Enzyme variability in natural populations of Daphnia magna

Abstract

SUMMARYGenotypic frequencies were analysed for two years in a permanent population of the cladoceran crustacean, Daphnia magna, which was polymorphic for an esterase and for malate dehydrogenase. Large temporal changes in genotypic frequencies occurred at both loci. There was no evidence of a seasonal pattern in the frequency changes. In most samples, genotypes at the two enzyme loci were non-randomly associated; these associations showed temporal changes. On some occasions marked spatial heterogeneity in genotypic frequencies existed within the population. Genotypic differences in parthenogenetic and sexual egg production were observed. In a primarily parthenogenetically reproducing population, non-random associations between genotypes at structural and regulatory loci will be the rule. The allozyme variants themselves may or may not be under selection. The relevance of these observations to ecological studies on Daphnia is considered.

Mechanisms, effects, and scales of dispersal in freshwater zooplankton

“…comm. ), and a number of species are now known to be narrowly endemic (Hebert 1995). A similar pattern has also been reported for lotic meiofauna, such as harpacticoid copepods (Rundle et al 2000).…”

“…These eggs provide both a long-term egg bank and a stage that can resist the harsh conditions of overland transport. Furthermore, egg cases such as Daphnia ephippia have spines and barbs (Hebert 1995), which enable attachment to fur and feathers, an adaptation analogous to the seed cases of many terrestrial plants. Zooplankton are linked to a wide variety of vectors enabling passive dispersal (Table 1).…”

“…Instead, low rates of gene flow might result from low dispersal rates. However, an alternative explanation is that the pattern is a result of founder and priority effects (Hebert 1974), an idea expanded recently into the ''monopolization hypothesis'' (De Meester et al 2002). This hypothesis states that early-arriving clones quickly develop a numerical advantage through rapid population growth rates, development of an egg bank, and local adaptation, and this advantage leads to competitive exclusion of later invaders.…”

Enzyme variability in natural populations of Daphnia carinata king

“…A Tris-glycine electrode buffer was used for both types of gel. Gel buffers and staining procedures were similar to those described in Hebert (1972). Fifteen populations were screened for variation at all 16 loci and gene frequencies at the LAP-2 locus were determined in an additional 15 populations.…”

Genetic similarity and diversity of parthenogenetic and bisexual populations of the freshwater snail Melanoides tuberculata (Gastropoda: Prosobranchia)

“…Indeed, some investigations showed very limited genetic variation and clonal structure of parthenogenetic populations (Herbert, 1978;Wool et al, 1978;Herbert & Moran, 1980;Ochman et al, 1980). Contrary to this, other studies showed that in some parthenogenetic species the genetic heterogeneity of populations is not lower than in bisexual species (Lokki et al, 1975;Suomalainen et ul., 1976).…”