Eagle Hill Masthead



Southeastern Naturalist
    SENA Home
    Range and Scope
    Board of Editors
    Staff
    Editorial Workflow
    Publication Charges
    Subscriptions

Other EH Journals
    Northeastern Naturalist
    Caribbean Naturalist
    Urban Naturalist
    Eastern Paleontologist
    Eastern Biologist
    Journal of the North Atlantic

EH Natural History Home

  Help

About Southeastern Naturalist

 

Clonal Diversity in Differently Aged Patches of the Dune Grass Uniola paniculata
Stephen P. Bush and Marcio E. Stelato

Southeastern Naturalist, Volume 6, Number 2 (2007): 359–364

Full-text pdf (Accessible only to subscribers.To subscribe click here.)

 

Site by Bennett Web & Design Co.
2007 SOUTHEASTERN NATURALIST 6(2):359–364 Clonal Diversity in Differently Aged Patches of the Dune Grass Uniola paniculata Stephen P. Bush1,* and Marcio E. Stelato1,2 Abstract - Uniola paniculata (sea oats) is a perennial, clone-forming dune grass of coastal beaches in the southeastern United States. We used random amplified polymorphic DNA (RAPD) markers to compare clonal diversity in younger and older patches of U. paniculata. Older patches were found to contain a significantly higher level of clonal diversity, suggesting that, in some cases, U. paniculata populations may increase in clonal diversity over time. The high level of clonal diversity found in the older patches provides further evidence for the important role of sexual reproduction in maintaining diversity in U. paniculata. Introduction Uniola paniculata L. (sea oats), the dominant grass on dunes of the Atlantic and Gulf coasts of the southeastern United States, plays a critical ecological role in the formation and stabilization of coastal sand dunes. Sea oats is among the initial colonizers that invade bare sands of coastal beaches to initiate dune building. Colonizing plants then trap wind-blown sand and, through subsequent episodes of sand trapping followed by dune grass growth, dunes are formed (Wagner 1964, Woodhouse et al. 1968). Uniola paniculata also helps to stabilize established dunes through an extensive underground network of roots and rhizomes. In facilitating sand dune formation and stabilization, populations of perennial, clone-forming sea oat plants persist for many years. Clonal plants are very common in the early stages of vegetative succession (Prach and Pysek 1994). For example, clonal taxa are important colonizers of man-made disturbed sites in Europe (Prach and Pysek 1994, 1999), of accreting shorelines of the Great Lakes in the United States (Cowles 1899), and of habitat exposed by glacial retreat (Stocklin and Baumler 1996). Through lateral growth, clonal plants are able to rapidly colonize newly exposed habitats in early successional sites (Macdonald and Lieffers 1991, Prach and Pysek 1994). Clonal growth likely influences the population genetic structure of colonizing species. At one extreme, the growth of vigorous clones may produce populations with low levels of clonal diversity (Ellstrand and Roose 1987). Thus, even when populations are founded by a wide variety of propagules, extensive vegetative growth by better-adapted clones may reduce clonal diversity (Ellstrand and Roose 1987, Macdonald and Lieffers 1991). In the predominantly clone-forming Ammophila breviligulata Fern. (dune grass), Laing (1967) proposed that populations are established in brief periods by an initial number of individuals. Once established, clonal diversity is likely to decrease, 1Department of Biology, Coastal Carolina University, Conway, SC 29526. 2Current address - Dakocytomation, 6392 Via Real, Carpinteria, CA 93013. *Corresponding author - bush@coastal.edu. 360 Southeastern Naturalist Vol. 6, No. 2 so that a few large clones dominate the dune vegetation (Laing 1967). In sea oats, vegetative reproduction via rhizomatous growth is widespread (Wagner 1964, Woodhouse et al. 1976), while recruitment of sea oat seedlings is infrequently observed (Wagner 1964, Franks 2003). Therefore, clonal diversity in sea oats was hypothesized to be low (Franks et al. 2004). After a habitat is colonized, environmental conditions may become more favorable for sexual recruitment, and clonal plants may, therefore, maintain levels of variation similar to those found in predominantly sexual species (Macdonald and Lieffers 1991). For example, in a recent study of succession in coastal dunes inhabited partly by sea oats, seedling establishment was found to be more likely in vegetated areas (Franks 2003). Seeds were more abundant under established dune plants than in unvegetated sands, and more seeds emerged and survived when growing under established plants than in open areas (Franks 2003). Seeds likely accumulate as established plants trap wind-blown propagules, and dune vegetation then increases the survival of seedlings by protecting against excessive sand movement that may either bury or expose emerging seedlings growing in open areas (Franks 2003). Therefore, although clonal