High Clonal Diversity Research Articles

Genetic characterization of breeding systems, ploidy levels and species boundaries in Cypricercus (Ostracoda)

Although freshwater ostracod crustaceans show an exceptionally high incidence of transitions from sexual reproduction to parthenogenesis, no prior studies have examined genetic relationships among congeneric species showing breeding system variation. The present study addresses this gap by examining patterns of allozyme diversity among three unisexual and three sexual species in the genus Cypricercus from 46 North American sites. Patterns of genetic relatedness among these taxa suggest that parthenogenesis has evolved on at least three occasions within the genus, and that one all-female taxon is closely related to a sexual species. One unisexual, C. reticulatus, showed very high clonal diversity with many polyploids as well as an allelic array suggesting that much of its diversity originated through interbreeding with sexual relatives. The other unisexuals showed both lower clonal and allelic diversity, but the prevalence of triploid clones suggested that variation might originate from hybridization between diploid asexuals and males of relict sexual populations. The prevalence of multiple X-Y sex determination systems in the ostracods may explain the marked variation in chromosome numbers evident among polyploids. This study suggests that the success of unisexuals may be linked to their ability to recruit clonal diversity through interbreeding with close sexual relatives.

Extreme clonal uniformity of Phoxinus eos/neogaeus gynogens (pisces: Cyprinidae) among variable habitats in northern Minnesota beaver ponds.

Genetic surveys of parthenogenetic vertebrate populations have demonstrated a common pattern of relatively high degrees of clonal variation and the coexistence of numerous clones. In striking contrast, the Phoxinus eos/Phoxinus neogaeus/hybrid gynogen complex of cyprinid fishes exhibits no clonal variation within a northern Minnesota drainage characterized by successional beaver ponds. Gynogens were sampled from three habitats in each of four different pond types in a single drainage in Voyageurs National Park, Minnesota. The abundance of gynogens relative to sexual dace varied with pond type, being least common in deep upland ponds and most common in shallow, collapsed, lowland ponds (13.4% and 48.6%, respectively). Simple-sequence multilocus DNA fingerprinting of 464 individual gynogens detected one, and only one, clone. DNA fingerprints, generated sequentially by using three oligonucleotide probes, (CAC)5, (GACA)4, and the Jeffreys' 33.15 probe, all revealed the same unprecedented lack of variation. The extreme lack of clonal diversity in these gynogens across a range of habitat types does not fit the general pattern of high clonal diversity found within populations of other vertebrate parthenogens.

Enzyme variability in large-lake Daphnia populations

Allozyme studies of two primarily parthenogenetic, large-lake Daphnia species, D. galeata mendotae and D. cucullata, revealed high clonal diversity and levels of enzyme polymorphism similar to those found in other groups of organisms. Temporal analyses showed moderate stability of genotypes. Hardy–Weinberg deviations were detected on some dates in D. cucullata, most often resulting from homozygote excesses. Thus, these populations show higher genetic diversity and greater temporal stability than expected on the basis of previous studies of permanent pond populations of other cladocerans.