Microsatellite Development in Platanus For
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MICROSATELLITE DEVELOPMENT IN PLATANUS FOR DOCUMENTING GENE FLOW AMONG SPECIES ____________ A Thesis Presented to the Faculty of California State University, Chico ____________ In Partial Fulfillment of the Requirements for the Degree Master of Science in Biological Sciences ____________ by Kylene R. Lang Fall 2010 MICROSATELLITE DEVELOPMENT IN PLATANUS FOR DOCUMENTING GENE FLOW AMONG SPECIES A Thesis by Kylene R. Lang Fall 2010 APPROVED BY THE DEAN OF GRADUATE STUDIES AND VICE PROVOST FOR RESEARCH: Katie Milo, Ed.D. APPROVED BY THE GRADUATE ADVISORY COMMITTEE: _________________________________ _________________________________ Abdel-Moaty M. Fayek Kristina A. Schierenbeck, Ph.D., Chair Graduate Coordinator _________________________________ Tag N. Engstrom, Ph.D. _________________________________ Kristopher A. Blee, Ph.D. TABLE OF CONTENTS PAGE List of Tables.............................................................................................................. iv List of Figures............................................................................................................. v Abstract....................................................................................................................... vi CHAPTER I. General Background................................................................................. 1 Systematics/Evolutionary History................................................ 1 Evidence of Platanus in the Fossil Record................................... 4 Morphology .................................................................................. 4 Habitat and Range ........................................................................ 6 Growth and Reproduction ............................................................ 8 Hybridization................................................................................ 10 Microsatellites .............................................................................. 12 Significance of this Research ....................................................... 12 II. Methods.................................................................................................... 15 III. Results...................................................................................................... 21 IV. Discussion................................................................................................. 27 Microsatellite Data ....................................................................... 27 Admixture Analysis...................................................................... 28 Conservation Implications............................................................ 29 Potential Future Directions for Platanus Hybridization Studies... 31 Literature Cited........................................................................................................... 32 Appendix A. Sample Names and Collection Information ............................................. 39 iii LIST OF TABLES TABLE PAGE 1. Characterization of 13 Microsatellites in Platanus spp............................ 22 2. Private Alleles Discovered in Platanus racemosa, P. occidentalis, and P. x acerifolia.................................................... 23 3. Genetic Diversity Estimates: Average Number of Alleles Per Sample (A), Average Number of Phenotypes Per Sample (P), Average Number of Unshared Alleles Between Pairs of Individuals Within a Species (H’S), Average Number of Unshared Alleles Between Pairs of Individuals Across All Species (H’T), the Proportion of Total Diversity Found Between Species (F’ST), and A Yes/No Record of Locus Polymorphism (PM 1/0).................................................................... 26 iv LIST OF FIGURES FIGURE PAGE 1. Bar Plot of Estimates of Q (Estimated Membership Coefficient for Each Individual) Indicating Admixture in Platanus Populations..................................................................... 25 v ABSTRACT MICROSATELLITE DEVELOPMENT IN PLATANUS FOR DOCUMENTING GENE FLOW AMONG SPECIES by Kylene R. Lang Master of Science in Biological Sciences California State University, Chico Fall 2010 Hybridization is a primary source of invasive genotypes and has been shown to contribute to the loss of diversity in a number of locally adapted species. The focus of this study is to develop microsatellite markers with the intent to quantify gene flow within the ancient genus Platanus between the native taxa (P. racemosa, P. racemosa var. wrightii, P. occidentalis, and P. orientalis) and the ornamental P. x acerifolia. Pla- tanus is wind-pollinated, and its species readily hybridize. The horticultural P. x aceri- folia is widely planted for its tolerance to infection and other