growth may increase the frequency of some genotypes, it may also increase sexual recruitment by providing favorable conditions for seedling establishment (Franks 2003). A recent study of clonal diversity in eight patches of sea oats found that diversity differed greatly among sampling sites. The authors suggested that both vegetative growth and sexual recruitment are important factors in maintaining genetic diversity in sea oats (Franks et al. 2004). The persistence of diversity in many patches of sea oats despite clonal growth is not atypical of clonal plants. Numerous predominantly clonal species have been investigated, and surveys indicate that populations typically contain a diversity of clones (Ellstrand and Roose 1987, Widen et al. 1994), and that the distribution of genetic diversity within and among clonal plant populations is similar to that found in predominantly sexually reproducing species (Hamrick and Godt 1996). We hypothesized that clonal diversity may be higher in older patches of sea oats due to the facilitation of seedling recruitment by established plants. We used random amplified polymorphic DNA (RAPD) markers to investigate clonal diversity in differently aged patches of sea oats, comparing recently vegetated beaches to patches found on large, established dunes. RAPDs are neutral markers that are unlikely to be altered by mutations (Van de Ven and McNicol 1995). Thus, RAPDs are typically conserved among the ramets of a genet (Bush and Mulcahy 1999, Eckert et al. 2003, Kjolner et al. 2004), and have been utilized in numerous studies of clonal plants. Methods Patches of sea oats were sampled on Waites Island (33°50'43"N, 78°35'12"W), an undeveloped barrier island on the North Carolina/South Carolina state line. The foredunes on Waites Island were destroyed by Hurricane Hugo; however, large dunes towards the interior of the island survived the hurricane. Therefore, using beach profiles of Waites Island taken before 2007 S.P. Bush and M.E. Stelato 361 and after the hurricane, differently aged patches of sea oats were located and sampled. These included two younger patches (aged less than seven years) that were situated on foredunes that had developed since the hurricane, and two older patches located on dunes present prior to the hurricane. While the exact age of these older patches could not be determined, their large size suggested an age considerably greater than seven years. All four patches were less than 1.5 km inland from the shoreline. In each patch, rectangular grids were sampled by collecting leaf tissue from the closest ramet at each 1.0-m interval throughout the grid. Samples were placed on ice upon collection, and later stored at -80 °C until DNA extraction. DNA was isolated using a standard CTAB protocol (Berntazky and Tanksley1986), and then further purified using the NucleiClean kit (Sigma, St. Louis, MO). The DNA concentration of each sample was next quantified using a DyNA Quant 200 Flourometer (Hoefer, San Francisco, CA). Polymerase chain reactions were prepared in 12.5-ml volumes that contained: 0.5 units Taq polymerase (Promega, Madison, WI); 1.25 􀂗l 10X buffer; 0.25 mM each of dNTP, 0.5-􀂗l 20-mM MgCl2, and 0.5-􀂗l 10-mM primer; and 12.5 ng of template DNA. Each reaction mixture was then covered with a drop of mineral oil and amplified with the polymerase chain reaction. Each of the three initial polymerase chain-reaction cycles consisted of 1 min at 94 °C, 1 min at 35 °C, and 1 min at 72 °C. The remaining 42 cycles were: 5 sec at 94 °C, 1 min at 35 °C, and 2 min at 72 °C. Polymerase chain-reaction products were subjected to electrophoresis on 1.5% agarose gels and then stained with ethidium bromide and photographed. To identify informative polymerase chain-reaction primers for sea oats, two plants were initially screened with 100 primers of random sequence, and seven that yielded clear, polymorphic bands were selected for the study (Operon primers OP-H5 and OP-G18, and University of British Columbia primers UBC-215, UBC-226, UBC-227, UBC-353, and UBC-363). All 57 individuals were treated with these seven primers, and all polymerase chain reactions were performed in duplicate. Twelve bands, scored as either present or absent, were tallied in all individuals. The probability that two ramets of different genets could, by chance, share the same multilocus RAPD band phenotype, or the genotype probability (Bush and Mulcahy 1999, Sydes and Peakall 1998), was calculated as: Pgen = 􀁗pi, where pi is, for the genotype at each locus, the observed frequency of the locus genotype among all 57 plants sampled. Standard measures of clonal diversity were calculated for each patch, including G/N (the number of genets/ramet) and the genotypic diversity (Simpson’s D), which is: D = 1 - 􀀭 {[ni(ni - 1)]/N(N - 1)]}, where ni is the number of individuals of genet i and N equals the total number of ramets within the patch. Potential differences in clonal diversity among the differently aged patches was also