Polymorphism and Food Limitation in Three Daphnia carinata Populations

Abstract

The annual cycles of Daphnia carinata in three fish-free ponds in southern New Zealand (Quarry, Taieri and Raupo Ponds) are described. Although breeding was continuous, the populations were frequently dominated by distinct cohorts and there was a sexual phase in spring. Growth rates, particularly in Quarry Pond, were often slow, and clutch sizes generally small. Egg and neonate sizes changed seasonally, but changes were not closely related to clutch sizes and body lengths. In Taieri Pond and Raupo Pond some D. carinata grew to 6.14 mm and carried clutches of up to 154 eggs. The potentially high fecundity associated with large size makes D. carinata a good coloniser, but our studies showed that it also survives well in poor food conditions by growing slowly and producing only 1-2 eggs per clutch.D . carinata showed marked seasonal 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 notonectid, 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 development increased in the presence of Anisops. These increases may be due to water-soluble factor(s) produced by Anisops.

Summer distribution patterns of the backswimmer,Anisops wakefieldi(Hemiptera: Notonectidae), in a New Zealand pond

“…This decrease is evident from both the sweep-net samples (Table 2) and the surface (0.1 m) Schindler-trap samples (Table 4). A similar decrease in Anisops abundance during these months in Quarry Pond was reported by Chapman & Burns (1994). The decline could be the result of mortality or emigration.…”

“…are mallard ducks {Anas platyrhynchos platyrhynchos L.), paradise shelducks (Tadorna variegata (Gmelin)), and welcome swallows (Hirundo tahitica neoxena Gould). No potential invertebrate predators on Anisops were observed or previously reported (Chapman & Burns 1994). Information on the zooplankton community and on seasonal variation in temperature is available (Chapman & Burns 1994;Couch etal.…”

“…No potential invertebrate predators on Anisops were observed or previously reported (Chapman & Burns 1994). Information on the zooplankton community and on seasonal variation in temperature is available (Chapman & Burns 1994;Couch etal. 1999).…”

“…Around the shoreline there are clumps ofTypha orientalis C. Presl and Callitriche stagnalis Scop, and scattered mats of the floating plants Lemna minor L. and Azolla filiculoides Lam. The pond is fishless and contains a large population of Anisops wakefieldi (Chapman & Burns 1994). Potential vertebrate predators on Anisops spp.…”

Do potential predators induce an avoidance response inDaphnia carinata?

“…The pond is c. 20 m in diameter, with a maximum depth of less than 1 m (Chapman & Burns 1994). Numerous Anisops, and occasionally fish (Perca fluviatilis), have been recorded in the pond (Chapman & Burns 1994;Couch 2000).…”