Intraspecific variation in functional traits in the wolf spider Lycosa fasciiventris : Implications for trophic cascades

Intraspecific variation has recently been acknowledged as an important factor affecting ecosystems. Indeed, levels of intraspecific variation in natural populations can be very high, even surpassing interspecific variation. In particular, variation in foraging traits can significantly impact ecological processes. The aim of this thesis was to measure the relative strength of drivers of intraspecific variation in foraging traits in the cannibalistic wolf-spider Lycosa fasciiventris and its potential impacts on trophic interactions and consequently trophic cascades. We evaluated trait variation using a half-sib split brood design, by crossing each male with two females and separating offspring from each family into 2 different rearing environments. The offspring was scored for several morphological, physiological and behavioral traits and heritability, maternal effects and environmental interactions (genotype-by-environment and maternal-by-environment interactions) were determined as well as genetic and maternal correlations. Maternal effects were predominant over additive genetic effects in all traits and their correlations, except in traits related to cannibalism, in which both genetic and maternal effects were absent. In this case, trait variation was explained by the social environment faced by spiders (conspecific cues). We then evaluated the impacts of intraspecific variation in ecological processes by performing mesocosms experiments. To this aim, we experimentally manipulated intraspecific variation and evaluated its effects upon trophic cascades. Results showed that variation in foraging traits due to maternal and environmental effects can modulate ecological processes, namely trophic cascades. Mesocosms with higher trait diversity displayed stronger trophic cascades, attributable not to a higher prey mortality but to a change in their behavior, while environmental diversity was reflected in a higher rate of cannibalism but not enough to dampen trophic cascades. The results of this thesis highlight the importance of maternal effects and other indirect genetic effects as drivers of intraspecific variation, modulating ecological processes and shaping community structure