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.