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BOR - Papers in Press, published online ahead of print September 8, 2004.
Biol Reprod 2004, 10.1095/biolreprod.104.033001
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BIOLOGY OF REPRODUCTION 72, 150–156 (2005)
DOI: 10.1095/biolreprod.104.033001
© 2005 by the Society for the Study of Reproduction, Inc.

17{alpha}-Ethinylestradiol Reduces the Competitive Reproductive Fitness of the Male Guppy (Poecilia reticulata)1

Thomas Kristensen, Erik Baatrup, and Mark Bayley2

Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, DK-8000 Aarhus C, Denmark

Whether endocrine disruption in an individual male is actually translated into reduced reproductive success in a natural competitive environment is extremely difficult to predict. Here, we have used paternity analysis to provide new information on the ability of an endocrine disruptor to deleteriously affect male guppy reproductive fitness by including the effect of intermale competition. Groups of male guppies were exposed to 10.5, 44.4, or 112 ng/L of the synthetic estrogen 17{alpha}-ethinylestradiol (EE2) from birth to adulthood. Subsequently, an exposed male competed against an unexposed male for the opportunity to fertilize a receptive female. The successful males siring the majority of the offspring in each brood were then identified using microsatellites in genetic paternity analysis. Only the highest dose of EE2 produced harmful effects with a significantly female-biased sex ratio, significant reductions in male sperm count, testis weight, body coloration and courtship behavior, and a significant increase in body size. These feminizing effects were translated into a highly significant reduction in fertility, where only 1 of the 17 exposed males sired offspring in competition with unexposed males. The evidence suggests that EE2-treated males have reduced reproductive fitness compared with untreated males, possibly the result of EE2 effects on multiple fitness traits. To our knowledge, this is the first study providing evidence of endocrine disruption at the population level that has included the ecologically highly relevant effect of sexual competition on male reproductive fitness.

1 Supported by the Danish Environmental Research Program.

2 Correspondence: Mark Bayley, Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Building 135, DK-8000 Aarhus C, Denmark. FAX: 45 8612 5175; Mark.Bayley{at}biology.au.dk






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Copyright © 2005 by the Society for the Study of Reproduction.