Analysis of Genetic Diversity and Outcrossing Rates in the Federally Endangered Echinacea laevigata

Maintaining high genetic diversity is vital to the persistence of a species. Information on genetic diversity and breeding systems of endangered species is essential to conservation managing strategies. Echinacea laevigata, the smooth-purple coneflower, is a herbaceous perennial in the sunflower family (Asteraceae). The species is a federally endangered species with 24 current populations found in only four states (GA, SC, NC, and VA) (CPC 2003, USDA 2002). Analysis of genetic diversity based on allozyme data including 11 populations from SC, NC, and VA (Apsit and Dixon 2001) detected unequal distribution of genetic variation among populations and regional population genetic differentiation, suggesting that the species may be adapting to environmental heterogeneity. The study also revealed that the level of genetic diversity in E. laevigata is comparable to its closely related congeneric, widely spread species E. angustata. However, genetic diversity measures cannot predict how the populations will respond to environmental conditions in the future. The manner in which gametes combine to form the next generation (mating system) defines future genetic diversity, thus important to the self-sustaining of the species. Outcrossing rates at multilocus and single locus, which indicate the level of outcrossing and mating between related individuals, is an important parameter in predicting future genetic diversity in the species. Low outcrossing rates in species would indicate a future decrease in genetic diversity if no special management is taken.

In our study, we will examine the outcrossing rates in E. laevigata and determine the evolutionary relationships among populations using microsatellite markers. The study will include all current populations of E. laevigata. Microsatellite markers are similar to allozymes, both are co-dominant, permitting the determination of genotype at each locus in each individual. However, alleles of a microsatellite locus differ by the number of repeats of simple nucleotide sequences, and are highly variable within a population (more variable than allozyme markers). Thus the data from microsatellite will provide finer scale information on genetic structures of populations and give more accurate estimates of genetic diversity in the populations. The genetic structure of populations will provide the basis for estimating the outcrossing rates. Phylogenetic analysis of the data will identify whether distinct evolutionary lineages exist in the species. This information together with that on outcrossing rates will provide guidance in the conservation management of the species.

References

Apsit, V.J., and P.M. Dixon. 2001. Genetic Diversity and Population Structure in Echinacea laevigata (Boynton and Beadle) Blake, and Endangered Plant Species. Natural Areas Journal 21: 71-77.

Center for Plant Conservation (CPC). CPC National Collection Plant Profile: Echinacea laevigata. <http://ridgwaydb.mobot.org/cpcweb/CPC_ViewProfile.asp?CPCNum=1541#References> (September 5, 2003).

USDA, NRCS. 2002. The PLANTS Database, Version 3.5 (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Publication:

Peters*, M., QY(J) Xiang, and J Stucky. 2009. Genetic analyses of the
federally endangered Echinacea laevigata using amplified fragment length
polymorphisms (AFLP) - Inferences in population genetic structure and mating
system. Conservation Genetics. 10: 1-14. 2008 online.