Resting stage density and hatching of two cladoceran species from small ephemeral waters
Hotový, Jiř í Petrusek
published: Sep 5, 2007
ArtNo. ESP141016903001, Price: 29.00 €
We investigated resting stage densities of two cladocerans, Daphnia obtusa and Moina macrocopa, in very small and ephemeral water bodies (temperate zone rain puddles) and tested whether these species exhibit a prolonged diapause in such an environment. Densities of ephippia as well as resting eggs in puddles ranged between 102 and 104 per m2, and varied substantially within as well as among puddles. We determined the hatching success and temporal dynamics for resting stages collected from natural habitats and incubated at 15 °C with a 14L:10D light regime. Hatching success of both species was high (> 80 %) and steady, with new hatchlings appearing mostly within 3-8 days. M. macrocopa hatched significantly faster and slightly more successfully than D. obtusa. Decapsulation of D. obtusa ephippia had no effect on the hatching success but slowed down the hatching dynamics. Hatching of egg pairs from the same ephippium was mostly synchronised - in only less than 10 % of cases one egg hatched and the other remained potentially viable for the next flooding event. We compare our results with available data on cladoceran resting egg densities and hatching success, and discuss the possible causes of the high and steady hatching proportion of puddle cladocerans. A physiologically-based bet-hedging strategy may not be necessary if only a certain proportion of eggs are exposed to hatching cues or when the hydroperiod of temporary waters is longer than the cladoceran life cycle. Additionally, frequent destruction of localities may promote instantaneous termination of diapause even in ephemeral habitats such as puddles.