Thermal effects on body size and stoichiometry: A case study in a desert spring fish, Gambusia marshi

Authors: Eric K. Moody, Jessica R. Corman, Héctor Espinosa-Pérez, Jorge Ramos, James J. Elser

Year: 2014 (xlvi)

Abstract

Organisms reared at cooler temperatures tend to mature at larger sizes than warm-reared conspecifics. As body size is an important trait that influences many metabolic processes including the storage and recycling of nutrients by consumers, examining the linkages between temperature, body size, and organismal stoichiometry can improve our mechanistic understanding of how organismal traits affect ecosystem function. We tested whether temperature affects adult body size and in turn the stoichiometric ratios of fish bodies and excretion in the poeciliid fish Gambusia marshi. We conducted this study in the Cuatro Ciénegas basin in Coahuila, Mexico, where G. marshi inhabit spring pools (pozas) which are thermally stable but individually range in temperature from 25-33 Á‚Â°C. Among eight pozas, we found a significant decline in adult female body mass with increasing water temperature. Body %P increased with body mass across all sites, but separate analysis of cooler (<27 Á‚Â°C) and warmer (>29 Á‚Â°C) springs revealed a greater intercept and slope for warmer populations. Body %C decreased with body mass at warmer sites but was not significantly related to body mass at cooler sites, and %N was unrelated to body mass among all sites. Individually, excretion rates of both nitrogen (N) and phosphorus (P) increased with fish mass. Contrary to predictions, the N:P ratio of excreted nutrients decreased with body mass in warmer springs and did not change significantly with body mass in cooler springs. Our results suggest that changing mean temperature can alter the storage of nutrients in fishes due to the size-specific relationships of C and P contents, but that other factors such as changes in diet quality are more important to driving variance in excretion ratios among sites.

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