Developmental trade-offs in caddis flies: increased investment in larval defence alters adult resource allocation

Developmental trade-offs in resource allocation across life-history stages and between different body parts are predicted by life-history theories. Ho wever, there is very little empirical evidence that these occur. We investi gated these trade-offs in caddis flies by experimentally manipulating larva l case construction and thereby silk expenditure. Case building diverts pro tein resources away from larval stores, which are of major importance to ad ult development in species with little or no adult feeding. We induced fift h-instar Odontocerum albicorne to build new cases and examined the conseque nces for the morphology of the resulting adults. Rebuilding did not alter l arval food consumption or the date of entering pupation, but shortened the duration of the pupal period. Adults that had been induced to expend more s ilk as larvae had lighter thoraces and smaller wings than the controls, but their abdomens did not differ significantly in mass or nitrogen content. T hese results suggest a trade-off between larval silk production and the pat tern of resource allocation within the adult. The maintenance of the abdome n is likely to preserve reproductive potential, while the reduction in thor acic and wing investment will have negative consequences for flight and ass ociated activities, and possibly for adult longevity.