city stresses, and through hybridization events is endangering the genetic integrity of native Platanus populations in already compromised, shrinking riparian habitats. Thirteen of 28 developed microsa- tellite primer pairs amplified simple sequence repeat (SSR) loci for all Platanus taxa. Species specific alleles were discovered in P. racemosa (n = 18), P. occidentalis vi (n = 31), and P. orientalis (n = 13). Alleles otherwise found only in P. occidentalis and P. orientalis were also found in putative P. racemosa X P. x acerifolia hybrids. Genetic admixture was apparent upon analysis with STRUCTURE; notably putative P. ra- cemosa X P. x acerifolia hybrids clustered primarily with P. racemosa, but also with P. occidentalis and P. orientalis. Genetic differentiation estimates (F’ST) ranged from 0.047 to 0.549 (omitting 1 monomorphic locus). These data will serve as the basis for a larger scale sampling efforts to predict the long-term consequences of gene movement out of P. x acerifolia and into their native congeners at the regional and landscape level. vii CHAPTER I GENERAL BACKGROUND Systematics/evolutionary history—Platanus (plane tree, sycamore), the only genus within the Platanaceae, is a relict of an ancient lineage as evidenced by platanoid fossils dating to the early Cretaceous (Sudworth, 1967; Crane et al., 1993). There are seven extant species distributed in the Northern Hemisphere (Stuart and Sawyer, 2001; Nixon and Poole, 2003; Feng et al., 2005). Five distinct species and three varieties are native to North America; Platanus racemosa Nutt. and Platanus racemosa var. wrightii (S. Watson) L.D. Benson (Western North America); Platanus occidentalis L. and Platanus occidentalis var. palmeri (Kuntze) K. Nixon & J. Poole ex Geerinck (Eastern North America); and Platanus rzedowskii Nixon & J.M. Poole; and Platanus mexicana Moric. and Platanus mexicana var. interior Nixon & J.M. Poole found in Mexico and adjacent Guatemala (Nixon and Poole, 2003; Grimm and Denk, 2008). Platanus orientalis L. is native to southeastern Europe and western Asia, and Platanus kerrii Gagnep. is found in Laos and North Vietnam (Hsiao, 1973; Nixon and Poole, 2003; Grimm and Denk, 2008). Placement of Platanus in the Platanaceae seems secure, but the family recently has been placed within the clade Proteales with the Proteaceae and Nelumbonaceae (Grimm and Denk 2008; Judd et al., 2008). Hybridization is a documented phenomenon within Platanus, both ancient and recent (Besnard et al., 2002; Feng et al., 2005), and poses a threat to the genetic integrity of P. 1 2 racemosa (Rhymer and Simberloff, 1996; Nixon and Poole, 2003; Whitlock, 2003; Grimm and Denk, 2008). Platanus x acerifolia (Aiton) Willd., a hybrid between P. occidentalis and P. orientalis, is widely planted as an ornamental in temperate regions, in part due to its disease resistance and tolerance of air pollution (Besnard et al., 2002; USDA, NRCS, 2008). Plantings in European cities are extensive, composing 40% of tree plantations in Paris, even more in London (Besnard et al., 2002), and as much as 60% in Milano (Anselmi et al., 1994). Ornamental plantings are equally common in the United States. Species within this ancient genus are hypothesized to be threatened with extinction via genetic homogenization mediated via the human dispersal of P. x acerifolia. The historic placement of the Platanaceae (Sudworth, 1967; Hickman, 1993; Keator, 2002; USDA, NRCS, 2008; Nixon and Poole, 2003) within the subclass Hamamelidae (Thorne, 1973; Cronquist, 1981; Zavada and Dilcher, 1986; Schwarzwalder and Dilcher, 1991) was based on the reduced, wind-pollinated flowers often aggregated into dangling inflorescences (Cronquist, 1981, 1988; Takhtajan, 1980) and was supported by comparative pollen data (Zavada and Dilcher, 1986). Cronquist (1981) recognized the Platanaceae as an ancient taxon, well-established in the fossil record and suggested Hamamelidales (an order containing Platanaceae within Hamamelidae) evolved from a Magnoliid, or a Magnoliid-derived taxon. Morphological similarities between Platanaceae and Hamamelidaceae, specifically gross leaf and floral resemblance with members of the recently separated Altingiaceae (includes Liquidambar), supported the alliance (Schwarzwalder and Dilcher, 1991; Nixon and Poole, 2003). 3 Although morphologic similarities are evident, it became increasingly apparent the subclass Hamamelidae is a polyphyletic group (Qiu et al., 1998). Cronquist (1981) recognized incongruence in the Platanaceae-Hamamelidaceae association determining neither family could be derived from the other. He described the flowers of Platanus as more primitive than those of Hamamelidaceae, while Tippo (1938) pointed out the more advanced nature of Platanus wood. Ernst (1963) described Platanus as belonging within Hamamelidae,