The role of boldness and other personality traits in the ecology of juvenile marine fishes

The theory of animal personality focuses on quantifying variation in behavior within and among individual organisms and attempts to account for the maintenance of differences in behavior that occur in a consistent manner among individuals. Personality has potentially important ecological consequences (e.g. behavioral tradeoffs) and can be shaped by population dynamics through selective mortality. Flexibility in behavior is advantageous for organisms that transition between stages of a complex life history. However, various constraints can set limits on plasticity, giving rise to the existence of personalities that have associated costs and benefits. One particularly important behavioral trait, boldness, is defined as the propensity of an animal to engage in risky behavior. Many variations of novel-object or novel-environment tests have been used to quantify the boldness of animals, although the relationship between test outcomes has rarely been investigated. Furthermore, the relationship of boldness measures to any ecological aspect of fitness is generally assumed, rather than measured directly. Understanding the costs and benefits of different behavioral phenotypes requires a greater understanding of structure and temporal consistency of intra-individual behaviors. More research is necessary for identifying the traits with potential fitness costs or showing how any trade-offs are manifested. This study therefore investigated the situational and temporal consistency of behavior, appropriateness of various boldness measures, and the relationships between different behavioral traits in order to better understand how coral reef fishes balance trade-offs related to risk. To understand the stability of fish behavior across various field and laboratory settings, there is a need to understand the behavioral structure throughout different situations. Chapter 2 tested for any evidence in consistency of behavior across situations in juveniles of a common damselfish, Pomacentrus amboinensis (Pomacentridae) at the transition between larval habitats in the plankton and juvenile habitats on the reef. Naïve fish leaving the pelagic phase to settle on reefs were caught by light traps and their behaviors observed using similar methods across three different situations (small aquaria, large aquaria, field setting); all of which represent low risk and well-sheltered environments. Seven behavioral traits were compared within and among individuals across situations to determine if consistent behavioral syndromes existed. No consistency was found in any single or combination of behavioral traits for individuals across all situations. We suggest that high behavioral flexibility is likely beneficial for newly-settled fishes at this ontogenetic transition and it is possible that consistent behavioral syndromes are unlikely to emerge in juveniles until environmental experience is gained or certain combinations of behaviors are favored by selective mortality. Despite the lack of evidence for behavioral syndromes, individual juvenile coral reef fish are likely to show behavioral repeatability within a single situation, over time (i.e. personality). Chapter 3 documented a field and laboratory experiment that examined the consistency of measures of boldness, activity, and aggressive behavior in young P. amboinensis immediately following their transition between pelagic larval and benthic juvenile habitats. Newly-settled fish were observed in aquaria and in the field on replicated patches of natural habitat cleared of resident fishes. Seven behavioral traits representing aspects of boldness, activity and aggression were monitored directly and via video camera over short (minutes), medium (hours), and longer (3 days) time scales. With the exception of aggression, these behaviors were found to be moderately or highly consistent over all time scales in both laboratory and field settings, implying that these fish show stable personalities within various settings. The various operational definitions and employed methodology for studying 'boldness' in animals confounds comparisons among behavioral studies. Also, little is known how these various techniques compare in an ecologically meaningful way. Chapter 4 compared how the outcomes of the same test of boldness differed among observers and how different tests of boldness related to the survival of individuals in the field. Newly-metamorphosed lemon damselfish, P. moluccensis, were placed onto replicate patches of natural habitat. Individual behavior was quantified using four tests (composed of a total of 12 different measures of behavior): latency to enter a novel environment, activity in a novel environment and reactions to threatening and benign novel objects. After behavior was quantified, survival was monitored for two days during which time fish were exposed to natural predators. Variation in estimates of behavior among observers was low for most of the 12 measures, except distance moved and the threat test (reaction to probe thrust), which displayed unacceptable amounts of inter-observer variation. Body size and distance ventured from shelter were the only variables that had a direct and positive relationship with survival. Overall, the results of the behavioral tests suggested that novel environment and novel object tests quantified similar behaviors, yet these behavioral measures were not interchangeable. Being more bold or shy is likely to produce a trade-off with other important facets of an individual animal's behavioral phenotype. Chapter 5 used a laboratory experiment to examine the link between boldness and learning in juveniles of P. amboinensis. Newly-metamorphosed fish were ranked individually on a boldness-shyness axis on the basis of their willingness to emerge into a novel environment in an aquarium. Each fish was then given a simple task four times, which involved learning how to navigate a maze to reach a food source. A greater number of fish ranked with high boldness successfully navigated the maze compared to shy ranked fish. This result suggests that boldness is likely to be closely linked with learning appropriate behaviors while exploring new habitats. Although a higher level of boldness is inherently risky in a habitat where animals are subject to high rates of predation, the potential for increased rewards associated with this trait may explain why boldness persists as a behavior in natural populations. This study is among the first to examine the consistency of behaviors in both field and laboratory settings in over various time scales at a critically important phase during the life cycle of a coral reef fish. Multiple measures of behavior within the context of novel environment were the most robust way to assess boldness, and these measures have a complex relationship with survivorship of young fish in the field. The persistence of multiple alternative behavioral phenotypes despite strong selective pressure from predation may reflect the balance between foraging and predator vigilance. Shy individuals may allocate more attention to exploring and searching environments in greater detail, since their inherent shyness means that they are naturally under lower predation threat than bolder individuals. Conversely, bolder individuals may allocate less attention to searching because of the need to have a greater degree of predator vigilance. If such a relationship exists, this would predict that greater numbers of bold individuals should occur within stable (e.g., consistent predator distribution and abundance) compared to variable environments. Thus, the ratio of bold to shy individuals of adult populations of coral reef fish might be influenced by the stability of the local environment they experienced as juveniles