title: Investment in boney defensive traits alters organismal stoichiometry and excretion in fish.
abstract: Understanding how trait diversification alters ecosystem processes is an important goal for ecological and evolutionary studies. Ecological stoichiometry provides a framework for predicting how traits affect ecosystem function. The growth rate hypothesis of ecological stoichiometry links growth and phosphorus (P) body composition in taxa where nucleic acids are a significant pool of body P. In vertebrates, however, most of the P is bound within bone, and organisms with boney structures can vary in terms of the relative contributions of bones to body composition. Threespine stickleback populations have substantial variation in boney armour plating. Shaped by natural selection, this variation provides a model system to study the links between evolution of bone content, elemental body composition, and P excretion. We measure carbon:nitrogen:P body composition from stickleback populations that vary in armour phenotype. We develop a mechanistic mass-balance model to explore factors affecting P excretion, and measure P excretion from two populations with contrasting armour phenotypes. Completely armoured morphs have higher body %P but excrete more P per unit body mass than other morphs. The model suggests that such differences are driven by phenotypic differences in P intake as well as body %P composition. Our results show that while investment in boney traits alters the elemental composition of vertebrate bodies, excretion rates depend on how acquisition and assimilation traits covary with boney trait investment. These results also provide a stoichiometric hypothesis to explain the repeated loss of boney armour in threespine sticklebacks upon colonizing freshwater ecosystems.
authors.affiliation: Department of Biology, University of Victoria, P.O. Box 1700, Station CSC, Victoria, BC, V8W 2Y2, Canada. rana@uvic.ca.
authors.forename: Rana W
authors.initials: RW
authors.lastname: El-Sabaawi
authors.affiliation: Department of Biology, University of Victoria, P.O. Box 1700, Station CSC, Victoria, BC, V8W 2Y2, Canada.
authors.forename: Misha L
authors.initials: ML
authors.lastname: Warbanski
authors.affiliation: Department of Zoology, University of British Columbia, 4200-6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada.
authors.forename: Seth M
authors.initials: SM
authors.lastname: Rudman
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA, 98195, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Hovel
authors.affiliation: Department of Aquatic Ecology, Center for Ecology, Evolution and Biogeochemistry, Eawag, Kastanienbaum, 6047, Switzerland.
authors.forename: Blake
authors.initials: B
authors.lastname: Matthews
mesh_terms: D000818:Animals; D005075:Biological Evolution; D017753:Ecosystem; D005399:Fishes / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism
chemical_list: D010758:Phosphorus; D009584:Nitrogen
keywords: Eco-evolutionary interactions; Elemental phenotype; Nitrogen; Nutrient cycles; Phosphorus