Growth strategies and optimal body size in temperate pararginii butterflies

In temperate insects the evolution of growth strategies andthe optimal age and size at maturity will depend strongly onseasonal variation in temperature and other resources. However,compared to photoperiod, temperature itself is a relativelypoor predictor of seasonal change and timing decisions in insectsare often most strongly influenced by the photoperiod. HereI review the evolution of seasonal growth strategies in thebutterfly tribe Pararginii (Satyrinae: Nymphalidae) and relateit to life history theory. The results indicate that individuallarvae may adjust their growth trajectories in relation to informationon time horizons obtained from the photoperiod. The growth strategiescan be characterized by a set of state-dependent decision rulesthat specify how an individual should respond to its internalstate and external circumstances. These decision rules may alsoinfluence how individual growth change with a rise in temperature,showing that the standard expectation of increased growth rateswith increasing temperatures may not always be true. With lesstime available individual larvae increase growth rates and therebyachieve shorter development times, most often without any effectson final sizes. One reason for the apparent optimization ofgrowth rate seems to be that growing fast may incur costs thatlarvae developing under lower time limitations chose to avoid.The patterns of growth found in these and many other studiesare difficult to reconcile with common assumptions of what typicallydetermines optimal body size in insects. In particular it seemsas if there should be some costs of a large body size that,so far, have been poorly documented.