Relationships of a Northern Maine Population of Amelanchier (Rosaceae) Matthew R
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Maine The University of Maine DigitalCommons@UMaine Honors College Spring 2015 Relationships of a Northern MAine Population of Amelanchier (Rosaceae) Matthew R. Sheltra University of Maine - Main, [email protected] Follow this and additional works at: https://digitalcommons.library.umaine.edu/honors Part of the Biology Commons Recommended Citation Sheltra, Matthew R., "Relationships of a Northern MAine Population of Amelanchier (Rosaceae)" (2015). Honors College. 230. https://digitalcommons.library.umaine.edu/honors/230 This Honors Thesis is brought to you for free and open access by DigitalCommons@UMaine. It has been accepted for inclusion in Honors College by an authorized administrator of DigitalCommons@UMaine. For more information, please contact [email protected]. RELATIONSHIPS OF A NORTHERN MAINE POPULATION OF AMELANCHIER (ROSACEAE) by Matthew R. Sheltra A Thesis Submitted in Partial Fulfillment of the Requirements for a Degree with Honors (Biology) The Honors College University of Maine May 2015 Advisory Committee: Christopher S. Campbell, Professor of Plant Systematics, Advisor Eric T. Doucette, PhD student, EES Joyce E. Longcore, Research Scientist Seth Tyler, Professor of Zoology and Cooperating Professor of Marine Sciences Melissa Ladenheim, Adjunct Assistant Professor in Honors (Folklore) ABSTRACT Amelanchier is a genus of plants that produces seeds both sexually and by apomixis (asexual seed production). Asexuality is the dominant mode of reproduction in tetraploids (which contain four sets of chromosomes) and has created uncertainty about species delimitation in this genus. A tetraploid population of Amelanchier at a site called Pudding Rock on the Aroostook River in northern Maine has long been hypothesized to belong to Amelanchier gaspensis, a member of the Amelanchier sanguinea species complex. Using structural features (morphology), knowledge of the number of sets of chromosomes (ploidy level), and DNA sequence data, I tested this hypothesis. Analyses of my samples plus those obtained by others falsify this hypothesis because A. gaspensis does not form a distinct morphological or genetic cluster that includes the Pudding Rock population and that would warrant species status. Instead, my results confirm other data supporting the conclusion that plants that have been called A. gaspensis are members of a massive hybrid swarm. ACKNOWLEDGMENTS I would like to thank my advisor Dr. Christopher Campbell and Eric Doucette for all the time they spent and the knowledge they shared with me through this project, as well as Kevin Cushman and Garth Holman. Additionally, I would like to thank the members of my committee for their review of this thesis. Lastly, I would like to thank my family and friends for their constant support throughout this project and my college career. iii TABLE OF CONTENTS ACKNOWLEDGMENTS ........................................................................................................... iii LIST OF TABLES ........................................................................................................................ v LIST OF FIGURES ..................................................................................................................... vi INTRODUCTION ........................................................................................................................ 1 MATERIALS AND METHODS ................................................................................................. 4 RESULTS .................................................................................................................................... 13 DISCUSSION .............................................................................................................................. 17 LITERATURE CITED………………………………………………………………………...20 BIOGRAPHY OF THE AUTHOR............................................................................................23 iv LIST OF TABLES Table 1. Accessions for which morphological data were obtained for this thesis……….5 Table 2. Morphological taxonomic characters in Amelanchier………………………….6 Table 3. Accessions used for morphological analyses…………………………………...9 Table 4. Characters demonstrating morphological intermediacy and that accession 14-005 is a hybrid between 14-004 and 14-007………………………………………..19 v LIST OF FIGURES Figure 1. Principle component analysis (PCA)…………………………………………14 Figure 2. Principle coordinate analysis (PCoA)………………………………………...15 Figure 3. Dendrogram…………………………………………………………………..16 Figure 4. Bootstrap 50% majority-rule consensus tree based on the LFY2int2d gene for diploid members of the genus