The role of nutrition in regulation of predator-induced crests of Daphnia carinata
1995
Barry, Michael J.
1. The effects of food level on the development of crests by Daphnia carinata in the presence of Anisops grains (Notonectidae) were investigated in two laboratory experiments and in the field. 2. In the laboratory experiments D. carinata were grown at different food levels either in the presence of A. gratus or in predator-free water. In the field study the effects of six variables (temperature, food level, density of Daphnia, density of Anisops, brood size and maternal nutrition) on development of crests in the next generation of Daphnia were investigated over a 12-month period at a single field site. 3. In the laboratory food level had a small but significant effect on relative crest height of D. carinata. In the presence of notonectid predators the rate of crest growth relative to body length was higher than for control D. carinata only during embryogenesis and/or the first two neonatal instars. Beyond this age the rate of crest growth was similar in both morphs. 4. In the field study, crest height was negatively correlated with density of Daphnia and positively correlated with density of Anisops and maternal nutrition (maternal nutrition was defined as the somatic weight of a female with a body length of 2.5 mm, calculated from the length-dry weight regression based on a sample of the population). However, these data were biased by a short period when no Anisops were present in the pond. When these data were excluded, the only factor which significantly correlated with crest height was maternal nutrition. This finding indicated that relative crest height of the next generation was determined primarily during embryogenesis on the basis of maternal feeding success and possibly on food availability during the first two instars.
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