Selective Predation of Ephippal Daphnia and the Resistance of Ephippal Eggs to Digestion

Abstract

In the spring and autumn, Daphnia populations may produce resting eggs contained in pigmented envelopes called ephippia. Pumpkinseed sunfish and yellow perch preyed selectively on ephippial over similarly sized, nonephippial Daphnia galeata mendotae Birge in Fuller Pond, Connecticut. The D. galeata mendotae with darker ephippia were consumed at a greater frequency than those with less pigmented ephippia. In the laboratory pumpkinseeds and—spotted newts preyed selectively on ephippial over nonephippial Daphnia pulex Leydig under natural light intensities. Ephippium tanning and hardening probably evolved and persisted because of the increased protection given to the resting eggs after natural release of the ephippia from the maternal Daphnia. Darker ephippia retained their normal complement of two resting eggs twice as well as less pigmented ephippia did during passage through newt and perch digestive tracts. D. galeata mendotae and D. pulex ephippial eggs hatched after passage through pumpkinseed and yellowbelly sunfish, golden shiners, and newts. Seventy percent of the 27 planktivorous fish collected from Fuller Pond in October and November contained ephippia. Large numbers of ephippia were found within the digestive tracts of some of these perch and sunfish. Daphnia pulex and D. galeata mendotae ephippial eggs hatched after passage through a Black—Crowned Night Heron and laboratory rats. This suggests a possibility for Daphnia resting egg dispersal by fish—eating birds and mammals feedings on planktivores that prey selectively on ephippial Daphnia.