Polyploidy and clonal diversity in an arctic cladoceran

Abstract

Genome size determinations were coupled with allozyme and mtDNA studies to gain insights into the origin of polyploidy and clonal diversity in populations of Daphnia tenebrosa from Churchill, Manitoba. Allozymic variation at five enzyme loci allowed the detection of 32 clones. Analyses of 73 populations in 1981, 27 in 1987 and 45 in 1991 revealed that clonal frequencies were relatively stable and that D. tenebrosa was more clonally diverse (average of three clones per pond) than other species of the D. pulex complex at the same site. Genome size determinations revealed the presence of two clonal assemblages with averages of 0.53 (± 0.01) pg and 0.89 (± 0.03) pg, corresponding to diploid and tetraploid clones. Clustering of allozyme distances revealed three groups, with no association between ploidy level or pigmentation. Similarly, diploid and polyploid clones did not form distinct clusters on the mtDNA dendrogram. The high sequence divergence between the two mtDNA clusters as well as the lack of correspondence between allozyme distance and mtDNA divergence among clonal pairs both suggest that polyploidy arose following reciprocal hybridizations between genetically divergent populations of this species.

Mitochondrial Capture Misleads about Ecological Speciation in the Daphnia pulex Complex

“… Daphnia tenebrosa is genetically highly variable relative to the other species (Table 3), which suggests a comparably high long-term effective population size. Some variation might have originated from introgressive hybridization (before the transition to asexuality or via rare sexual reproduction), but we propose that a large number of clones (often polyploid [62]) occurring across vast expanses of the Holarctic slow down the lineage sorting and yields paraphyletic genealogies with respect to D . pulicaria (Figure 2).…”

Linking biochemical and elemental composition in freshwater and marine crustacean zooplankton

“…Therefore, the difference between the 2 freshwater copepod groups and the marine group is probably not related to their different habitat, but is a result of the individual characteristics of the different species. In contrast to copepods, cladocerans had a lower and more constant DNA content, which is probably due to their 'miniature' genome size (Beaton & Hebert 1989, Dufresne & Hebert 1995.…”

Long-term changes in metapopulation genetic structure: a quarter-century retrospective study on low-Arctic rock poolDaphnia

“…salt spray, fluctuating conductivity/ salinity levels) than bluff B. Previous work by Dufresne & Hebert (1995) examined changes in clonal composition and clonal diversity in Daphnia tenebrosa populations (another member of the D. pulex species complex) in tundra ponds at Churchill. They found relatively stable clonal distributions and clonal compositions in these habitats over a 10-year (1981 -1991) period.…”

“…Previous genetic work, particularly focusing on the Churchill Daphnia pulex complex (Weider 1987;Weider & Hebert 1987a,b;Wilson & Hebert 1993;Dufresne & Hebert 1995;Weider et al 1999a,b), has shown that this Arctic complex includes of a mixture of distinct lineages/ species that are obligately parthenogenetic and that include both diploid (non-melanic) and polyploid (melanic) clones. Work on melanic clones in this complex (Weider 1987;Weider & Hebert 1987a,b) revealed microgeographic heterogeneity in their distributions that was strongly influenced by physico-chemical variation among rock pools, in particular salinity gradients.…”