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2006.04.26 > For Immediate Release
contact: Teresa Gleason - University Affairs
phone: 402.554.2762 - email: tmgleason@mail.unomaha.edu

Dominant Spotted Hyena Moms Pass Trait to Offspring Via Hormones

Omaha - In the world of the spotted hyena, nature's experiment in behavioral endocrinology, high-ranking mothers may provide their cubs with a hormonal "gift" in the womb that may make them more successful when they become adults.

The study, reported in the April 26 issue of Nature, is the first demonstration that a female mammal's hormones influence her offspring's behavior and appearance in apparently adaptive ways.

Jeffrey French, the Varner Professor of Psychology and Biology at the University of Nebraska at Omaha (UNO), and Michigan State University zoology faculty Kay Holekamp and Ph.D. student Stephanie Dloniak are investigating the relationship between endocrine function and reproductive success among members of a hierarchical society.  Their findings are the result of nearly two decades of National Science Foundation-funded field research on wild spotted hyena populations in the Masai Mara Game Reserve in western Kenya.

The female spotted hyena's genitalia have evolved into something that looks more like a penis than a vagina.  In addition, females have been found to show more aggression than males, are first to the kill and are dominant in clan life – the reverse of the norm in mammals.

The team monitored androgen hormone levels of dominant and lower-ranking hyena mothers during their pregnancies.  No differences were noted in the first trimester.  During the third trimester, however, the androgen levels of the dominant females were substantially higher than their lower-ranking counterparts.

"It has been known for decades that pregnant female hyenas have high levels of the male-typical androgen hormones," French said, "but our study is the first to show that levels in pregnant females differ by the dominance status of the soon-to-be moms." 

These differences in hormones have important consequences for behavior after the cubs are born.  French and colleagues analyzed play bouts in the cubs, and instances of both aggressive and sexual behavior were charted. 

The cubs born to mothers with high levels of androgen during pregnancy displayed higher levels of both aggressive and sexual behavior during their play bouts than cubs born to mothers with low levels of androgen, French said.  "Play is serious business for hyena cubs, where they learn much about the kinds of behavior that will make them successful as adults," he noted.

Although the research team was unable to weigh individual cubs, French said, it's likely that cubs born to mothers with high androgen levels weighed more at birth and were more competitive for nursing bouts, given the anabolic effects of androgen.

The Nature paper highlights a novel finding in behavioral development.  "Modification of offspring morphology and behavior by early hormones has been documented for about a decade in birds," French said, "but the hyena work is the first demonstration that a female mammal's hormones influence her offspring's behavior and appearance in apparently adaptive ways." 

Mammalian mothers play an important role in how their offspring develop, and the hyena study suggests that a mother's influence includes her hormone levels during pregnancy. 

French's Endocrine Bioservices Lab on the UNO campus has developed non-invasive research techniques that allow scientists such as the Michigan State team to monitor subtle changes in the hormone concentrations of mammals that live in social groups in complex environments.  The techniques also minimize the need to restrain animals for sample collection or to disrupt ongoing social interactions.

The research in French's UNO lab has been supported by grants from the National Institute of Health and the National Science Foundation since 1987.  Since 1991, his lab at UNO has focused on the black tufted-ear marmoset and the white-faced marmoset, two of South America's endangered primate species.

For more information, contact French at 402.554.2558 or jfrench@mail.unomaha.edu.

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