Do reproduction and parenting influence personality traits? Insights from threespine stickleback

Abstract

Although one of the hallmarks of personality traits is their consistency over time, we might expect personality traits to change during life history shifts. Becoming a parent is a major life history event, when individuals undergo dramatic behavioural and physiological changes. Here we employ a longitudinal experiment to ask whether personality changes in response to the experience of parenting in male threespine sticklebacks, Gasterosteus aculeatus. Life history theory predicts that males should be less risk averse after successfully parenting, and the neuroendocrinology of parenting suggests that parenting could reorganize the hormonal landscape and behaviour of fathers. We randomly assigned males to either an experimental group (reproduced and parented) or a control group (did not reproduce and parent), and repeatedly measured a personality trait ('boldness') and 11-ketotestosterone levels (11-kT, the major androgen in fishes) in individual males. In the control group, males became bolder over time. However, in the experimental group, boldness did not change. Furthermore, 11-kT changed dramatically in the experimental group, and changes in 11-kT in parents were associated with boldness after parenting ceased. Our study is one of the first to assess proximate and ultimate explanations for changes in personality as a function of reproduction and parenting.

Keywords: behavioural syndrome; boldness; fathers; hormones; individual differences; paternal care.

Figure 1

Overview of the experimental design. Experimental and control male sticklebacks experienced the same assays, with the exception that males in the control treatment were not allowed to spawn with a female. Each control male was paired with an experimental male upon finishing the first three boldness trials (risk-taking behaviour in response to a model predator before reproduction and parenting by experimental males, Before). Once both males in a pair had built nests, we conducted all behavioural and 11-ketotestosterone (11-kT) measurements on the same day for both experimental and control males (i.e. 3 days post-experimental male spawning (eggs), 3 days post-experimental male eggs hatching (fry), and in response to a model predator after reproduction and parenting by experimental males (After)), which allowed us to control for variation among experimental males in time to spawn and time to complete a clutch.

Figure 2

Mean ± SE (a) latency to eat, (b) number of pecks at food and (c) number of squares moved by male threespine sticklebacks in response to a model predator before (Before) vs after (After) reproduction and parenting by experimental males.

Figure 3

Mean ± SE release rate of 11-ketotestosterone (11-kT) over time in experimental and control groups of male threespine sticklebacks.

Figure 4

Shifts in 11-ketotestosterone (11-kT) and its correlation with number of pecks at food in experimental and control groups of male threespine sticklebacks before (Before) vs after (After) reproduction and parenting by experimental males. The dashed line indicates no change After vs Before; points above the line indicate males with greater 11-kT After and points below the line indicate males with lower 11-kT After.