Intraspecific Variation in Organismal Stoichiometry and Elemental Excretion in the Atlantic Molly (Poecilia mexicana)

Ecological stoichiometry (ES) uses the study of elemental mass balance in biological systems to integrate physiology, ecology, and evolutionary biology. A central tenet of ES is that organisms of higher trophic levels have a more tightly regulated ratio of elemental content than that of lower trophic levels. Relatively few studies have tested intraspecific stoichiometric variation that may potentially affect ecosystem processes such as elemental cycling. Here, we studied intraspecific stoichiometric variation in the live bearing fish, Poecilia mexicana to measure stoichiometric variation in these vertebrate consumers. We measured carbon, nitrogen, phosphorus and sulfur content of somatic tissue using an Elementar microvario cube and modified sulfuric acid digestion method on P. mexicana inhabiting sulfidic and non-sulfidic habitats of Tabasaco, MX. We found greater sulfur content in the sulfidic populations as well as variation in carbon, nitrogen and phosphorus content. This supports the existence of intraspecific variation in what has been presumed to be tightly regulated stoichiometric content. Data on nutrient excretion indicate such variation in somatic stoichiometry is ecologically relevant which may affect elemental availability to other trophic levels within ecosystems.