Bisphenol A (BPA) is a chemical compound used in the manufacture of many common products, including plastic beverage bottles, metal cans used to package food, till slips and some resins. BPA is a endocrine disrupting compound that is known to have negative health affects on both animals and humans exposed to it. It tends to linger in the environment, often making its way into freshwater systems such as streams, rivers and lakes, where it accumulates, negatively impacting aquatic organisms, such as turtles, that inhabit these ecosystems.
In a study conducted last year, researchers from the University of Missouri found that BPA is able to disrupt sexual functioning in painted turtles, and can cause male turtles to develop female sex organs. In a more recent study, the researchers show that BPA not only has the ability to change the turtles’ sex organs, but can also change the sexual behavior of male turtles, rewiring their brains so that they show behavioral traits associated with females. The researchers are concerned that this could cause the population of painted turtles to decline.
“Previously, our research team found that BPA and ethinyl estradiol (EE2), a hormone found in birth control pills, could ‘sex-reverse’ turtles from males to females,” said Cheryl Rosenfeld, an associate professor of biomedical sciences in the MU College of Veterinary Medicine and an investigator in the Bond Life Sciences Center. “Painted turtles and other reptiles lack sex chromosomes. The gender of painted turtles and other reptiles is determined by the incubation temperature of the egg during development. Studies have shown that exposure to endocrine-disrupting chemicals (EDCs), such as BPA, can override incubation temperature and switch the sex of males to females. In our latest study, we found that BPA also affects how the male brain is ‘wired,’ potentially inducing males to show female type behavioral patterns.”
For the study, the researchers coated painted turtle eggs with BPA (in liquid form) and ethinyl estradiol, and then incubated the eggs at a temperature that would normally produce males. When the turtles were five months old, they were subjected to a spacial navigation test to determine whether exposure to BPA and EE2 would improve their navigational skills — i.e. to determine whether their navigational skills would be on a par with that of female turtles, as the researchers predicted. The results revealed that male turtles who were exposed to BPA and EE2 in the developmental stages had better spatial navigational learning and memory compared to a control batch of male turtles that were incubated at the same temperature, but who were not exposed to the contaminants.
“Previous studies have found that female turtles are much more adept at spatial navigation — think of female sea turtles that return many years later to the same beaches where they hatched to lay their own eggs,” Rosenfeld said. “We found that developmental exposure to BPA essentially overrides the brain development of male turtles as indicated by the enhanced navigational ability of the turtles we studied. While improved spatial navigation might be considered a good thing, it also may suggest that when they reach adulthood male turtles will not exhibit courtship behaviors needed to attract a mate and reproduce, which could result in dramatic population declines.”
Professor Rosenfeld points out that this scientific study reveals how these harmful chemical contaminants not only have the ability to change the turtle’s physical sexual traits, but they also have the ability to change how the brain functions, ultimately altering their sexual behaviour, which could in turn affect breeding performance and population status of turtles in the future.
Turtles are ‘indicator species’ that are often used to assess the environmental health and integrity of aquatic ecosystems. By getting a better handle on how these hormone disrupting chemicals affect sexual behaviour of turtles, we can gain a better understanding of how they can potentially impact other animals, including humans.