Antler growth as a cost of reproduction in female reindeer
The costs of reproduction are important in shaping individual life histories, and hence population dynamics, but the mechanistic pathways of such costs are often unknown. Female reindeer have evolved antlers possibly due to interference competition on winter-feeding grounds. Here, we investigate if variation in antler size explains part of the cost of reproduction in late winter mass of female reindeer. We captured 440 individual Svalbard reindeer a total of 1426 times over 16 years and measured antler size and body mass in late winter, while presence of a ‘calf-at-heel’ was observed in summer. We found that reproductive females grew smaller antlers and weighed 4.3 kg less than non-reproductive females. Path analyses revealed that 14% of this cost of reproduction in body mass was caused by the reduced antler size. Our study is therefore consistent with the hypothesis that antlers in female Rangifer have evolved due to interference competition and provides evidence for antler growth as a cost of reproduction in females. Antler growth was constrained more by life history events than by variation in the environment, which contrasts markedly with studies on male antlers and horns, and hence increases our understanding of constraints on ornamentation and life history trade-offs.
KeywordsHorn Interference competition Rangifer Svalbard reindeer Trade-off
We thank the Governor of Svalbard for permission to undertake the research. We are especially grateful to Steve Coulson, Mads Forchhammer and the logistical and technical staff at the University Centre in Svalbard (UNIS) for supporting the field campaigns. The work was supported mainly by grants from U.K. Natural Environment Research Council (GR3/1083), the Norwegian Research Council (POLARPROG project 216051 and KLIMAFORSK 267613) and the Macaulay Development Trust. We are grateful to Brage B. Hansen for providing antler mass data and to Jean-Michel Gaillard, Mark Hewison and one anonymous referee for providing valuable comments that greatly improved an earlier version of the manuscript.
Author contribution statement
LEL, SA, AS, JI, VV and ER managed the long-term Svalbard reindeer project, collected the data and conceived the idea for the study. GP and LEL did the analyses. LEL, AM and PEG wrote the first draft of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
Data accessibility statement
Data will be archived on Dryad (http://datadryad.com/) following acceptance.
Compliance with ethical standards
All applicable institutional and national guidelines for the care and use of animals were followed. Captures and handling of Svalbard reindeer were approved by the Norwegian Food Safety Authority (permission number 17/237024) and by the Governor of Svalbard (permission number 16/01632-9).
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