Some of the coolest results are those which were discovered by mistake.

Researchers studying the effects of cortisol (a steroid hormone released in response to stressful situations) on fat storage in female mosquiotofish found a rather surprising result: exposing the females to high concentrations of cortisol made them manly!

Females exposed to high levels of this naturally occurring hormone began to look and act like males. Male mosquiotofish have a modified anal fin called a gonopodium that deposits sperm (think of it as a fish penis). When females were treated with high levels of cortisol their anal fins began to change shape, so that they began to look like male gonopodiums! What an unpleasant surprise that must have been to wake up to!

Not only do the females begin to look like males, they also begin to court females as though they were male! In the video below (created by the Knapp Lab that conducted the research), you’ll see how male-like the cortisol-treated females have become:

The authors suggest that this increase in maleness is caused by an enzyme called 11β-HSD that happens to have multiple functions. One function of this enzyme is to decrease inappropriately high levels of cortisol. This is important because prolonged, high levels of cortisol can have detrimental physiological effects. The same hormone that brings down cortisol levels is also associated with the production of 11-ketotestosterone (or 11-KT). 11-KT is an androgen (like testosterone is an androgen) in fish which is important in controlling male sexual traits, including male morphology and behavior.

It’s possible that females whose bodies were attempting to decrease dangerously high cortisol levels inadvertently amped up their 11-KT production, causing the females to look and act like males.

Hopefully this study will get researchers excited about looking more closely at interactions between stress, sex steroids, and sexual traits so we can determine the extent to which this result is applicable to other vertebrates.

A link to the manuscript can be found here.

One Response to “Too much stress makes a man out of female mosquitofish”

  1. Jordan

    On a similar note, there’s a book of essays about biochemistry by Konrad Bloch that includes a chapter called “The Importance of Being Contaminated”. It’s about how a lot of discoveries were made because reagents contained contaminants. They range from discovering that phosphatidylcholine requires GTP, not ATP for synthesis to the discovery of glucagon from contaminated insulin samples to the biological role of vanadium. Definitely fascinating stuff.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.


September 1st, 2018

Graduate student position available studying alternative reproductive tactics at BGSU

We seek a graduate student for a newly NSF-funded project examining the life history decisions made by male smallmouth bass. […]

June 14th, 2018

Part of that World

The other day I was singing “Part of your World” from The Little Mermaid, but was changing some of the […]

June 13th, 2018

Parasite manipulation of host behavior in pop culture

I’m going to be giving a talk at the sure-to-be-amazing Zombie Apocalypse Medicine Meeting. The meeting celebrates all things zombie-related, and […]

June 4th, 2017

Soonish giveaway on Goodreads!

Five copies of the advance reader version of Zach and my new book Soonish are up for grabs on Goodreads! Click […]

March 7th, 2017

Soonish: Ten Emerging Technologies That’ll Improve and/or Ruin Everything

Zach and I wrote a book! Soonish: Ten Emerging Technologies That’ll Improve and/or Ruin Everything explores 10 emerging technologies, and discusses the roadblocks […]

January 26th, 2017

Tales from the Crypt: a parasitoid manipulates the behaviour of its parasite host

I have a new paper out with Dr. Scott Egan, Dr. Andrew Forbes, and Sean Liu! The paper is Open Access […]

May 30th, 2016

Postdoc with Dr. Ryan Hechinger (and me!)

We’re looking for a postdoc! See below! —————— Postdoctoral Opportunity with the Marine Biology Research Division at SIO Postdoctoral Scholar […]

May 7th, 2016

Science…sort of Episode 240: Moon Rocks Don’t Glow

I co-hosted an episode of Science…sort of recently. I pasted the show notes below, but you’ll have to head over […]

February 24th, 2016

Books on parasites

I’m often asked by students to suggest books they can read about parasites. Below is a list of books that […]

August 22nd, 2015

Great Adaptations – A kid’s book about evolution

Zach Weinersmith and I contributed to Tiffany Taylor’s children’s book about evolution. Tiffany worked with scientists to create Seuss-style stories […]