Washington: A chemical commonly used in water bottles and food cans may induce behavioural changes in male turtle brains and cause them behave like females, which could lead to a decline in their population, scientists say.
Often, aquatic environments such as rivers and streams become reservoirs for Bisphenol A (BPA) - a chemical used in many consumer products including water bottles, metal food storage products and certain resins. Researchers led by the University of Missouri (MU) had earlier determined that BPA can disrupt sexual function in painted turtles, causing males to develop female sex organs.
Now, the team found that BPA also can induce behavioural changes in turtles, reprogramming male turtle brains to show behaviour common in females. "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, from the MU College of Veterinary Medicine.
"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," said Rosenfeld. "We found that BPA also affects how the male brain is 'wired,' potentially inducing males to show female type behavioural patterns," she added.
Researchers applied a liquid form of BPA and ethinyl estradiol to painted turtle eggs and incubated the eggs at a temperature that typically results in males.
Five months after hatching, turtles were tested with a spatial navigation test that included four food containers, only one of which was baited with food.
Each turtle was randomly assigned one food container that did not change over the trial period. Researchers predicted that male turtles exposed to BPA and
EE2 would exhibit improved navigational ability - similar to behaviours observed in female turtles.
Results showed that developmental exposure to BPA and EE2 improved spatial navigational learning and memory in males, as evidenced by increased number of times spent in the correct target zone and greater likelihood of solving the maze compared to control turtles, who were male based on the lower incubation temperature.
"Previous studies have found that female turtles are much more adept at spatial navigation," 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," she said.
"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 behaviours needed to attract a mate and reproduce, which could result in dramatic population declines," Rosenfeld said.
