Researchers have discovered that Bisphenol A affects the brain development of turtles, making male turtles act more like females. Bisphenol A is a common chemical that often ends up in local aquatic ecosystems so it’s critical to understand how it affects native animals. The team also found that ethinyl estradiol, found in birth control pills, had a similar effect. The details are in a paper just published in the journal Hormones and Behavior.
Bisphenol A, or BPA, is a synthetic chemical used in plastics and epoxy resins. BPA is found in everything from water bottles to DVDs. BPA has properties that mimic the hormone estrogen, raising concerns about its use in so many products. Ethinyl estradiol, or EE2, is a form of estrogen used in birth control pills. Both BPA and EE2 end up in bodies of water such as lakes and rivers. These chemicals persist in aquatic environments and the effects on the local animals are mostly unstudied. One species known to be affected by these endocrine disrupting chemicals is the painted turtle, the animal that was the focus of this new study.
Previous research has already shown that both BPA and EE2 can affect the sex of turtles. Sex determination in certain reptiles, including turtles, is based on temperature and not chromosomes. However, exposure to BPA and EE2 skews sex ratios by encouraging the development of females. Male turtles exposed to these chemicals begin to develop female sex organs, sometimes resulting in a full sex-reversal.
Researchers from the University of Missouri continued their previous research to look for other developmental changes in turtles exposed to BPA and EE2. They exposed developing painted turtle eggs to both chemicals in varying concentrations. Five months after the turtles hatched, they were tested with mazes to determine their spatial navigation skills. Female turtles tend to be better at spatial navigation since they must be able to locate nesting sites. These sex differences remained true for the control and low concentration groups. However, male turtles exposed to higher levels of endocrine disrupting chemicals performed just as well as the females in spatial navigation and memory tests. BPA and EE2 seemed to improve the navigation and memory abilities of male turtles. The researchers speculate that this is because their brains are developing the same way as female brains due to exposure to endocrine disrupting chemicals.
BPA and EE2, common endocrine disrupting chemicals found as pollutants in aquatic environments, improved spatial learning and memory in male painted turtles. The authors note that while this sounds positive, it actually means that the turtles are developing female brains and behavior patterns. This could result in males that don’t perform proper courtship behaviors, for example. The researchers are concerned that the chemicals will further disrupt turtle populations since it’s clear that both BPA and EE2 affect embryonic development. More research is required to fully understand how endocrine disruptors change local ecosystems.
Lindsey K. Manshack et al. Effects of developmental exposure to bisphenol A and ethinyl estradiol on spatial navigational learning and memory in painted turtles (Chrysemys picta). Hormones and Behavior (2016).