Background

The Delaware-Maryland-Virginia (Delmarva) poultry industry alone produces nearly 1.6 billion pounds of poultry litter annually. Poultry litter is applied in place of synthetic fertilizers during the spring and early summer. The timing of poultry litter application coincides with amphibian breeding and larval development. During rainfall, runoff from fields fertilized with poultry litter transports excess nutrients and endocrine disrupting chemicals (EDCs) into adjacent ponds, lakes, and streams.

Runoff containing poultry litter associated hormones (PLAH) can contaminate ephemeral ponds and surface water near amphibian habitats and breeding sites. PLAH include a variety of EDCs such as estradiol, estrone, estriol, and testosterone. Research has indicated that amphibians are particularly sensitive to these hormones. In particular, 17β-estradiol is a likely contributor to amphibian gonadal deformations in species such as Xenopus laevis, the African Clawed Frog.

While the threat posed by nutrient leaching of phosphorus and nitrogen from manure-treated fields is heavily studied, the threat posed by the synergistic effects of PLAH has received much less attention. Previous studies involving estradiol's effects on amphibians have failed to use environmentally relevant concentrations and have failed to account for natural hormonal degradation.

Our Research and Goals

To determine the extent that environmentally relevant concentrations of poultry litter associated hormones will affect the sexual development of X. laevis (African Clawed Frog).

Primary Data Endpoints

Gonadal development and abnormalities—Increasing poultry litter concentrations may cause mixed sex and intersex characteristics in amphibian gonads.

Sex ratios—Altered sex ratios and abnormal gonadal development could significantly reduce fertility and decrease or prevent successful breeding, causing population numbers to decrease via diminished recruitment of juveniles.

Mortality—Individuals must complete metamorphosis, survive to sexual maturity and successfully breed for a population to thrive and grow.

Secondary Data Endpoints

Time to metamorphosis—Metamorphosis time may fluctuate with an increase in poultry litter concentration. The time to metamorphosis is an indicator of the frogs' eventual success for survival.

Snout-vent length and wet weight—Large massed amphibians have a greater chance for survival to first reproduction and earlier reproduction.