Developmental trade-offs and life histories: strategic allocation of resources in caddis flies

Resource allocation trade-offs during development are potentially very impo rtant in the evolution of organism morphology and life-history strategy. Ho wever, they have rarely been demonstrated empirically. To, what extent thr division of limited resources between growing organs is a consequence of pa rticular developmental pathways or varies strategically in line with life-h istory predictions is unknown. It has been demonstrated in a number of holo metabolous insects that altering the resources available at pupation change s the pattern of allocation to adult tissues. but this has not been examine d in a life-history context. Using caddie flies (Trichoptera), we show here that the effect of depleted larval resources on the pattern of somatic and reproductive investment is not fixed but varies between species with diffe r ent life-history patterns. In particular we demonstrate that, in a long-l ived species, thorax size is preserved, which contrasts with the pattern pr eviously observed in a short-lived species. That the adult body can be diff erentially altered by the same resource depletion in the larvae demonstrate s that the allocation of resources amongst body parts is not a consequence of fixed pathways during development. Rather, the allocation of resources d uring development can occur in a manner consistent with the minimization of the effects on adult fitness.