Constitutive but no Triops induced differences in bet hedging strategies for hatching in Daphnia
Since cladocerans from the genus Daphnia are known to have evolved several inducible defenses (morphological and life history shifts) against the notostracan predator Triops, we investigated whether hatching was also altered in response to Triops. We tested whether dormant eggs of Daphnia magna are able to detect Triops cancriformis kairomones in the water as a signal of predation pressure and alter their hatching response accordingly to avoid predation. We predicted that, in the presence of Triops kairomones, hatching fractions might be reduced (postponing hatching to a next growing season) and/or that hatching might peak earlier (increasing chances to reproduce before Triops becomes predatory) We also tested whether this response depended on the origin of the population. Ephippia from three D. magna populations, originating from one permanent lake and two temporary pond systems, were exposed to Triops kairomone and control treatments. We observed significant population differences in hatching patterns, both in terms of the fraction of eggs that hatch as well as the timing of hatching, with evidence for within season bet hedging through delayed hatching in the populations inhabiting temporary habitats. However, no indication was found that the populations also adjust their hatching pattern to the presence of Triops kairomones.
Hydrobiologia