Spatial and temporal heterogeneity of Daphnia in Lake Constance; intra- and interspecific comparisons.

Allozymic surveys of the Daphnia galeata-hyalina species complex in Lake Constance (Bodensee) examined seasonal variation in daytime vertical distributions of Daphnia galeata (G), Daphnia hyalina (H), and G x H hybrids. During summer and early autumn, G was the dominant taxon in the upper 20 m of the water column, while H and G x H were most abundant below 30 m. From November until April, all three taxa were homogeneously distributed in the water. Seventeen distinct G clones were detected during the study, while six G x H clones and five H clones were detected. Single clones of G × H and H accounted for 93% (400/431 and 400/434, respectively) of the total number sampled. Results reconfirm previous studies, which observed spatial (vertical) separation of G and H, and confirm previous suspicions as to the existence of G x H hybrids in the lake.