UNIVERSITY OF CINCINNATI Date:___________________ I, _________________________________________________________, hereby submit this work as part of the requirements for the degree of: in: It is entitled: This work and its defense approved by: Chair: _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ Cultivation, overabundance, and establishment potential in the emerging invasive Pyrus calleryana A dissertation submitted to the Graduate School Of the University of Cincinnati In partial fulfillment of the requirements for the degree of Doctor of Philosophy In the Department of Biological Sciences Of the McMicken College of Arts and Sciences By Nicole A. Hardiman B.A., Biological Sciences University of Arkansas, Fayetteville, Arkansas, May 2000 Committee Chair: Dr. Theresa M. Culley ABSTRACT Pyrus calleryana is an emerging invasive species that appears to have had a recent and rapid increase in the rate of population spread. The species is a very popular ornamental tree, with as many as 29 different cultivated varieties. The species was originally thought to be of little invasive potential due to its genetically-controlled self-incompatibility mechanism and clonal propagation methods, so that cultivars were essentially clones of the same source tree. Virtually unknown as an invasive ten years ago, naturalized populations have since been identified in 26 states. Genetic analyses show that cultivars are highly genetically structured and are polymorphic at the self-incompatibility locus. Invasive trees were also highly admixed hybrid progeny of these different cultivars. In cross-pollination experiments, all cultivars were capable of freely crossing, indicating all are functionally different at the self-incompatibility locus. Measures of reproductive and establishment ability were used to compare different cultivars and hybrid types in terms of an advantage in contribution to invasive populations. All groups were found to be highly fecund, have low mortality, and have high biomass accumulation. Invasive trees also produced greater numbers of seeds than cultivated individuals, indicating that invasive populations may have an increasing rate of spread due to high reproductive output. Cultivated populations, therefore, appear to be the source for invasive populations, and invasive populations are self-sustaining and composed of highly productive individuals. In the case of the Callery pear, availability of multiple cultivar types and widespread horticultural use seems to have allowed the species to not only naturalize, but also increase reproductive output. ii iii ACKNOWLEDGMENTS I would like to thank my advisor, Theresa Culley, for her assistance, availability, guidance, and support. When trying to explain my relationship with Theresa, I have described her as “somewhere between a boss and a friend”, to which I later realized perfectly describes a mentor. My Research Advisory Committee, Ken Petren, Steven Rogstad, Sarena Selbo, and Jodi Shann, provided time, valuable discussion and feedback, and guidance. Their involvement not only improved my project, but also my personal development. Through many, many group discussions and one-on-one sessions, they have fundamentally altered who I am as a biologist and as a professional. Ed Romero also provided many, many hours of field assistance, helpful discussion, moral support, and professional support. Thanks to several present and past graduate students for helpful feedback, discussions, and recreational pursuits. Thanks to Margie Becus, Tom Fulcher, Brian Baumgartner, and Jan Haldeman for population identification. Funding sources include the U.S. Department of Agriculture, the University of Cincinnati Research Council, the Department of Biological Sciences, and the Botanical Society of America. Laboratory and field assistance was provided by Jessica Brzyski, Matt Klooster, Sarah McCann, Tracy Reeb, Brian Robin, Tegan Smedley, and Richard Stokes. I would also like to thank Google, for being the best information search engine on the planet. Much of the background and supporting information was generated using Google. It is an invaluable tool that I use approximately 20 times a day. iv TABLE OF CONTENTS Abstract……………………………………………………………………………………….……….…ii Acknowledgements………………………………………………………………………...………..…..iv List of Table and Figures……………………………………………………………………………...…vi Preface……………………………………………………………………………………………….....xiii Chapter 1: General Introduction…………………………………………………………………...……..1 Chapter 2: Cultivation and invasive potential: genetic evidence for intraspecific hybridization in Pyrus calleryana…………………………………………………………………………………….…24 Abstract……………………………………………………………………………..…………..25 Introduction………………………………………………………………………..