Developmental trade-offs and resource allocation in caddis flies
This thesis is an examination of developmental trade-offs occurring in the pupal stage of caddis flies, using both an experimental and correlational approach. Resources available at metamorphosis were manipulated by forcing caddis fly larvae, Odontocerum albicorne, to divert more silk, and hence protein, into their larval cases. The resultant adult forms had shorter wings and lighter thoraces (somatic investment) than control individuals, but abdomen mass (reproductive investment) was not affected. The results of this experiment could be due to mechanistic constraints of the developmental pathways during pupation, because resources from the breakdown of certain structures may be 'earmarked' for incorporation into specific adult structures. Equally, the observed response could represent a strategic preservation of reproductive reserves. O. albicorne is a short lived species which mates soon after adult emergence and so sacrificing somatic investment may have less drastic affects on fitness. To examine whether resource allocation pathways during development of the adult form are flexible in caddis flies, the same resource depletion experiment was performed on the caddis fly species, Glyphotaelius pellucidus. Adult life span is much longer in this species, which is an adaptation to loss of larval habitat for many months of the year. Here, somatic investment would be predicted to be of much greater importance in the life history, and so if the response to the nutrient deficiencies was strategic, somatic reserves would be expected to be preserved at the expense of reproductive potential. The pattern of resource allocation in the resultant adults was in line with predicted life history requirements, as abdomen mass was sacrificed so as to maintain thoracic mass.