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Photo of mosquitofish Research teamA team of researchers from the University of Oklahoma has recently found a fascinating link between stress and reproductive characteristics in a species of fish. The team has conducted experiments showing that female mosquitofish develop masculine fin shapes and male-typical behaviors when exposed to the stress hormone cortisol. The findings may have an impact on how scientists understand the relationships between the stress and sex hormones. The study was published online this week in Biology Letters, an academic journal of the Royal Society.

The paper was prepared by Rosemary Knapp, a behavioral endocrinologist in the University of Oklahoma’s department of zoology and Edie Marsh-Matthews, curator of ichthyology at the Sam Noble Museum. The study was based on experiments conducted in Marsh-Matthews’ laboratory facilities on OU’s south campus with help from OU undergraduate honors students Luanne Vo and Sarah Rosencrans. The team administered the stress hormone cortisol to female mosquitofish – a common Oklahoma species that gives birth to live young – originally with the intention of studying how stress affected the fishes’ transfer of nutrients to their unborn young.

Male and female mosquitofish“Cortisol is known to alter the condition of females in other fish, and in mammals this stress hormone affects to how much fat they store and where they store it,” Marsh-Matthews explained. “What we didn’t expect to find was that the females subjected to certain doses of this stress hormone developed modified anal fins that look like those of the male.”

The female fish receiving the stress hormone developed, over a period of some three to four weeks, an elongated anal fin typical of the male of the species, associated with the transfer of sperm. The affected females even began to behave like the males – pursuing other females as though attempting to mate.

“We know that female mosquitofish will express male characteristics if treated directly with androgens such as testosterone,” Marsh-Matthews said. “But it was a big surprise to find male characters expressed in response to stress hormone, especially among fully mature fish, not young fish still undergoing development.”

comparison of anal fins between normal female mosquitofish and cortisol treated mosquitofishThough the exact mechanisms are as yet unknown, the scientists think that the cortisol may be triggering increased production of an enzyme that helps deactivate the stress hormone. This same enzyme is involved in androgen production The study may have implications for understanding the interaction between these two hormonal systems, as the biological importance of this shared enzyme in the two steroid pathways has not received much experimental study.

The Royal Society, the national academy of sciences of the United Kingdom, is the world's oldest scientific academy in continuous existence, and has been at the forefront of enquiry and discovery since its foundation in 1660. Biology Letters publishes short, innovative, cutting-edge research articles and opinion pieces, accessible to scientists from across the biological sciences. Information about the publication can be found at http://royalsocietypublishing.org.



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