Evolutionary potential in Carex lutea (Cyperaceae), a rare North American endemic

1. a b Evolutionary potential in Carex lutea (Cyperaceae), a rare North American endemic Akanita Sangaumphai, Nathan Derieg, Jackie Campbell, and Leo P. Bruederle Department of Biology, University of Colorado at Denver and Health Sciences Center, Denver, CO 80217 Introduction The evolutionary potential of a species is correlated with the levels of genetic diversity maintained within and among populations. Carex lutea LeBlond (Cyperaceae) is a narrow endemic, restricted in distribution to approximately eight populations in Pender and Onslow Counties, North Carolina (Fig. 1-2). It was first described in 1994 from the Atlantic Coastal Plain, where it occupies wet sandy soils underlain by coquina limestone in rare wet savannas. Its closest relatives include C. cryptolepis Mack., a broadly distributed North American endemic, and the widespread C. flava L., within section Ceratocystis. Although expected to exhibit relatively low levels of genetic diversity, in general, endemics have proven to be unpredictable. Carex lutea, with its restricted distribution; small, isolated populations; habitat specificity; and caespitose habit was anticipated to meet expectations of low genetic diversity. The objective of this research was to describe genetic diversity and its apportionment within and among populations of C. lutea, a Federally listed endangered species. For comparative purposes, we enlist C. cryptolepis. Materials and Methods Soluble enzymatic proteins were extracted from leaf tissue (Bruederle and Fairbrothers, 1986) harvested from a total of 161 individuals of C. lutea collected “haphazardly” at five sites (N=13-50), as well as 322 individuals of C. cryptolepis representing ten sites (N=19-50) (Table 1). Extracts were stored at -70o until separation, which involved each of three starch gel and electrode buffer systems (Kuchel and Bruederle, 2000). Following electrophoresis, substrate-specific stains were used to visualize allozymes. Data were collected as genotypes for each individual at 19 putative loci , e.g., AAT, and analyzed to obtain common measures of genetic diversity, e.g., P and He, and structure, e.g., FST using GDA (Lewis and Zaykin, 2002). Table 3. Fixation indices for ten polymorphic loci in Carex lutea and C. cryptolepis; statistical significance (Fisher Measure) is indicated with bold. Discussion In contrast to expectations for a narrow endemic [e.g., Dodd and Helenurm (2002)], populations of C. lutea exhibit levels of genetic diversity that are significantly higher in comparison to its congener C. cryptolepis. However, this diversity is apportioned similarly. Carex lutea and C. cryptolepis display levels of inbreeding that are similar to other caespitose carices, likely a consequence of habit and self-compatibility. Typically, these species maintain a high percentage of genetic diversity as differences among populations; this was observed both for C. lutea and C. cryptolepis. Low levels of gene flow, coupled with large range, are likely responsible for higher levels of population differentiation in disjunct populations of C. cryptolepis, such as Ankeney Fen. For C. lutea and C. cryptolepis, it appears that distribution, broad or narrow, is not necessarily a reliable indicator of genetic diversity. Considering their shared life history (e.g., narrow niche, caespitose habit, small population size), we conclude that historical factors are largely responsible for the differences reported herein. The greatest threat to C. lutea is not a reduction in evolutionary potential (as a consequence of endemism), but rather loss of habitat. Table 1. Locations for five Carexlutea and ten C. cryptolepis populations sampled for allozyme analysis, where N equals number of individuals sampled. Results Seven loci were polymorphic in C. lutea: AAT, ADH, DIA-1, G3PDH, IDH-2, PGM-1, and SOD; while C. cryptolepis was polymorphic at eight loci: DIA-1, IDH-1, IDH-2, MDH-2, ME, PGI-2, PGM-1, and SDH (Table 2). Although total genetic diversity was low, (e.g., HT=0.078), populations of C. lutea harbored levels of diversity that were significantly higher than C. crypto-lepis, as well as averages reported for other caespitose carices (Bruederle, Yarbrough, and Kuchel, in press). For example, proportion of loci polymorphic (P) averaged across populations was 20.0% in C. lutea, 6.3% in C. cryptolepis, and 14.2% for other caespitose carices. However, C. lutea showed similar reductions in heterozygosity from expectations (He = 0.048 and Ho = 0.026), presumably due to inbreeding within populations. FIS – reduction in hetero-zygosity due to inbreeding – averaged 0.457 (Table 3). Population differentiation in C. lutea (FST = 0.411, 95% CI 0.047-0.498) was similar to that reported for other caespitose carices, but significantly less than that observed for C. cryptolepis (FST = 0.789, 95% CI 0.597-0.941). Fig. 1. Habit for (a) Carex lutea (www.herbarium.unc.edu) and (b) C. cryptolepis (www.botany.wisc.edu/herbarium). References Bruederle, L.P., S.L. Yarbrough, and S.D. Kuchel. In press. Allozyme variation in the genus Carex… 15 years later: 1986-2001. in: R. Naczi, editor. Sedges 2002: Uses, Diversity, and Systematics. Missouri Botanic Garden, St. Louis, Crins, W.J., P.W. Ball. 1988. Taxonomy of the Carex flava complex (Cyperaceae) in North America and northern Eurasia. II. Taxonomic treatment. Can. J. Bot. 67: 1048-1065. Dodd, S.C., and K. Helenurm. 2002. Genetic diversity in Delphiniumvariegatum: a comparison of two insular endemic subspecies and their widespread mainland relative. Amer. J. Bot. 89:613-622. Kuchel, S.D. and L.P. Bruederle. 2000. Genetic diversity and structure in North American populations of Carex viridula Michx. (Cyperaceae). Madrono 47: 147-158. Lewis, P. O., and D. Zaykin. 2001. Genetic Data Analysis: Computer program for the analysis of allelic data. Version 1.0 (d16c). http://lewis.eeb.uconn.edu/lewishome/software.html Acknowledgments. We thank Richard LeBlond for field assistance; UCDHSC Undergraduate Research Opportunity Program, Faculty Devel-opment, and Council Awards for Graduate Student Research for grant funding; and Ron Rinkle for a generous donation supporting this research. Fig. 2. Distribution of (a) Carex lutea (http://quickfacts.census.gov) and (b) C. cryptolepis (modified from Crins and Ball, 1988;). Table 2. Summary of genetic diversity statistics in Carexlutea and C. cryptolepis.