The effects of larval developmental conditions on adult personality: A study on two ecotypes of Pararge aegeria (Lepidoptera: Nymphalidae)

Details

Supervisors

Van Dyck, Hans

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

European landscapes have been modified for centuries by human use for agricultural practices and forest exploitation. Fragmentation leads to changes in land cover types, spatial pattern and associated modifications of microclimates, which are key components for habitat choice in ectotherm organisms. Adaptations to environmental conditions can be matched to the environmental context experienced at the adult stage by integrating cues from earlier, larval stages. This leads to individual differences to arise among adults, which is referred to as personality. Our study species, the speckled wood Pararge aegeria, is a bivoltine Nymphalid species that was typically found in closed woodland landscapes, but recently also colonized habitat in other, more open anthropogenic landscapes, like agricultural landscapes. Populations in woodland and agricultural landscape differ in a number of biological traits and are considered ecotypes. We reared larvae of P. aegeria of woodland and agricultural landscape ecotype and studied three adult personality traits: boldness, exploration, and activity. Boldness was tested under laboratory conditions, while exploration and activity were tested in outdoor cages. We showed significant repeatability for boldness. We observed landscape related differences in boldness with forested individuals being bolder. We also found an effect of the ecotype of the mother on boldness. This confirms the effect of plasticity but also highlights the genetic basis of behaviours possibly transmitted through generations, thus making these behavioural differences adaptative. We found that forest environments negatively affect boldness. We found that individuals reared in a forested environment were more explorative and more active than individuals reared in an agricultural setting. In more heterogenous landscapes such as agricultural ones, resources are more scattered, leading butterflies to fly more distance in the inhospitable matrix between suitable habitats than in more homogenous, woodland landscapes. Individuals in forest landscapes face softer barriers and are thus bolder and more explorative. But to face more heterogenous landscapes, individuals need to have higher levels of personality traits (such as boldness), which we show here. This suggest that individuals of P. aegeria may be negatively affected by landscape fragmentation but that this effect is behaviour dependent. Behavioural syndrome tests confirmed a positive boldness-exploration and boldness-activity correlation for individuals reared in a forest environment while the boldness-exploration and boldness-activity correlation was negative for agricultural individuals. While studies already highlighted species differences in behavioural syndromes, our study provide insight in the effect of larval conditions for adult behaviour in a butterfly. We also found sex related differences that could only be linked to experimental conditions. For the exploration and activity tests, females were tested by another experimenter, meaning that observation bias cannot be excluded. Females were also tested at higher temperatures than males, possibly constraining their exploration levels. Our study did not account for other potential stressors during development such as food intake for example. We assumed that the larval stage was the most sensitive to microclimatic cues and conditions. It would be interesting for future work to incorporate such other stressors and also study the effects of microclimatic conditions on other life stages (e.g. pupal stage).