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Genetic variation and ecological differentiation between two southern Utah endemics : U.S. federally threatened Townsendia aprica and a closely related congener, T. jonesii var. lutea (Asteraceae: Astereae) Jennings, Linda M.

Abstract

Townsendia aprica Welsh & Reveal (Asteraceae) is one of 17 rare plants in Utah receiving protection under the U.S. Federal Endangered Species Act. Townsendia aprica (last chance Townsendia) is an herbaceous perennial, narrow endemic, occurring along the Colorado Plateau in southeastern Utah. Recent discoveries have increased its known range from roughly 301 square kilometers at the time it was first listed to 4186 square kilometers. Many of these populations comprise fewer than 100 individuals. It was presumed that small population sizes together with geographical isolation would lead to low levels of genetic variation and inbreeding within the different populations, as a result of genetic drift and restricted gene dispersal. With the use of enzyme electrophoresis, nine informative loci were resolved to gain insight into the level and pattern of genetic variation within T. apnea's range. These patterns were compared with those of another narrow endemic that is a close congener, Townsendia jonesii var. lutea. Analysis of inter- and intra-taxon genetic distances for T. aprica and T. jonesii var. lutea provides important insights into the consequences of rarity, as well as into the genetic and ecological distinctness of the two narrowly endemic taxa. The two taxa have very similar, relatively high values estimated for genetic variation parameters based on isozyme analysis of nine loci (%P > 70, A > 2.0, and H e > 0.30), with much of the genetic variation being found within populations (F[sub ST] = 0.060 for T. jonesii var. lutea and F[sub ST] = 0.100 for T. aprica). No significant inbreeding found was in most populations of either taxon. Forty percent of the variation in genetic distance between populations of T. jonesii var. lutea could be explained by geographical distance, where as only about 10% of genetic variation in T. aprica's could be explained by physical distance. Bottlenecks were detected in more than half of each taxon's populations. The results also reveal that populations of each taxon are more similar to one another (F[sub PT] = 0.14), than to populations of the other taxon (F[sub ST] = 0.21). Significant differences were found in characteristics of the soils on which the two taxa occur, though so far, all measurable morphological characters are overlapping in these two taxa.

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