Ratio of neonate to adult size explains life history characteristics in cladoceran zooplankton

Abstract

The size ratio of adults to neonates varies greatly in cladocerans across taxa. In this study we tested the impact of this ratio (using length basis) on the selected life history parameters of nine species of freshwater cladocerans (Alona rectangula, Pleuroxus aduncus, Scapholeberis mucronata, Moina macrocopa, Moina wierzejskii, Ceriodaphnia dubia, Daphnia laevis, Diaphanosoma birgei and Daphnia pulex). Experiments were conducted on a mixed diet of Chlorella vulgaris (1.0 · 10 6 cells mL -i 1 and Scenedesmus acutus (0.5 · 10 6 cells mL -1 ) at (22 ± 1)°C. Using a cohort life table experimental design, we quantified age-specific reproductive output. Body sizes of neonates and adults as well as dry weight were determined using standard procedures. We found that the ratio of neonate to adult body length decreased with increasing body size of the adult. In terms of clutch size, however, smaller taxa produced lower numbers of offspring than larger ones. The influence of ratio neonate/adult size on average lifespan, age at first reproduction and at the maximum clutch showed U-shaped curves. In smaller taxa ( 1500 μm) the ratio between the neonate and adult body size was less than 0.4 or more than 0.6. In medium sized taxa (1000...1500 μm), the ratio of neonate to adult size was between 0.4 and 0.6. The results have been discussed in relation to the life history strategies of cladocerans.