Intraspecific variation in the bony traits and elemental phenotype of a marine and freshwater fish

Vertebrates affect aquatic nutrient cycling by storing, excreting, and egesting important nutrients. The elemental phenotype, which defines (1) elemental acquisition (diet), (2) intestinal elemental absorption and elemental incorporation into tissues, (3) elemental allocation to processes and structures, (4) body elemental composition, and (5) elemental release in wastes, can summarize and evaluate these effects. Trait investment may influence the elemental phenotype, as some traits exert or relieve nutritional demands. We test whether variation in bone, a phosphorus (P)-rich vertebrate trait, affects the P-specific elemental phenotype of a species with substantial bone variation: the threespine stickleback ( Gasterosteus aculeatus Linnaeus, 1758). Given bone's unique impact on nutrient demand, we predicted that increased bone would (1) increase whole-body %P, (2) decrease dietary P intake or intestinal P absorption, and (3) increase P excretion and egestion. Ultimately, increased bone increased whole-body %P and P excretion but did not affect diet, intestinal absorption, or fecal %P. Nonetheless, threespine stickleback absorbed relatively less P in their guts than carbon or nitrogen, suggesting that their P demand is low overall and masking relationships between bone and demand. Our results suggest that bone content may both increase P storage in threespine stickleback bodies and increase P release in wastes.