The Effects of a Model Androgen 5a-dihydrotestosterone on Mummichog (Fundulus heteroclitus) Reproduction Under Different Salinities

Abstract Endocrine disrupting substances (EDSs) have the potential to disrupt sensitive hormone pathways, including those involved in development and reproduction. Both fresh and estuarine water bodies receive inputs of EDSs from a variety of sources, including sewage effluent, industrial effluent, and agricultural runoff. Based on limited available literature, freshwater species appear to respond to lower levels of EDSs than estuarine or marine species. To address this potential difference, a short-term reproductive bioassay was carried out under low and high salinity conditions using mummichog (Fundulus heteroclitus), a euryhaline species that is native to the east coast of North America. The goal of the study was to determine the response of mummichog at multiple biological levels when exposed to an androgenic EDS and whether salinity affected the response. A second goal was to adapt a population model for mummichog to predict impacts from anthropogenic or environmental stressors on population status. A model androgen, 5-alpha dihydrotestosterone (DHT), was used because androgenic EDSs are not as well-studied as estrogenic EDSs. In the high salinity group egg production was significantly reduced (39-49%) in all exposure concentrations, while in low salinity conditions there were no significant differences in egg production based on DHT treatment. However, egg production in the low salinity control group was reduced by 55% relative to the high salinity control group. Additionally, DHT reduced sex steroid production in males and females at both salinities. This indicates that androgenic EDSs such as DHT may reduce the reproductive capacity of mummichog, and that osmotic stress from low salinity conditions likely diverted energy from reproductive output in the low salinity group. These results were applied in a mummichog population model which was adapted from a fathead minnow (Pimephales promelas) model. Observed changes in fecundity were employed in this predictive model to estimate the long term effects of exposure to anthropogenic (DHT) or environmental (low salinity) stressors on population status. Different model projections were developed based on the unique spawning patterns of the mummichog subspecies, the southern species Fundulus heteroclitus heteroclitus, and the northern subspecies Fundulus heteroclitus macrolepidotus. Results indicated that the reduction in fecundity over a 20 year period due to DHT exposure can lead to a reduction of 50% of carrying capacity in the southern subspecies and a near population collapse in the northern subspecies due to their shorter spawning season. In its current form, the model demonstrates that exposure to anthropogenic or environmental stressors (in this case DHT and low salinity) can have equally negative impacts on the population viability of mummichog. Future studies will focus on refinement of the model to account for temporal sensitivity over multiple generations as well as the effects of migration