Sexually selected weapons evolved to maximize the individual reproductive success of males in many polygynous breeding species. Many weapons are also retained outside of reproductive periods for secondary reasons, but the importance of these secondary functions is poorly understood. Here we leveraged a unique opportunity from the predator–prey system in northern Yellowstone National Park, WY, USA to evaluate whether predation by a widespread, coursing predator (wolves) has influenced a specific weapon trait (antler retention time) in their primary cervid prey (elk). Male elk face a trade-off: individuals casting antlers early begin regrowth before other males, resulting in relatively larger antlers the following year, and thus greater reproductive success, as indicated by research with red deer. We show, however, that male elk that cast their antlers early are preferentially hunted and killed by wolves, despite early casters being in better nutritional condition than antlered individuals. Our results run counter to classic expectations of coursing predators preferring poorer-conditioned individuals, and in so doing, reveal an important secondary function for an exaggerated sexually selected weapon—predatory deterrence. We suggest this secondary function played a key evolutionary role in elk; uniquely among North American cervids, they retain their antlers long after they fulfil their primary role in reproduction.
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Data used for analyses is available at https://datadryad.org/resource/doi:10.5061/dryad.j72tt79.
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We thank all Yellowstone Wolf Project field technicians and Gallatin Flying Services for data collection, and E. Stahler, K. Cassidy, K. Koitzsch and J. Jones for discussions. This work was supported by Yellowstone Forever (Tapeats Fund, anonymous donor, Frank and Kay Yeager, many individual donors), National Science Foundation (NSF) Long Term Research in Environmental Biology grants DEB-0613730 (D.W.S.), DEB-1245373 (D.R.S., D.R.M. and D.W.S.), DEB-1556248 (M.H.) and NSF grant OEI-0919781 (D.J.E.). M.C.M. was also supported by the Wesley M. Dixon Graduate Fellowship and Bertha Morton Scholarship from the University of Montana and a Graduate Enhancement Fellowship from the Montana Institute on Ecosystems funded through NSF Established Program to Stimulate Competitive Research.
The authors declare no competing interests.
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Metz, M.C., Emlen, D.J., Stahler, D.R. et al. Predation shapes the evolutionary traits of cervid weapons. Nat Ecol Evol 2, 1619–1625 (2018). https://doi.org/10.1038/s41559-018-0657-5
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