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

Abstract

Developmental trade-o¡s in resource allocation across life-history stages and between di¡erent body parts are predicted by life-history theories. However, there is very little empirical evidence that these occur. We investigated these trade-o¡s in caddis £ies by experimentally manipulating larval case construction and thereby silk expenditure. Case building diverts protein resources away from larval stores, which are of major importance to adult development in species with little or no adult feeding. We induced ¢fth-instar Odontocerum albicorne to build new cases and examined the consequences for the morphology of the resulting adults. Rebuilding did not alter larval food consumption or the date of entering pupation, but shortened the duration of the pupal period. Adults that had been induced to expend more silk as larvae had lighter thoraces and smaller wings than the controls, but their abdomens did not di¡er signi¢cantly in mass or nitrogen content. These results suggest a trade-o¡ between larval silk production and the pattern of resource allocation within the adult. The maintenance of the abdomen is likely to preserve reproductive potential, while the reduction in thoracic and wing investment will have negative consequences for £ight and associated activities, and possibly for adult longevity.

Lifetime allocation of juvenile and adult nutritional resources to egg production in a holometabolous insect

“…Larval reserves were largely found in the head^thorax fraction, which can be roughly approximated to the resources allocated to growth and somatic maintenance on emergence (Boggs 1981;Karlsson 1994;Stevens et al 1999), while only a small percentage was recovered from the abdomen. In contrast, most of the adult food ingested was recovered from the abdominal fraction and from the eggs, con¢rming the predominant role of host feeding in egg production in this species.…”

Investment in cocoon-silk and structure of the clusters of cocoons produced by gregarious microgastrine wasps (Hymenoptera: Braconidae)

“…Because of a mutual trade-off, the adult mass of cocoon-spinning insects is influenced by the amount of silk used in constructing the pupal case (Stevens et al, 1999). Therefore, the balance between economy and robustness of cocoons is important for cocoon-spinning insects.…”

The proximal costs of case construction in caddisflies: antioxidant and life history responses

“…Because most caddisfly adults feed minimally or not at all (Mosely, 1939), the acquisition of resources during the larval stage is crucial for growth, case construction, reproduction and maintenance. Several studies have shown that larvae forced to rebuild a case experience a severe increase in energy expenditure, and such an increase can impact the dispersal and reproductive capacities of the adults [Caddisfly (Stevens et al, 1999;Stevens et al, 2000;Jannot et al, 2007), Chironomid (McKie, 2004)]. In a previous study, we found that larvae of Limnephilus rhombicus Linnaeus (Trichoptera: Limnephilidae) forced to rebuild a case increased their oxygen consumption by 50% during the period of reconstruction, compared with control larvae (Mondy et al, 2011).…”

“…Tseng et al, 2011) and/or more rarely serve as signals (reviewed in Schaedelin and Taborsky, 2009). Several studies have already evaluated the cost of secretion of the material from which the structures are made (Eisner, 1994;Stevens et al, 1999;McKie, 2004;Hansell, 2005;Mondy et al, 2011) and the energetic costs, which include metabolic energy expended gathering materials and building the structure (Abarca and Boege, 2011;Mondy et al, 2011). However, the non-energetic costs of construction behaviour remain largely unknown.…”