Individual behavioural consistency and plasticity in an urban spider

Behaviour is generally plastic to some degree and allows an animal to react appropriately to changing and novel conditions. Consequently, a degree of plasticity is predicted to be a key determinant of an organismʹs ability to cope with novel (e.g. urban) environments. Yet behavioural plasticity is often genetically determined and many animals exhibit personalities (i.e. consistent between-individual differences in behaviours). We explored the degree of behavioural plasticity versus personality in the bridge spider, Larinioides sclopetarius, which occurs in extremely high densities in urban areas over the Holarctic. The spiders show extraordinary plasticity in life history. We investigated between- and within-individual variability, correlations and heritability for aggressiveness, boldness, behaviours in novel environment, and voracity towards prey. We predicted that these spiders would show high individual behavioural plasticity or that there would be a mix of individuals with different personalities. We found temporal consistency and moderate heritability in intra-sex aggressiveness and boldness, whereas behaviours in novel environment were repeatable but not heritable. Most behavioural traits showed high between-individual variability. We discuss the idea that low heritability of behaviours related to foraging success and a lack of behavioural correlations may be a result of developmental plasticity as a mechanism that promotes success in cities. In the next step, we experimentally tested whether composition of aggressiveness types affects spidersʹ mass gain and survival in a high-density group. Groups of only aggressive types had highest mass but also showed highest mortality, although not significantly. Our results lend support to the hypothesis that living in high densities does not necessarily require a reduction of mean aggressiveness levels but that a polymorphism in aggressive personalities maintained by negative frequency-dependent selection would be a possible scenario.