Behavioral repeatability of flour beetles before and after metamorphosis and throughout aging

Abstract: Behavioral repeatability is an important trait relevant to personality research and to behavioral ecology in general. We examined here the behavioral repeatability of two activity-related traits: movement and edge preference (proportion of time spent next to the test arena edge). We used the red flour beetle as our test species in order to determine whether repeatability changes throughout metamorphosis and aging and whether there are inter-sexual differences. Young adults moved more than larvae, but movement activity generally declined with age. Behavioral repeatability was high between two successive measurements for larvae and young adults, but did not persist through metamorphosis. These findings support most of the previous studies on insects and probably reflect the occurrence of phenotypic reorganization during metamorphosis. Neither of our predictions of an increase in behavioral repeatability throughout aging and of a higher repeatability of young adults than larvae held true, as repeatability levels estimates remained similar across ontogeny and aging. Similar to other studies on repeatability, estimates declined with the time interval between two pairs of measurements, suggesting an episodic physiological basis for the documented behaviors. Finally, we detected several inter-sexual differences. Females were more active than males and expressed a shallower decline in movement with aging. Female movement activity was also more repeatable, but female edge preference was less repeatable than that of males. We reason that such differences in repeatability may be driven by sex-specific selection pressures on behavioral tendencies. Significance statement: We investigate several questions regarding behavioral repeatability in insects. The two main questions asked are (1) whether inter-individual behavioral differences remain consistent across larvae and adult stage, and (2) how repeatability changes throughout aging. The first question has been only rarely tested in insects that undergo a full metamorphosis. It has been recognized as a timely question and as an opportunity for researchers studying animal personality. Previous results regarding amphibians and insects that undergo partial metamorphosis were inconclusive. The second question is important, because studies rarely follow individuals throughout their lives. This is essential to understand the consequences of aging. We also report on differences between males and females, probably indicating on differences in motivation for activity and in patterns of aging. Finally, the question, how behavior changes with ontogeny, has been already recognized by Tinbergen as a basic one in animal behavior.