Sex-specific tolerance to starvation in the copepod Acartia tonsa

We define tolerance to starvation as the ability to survive in the absence of food. We tested the hypotheses that adult male Acartia tonsa copepods are less tolerant to starvation than adult female copepods, and that tolerance to starvation is affected by prior diet, age of individuals and duration spent in the adult stage. We also tested whether, during the period of starvation, egg production affected tolerance to starvation in female adults. Field-collected male and female copepods were fed non-limiting rations of the toxic dinoflagellate Alexandrium fundyense, non-toxic Alexandrium tamarense, the nutritionally insufficient dinoflagellate Prorocentrum minimum, or a standard non-toxic diet (a mixture of the diatom Thalassiosira weissflogii, the flagellate Tetraselmis sp., and the green microalga Isochrysis galbana) for 24 h before starvation. In separate experiments, male and female field-caught copepods were either starved or fed non-limiting rations of the standard non-toxic diet. Finally, tolerance to starvation was measured in adults raised in laboratory cohorts. Tolerance to starvation was lower for adult males than females in all experiments, with all starved copepods dying within fifteen days. We observed a similar pattern for field-caught and laboratory-raised animals: differences in adult survivorship between the sexes were immediately apparent under starvation. In contrast, adult survivorship in fed animals was relatively constant and independent of sex during the first fifteen days. Subsequently, male survivorship was lower. In the laboratory-cohort experiments differences in tolerance to starvation between the sexes were not affected by age or by duration within the adult stage. Taken together, the results of this study suggest that adult male A. tonsa are physiologically less tolerant to starvation compared to females, and may explain observations of female-skewed adult sex-ratios in food-limited field and laboratory experiments. Further, total egg production and survivorship during starvation were uncorrelated. We suggest that the former is controlled by previous feeding history and the latter by basal metabolism. (C) 2013 Elsevier B.V. All rights reserved.