Maternal control of resting-egg production in Daphnia

Many planktonic organisms produce 'resting' stages when the environmental conditions deteriorate. Like seeds, resting stages can survive unfavourable conditions. The crustacean Daphnia normally reproduces by means of parthenogenetically produced normal, not resting, eggs-but occasionally switches to bisexual reproduction, which results in two resting eggs encased in a robust structure carried on the back of the female. This 'ephippium' is shed with the next moult, and can survive dormant for many years. The induction of resting-egg production requires multiple environmental stimuli, one of them being photoperiod(1,2). The switch from production of parthenogenetic eggs to resting eggs in Daphnia has recently been shown to be influenced by a maternal food effect(3). Here we present evidence that female Daphnia transmit information not only about food but also on photoperiod to their offspring, and influence the production of resting eggs in the next generation. The combined maternal effects can be relevant for the correct timing of resting-egg production-for example, in discriminating between spring and autumn conditions.