RESEARCH: Physiology of aging and reproduction in insects
I study the regulation of lifespan, or aging. In particular, I study the effects of reproduction on life span in grasshoppers.

Tracking ingested nutrients in long-lived individuals
Both reduced diet and reduced reproduction extend lifespan in many organisms. The disposable soma hypothesis predicts that reduced reproduction extends life span by allocating nutritional resources to reproduction at the cost of self-maintenance. There is a great deal of circumstantial evidence to support this, but directly testing the hypothesis requires tracking nutrients from ingestion to somatic tissues. We have accomplished this using diets with distinct stable isotope signatures. Ovariectomy eliminates reproductive output and increases life span in grasshoppers. We found that ovariectomized females have increased somatic storage, but do not change proportional allocation of ingested nutrients to somatic tissues (Judd et al. Aging Cell). These results are inconsistent with the disposable soma hypothesis. We are continuing this work in females on life-extending dietary restriction. This work is supported until 2013 by an R15 (aka. AREA) grant from the National Institute on Aging.

Team Nutrient Allocation – Matt Williams and Alicia Linquist

Physiological comparison of life-extension by reduced reproduction or reduced diet
Ovariectomy and dietary restriction each extend lifespan by about 15%. Further, ovariectomy extends life span and is accompanied by a ~45% reduction in feeding, which is similar to the level of dietary reduction used to extend life span. Hence, the feeding and lifespan data hint that ovariectomy and dietary restriction may be acting through the same mechanism(s). However, females that were both ovariectomized and on dietary restriction (i.e., 70% of that eaten by ovariectomized females with free access to food) lived longer than females on either single treatment. Ovariectomized females also have greatly elevated levels of egg yolk-precursor protein (Vg). This suggests that ovariectomy and dietary restriction each work through separate pathways to extend lifespan (Drewry et al. Experimental Gerontology).

Team Reduced diet vs. Reduced reproduction – Ephraim Viray and James Kellenberger

To further explore these presumably separate pathways, we have reared dietary restricted females on the same feeding rates as ovariectomized females. Ovariectomy doubles some measures of somatic storage. We are pursuing further physiological measurements of these treatments (viz., anti-oxidant activities, mitochondrial counts, and levels of TOR mRNA). Early results suggest that anti-oxidant activities are similar.

RNAi knockdown of proteins involved in reproduction
Reduced reproduction extends life span. The contributions of various aspects of reproduction to longevity are unclear. In female grasshoppers, production of the egg yolk protein-precursor vitellogenin is a major investment for reproduction. With Dan Hahn at the University of Florida, we use RNAi (interference) to knockdown vitellogenin levels in grasshoppers to directly test the role of the investment of this protein in reproductive tactics. Vitellogenin knockdown halts egg production and doubles fat body storage. Ultimately, we hope to suppress vitellogenin levels throughout adulthood and measure the effects on life span.

Team RNAi – Joe Canzano, Derek Tokar, and Katie Veleta

Some past students
Jason Alvarez – B.S. in biology in 2011. Applying to medical schools.
Matt Williams – B.S. in biology in 2011. Now a technician in my lab.
Michelle Drewry – M.S. in 2010. Now a visiting lab instructor at Jacksonville University.
Ligia Bastea – B.S. in biology in 2009. Now a research assistant at Mayo Clinic.
Evan Judd – B.S. in biology in 2008. Now a Ph.D. student in biochemistry at Boston University.
Kevin Brix – B.S. in Biology in 2008. Now a Ph.D. student in invertebrate physiology at University of Miami (FL).
Raime Fronstin – M.S. in 2007. Now a Ph.D. student in evolutionary physiology at Simon Fraser University (Canada).
Erin Wright – post-bac in pre-med studies in 2006. Now in the MD program at University of Chicago.
Sean Wells – B.S. in Athletic Training in 2006. Now a Physical Therapist.
 
Contact Information

John D. Hatle
Associate Professor
Univ. of North Florida
Biology Department
1 UNF Drive
Jacksonville, FL 32224
Building 3, Room 2244
904-620-2778 (phone)
904-620-3885 (FAX)
jhatle@unf.edu