Exposure to bisphenol A (BPA), a chemical used in the manufacture of polycarbonate and other plastics, changes the appearance and behavior of river fish enough to encourage inter-species breeding, say the authors of a new study published online this week, that warns of the potential threat to biodiversity from blurring of inter-species boundaries.

BPA is an organic compound with estrogen-like properties that can disrupt hormones in the body: it is described as an endocrine-disrupting chemical or EDC. It is currently banned from baby bottles and children’s cups in 11 states of the US.

In a paper published in the 10 July issue of Evolutionary Applications, authors Jessica L Ward, from the University of Minnesota, and Michael J Blum from Tulane University in New Orleans, conclude that their findings:

“… indicate that environmental exposure to EDCs can lead to population declines via the erosion of species boundaries and by promoting the establishment and spread of non-native species via hybridization.”

Fo the study, Ward and Blum used two species of fish found in rivers across the US: the Blacktail Shiner (Cyprinella venusta), a native species, and the Red Shiner (Cyprinella lutrensis), a species that is considered to be invasive.

They collected individuals from both species from two streams in Georgia and kept them in separate tanks for 14 days. Some of the tanks contained BPA.

On the 15th day, they conducted detailed observations as they put individuals from separate tanks together. The researchers looked for physiological differences in the fish, such as color, and behavioral differences, such as signals they send to each other, and mate choice.

They found that the fish exposed to BPA showed “changes in the expression of male secondary traits as well as male and female mate choice”.

The researchers suggest that by disrupting their hormones, BPA caused changes in behavior and appearance of the fish, leading individuals from different species to see each other as potential mates.

The changes to female mate choice were not tightly linked to changes in the male traits, suggesting that exposure to BPA affected mating choice via two routes: it changed male appearance and behavior so it confused the females, and it also directly affected the females themselves.

Ward told the press:

“Chemicals from household products and pharmaceuticals frequently end up in rivers and BPA is known to be present in aquatic ecosystems across the United States.”

“Until now studies have primarily focused on the impact to individual fish, but our study demonstrates the impact of BPA on a population level,” she added.

The authors suggest the findings reveal the potential long-term effect of BPA in the aquatic environment: especially in those regions under pressure from invasive species.

Note that the authors do not preclude the fact that inter-species breeding occurs naturally.

The US Geological Survey has been studying the Red Shiner for years. In a 2002, they reported that:

“Red shiner introductions have caused multiple harmful effects among native fishes, including fishes placed on the federal list of threatened and endangered species.”

Ward explained:

“Our research shows how the presence of these manmade chemicals leads to a greater likelihood of hybridization between species.”

“This can have severe ecological and evolutionary consequences, including the potential for the decline of our native species” she warned.

Written by Catharine Paddock PhD