Testing models of the adaptive evolution of consistent individual differences in behavior using sticklebacks

Laskowski, Katie

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Description

Title

Testing models of the adaptive evolution of consistent individual differences in behavior using sticklebacks

Author(s)

Laskowski, Katie

Issue Date

2013-08-22T16:41:09Z

Director of Research (if dissertation) or Advisor (if thesis)

Bell, Alison M.

Doctoral Committee Chair(s)

Bell, Alison M.

Committee Member(s)

• Fuller, Rebecca C.
• Suarez, Andrew V.
• Roberts, Brent W.

Department of Study

School of Integrative Biology

Discipline

Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• behavioral ecology
• animal personality
• repeatability
• behavioral syndromes
• responsiveness

Abstract

Traditionally considered one of the most plastic traits an individual could exhibit, there is now mounting evidence that individuals within the same population often differ in their behavior and that these differences are consistent over time and/or across context. This does not necessarily imply that individuals are rigid in their behavioral expression, but rather that each individual can only display a subset of the potential total behavioral variation. Therefore explaining these consistent individual differences in behavior is a recent challenge for evolutionary biology in general and behavioral ecology in particular. While there is some evidence that this limited behavioral plasticity may be a result of physiological or genetic constraints, there is growing theoretical evidence suggesting that instead, consistent individual differences may be the result of adaptive evolution. Several mechanisms have been proposed to generate and maintain consistent individual differences in behavior. In particular, three ecological factors have been implicated in several models: competition, social interactions and environmental uncertainty. Therefore for my dissertation I tested whether these factors influence consistent individual differences as predicted by theory. Additionally, these models make several assumptions about the costs and benefits of different behaviors, which have yet to be tested as to whether they are realistic assumptions to make of natural populations. To test whether competition, social interactions and environmental uncertainty generate consistent individual differences, I measured the behavior of threespined sticklebacks in a foraging context. Foraging provides an ideal context because competition is an inherent quality of any foraging group of individuals, social interactions will occur among foragers, and it is easy to manipulate the level of uncertainty in resource availability. The first hypothesis, the competition avoidance hypothesis, states that competition in a heterogeneous environment might promote consistent individual differences in behavior because among-individual behavior variation can help reduce direct competition among individuals. This hypothesis predicts that consistent individual differences in behavior should be greater when there is the opportunity to avoid competition, compared to when it is unavoidable. To test this, I tested groups of sticklebacks in two different foraging environments that differed in the number of available food patches: one environment contained only one patch at a time making competition unavoidable, whereas a second environment contained two patches where individuals could reduce competition by utilizing both patches. In support of the competition avoidance hypothesis, I found consistent individual differences in social foraging behavior in the two-patch environment; some individuals consistently used the second patch, whereas other individuals continued to only use the first patch. I also found that among-individual differences in foraging behavior grew stronger the longer the group of foraging sticklebacks had been together, evidence of positive feedback, a crucial assumption of most models. In addition, individuals maintained their foraging behavior even when placed in a new social group demonstrating that even though individuals can exhibit some plasticity from context to context, there is still rank-order consistency among individual behavior. The second hypothesis, the social niche specialization hypothesis, states that repeated social interactions should favor consistent individual differences if predictable behavior helps individuals exploit interactions with others. The social niche specialization hypothesis therefore predicts that consistent individual differences in behavior should be greater in groups of individuals that are more familiar with each other. I explicitly tested this hypothesis by manipulating the opportunity for repeated social interaction and comparing the social foraging behavior of groups of individuals that were familiar with one another to groups of individuals that were unfamiliar. Additionally, I tested whether individuals exhibited behavioral types by repeatedly measuring individual behavior in three different contexts: a novel environment, when presented with an opportunity to associate with conspecifics, and when confronted by an intruder. I found no evidence that repeated social interactions increased among-individual variation in social foraging behavior. Instead, variation in social foraging behavior was related to variation in behavioral types. In particular, high shoaling individuals took longer to utilize a new food patch while foraging in a social group compared to low-shoaling individuals. Altogether, the results of this experiment do not support the social niche specialization hypothesis that repeated social interactions generate consistent individual differences in behavior. Instead, they suggest that an individual’s social behavior is largely influenced by their behavioral type. The third hypothesis, the environmental uncertainty hypothesis, states that consistent individual differences in behavior are a result of individuals coping with uncertainty about their environment. This hypothesis predicts that consistent individual differences in behavior should be greater when individuals are in an uncertain environment, compared to a certain environment. I tested groups of foraging sticklebacks in a two patch environment where the patch profitability varied: one environment where patch profitability was certain and reliable, and a second environment where patch profitably varied and was uncertain. Additionally, most models on the influence of environmental uncertainty on consistent individual differences consider solitary foraging animals, however many animals forage in groups where the presence of conspecifics competitors may alter the costs and benefits of foraging behavior. Therefore all individuals were tested both while alone, and while in a group. In support of the environmental uncertainty hypothesis, I found evidence for consistent individual differences in foraging behavior when individuals foraged alone. However, when individuals foraged in groups, consistent individual differences in foraging behavior were present under both certain and uncertain environments. There was also little carryover in how individuals behaved while alone and while in a group. Taken together these results suggest that while uncertainty about some factors such as resource availability may be important drivers of consistent individual variation in behavior when individuals are alone, the presence of social competition can mask these effects. In conclusion my research has demonstrated that competitive interactions among individuals may be one of the most important drivers of consistent individual differences in behavior, at least in sticklebacks. While repeated social interactions did not appear to directly influence behavioral variation, this hypothesis may be more applicable to groups of animals with more stable social groups. Finally, whether or not environmental uncertainty influences consistent individual differences in behavior may be mediated again, by the competitive environment. This suggests that theories surrounding the role of environmental uncertainty may need to incorporate how uncertainty from different types of factors such as resources, or predators, or social partners can work in concert or opposition to influence individual behavior. While interest in consistent individual differences in animal behavior continues to grow, the field can only move forward with more empirical tests of theoretical predictions to determine under which ecological conditions we should expect to find consistent individual differences, and when we should not.

Graduation Semester

2013-08

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Copyright 2013 Katie Laskowski

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