Effects of rearing conditions on behavioural phenotypes in specialist versus generalist leaf beetles

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The food quality experience during early ontogenetic stages is expected to lead to a fixation of preference for this particular diet later in ontogeny. Moreover, early experience might affect the overall behavioural phenotype of adults. Within the first funding period, leaf beetles with different degrees of food specialisation, the specialist Phaedon cochleariae and the generalist Galeruca tanaceti, were reared either on low quality diet, on high quality diet, or they received a mixed food, i.e., alternately low and high quality food in a 2 d interval. We found that adults preferred diet of higher quality when they had been reared on this diet. In contrast, individuals reared on mixed quality diet did not show clear preferences. The behaviour was highly consistent across various contexts (5 test batteries with 9 variables in total were recorded) and time (3 time-points during adulthood were measured). Furthermore, the behavioural phenotypes strongly depended on the experienced food quality; individuals having fed on low quality diet were bolder but less active than individuals reared on high quality food. The different behaviours may be caused by contrasting life histories, as beetles reared on low quality diet developed slower, reached lower body masses and probably lay fewer eggs. According to the asset-protection principle, they may thus have less to lose and therefore be more risk-prone compared to adults reared on high quality diet. The low diet quality received by these individuals may result in lower activity due to a lack of energy resources and thus be a constraint rather than an adaptation. In the second funding period, we aim to determine 1) the fitness consequences of different diet experience at various time points during the adult stage in relation to the behavioural phenotype; 2) the time-point or stage during development at which the preference for quality diet as well as the behavioural phenotype is shaped in individuals experiencing different food quality; 3) in how far transgenerational effects on offspring traits occur; and 4) whether mate-choice occurs. Insects will be kept on either single or mixed diet differing in quality and their preferences, reproductive outputs and behavioural phenotypes tested now at an extended number of time-points, starting already within the second larval instar (for behaviours). Match-mismatch experiments will be conducted to determine whether and when a shaping occurs and whether it is adaptive. In case assortative mating becomes evident, the underlying principles will be identified using chemical ecological methods. This comprehensive approach will offer a deep insight in the plasticity of behaviour in two insect species differing in diet breadth.