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Divergent juvenile growth and development mediated by food limitation and foraging in the water strider Aquarius remigis (Heteroptera: Gerridae)


Wolf U. Blanckenhorn, Zoologisches Museum, Universität Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland. Fax: ++41 44 635 4755


The factors leading to variation in growth, development and body size are of central importance for the study of life histories. I investigated the effect of food limitation on patterns of growth and development in the water strider Aquarius remigis (Heteroptera: Gerridae). Groups of 10 juveniles were allowed to develop under field conditions at three different food levels. Food limitation prolonged juvenile development, reduced growth rates and led to smaller adult body size and weight, the most common life-history response in ectotherms; it also increased the variance among individuals in these traits, demonstrating variance accumulation suggesting divergent growth. Evidence that this resulted from competition among individuals for limited food was equivocal. On the one hand, direct observation of foraging nymphs showed that larger instar individuals were more likely to obtain monopolizable prey items than expected by chance, independent of food level. On the other hand, there was only a trend for the variance in moulting dates to increase when striders were raised in groups as opposed to singly at various temperatures in a controlled laboratory experiment. When food limitation prolongs juvenile development, variance accumulation with age can result from food limitation per se, as well as from random or heritable variation in growth trajectories. Foraging competition may amplify this effect, but not necessarily so. Therefore, it must not be assumed that divergent growth is necessarily caused by food competition.