assessed using a chi-square test. 362 Southeastern Naturalist Vol. 6, No. 2 Results The seven random primers yielded 12 loci that were polymorphic in sea oats. Eight of the twelve loci were polymorphic in two or more patches, although no loci were variable in patch 1 (Table 1). The overall proportion of genets distinguishable, or G/N, was 0.40, as 23 multilocus genotypes were identified out of 57 plants sampled (Table 1). The Pgen values, which represent the chance that two different genets could randomly share the same multilocus phenotype, were all less than 5% (mean = 0.74%). Therefore, as each multilocus genotype was also restricted to a single patch, plants sharing the same multilocus phenotype could confidently be assigned to the same genet. Diversity varied greatly among patches, and older patches contained a higher level of clonal diversity. Little to no diversity was detected in the two younger-aged patches. Only three genets were distinguished among the 27 ramets sampled in the two young patches (G/N = 0.11), and the mean patch genotypic diversity (D) was 0.23. The two old patches were much more diverse, containing a total of 21 genets out of 30 ramets genotyped (G/N = 0.7), with a mean D value of 0.95. The mean number of genets was significantly higher in older patches than in younger patches (chi-square = 14.5, d.f. = 3, p < 0.005). Genotypic diversity among all patches was 0.59. Discussion A previous study of sea oats examined both geographical genetic variation and fine-scale clonal diversity (Franks et al. 2004). The estimates of withinpopulation genetic diversity in U. paniculata were generally comparable to species with similar life-history traits. However, genetic differentiation among sea oat populations was higher than most outcrossing species, indicating moderate restriction of gene flow. Clonal diversity differed widely among the eight patches studied, as the proportion of genotypes distinguishable with a patch (G/N) ranged from 0.033 to 0.263. The causes of this variation could not be determined; however, it was suggested that episodic sexual recruitment was likely a contributing factor (Franks et al. 2004). Our estimate of genotypic diversity was similar to that found in the previous study of sea oats (0.60; Franks et al. 2004). However, overall clonal diversity among all of the plants that we sampled (G/N = 0.4) was considerably higher Table 1. Clonal diversity in patches of Uniola paniculata. The percent loci polymorphic in each patch (P), and the number of ramets sampled (N), the number of genets (or clones) identified (G), the proportion of genets distinguishable (G/N), and Simpson’s genotypic diversity (D) are reported for each patch, as well as their mean values in the old and young patches. P N G G/N D Young patches 1 0 14.0 1.0 0.07 0.00 2 8 13.0 2.0 0.15 0.46 Mean 13.5 1.5 0.11 0.23 Old patches 3 92 15.0 9.0 0.60 0.99 4 67 15.0 12.0 0.80 0.91 Mean 15.0 10.5 0.70 0.95 2007 S.P. Bush and M.E. Stelato 363 than in the previous study (G/N = 0.11). Furthermore, the average level of clonal diversity found in the two older patches sampled here (mean G/N = 0.70) was far greater than has been found previously in any patch of sea oats. Among studies of clonal plants, the number of loci examined is positively correlated with the number of clones identified (Ellstrand and Roose 1987). Although the greater number of polymorphic loci that we utilized may have slightly increased the level of clonal resolution, it is unlikely to have resulted in the observed four-fold increase in diversity. Instead, our findings likely reflect actual differences in population diversity. Given the limited number of individuals and patches sampled, the conclusions that can be made regarding diversity and population age in sea oats are somewhat limited. Processes that are independent of population age may have, by chance, contributed to the differences in clonal diversity among younger and older patches. Nevertheless, the higher number of clones in older patches suggests that, in some cases, sea oat populations may increase in clonal diversity over time. An initial surge of vegetative reproduction in sea oats may then be followed by an accumulation of different clones over time. Genetic diversity in newly formed populations is influenced by the level of genetic diversity among the initial colonists, as well as by subsequent rates of vegetative and sexual reproduction. It is likely that the colonization patterns of sea oat seedlings and plant fragments on newly exposed sands varies. Instances of rapid colonization of bare sands by sea oat seedlings have been observed (Ehrenfeld 1990), although the survival of sea oat seedlings in open areas has also been found to be lower than on vegetated dunes (Franks 2003). Sea oats are also capable of regeneration via rhizome fragments that are detached from established plants during storms (Miller et al. 2003). These fragments are capable of surviving transport via ocean currents, and