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Is hormone provisioning an adaptive, plastic phenotype in wild crickets?

Project Abstract: 
Environments on Earth are changing rapidly, and animals must adapt to these changes or perish. Not only must animals adapt to environmental changes that occur within their lifetime, but their fitness depends on producing offspring that will survive future conditions. One common mechanism animals are thought use to prepare offspring for future conditions is to vary the titers of hormones available to offspring during development. Such variability in hormone provisioning can dramatically affect offspring phenotype and fitness: effects may be immediate or delayed; temporary or sustained. Whether such hormone-mediated effects are an adaptive, plastic parental phenotype or merely reflect parent quality, environmental or physiological limitations on parental resources remains an open question. Ecdysteroid hormones (ESH), a major invertebrate hormone group, control insect development. Most work on ESH has focused on their immediate mechanistic roles, but there is evidence that ESH can link juvenile environment to adult behavior and to other ecologically relevant traits. However, the published examples remain unconnected by a general model of long-term phenotypic effects of ESH: more work is needed to establish such a framework. My preliminary data indicate that, in lab-raised Acheta domestica, (a) parental environment and clutch size affect ESH titers deposited in eggs, and (b) elevated ESH titers in eggs correlate with faster rates of development in the crickets that hatch from those eggs. ESH titers in eggs thus connect the parental environment to life history traits of the offspring, providing a potential mechanism for transgenerational adaptation to environmental conditions. When conclusions about fitness are drawn from lab experiments, it is possible that the measurements are lab artifacts rather than indicators of ecologically relevant traits. I will test the hypotheses that variable ESH provisioning (H1) affects development and phenotype in wild crickets and (H2) is affected by parent quality and environment. I predict that (P1) ESH provisioning affects wild cricket development similarly to lab-raised crickets, (P2) same-species crickets captured in cooler habitats will provide more ESH to their eggs than those from warmer habitats regardless of parent quality, and (P3) species with a long hatch-maturity interval will deposit less ESH in eggs than species with a shorter hatch-maturity interval.
Status of Research Project: 
Years Active: 
The Spring and Fall Field Crickets (Gryllus veletis and G. pennsylvanicus, respectively) are both native to Michigan. G. veletis mature 9 months after hatching: they hatch in summer, overwinter in burrows, and mature the following spring. G. pennsylvanicus overwinter as eggs, hatch in late spring, and mature 3 months later, producing eggs before dying in early fall. For each species, I will use pitfall traps and opportunistic hand-catching to capture mature crickets from three sites, measure a proxy of parent quality (body size), and form mating pairs. I will gather and count eggs from each pair, half of which I will incubate until hatching in a lab environment; the other half will be assayed for ESH content using an Enzyme Immunoassay (EIA). I will then raise offspring in a common garden (to control for environmental variation effects on phenotype) and measure offspring development rate and quality at maturity. These data will demonstrate whether ESH variation affects development and phenotype in wild crickets (H1:P1). Data will begin to address whether ESH provisioning could be an adaptive reproductive strategy by testing whether parent quality and environment influence the amount of ESH provided to offspring (H2:P2, P3).
Funding agency: 
Orthopterists' Society