Size-induced phenotypic reaction norms in a parasitoid wasp: An examination of life-history and behavioural traits

The amount of resources available during development often affects body size, causing phenotypic variation in life-history traits and reproductive behaviours. However, past studies have seldom examined the reaction norms of both life-history and behavioural traits versus body size. We measured the phenotypic plasticity of several life-history (age-specific egg load, egg size, longevity) and behavioural (oviposition rate, host marking rate, walking speed) traits of the egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae) in response to body size variation. We predicted that life-history traits would show more evidence of size compensation than behavioural traits, resulting in fewer positively-sloped size versus trait reaction norms among the former. As predicted by life-history models, smaller wasps appear to shift resource allocation towards early-life reproduction, having a similar egg load to large individuals 9 days after emergence. Surprisingly, longevity was unaffected by body size. However, egg size, the number of offspring produced during oviposition bouts, and the rate of subsequent egg synthesis were greater for larger individuals. In addition, as predicted, the reaction norms of behavioural traits versus body size were all positively sloped. Thus, despite possible adaptive compensatory plasticity of life-history traits by small individuals, behavioural constraints directly related to body size would contribute to maintaining a positive size-fitness relationship.