Endosulfan Exposure Disrupts Pheromonal Systems in the Red-Spotted Newt: A Mechanism for Subtle Effects of Environmental Chemicals

Environmental Health Perspectives, July, 2001 by Daesik Park, Steven Hempleman, C., Catherine R. Propper

Endosulfan exposure affected mating success of red-spotted newts possibly via the disruption of pheromonal systems and through potential neurologic system damage involved in sexual behavior as well. During our study, endosulfan exposure induced a significant decline in mating success, suggesting that decreased individual interactions via the disrupted pheromonal systems may result in decreased mating success. On the other hand, because we provided a relatively small courtship arena, which may allow male and female newts to easily come in contact, it is also possible that endosulfan may cause changes in reproductive interactions through mechanisms that were not detected in this study. Several investigations have documented neurobehavioral changes after endosulfan exposure. Rats treated with endosulfan showed increased aggressive behavior and deficits in operant learning performance (14). Such changes were correlated with changes in levels of neurohormones and neurotransmitters such as noradrenaline, dopamine, acetylcholine, and serotonin in the brain (14). One study in the fish Tilapia rendalli reported that brains from animals exposed to endosulfan exhibit abnormal encephalitis, meningitis, and edema, with an associated inflammatory infiltrate of eosinophilic granule cells (34). Thus, in our study, it is possible that endosulfan not only disrupted the female pheromonal systems, but that it also interfered with female neural pathways involved in the performance of appropriate reproductive behavior even though it did not disrupt behaviors associated with general activity. Males may not have continued courtship or insemination attempts with females who were nonresponsive.

Our results are the first to document that the disruption of pheromonal communication systems can be induced by exposure to low concentrations of environmental chemicals without overt signs of toxicosis. This study suggests that amphibian pheromonal systems could be one of the systems mediating subtle effects of environmental chemicals. In addition to local climate change, habitat fragmentation, infectious disease, and increased UV-B irradiation, increased use of environmental chemicals has been suggested to be one of the major factors underlying recent amphibian declines (1-3,35-39). Therefore, disruption of amphibian pheromonal systems by such chemicals are possibly one other mechanism facilitating population declines because the system plays a critical role in the daily life of amphibians such as conspecific recognition, migration, social behavior, and reproduction.

REFERENCES AND NOTES

(1.) Stebbins RC, Cohen NW. A Natural History of Amphibians. Princeton, NJ:Princeton University Press, 1995.

(2.) Kirk JJ. Western spotted frog (Rana pretiosa) mortality following forest spraying of DDT. Herpetol Rew 19:51-53 (1988).

(3.) Pickford DB, Morris ID. Effects of endocrine-disrupting contaminants on amphibian oogenesis: methoxychlor inhibits progesterone-induced maturation of Xenopus/aevis oocytes in vitro. Environ Health Perspect 107:285-292 (1999).