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Mating with the wrong species: plastics make it possible

The views expressed are those of the author and are not necessarily those of Scientific American.


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Despite only being around for the past century or so, plastics have become ubiquitous in modern life and for good reason: the final product is incredibly versatile. From grocery bags to IV bags to the teflon on non-stick pans, plastics really do make almost everything possible.

But, such a useful product comes at a cost. One of the chemicals used in making certain plastics, BPA, has been linked to a suite of ecological and human health problems. Now, scientists have discovered that the effects of BPA are so strong, certain species of fish lose their ability to tell their own species apart from another.

BPA is the building block of polycarbonate plastics, and is used in other kinds of plastics alter their flexibility. The trouble is, BPA doesn’t stay neatly locked in – it’s known to leech out, contaminating food and liquids that come in contact with BPA containing plastics. Studies have shown that BPA is now in our lakes and rivers, affecting all kinds of creatures that rely on those water sources.

The real trouble with BPA is that it looks a lot like one of the most potent animal hormones: estrogen. It tricks animal cells. Because estrogen controls a number of very important bodily functions, the potential affects of BPA on animals – including us – are severe and range widely.

In animals like mice and rats, doses as low as 0.025 µg/kg/day can causes permanent changes to the genital tract and predispose breast cells to cancerous activity. Between 1 and 30 µg/kg/day can lead to long-term reproductive changes like earlier puberty and longer periods, decline in testicular testosterone, and prostate cell changes indicative of cancer, as well as behavioral effects like decreased maternal instincts and even reversed sex roles.

Jessica Ward and her colleagues were particularly concerned with how BPA is affecting fish in contaminated waters. In Georgia waters, an introduced species of fish – the red shiner (Cyprinella lutrensis) - is encroaching upon the habitat of a native species, the blacktail shiner (Cyprinella venusta). To determine the short term effects of BPA exposure on these two species, the research team placed male and female fish in BPA and control treatments for two weeks, then looked for physical and behavioral changes.

Males that were exposed to BPA changed color, losing some of their distinctive coloring that females use in mate choice (image from the paper on the right). This loss of color affected the females’ behavior: they were less choosy when it came to their mates. Exposure to BPA led to more mixed-species pairings.

“This can have severe ecological and evolutionary consequences,” said Ward, “including the potential for the decline of our native species.” Already, hybridization with red shiners is altering the community composition of native shiners in southern waterways and facilitating the invasion. With BPA and other hormone-mimicking pollutants speeding up the process of invasion, our native species are in for the fight of their life.

While we knew BPA was a problem, this is one of the first studies to reveal how broad its effects really are. “Until now studies have primarily focused on the impact to individual fish, but our study demonstrates the impact of BPA on a population level,” said Ward. Additional studies like this one on other species, from insects to mammals, will help us better understand how BPA and other hormone-mimicking chemicals are affecting our ecosystems. Given the dire situation many of our ecosystems currently face, such knowledge is vital in the effort to protect what biodiversity we have left for further generations.

 

Citation: Ward, J.L. & Blum, M.J. (2012). Exposure to an environmental estrogen breaks down sexual isolation between native and invasive species, Evolutionary Applications, n/a. DOI: 10.1111/j.1752-4571.2012.00283.x

Christie Wilcox About the Author: Christie Wilcox is a science writer and blogger who moonlights as a PhD student in Cell and Molecular Biology at the University of Hawaii. Follow on Google+. Follow on Twitter @NerdyChristie.

The views expressed are those of the author and are not necessarily those of Scientific American.



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  1. 1. Percival 3:11 am 07/12/2012

    The term “native species” is almost meaningless unless a particular time scale is specified, and it NEVER IS in articles like this.

    That aside, I’m seeing lemonade, not lemons.

    BPA isn’t the only chemical that mimics estrogen, there are plenty of “natural” xenoestrogens.

    Standard evolutionary theory says species spawn new species strictly branchwise.

    Well, suppose those branches re-entwine once in a while? When two closely related populations of similar but distinct species are exposed to xenoestrogens of natural or artificial origin and get “less choosy”, might they not swap genes that have arisen since they speciated, thus enriching both populations or even bringing new species into existence?

    Yes, we humans are twisting the knobs on Starship Earth’s control panels at random, but perhaps it isn’t always a bad thing.

    Link to this
  2. 2. Tomsing 1:07 pm 07/16/2012

    You mention doses as low as 0.025 µg/kg/day causing changes, but you don’t relate that to the dose an animal in any particular environment might get. Is that a lot, or a little?

    Also, are the mixed species shiner pairings producing fertile offspring?

    Link to this

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