Environmental Signaling

Case 2: The Case of the Cross-Dressing Carp

Session Objectives

Students will be able to:
  • Explain what endocrine disruption is
  • Explain what a phytoestrogen is
  • Explain how endocrine disruption might work, using an organ-system level approach
  • Give examples of cases of endocrine disruption based on the scientific literature, and citing primary research
  • Briefly summarize the history of the idea of endocrine disruption

In this case students consider news headlines, and ponder whether they represent a common problem. After a discussion they define central concepts in endocrine disruption. Read the following headlines to students:

Streamwater turns male fish female

Cheetahs in captive breeding program develop liver disease and infertility

Scientist finds male frogs with egg-filled ovaries

Moldy corn feed advances puberty of young swine

Wild seals suffering from human-like uterine disease

Drought-stricken plants cause quail infertility

Florida alligators have shrinking penises

Poor pasture: some clover prevents sheep reproduction

Divide the students into small groups and give each group a copy of one of the references. Emphasize that they are to get just the main phenomenon described, and not get into the methods of the study. Then have each group share the phemonmenon they have learned about. At the end discuss the questions, moderating so that they try to figure out the pattern of the different situations.

In small groups you and your classmates will investigate these bizarre phenomena and try to figure out what is going on. Each group will summarize their assigned research article in 4 or 5 sentences, and then share that summary with the whole group. You should take notes on these summaries to use later.

As a whole group we will discuss the situation. Are these isolated incidents, or parts of a larger pattern? If there is a larger pattern, what is the root cause? What do these real scenarios have in common, and what can we learn from these intersections?

When each group has contributed its summary, facilitated group discussion will address the questions below. Record the group’s consensus answers.

Discussion Questions:

Are these isolated incidents, or parts of a larger pattern?
What evidence and reasoning supports this conclusion?
If there is a larger pattern, what is the root cause?
What evidence and reasoning supports this conclusion?

Have the students sign up in groups to address each question, and explain to them the kind of answers you are looking for in terms of length, detail, and examples.

Case Assignment

You will be assigned to groups, and each group will have one of the following writing assignments:

  1. Define endocrine disruption, and give examples.
  2. Define phytoestrogen, and give examples.
  3. Describe, at an organ-system level, how endocrine disruption might work.
  4. Find and reference primary research articles detailing other examples of endocrine disruption in wildlife, using pubmed and sciencedirect.
  5. What is the history of the idea of endocrine disruption? When was the phrase first used to discuss wildlife or livestock, and when did it achieve widespread usage? What impacts on politics and policy has this discovery made?


  • Biggers, JD and Curnow, DH. 1954. Oestrogenic activity of subterranean clover. Biochemical Journal 58(2):278-82.
  • Bristol, FM, Djurickovic, S. 1971. Hyperestrogenism in female swine as the result of feeding mouldy corn. Canadian Veterinarian Journal 12(6):132-5.
  • Leopold, AS, Erwin, M, Oh, J, and Browning, B. 1976. Phytoestrogens: adverse effects on reproduction in California Quail. Science 191:98-100.
  • Setchell, KDR, Gosselin, SJ, Welsh, MB, Johnston, JO, Balistreri, WF, Kramer, LW, Dresser, BL, and Tarr, MJ. 1987. Dietary estrogens--a probable cause of infertility and liver disease in captive cheetahs. Gastroenterology 93:225-33.
  • Guillette, LJ Jr, Gross, TS, Masson, GR, Matter, JM, Percival, HF, Woodward, AR. 1994. Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida. Environmental Health Perspectives 102(8):680-88.
  • Hayes, TB, Collins, A, Lee, M, Mendoza, M, Noriega, N, Stuart, AA, and Vonk, A. 2002. Hermaphroditic, demasculinized frogs after exposure to atrazine at low ecologically relevant doses. PNAS 99:5476-80.
  • Backlin, BM, Eriksson, L, and Olovsson, M. 2003. Histology of uterine leiomyoma and occurrence in relation to reproductive activity in the Baltic Gray Seal (Halichoerus grypus). Veterinary Pathology 40(2):175-80.
  • Beresford, N, Jobling, S, Williams, R, and Sumpter, JP. 2004. Endocrine disruption in juvenile roach from English rivers: a preliminary study. Journal of Fish Biology 64:580-86.