RESEARCH: Physiology of aging and reproduction in insects

I am interested in the physiological abilities of animals to adjust life history tactics (i.e., post-embryonic development) in response to the environment. In particular, I study the effects of reproduction on lifespan in grasshoppers and flesh flies.

Both reduced diet and reduced reproduction extend lifespan in many organisms. The disposable soma hypothesis predicts that reduced reproduction extends lifespan by allocating nutritional resources to reproduction at the cost of self-maintenance. Reduced diet similarly extends lifespan because it causes a reduced reproductive output. In phytophagous insects such as grasshoppers, protein is the limiting nutrient for reproduction, so if nutrients are involved in the reproduction vs. longevity trade-off, protein is likely to be important. Hence, we have focused on allocation of protein in examining the disposable soma hypothesis in grasshoppers.

Reducing diet extends lifespan by 50% in female grasshoppers, but this does not significantly reduce lifetime fecundity or levels of hemolymph storage proteins (Hatle et al. 2006. Mech Age Dev. see Publications link for PDFs). This is a strong contrast to most animals on dietary restriction, in which lifespan is extended but reproduction is reduced. On the other hand, reducing reproduction by ovariectomy extends lifespan by 30%, in ways that are consistent with the disposable soma hypothesis. Grasshoppers are a novel system to testing this hypothesis, because ovariectomy does not eliminate allocation of protein to reproduction. In fact, at the age of first clutch in controls, ovariectomized and control females had similar levels of total reproductive proteins. At older ages, ovariectomized females reduced allocation to reproductive proteins and increased allocation to storage proteins (Hatle et al. in press. Exp Gerontology). This work on the effects of reproduction on aging in grasshoppers is supported by an AREA grant from the National Institute of Aging.

We are now rigorously addressing the allocation of nutrients in ovariectomized and control females. Specifically, we are testing for a shift in allocation to reproduction (i.e., eggs, oocytes, or hemolymph vitellogenin) vs. the soma (e.g., fat body, femur muscle, hemolymph storage proteins) at the transition from the first to the second clutch. We are using diets that differ in levels of 13C to address this question of nutrient investment.

Working on nutrient allocation in grasshoppers are, from left to right: Evan Judd, Michelle Drewry, Kat Wright, and John Hatle).

In collaboration with Dan Hahn at University of Florida Entomology (http://danhahn.ifas.ufl.edu/), we are addressing affects of diet on longevity in female flesh flies. We have demonstrated that flesh flies offered liver for the first 2 days of adulthood commit to laying a clutch, but produce this clutch most slowly than flies that are fed for 4 days. This post-threshold plasticity is different from most other examples of life history plasticity in insects, in which attaining a threshold eliminates further plasticity. These changes in reproductive tactics are associated with levels of Larval Storage Protein-2, but not Larval Storage Protein-1 (Hahn et al. 2008. Functional Ecology).

Our lab is extending this work to examine aging in flesh flies. We have found that, as in fruit flies, male presence reduces female lifespan. We are now testing diets that extend lifespan cages with only females. We intend to rigorously track nutrient allocation in flies on life-extending dietary restriction. This is extremely expensive in fruit flies, but much cheaper in flesh flies. In the lab, flesh flies eat only fresh liver and sugar, both of which are available in low- or high-13C forms.

Working on longevity in flesh flies are, from left to right: Michelle Drewry, Ligia Bastea, and John Hatle.

Some past students
Raime Fronstin – M.S. in 2007. Now a Ph.D. student in evolutionary physiology at Simon Fraser University (Canada).
Sean Wells – B.S. in Athletic Training in 2006. Now a graduate student in Physical Therapy at UNF.
Erin Fuller – B.S. in Biology in 2007. Now working in industry.
Erin Wright – post-bac in pre-med studies in 2006. Now in the MD program at University of Chicago.
Kevin Brix – B.S. in Biology in 2008. Now a Ph.D. student in invertebrate physiology at University of Miami (FL).
John Quattrochi – post-bac in biology in 2004. Now a Ph.D. student in Public Health at Harvard.

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