| Popis: |
Morphological studies of the short-beaked members of Carex sect. Vesicariae have indicated that three species can be recognized: C. saxatilis (incl. C. miliaris and C. physocarpa), C. membranacea, and C. rotundata. To assess genetic relationships among species and gene diversity within species, 44 populations from throughout North America were surveyed electrophoretically for 12 enzymes encoded by 17 putative loci. Populations of the same species exhibited high genetic identities, with average values exceeding 0.950. Interspecific genetic identities ranged from 0.636 (between C. saxatilis and C. rotundata) to 0.880 (C. membranacea and C. rotundata). Alleles for the isozymes AAT-1, AAT-2, 6-PGD, PGI-2, PGM-2, and SKDH were useful in distinguishing C. saxatilis from C. membranacea and C. rotundata. Carex membranacea and C. rotundata were best distinguished by alleles of 6-PGD. There was little allozyme differentiation within the C. saxatilis complex; however, a weak east/west cline was evident. Within populations, observed heterozygosity closely matched expected levels of heterozygosity: F values averaged 0.039, indicating outcrossing is prevalent. Genetic variation was found to be largely apportioned within populations as Nei's gene diversity statistic (GST) was close to 0.19 in each species. Past electrophoretic studies of Carex have disclosed low levels of intrapopulation genetic variation and high levels of interpopulation differentiation indicating high levels of inbreeding. Large population sizes, dichogamy, a rhizomatous habit, and self-incompatibility are discussed as possible mechanisms for maintaining genetic diversity within populations of the short-beaked species. |
