Developmental thresholds, life history trade-offs, and resource allocation in wetland caddisflies (Trichoptera)
Abstract
Our ability to predict how populations will respond to environmental change depends, in part, on knowing how juvenile life experiences influence adult life history traits (e.g., time to sexual maturity, adult size, female fecundity, male mating success, and longevity). Data on this connection are severely lacking. Both biotic and abiotic environmental conditions can influence life history traits by affecting biological processes such as growth, development, and reproduction. Life history traits themselves influence each other through positive correlations and negative trade-offs. Trade-offs occur because limited resources must be allocated to competing functions over the life of the organism. For example, resources allocated at an early point in development often cannot be re-allocated to other functions later in life; thus, large investments in early reproductive output can negatively impact future survival. The strength and sign of these life history correlations depends on environmental conditions. Utilizing three species of caddisflies (Trichoptera), I investigated how environmental conditions during the larval stage influence adult life history traits. Caddisflies are a good model organisms for investigating life history because their complex life cycle is partitioned into functionally different life history phases (larval stage = growth; pupal stage = development and allocation; adult stage = reproduction). In a series of mesocosm and microcosm experiments, I manipulated larval nutritional conditions and pond-drying to examine how larval and pupal environmental conditions influence larval growth rates, larval and pupal developmental rates, size at sexual maturity, and resource allocation to adult life history traits. My results indicate that: (1) minimum size thresholds for metamorphosis might prevent adaptive responses to pond-drying and limit the ability of holometabolous insects to respond to global climate change; (2) the relationship between size and age at maturity was negative across all 3 species studied, consistent with a recent model predicting size and age at maturity in the presence of developmental thresholds; (3) nutritional stress during the larval stage can be mitigated during metamorphosis by strategically reallocating resources away from less important adult functions toward more critical adult life history traits; and (4) high larval growth rates and pupal developmental rates can negatively impact adult life history trait.
Degree
Ph.D.
Advisors
Howard, Purdue University.
Subject Area
Ecology|Entomology
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