Feb. 1, 2019

Gender fluidity in the water: What we learn from the feminization of fish

The past couple of decades have opened up new conceptions of sex and gender. The idea that there are only two biologically based genders — male and female — is being replaced by a more fluid understanding where masculinity and femininity overlap, shift and combine.

Some of the most eloquent voices in debates around gender come from gender theorists. But scientists, too, are making valuable contributions. Researchers like Dr. Leslie Henderson, PhD, professor of physiology and neurobiology at Dartmouth University’s Geisel School of Medicine, unpacks the complexities of studying the science of gender. Says Henderson:

            I have spent more than two decades studying sex-specific differences in the brain. I hazard a guess that I know more than most people on this issue, although I also know that we scientists have only a rudimentary understanding of how genetic, epigenetic, hormonal and environmental factors interact during brain development and into adulthood to form the incredibly diverse and complex spectrum that forms gender roles and gender identity.

Henderson’s suggestion that hormonal and environmental factors may be responsible for the complexity of sex and gender is borne out by research done by Dr. Lee Jackson, PhD, a professor of ecology and evolutionary biology in UCalgary's Faculty of Science. Jackson's team studies the impact of environmental conditions on Southern Alberta rivers and lakes. Also, as scientific director of Calgary's Advancing Canadian Wastewater Assets (ACWA) initiative, Jackson's research involves finding new ways to remove contaminants from wastewater before it's released back into the environment.

The feminization of fish

One of Jackson’s key findings to date is that environmental contaminants are changing the reproductive biology of fish. Jackson has co-authored a paper demonstrating a link between water-borne chemicals and the feminization of fish in Alberta's Oldman and Red Deer rivers.

Jackson looked specifically at a native minnow called the longnose dace, and found that male fish had eggs in their testes — a characteristic that indicates they have become feminized. In biological science, “feminization” means that genetically male fish express characteristics typical of genetically female fish.  “In the case of the longnose dace,” says Jackson, “the feminization is a response to exposure to environmental contaminants that have hormone-like activity.”

The feminization is a response to exposure to environmental contaminants.

Chemical analysis of the water showed the presence of organic contaminants, including synthetic and natural estrogen (released naturally by female mammals or from birth control pills), bisphenol A (a chemical used in making plastics), and natural and synthetic steroids (common by-products of agricultural and cattle farming activity).

To define the link between environmental factors and feminization, Jackson looked at the reproductive tissues of the fish at a microscopic level. “We’re trying to understand the link between chemicals, the genome of the minnow, how those chemicals act on the genome and change the proteins that are produced, and how that is ultimately expressed in fish populations,” says Jackson. "It's like peeling away layers of an onion to understand how the external environment acts on the genome and affects each layer."

Dramatic changes: interpreting the findings

Jackson may not be sure how the chemicals relate to feminization, but he knows this isn't the typical state of affairs for Southern Alberta. Existing research shows that the environment must change drastically to produce such a strong feminization effect. “A lot of things have to go wrong for this to happen,” says Jackson. “You have to have either very high concentrations of estrogen or estrogen-like chemicals, or long-term exposure, or exposure at a key period of development for the fish.”

The other finding that raised research flags for Jackson was discovering that in downstream areas of the Oldman River, south of Fort Macleod and Lethbridge, females made up to 85 percent of the adult longnose dace population. In upstream locations, only 55 percent were female, which is similar to sites throughout the Red Deer River.

This statistic seems to scream that something in the downstream river flow is changing male fish to females. But Jackson cautions that the statistic could be explained in several ways. “When we see skewed sex ratios,” he says, “there might be many possible explanations. Yes, the chemicals could be changing the expression of the genetics of the fish. Then again, maybe the boys are just getting eaten for some other reason that has nothing to do with contaminants.”

This is happening over hundreds of kilometres and it's linked to multiple land uses.

The enigmatic genetics of minnows complicate matters. “We still have not found a master sex determinant gene in longnose dace,” says Jackson. “It’s not like human genes, where being male is associated with the Y chromosome. When we look at a longnose dace that has female characteristics, we don't know for sure if it was originally programmed to be male or female.”

But Jackson has been able to clearly distinguish male from female subjects. “We haven't seen a situation yet where we've examined a fish, seen the reproductive organs and said, ‘I don't know what that is. I've never seen anything like that.’ We always see either testes or ovaries.”

Study findings to date lead Jackson to believe that he’s looking at a contamination issue that is widespread throughout the South Saskatchewan River Basin. “It's not just at one site where there's an associated pipe putting contaminants into the water," says Jackson. "This is happening over hundreds of kilometres and it's linked to multiple land uses."

What can we learn from the feminization of fish?

Jackson realizes that people will likely make connections between his research and the broader discussions about deconstructing the gender binary. “One thing we could be asking ourselves as biologists is whether there are other options for gender in fish, other than just male and female,” Jackson says, echoing Leslie Henderson’s acknowledgement that science and its understanding of gender is in its early days. “I honestly don’t know what a broader gender spectrum would look like in something like the minnow. But we know that if we expose fish in an aquarium to androgenic compounds or estrogenic compounds, we can essentially turn males into females and females into males.”

But what does that say in a larger, more philosophical sense, about about the relationship between sex and gender? “I’m not sure. At some point we may find that what we think is a binary in animals — male or female — may turn out to be something else."

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Dr. Leland (Lee) Jackson, PhD, is a professor of Ecology and Evolutionary Biology in UCalgary's Faculty of Science and scientific director of Calgary’s Advancing Canadian Wastewater Assets (ACWA) research initiative. Read more about Lee

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