However, few studies have investigated the role of animal personality in the context of territorial conflicts and how the contest outcome itself may influence personality traits. We studied personality in male Speckled wood butterflies, Pararge aegeria, before and after territorial contests for sunspot territories. Before interactions, boldness decreased with age, while activity and exploration were only influenced by ambient conditions. Neither age nor morphology did influence the probability to win contests, but winners were more active and more explorative than losers and, moreover, males that received a red wing mark were more likely to be winners. Butterflies that lost a contest showed pronounced behavioural changes. Mean boldness increased and its repeatability was disrupted, while no such change was detected in winners. The observed boldness increase in losers may be explained by a ‘desperado effect’, though its implication for successive contests remains unknown. Given that territoriality is expected to have important consequences for reproductive success, our results suggest that personality traits may indirectly contribute to individual fitness by influencing the ability to gain access to mate-location patches.

The influence of environmental gradients on individual behaviour: Individual plasticity is consistent across risk and temperature gradients

The expression of individual behaviour as a function of environmental variation (behavioural plasticity) is recognized as a means for animals to modify their phenotypes in response to changing conditions. Plasticity has been studied extensively in recent years, leading to an accumulation of evidence for behavioural plasticity within natural populations. Despite the recent attention given to studying individual variation in behavioural plasticity, there is still a lack of consensus regarding its causes and constraints. One pressing question related to this is whether individual plasticity carries over across temporal and environmental gradients. That is, are some individuals more plastic (responsive) than others in general? Here, we examined the influence of temporal and environmental gradients on individual behavioural responses in a marine gastropod, Littoraria irrorata. We measured individual boldness repeatedly over time and in response to tidal cycle (high vs. low, an index of risk) and daily temperature fluctuations (known to affect metabolism), in a controlled field experiment. On average, boldness increased from high to low tide and with increasing temperature but decreased marginally over time. Individuals also differed in their responses to variation in tide and temperature, but not over time. Those which were relatively bold at high tide (when predation risk is greater) were similarly bold at low tide, whereas shy individuals became much more "bold" at low tide. Most notably, individuals that were more responsive to tide (and thus risk) were also more responsive to temperature changes, indicating that plasticity was correlated across contexts (r = 0.57) and that bolder individuals were least plastic overall. This study provides a rare and possibly first example of consistency of individual behavioural plasticity across contexts, suggesting underlying physiology as a common mechanism, and raises the possibility of correlational selection on plasticity.