may then resume growth when redeposited on a beach. Following colonization by either seed or rhizome fragments, rapid clonal growth may be favored by the foredune environment. Sand deposition, which stimulates rhizomatous growth in sea oats (Wagner 1964), occurs at a high rate on vegetated dunes near the shoreline. Therefore, whatever the source of colonization, clonal growth likely enables sea oats to spread quickly over previously unvegetated areas. Young populations like those sampled in this study may then contain little clonal diversity. Seedling establishment is likely to increase after sea oat populations become established, as vegetated dunes create conditions that are suitable for sexual recruits. The high level of clonal diversity found in the older sampled patches, suggestive of either sustained or episodic seedling growth, provides further evidence for the fundamental role of sexual reproduction in maintaining diversity in sea oats. Genetic diversity is critical for the continued adaptation of populations to changing environments like the maturing sand dunes. Thus, whether frequent or uncommon, sexual recruitment likely generates new genotypes that are important for the persistence of sea oat populations. Literature Cited Berntazky, R., and S.D. Tanksley. 1986. Genetics of actin-related sequences in tomato. Theoretical and Applied Genetics 72:314–321. 364 Southeastern Naturalist Vol. 6, No. 2 Bush, S.P., and D.L. Mulcahy. 1999. The effects of regeneration by fragmentation upon clonal diversity in the tropical forest shrub Poikilacanthus macranthus: RAPD results. Molecular Ecology 8:865–870. Cowles, H.C. 1899. The ecological relations of the vegetation on the sand dunes of Lake Michigan. Botanical Gazette 27:95–117, 167–202, 281–308, 361–391. Eckert, E.G., K. Lui, K. Bronson, P. Corradini, and A. Bruneau. 2003. Population genetic consequences of extreme variation in sexual and clonal reproduction in an aquatic plant. Molecular Biology 12:331–344. Ehrenfeld, J.G. 1990. Dynamics and processes of barrier island vegetation. Reviews in Aquatic Sciences 2:437–480. Ellstrand, N.C., and M.L. Roose. 1987. Patterns of genotypic diversity in clonal plant species. American Journal of Botany 74:123–131. Franks, S.J. 2003. Facilitation in multiple life-history stages: Evidence for nucleated succession in coastal plants. Plant Ecology 168:1–11. Franks, S.J., C.L. Richards, E. Gonzales, J.E. Cousins, and J.L. Hamrick. 2004. Multiscale genetic analysis of Uniola paniculata (Poaceae): A coastal species with a linear, fragmented distribution. American Journal of Botany 91:1345–1351. Hamrick, J.L., and M.J.W. Godt. 1996. Effects of life history traits on genetic diversity in plant species. Philosophical Transactions of the Royal Society of London, Series B 351:1291–1298. Kjolner, S., S.M. Sastad, P. Taberlet, and C. Brochmann. 2004. Amplified fragment length polymorphism versus random amplified polymorphic DNA markers: Clonal diversity in Saxifraga cernua. Molecular Ecology 13:81–86. Laing, C.C. 1967. The ecology of Ammophila breviligulata II. Genetic change as a factor in population decline on stable dunes. American Midland Naturalist 77:495–500. Macdonald, S.E., and V.C. Lieffers. 1991. Population variation, outcrossing, and colonization of disturbed areas by Calamagrostis canadensis: Evidence from allozyme analysis. American Journal of Botany 1991:1123–1129. Miller, D.L., L. Yager, M. Thetford, and M. Schneider. 2003. Potential use of Uniola paniculata rhizome fragments for dune restoration. Restoration Ecology 11:359–369. Prach, K., and P. Pysek. 1994. Clonal plants: What is their role in succession? Folia Geobotanica Phytotaxonomica 29:307–320. Prach, K., and P. Pysek. 1999. How do species dominating in succession differ from others? Journal of Vegetation Science 10:383–392. Stocklin, J., and E. Baumler. 1996. Seed rain, seedling establishment, and clonal growth strategies on a glacier foreland. Journal of Vegetation Science 7:45–56. Sydes, M.A., and R. Peakall. 1998. Extensive clonality in the endangered shrub Haloragodendron lucasii (Holoragaceae) revealed by allozymes and RAPDs. Molecular Ecology 7:87–93. Van de Ven, W.T.G., and R.J. McNicol. 1995. The use of RAPD markers for the identification of Sitka spruce (Picea sitchensis) clones. Heredity 75:126–132. Wagner, R.H. 1964. The ecology of Uniola paniculata L. in the dune-strand habitat of North Carolina. Ecological Monographs 34:79–96. Widen, B., N. Cronberg, and M. Widen. 1994. Genotypic diversity, molecular markers and spatial distribution of genets in clonal plants: A literature survey. Folia Geobotanica Phytotaxonomica 29:245–263. Woodhouse, W.W., E.D. Seneca, and A.W. Cooper. 1968. Use of sea oats for dune stabilization in the southeast. Shore and Beach 36:15–21. Woodhouse, W.W., E.D. Seneca, and S.W. Broome. 1976. Ten years of development of man-initiated coastal barrier dunes in North Carolina. North Carolina Agricultural Experiment Station. Bulletin No. 435.