Linking Life History Strategies and Ontogeny in Crustacean Zooplankton: Implications for Homeostasis

• Published in: Ecology (Durham) 2002-07, Vol.83 (7), p.1899-1914
• Main Authors: Villar-Argaiz, Manuel, Medina-Sánchez, Juan M., Carrillo, Presentación
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Carbon; Chemical composition; Ecological life histories; Fundamental and applied biological sciences. Psychology; homeostasis; life history strategies; lipid ratio; Lipids; Nauplii; Nitrogen; Nutrients; Ontogeny; phosphorus; Plankton; Protozoa. Invertebrata; rheostasis; stoichiometry; Zooplankton
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/0012-9658(2002)083[1899:LLHSAO]2.0.CO;2

Work to date has established that consumers are constrained in their chemical content variability. Such a constraint generates many different kinds of ecological relationships ranging from aspects of animal mineral nutrition to factors affecting consumer-driven nutrient recycling. Although previous studies have shown variation in zooplankton nutrient content within and between taxa, most stoichiometric studies assume that consumers are homeostatic in their elemental composition. In this paper, this assumption is reexamined as we describe the variability in the elemental content of the calanoid copepod Mixodiaptomus laciniatus Lilljeborg throughout its ontogeny (interstage variability) and for its specific developmental stages (intrastage variability). Mean copepod carbon content as dry mass increased significantly during ontogeny from 36.3% in nauplii to 51.5% in immature copepodites and 55.8% in adults. Mean phosphorus content decreased from 0.98% in nauplii to 0.87% in immature copepodites and 0.51% in adults. The copepod molar C:N:P ratio was 99:3:1 for nauplii, 165:13:1 for immature copepodites, and 234:25:1 for adults. These ontogenetic variations in stoichiometry within a single copepod species are comparable to the previously described range between taxa. Stoichiometric and physiological approaches are used as complementary tools to explain the two-part life history strategy of this copepod. First, the nauplii and early copepodite stages (CI-CIV) with high carbon demands adopt a growth strategy during which carbon sources are mainly allocated to increases in body size. The susceptibility of these copepodite stages to carbon limitation is reflected in the decline in the carbon content for a given stage (e.g., from 66% to 38% C in CII) and in the 40-fold decrease in neutral-to-polar lipid ratio toward the end of the ice-free season, suggesting a mobilization of food reserves toward growth. In contrast, copepodite stage CV and adults with less carbon demands for growth followed a survival-reproductive strategy, where the invariability in carbon content as dry mass (near 60%) and in neutral-to-polar lipid ratio through time indicates no accumulation of storage lipids, but instead an allocation of resources toward maintenance or reproduction. The basic assumption of predictions of stoichiometric models that elemental composition remains constant with time are not supported by changes in the intrastage carbon and nitrogen contents of Mixodiaptomus lacinia