Amelanchier bearing this gene plus sequences for nine clones of accession 14-004……………………………………………...17 vi INTRODUCTION Commonly called shadbush or serviceberry, Amelanchier consists of trees and shrubs that are widespread across North America. This genus has long been a taxonomic challenge primarily due to the presence of polyploids (containing three or more sets of chromosomes; Judd et al. 2008) that reproduce both sexually and apomictically. One group of tetraploids, Amelanchier gaspensis (Wieg.) Fernald & Weath., was first described as a species from the Gaspé Peninsula of Quebec (Fernald and Weatherby 1931). Jones (1946) considered this species to extend west to the James Bay and Michigan, and Fernald (1950) and Haines (2011) reported it from northern Maine. I studied a population of Amelanchier at a site along the Aroostook River in Ashland, Maine, called Pudding Rock. Pudding Rock Amelanchier has long been considered to be A. gaspensis. Material I collected from this population was determined by Eric Doucette (a member of my Honor’s thesis committee and a PhD candidate who works on Amelanchier for his thesis) to be tetraploid, like numerous previously studied samples of the sanguinea complex. Diploid organisms have two sets of chromosomes, while tetraploids have four. Diploid Amelanchier are mostly sexual, and tetraploids reproduce almost exclusively by apomixis (Campbell et al.1985, 1987; Weber and Campbell 1989; Campbell and Wright 1996; Dibble et al. 1998; Burgess et al. 2014). Apomixis bypasses the two steps of sexuality, meiosis and fertilization. In apomixis, the egg cell develops by apomeiosis, without meiotic reduction, and therefore has the same number of chromosome sets as the mother plant. The egg develops into an embryo without fertilization, a process called parthenogenesis (Campbell et al. 1991, Koltunow and Grossniklaus 2003). 1 In plants generally, diploid species commonly diverge over long periods of time, millions of years in some cases. In contrast, polyploid species can arise in as few as two generations (Rieseberg and Willis 2007). As soon as a tetraploid develops, it is reproductively isolated from and will often not mate with its diploid parents due to the difference in ploidy (Coyne and Orr 2004). Amelanchier diploids form groups that are distinct morphologically, ecogeographically, and mostly genetically (Burgess 2010, Burgess et al. in prep.). Sexual polyploids, which have not been reported in Amelanchier, often form distinct species that may be numerous and thereby generate some complexity. The addition of apomixis to polyploidy affects diversification and leads to complexity in two primary ways. First, apomixis replicates successful genotypes into microspecies, which are morphologically uniform and minimally differentiated from one another. Microspecies are often narrowly distributed and can be numerous, occurring by the thousands within a genus. The problem is that microspecies are like species, and their recognition makes the classification of a group difficult. A second problem is that apomicts, including those in Amelanchier, retain a small percentage of sexuality (1-3%) in seed production and also produce pollen sexually. As a result Amelanchier tetraploid apomicts hybridize with diploids and other tetraploids. Polyploids resulting from these hybridizations are apomictic (Burgess et al. 2014) and often morphologically semi-cryptic, or showing close morphological similarity, compared to diploids, making it difficult to distinguish diploids from tetraploids. Semi-cryptic ploidy variation is pronounced in Amelanchier, in which about 55% of traditionally recognized species contain both diploids and tetraploids (Burgess et al. 2014). In general, 12– 13% of plant species contain multiple ploidy levels (Wood et al. 2009). Sexual diploid hybrids produce unreduced gametes more frequently (27%) than nonhybrids (0.56%) (Ramsey and Schemske 1998). Fusion of an unreduced gamete (a 2x egg or 2 sperm; “x” refers to the number of sets of chromosomes) and a reduced gamete (a 1x sperm or egg) can result in a triploid embryo (Yamauchi et al. 2004). Triploids are often sterile, but they can have an average pollen fertility rate of 30% (Coyne and Orr 2004, Ramsey and Schemske 1998), allowing production of some 1x, 2x, and 3x gametes that, when combined with a gamete of the right ploidy level, produce a tetraploid (Ramsey and Schemske 1998, Husband 2004). The triploid thus mediates the formation of a polyploid in a pathway called the triploid bridge (Yamauchi et al. 2004). The presumed importance of diploid hybrids in polyploid formation is consistent with the observation that almost all Amelanchier polyploids that have been studied are derived from two or three diploid ancestors. To determine if