title: Size dependence in non-sperm ejaculate production is reflected in daily energy expenditure and resting metabolic rate.
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.
authors.affiliation: School of Biological Sciences, University of Sydney, Heydon-Laurence Bldg AO8, Science Rd, Sydney, NSW 2006, Australia Department of Zoology, Oregon State University, Cordley Hall 3029, Corvallis, OR 97330, USA christopher.friesen@sydney.edu.au.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Friesen
authors.affiliation: Department of Biology, George Fox University, Edwards-Holman Science Center, Newberg, OR 97132, USA.
authors.forename: Donald R
authors.initials: DR
authors.lastname: Powers
authors.affiliation: Department of Biology, George Fox University, Edwards-Holman Science Center, Newberg, OR 97132, USA Department of Botany and Program in Ecology, University of Wyoming, Aven Nelson Building 130, Laramie, WY 82071, USA.
authors.forename: Paige E
authors.initials: PE
authors.lastname: Copenhaver
authors.affiliation: Department of Zoology, Oregon State University, Cordley Hall 3029, Corvallis, OR 97330, USA.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Mason
mesh_terms: D000818:Animals; D001481:Basal Metabolism; D017812:Colubridae / Q000502:physiology*; D004734:Energy Metabolism; D008297:Male; D012098:Reproduction; D012726:Sexual Behavior, Animal; D013094:Spermatozoa / Q000502:physiology*
keywords: Copulatory plug; Ejaculates; Energetic costs of reproduction; Size dependence; Thamnophis