Abstract

Introduction: Behavioural traits can differ considerably between individuals, and such differences were found to be consistent over the lifetime of an organism in several species. Whether behavioural traits of holometabolous insects, which undergo a metamorphosis, are consistent across ontogeny is virtually unexplored. We investigated several behavioural parameters at five different time points in the lifetime of the holometabolous mustard leaf beetle Phaedon cochleariae (Coleoptera: Chrysomelidae), two times in the larval (second and third larval stage) and three times in the adult stage. We investigated 1) the stability of the behavioural phenotype (population level), 2) whether individuals rank consistently across behavioural traits and over their lifetime (individual level), and 3) in how far behavioural traits are correlated with the developmental time of the individuals.Results: We identified two behavioural dimensions in every life stage of P. cochleariae, activity and boldness (population level). Larvae and young adults ranked consistently across the investigated behavioural traits, whereas consistency over time was only found in adults but not between larvae and adults (individual level). Compared to adult beetles, larvae were less active. Moreover, younger larvae were bolder than all subsequent life stages. Over the adult lifetime of the beetles, males were less active than females. Furthermore, the activity of second instar larvae was significantly negatively correlated with the development time.Conclusions: Our study highlights that, although there is no individual consistency over the larval and the adult life stage, the behavioural clustering shows similar patterns at all tested life stages of a holometabolous insect. Nevertheless, age- and sex-specific differences in behavioural traits occur which may be explained by different challenges an individual faces at each life stage. These differences are presumably related to the tremendous changes in life-history traits from larvae to adults and/or to a niche shift after metamorphosis as well as to different needs of both sexes, respectively. A faster development of more active compared to less active second instar larvae is in line with the pace-of-life syndrome. Overall, this study demonstrates a pronounced individuality in behavioural phenotypes and presumably adaptive changes related to life stage and sex.

Highlights

  • Behavioural traits can differ considerably between individuals, and such differences were found to be consistent over the lifetime of an organism in several species

  • We investigated 1) the stability of the behavioural phenotype, 2) whether individuals rank consistently across behavioural traits and over their lifetime, and 3) in how far behavioural traits are correlated with the developmental time of the individuals

  • Applying an agglomerative cluster analysis on the measured behaviours combined with a Silhouette plot to determine the likely number of behavioural groups for each life stage separately, two dimensions of behavioural traits could be identified for L2 and L3 larvae as well as young adults (10-17 d old, adulthood [between day 10-17 (A1)) at the population level (Fig. 1)

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Summary

Introduction

Behavioural traits can differ considerably between individuals, and such differences were found to be consistent over the lifetime of an organism in several species. Age- and sex-specific differences in behavioural traits occur which may be explained by different challenges an individual faces at each life stage These differences are presumably related to the tremendous changes in life-history traits from larvae to adults and/or to a niche shift after metamorphosis as well as to different needs of both sexes, respectively. Animals exhibit an enormous array of life-histories which offers the opportunity to study stabilities or changes in behavioural traits over the entire ontogeny of an organism. For such studies, invertebrates are convenient model organisms due to their usually shorter life span compared to vertebrates [15,16]. Mainly hemimetabolous insects were studied [17,18,19], whose life-history trajectories are, more stable than that of holometabolous insects (but see [20])

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