…………....26 Materials and Methods……………………………………………………………..…………. .29 Results……………………………………………………………………………..…………....34 Discussion……………………………………………………………………………..………..38 References Cited……………………………………………………………………….………..43 Figure Legends………………………………………………………………………………….48 Chapter 3: Reproductive success of cultivated Pyrus calleryana and establishment ability of invasive, hybrid progeny……………………………………………………………..................................58 Abstract………………………………………………………………………………………....59 Introduction……………………………………………………………………………..............60 Materials and Methods………………………………………………………………………….63 Results…………………………………………………………………………………..............68 Discussion……………………………………………………………………………………....70 References Cited………………………………………………………………………………...76 Figure Legends………………………………………………………………………………….80 Chapter 4: The role of self-incompatibility in invasive potential of Pyrus calleryana………………....91 Abstract…………………...……………………………………………………………………92 Introduction…………………………………………………………………………………….93 Materials and Methods………………………………………………………………………....96 Results……………………………………………………………………………….. ……..100 Discussion…………………………………………………………………………….............102 References Cited………………………………………………………………………. …….106 Figure Legends………………………………………………………………………………..112 Chapter 5: General Discussion…………………………….…………………………………………..121 Appendix 1…………………………………………………………………………………………….133 LIST OF TABLES AND FIGURES Table 1.1: List of cultivars of Pyrus calleryana, including the year each became commercially available, the site of development, United States patent or trademark number, and the parental source, if known…...………………………………………………………………………………………………17 Table 2.1: Disease and pest susceptibilities, as well as environmental tolerances, of seven Pyrus calleryana cultivars……………………………………………………………………………………..20 Figure 1.1: Pictures of Pyrus calleryana (a) in cultivation and (b) in the wild. …………...…………...21 Figure 1.2: Locations of Pyrus calleryana seed collections by Francis Meyer and Frank Reimer across Asia………………………………………………………………….…………………………………..22 Table 2.1: Polymorphic microsatellite primers amplified in Pyrus calleryana…………………………49 Table 2.2: Descriptive population statistics for Pyrus calleryana cultivars and sampled populations…50 Table 2.3: Descriptive population statistics by locus across Pyrus calleryana cultivars of known type.51 Table 2.4. Coefficients for θ (below diagonal) and Nei's (1978; above diagonal) genetic identity for nine Pyrus calleryana cultivars……………………………………………………………..…………..52 Table 2.5: Frequency of diagnostic alleles for each cultivar in each invasive and putative parent population…...…………………………………………………………………………………………..53 Figure 2.1: Principle coordinates analysis comparing cultivars to putative parent and invasive populations of Pyrus calleryana...………………………………………………………………………55 Figure 2.3: (a) The number of cultivars found to contribute to each invasive individual‟s multi-locus genotype, based on diagnostic alleles for each cultivar found in the putative parent populations, and (b) the proportion of putative parent individuals who were identified as having more than one cultivar‟s diagnostic alleles………………………………………………………………..………………………56 Figure 2.4: The relationship between the average number of diagnostic alleles in invasive individuals and the LOD score………………………………………………………………………………………57 Table 3.1: Statistical analyses for cultivar reproductive measures and hybrid progeny establishment ability measures for Pyrus calleryana……………………………………………………………….…..……82 Table 3.2: Statistical analyses for reproductive ability for cultivated and invasive parents, and establishment ability measures between early-generation and late-generation hybrid progeny..………83 Table 3.3: Statistical analyses for ecophysiology measures between early-generation and late- generation hybrid progeny………………………………………………………………………………84 vi Figure 3.1: Comparisons of maternal reproductive success characters, measured as fruit mass, seed mass, and seed viability, among Pyrus calleryana cultivar types………………………………………85 Figure 3.2: Comparisons of establishment ability, measured as percent germination, percent mortality and above and below-ground biomass, in early-generation hybrid progeny of Pyrus calleryana...……86 Figure 3.3: Photosynthetic and conductance rates, as well as water use efficiency (WUE) measured across early-generation hybrid types...………………………………………………………………….87 Figure 3.4: Comparisons of maternal reproductive success characters, measured as fruit mass, seed mass and seed viability, between cultivated parents of early generation hybrids and invasive parents of late generation hybrids………………………………………………………………………………….88 Figure 3.5: Comparisons of establishment ability, measured as percent germination, percent