RESEARCH: Physiology of aging and reproduction in insects
The regulation of lifespan is a basic question in biology, and understanding how aging occurs may have implications for health care. Hence, I study the effects of reproduction on lifespan in grasshoppers and flesh flies.

Team Grasshopper: Matt Williams, Michelle Drewry, John Hatle, Matt Grove, and Evan Judd.

Nutrient allocation in long-lived grasshoppers
Both reduced diet and reduced reproduction extend lifespan in many organisms. The disposable soma hypothesis predicts that reduced reproduction extends lifespan by allocating nutrients to reproduction at the cost of somatic maintenance. Reduced diet is thought to extend lifespan similarly because it typically causes a reduced reproductive output. An explicit prediction of this hypothesis is that allocation of ingested nutrients to somatic tissues would be greater in long-lived phenotypes.

We have found that reduced 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%, and investment in reproduction is greatly reduced in old ovariectomized females (Hatle et al. 2008. Exp Gerontology).

We are using diets with distinct stable isotope signatures (13C and 15N) to rigorously track ingested nutrients to somatic tissues in ovariectomized females. Thus far, we have shown that ovariectomized females have fat body and perhaps hemolymph hypertrophy, consistent with data from other animals showing greater storage in individuals with reduced reproduction. However, nutrient tracking to the femur muscle suggests that ovariectomized individuals do not increase allocation of adult-ingested nutrients to this tissue, inconsistent with the prediction of the disposable soma hypothesis. Other tissues will be tested to determine whether allocation to multiple organs responds to ovariectomy.

In the future, we plan a similar experiment with grasshoppers on life-extending dietary restriction. Further, we plan to measure anti-oxidant activity or chaperone levels to determine whether changes in nutrient allocation result in changes in cellular maintenance.

Are life extensions from dietary restriction and ovariectomy additive?
Both reduced reproduction and reduced diet extend lifespan, and the longstanding idea has been that both act through the same mechanism. To test this, we are determining whether the life extensions due to dietary restriction and ovariectomy are additive by applying both treatments to single individuals. If these ovariectomized individuals on dietary restriction live longer than individuals on either treatment alone, it will suggest that the treatments extend lifespan by distinct mechanisms.

This work on the effects of reproduction on aging in grasshoppers is supported by an R15 (aka. AREA) grant from the National Institute on Aging.

Nutrient allocation in long-lived flesh flies
In addition, we are studying effects of diet on lifespan of flesh flies. The lab diet of adult flesh flies is raw liver (almost entirely protein) and sugar cubes; hence, dietary protein and carbohydrates are separable. Fruit flies, a major genetic model, are widely used to study longevity, but the yeast in their diet includes protein, carbohydrates and lipid. By using flesh flies we hope to determine the allocation of these ingested nutrients in flies on life-extending dietary restriction. Our current work is focused on identifying a diet that robustly extends lifespan. Flesh flies fed sugar only live longer and have little reproductive development. Next we will use stable isotopes to track ingested nutrients in long-lived flesh flies. This work on flesh flies is in collaboration with Dan Hahn at University of Florida Entomology (http://danhahn.ifas.ufl.edu/).

Team Fly: (Clockwise from top left) Ligia Bastea, Angela Virgilio, Leisa Walker, and John Hatle.

Some past students
Evan Judd – undergrad 2007-9. Now a Ph.D. student in molecular biology at Boston University
Ligia Bastea – undergrad 2007-9. B.S. in Biology from UNF. Working at Mayo Clinic and applying to medical school.
Katharine Wright – post-bac in 2007-8. Completed UNF Nursing program.
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, D.P.T in 2009. Now employed in Physical Therapy in Naples, FL.
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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