Patterns of genetic variation in Salix section Longifoliae (Salicaceae)

• Published in: American journal of botany 1991-06, Vol.78 (6), p.855-869
• Main Authors: Brunsfeld, S.J. (University of Idaho, Moscow, ID), Soltis, D.E, Soltis, P.S
• Format: Article
• Language: English
• Subjects: AMERICA DEL NORTE; AMERIQUE DU NORD; BIOCHEMICAL POLYMORPHISM; Biological and medical sciences; Biological evolution; Biological taxonomies; Botany; DIPLOIDIA; DIPLOIDIE; DIPLOIDY; DISTRIBUCION NATURAL; DISTRIBUTION NATURELLE; ENZIMAS; ENZYME; ENZYMES; Evolutionary genetics; Fundamental and applied biological sciences. Psychology; Genetic diversity; Genetic loci; GENETIC VARIATION; Genetics; Genetics of eukaryotes. Biological and molecular evolution; GEOGRAPHICAL DISTRIBUTION; GEOGRAPHICAL RACES; HIBRIDACION; HYBRIDATION; HYBRIDIZATION; MEXICO; MEXIQUE; NATURAL DISTRIBUTION; NORTH AMERICA; Plants; POLIMORFISMO BIOQUIMICO; POLYMORPHISME BIOCHIMIQUE; Population genetics; Population mean; SALIX; salix exigua; salix interior; salix melanopsis; salix taxifolia; Taxa; TAXONOMIA; TAXONOMIE; TAXONOMY; Trees; VARIACION GENETICA; VARIATION GENETIQUE; VARIEDADES; VARIETE; VARIETIES
• ISSN: 0002-9122; 1537-2197
• DOI: 10.1002/j.1537-2197.1991.tb14488.x

Enzyme electrophoresis was used to examine genetic relationships within a taxonomically complex group of diploid willows (Salix section Longifoliae). Forty-eight populations representing seven morphogeographic taxa were analyzed for 15 putative enzyme loci. Levels of genetic variation (A, P, He, and HT) differed greatly among populations, but were generally lower than those reported for other species with similar life history traits. In populations and species from southern latitudes, where populations tend to be smaller and more isolated, genetic variation decreased and population differentiation increased. Genetic identity values suggest that the section is divisible into four major elements: 1) Salix interior, 2) S. taxifolia, 3) the S. exigua group, and 4) S. melanopsis. The first three occupy eastern, southern, and western portions of the continent, respectively. Salix melanopsis is sympatric with the S. exigua group in western North America, but is ecologically distinct. The S. exigua group is differentiated into four major geographic entities: S. hindsiana from west of the Sierras in California and southwest Oregon, S. sessilifolia from west of the Cascades in central Oregon to British Columbia, and a northern and southern race of S. exigua in the Intermountain West. The relationships suggested by allozyme data do not agree with traditional taxonomic concepts. Evidence of hybridization was obtained at five points where taxa come into contact, and Salix fluviatilis may be of hybrid origin. Taxonomic confusion appears to be largely the result of frequent hybridization events and overemphasis of a few highly variable morphological traits. The section appears to be a syngameon undergoing geographic speciation, with one taxon gaining reproductive isolation by a shift in habitat preference.