ABSTRACT
The non-sperm components of an ejaculate, such as copulatory plugs, can be essential to male reproductive success. But the costs of these ejaculate components are often considered trivial. In polyandrous species, males are predicted to increase energy allocation to the production of non-sperm components, but this allocation is often condition dependent and the energetic costs of their production have never been quantified. Red-sided garter snakes (Thamnophis sirtalis parietalis) are an excellent model with which to quantify the energetic costs of non-sperm components of the ejaculate as they exhibit a dissociated reproductive pattern in which sperm production is temporally disjunct from copulatory plug production, mating and plug deposition. We estimated the daily energy expenditure and resting metabolic rate of males after courtship and mating, and used bomb calorimetry to estimate the energy content of copulatory plugs. We found that both daily energy expenditure and resting metabolic rate were significantly higher in small mating males than in courting males, and a single copulatory plug without sperm constitutes 5–18% of daily energy expenditure. To our knowledge, this is the first study to quantify the energetic expense of size-dependent ejaculate strategies in any species.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
C.R.F. conceived of the conceptual design of the whole project, conducted all of the DLW and bomb calorimetry studies, analysed all data and wrote the manuscript. D.R.P. helped to write the manuscript and designed the RMR and SMR experiments and conducted the work with the help of P.E.C. R.T.M. helped to write the manuscript and helped to conduct the DLW experiment.
Funding
This study was funded by National Science Foundation (NSF) grant IOS-06125 (R.T.M.), NSF DDIG IOS-1011727 (C.R.F.), George Fox University (GFU) Faculty Development Grant (D.R.P.) and a GFU Richter Scholar Grant (P.E.C.).
Supplementary material
Supplementary material available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.120402/-/DC1
- © 2015. Published by The Company of Biologists Ltd
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