POLYMORPHISM AND FOOD LIMITATION IN 3 DAPHNIA-CARINATA POPULATIONS

The annual cycles of Daphnia carinata in three fish-free ponds in sout hern New Zealand (Quarry, Taieri and Raupo Ponds) are described. Altho ugh breeding was continuous, the populations were frequently dominated by distinct cohorts and there was a sexual phase in spring. Growth ra tes, particularly in Quarry Pond, were often slow, and clutch sizes ge nerally small. Egg and neonate sizes changed seasonally, but changes w ere not closely related to clutch sizes and body lengths. In Taieri Po nd and Raupo Pond some D. carinata grew to 6.14 mm and carried clutche s of up to 154 eggs. The potentially high fecundity associated with la rge size makes D. carinata a good coloniser, but our studies showed th at it also survives well in poor food conditions by growing slowly and producing only 1-2 eggs per clutch. D. carinata showed marked seasona l polymorphism in tailspine length and development of head crests. In winter, crests were absent and tailspines were short and varied little with body length. Crests were first apparent, and tailspines began to elongate, in early spring, before the first appearance of a notonecti d, Anisops wakefieldi. By midsummer, tailspines had increased markedly with body length but the slope of the relationship declined in autumn . Laboratory trials showed that both tailspine length and crest develo pment increased in the presence of Anisops. These increases may be due to water-soluble factor(s) produced by Anisops.