An Examination of the Co-Evolutionary Relationships Among Mating System, Lifespan and Chromosome Number in the Rosaceae and Asteraceae
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An examination of the co-evolutionary relationships among mating system, lifespan and chromosome number in the Rosaceae and Asteraceae by James Ryan Ozon Thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science (Biology) Acadia University Fall Convocation 2008 © by James Ryan Ozon, 2008 I, James Ryan Ozon, grant permission to the University Librarian at Acadia University to reproduce, loan, or distrubute copies of my thesis in microform, paper or electronic formats on a non-profit basis. I, however, retain the copyright in my thesis. Signature of Author Date This thesis by James Ran Ozon was defended successfully in an oral examination on April 25, 2008. The examining committee for the thesis was: Dr. John Roscoe, Chair Dr. B. Barringer, External Reader represented by Dr. Kirk Hillier Dr. Sam Vander Kloet, Internal Reader Dr. Sara Good-Avila, Supervisor Dr. Marlene Snyder, Head This thesis is accepted in its present form by the Division of Research and Graduate Studies as satisfying the thesis requirements for the degree Master of Science (Biology). Table of Contents List of Tables v List of Figures vi Abstract vii Acknowledgements viii Materials and Methods 7 Data collection 7 Character State Definitions 8 Mating system 8 Chromosome number 9 Lifespan(Growth Habit) 9 Sequence Alignment 10 Phylogenetic reconstruction 11 BayesDiscrete & BayesMultistate Analyses 12 Chromosome number vs. Mating system 16 Lifespan vs. Mating System 17 Lifespan vs. Polyploidy 19 Discussion 20 Literature Cited 31 Appendix 61 iv List of Tables Table 1. Summary of co-evolutionary analyses performed in the Asteraceae and Rosaceae 59 Table 2. Summary of the number of individuals that exhibit each pair of traits in the Rosaceae and Asteraceae. 59 Table 3. Summary of the top evolutionary models from the Bayesian analysis of the relationship between Mating System and Polyploidy and Life History in the Asteraceae and Rosaceae 60 Table 4. Summary of In likelihoods and BIC values for analyses run in BayesMultistate 60 v List of Figures Figure 1. Phylogenetic tree of the 88 species of the Asteraceae showing Bayesian Posterior Probabilities 40 Figure 2. Phylogeny of 211 Asteraceae species showing Bayesian Posterior Probabilities 43 Figure 3. Phylogeny of 211 Asteraceae taxa used in life history analyses with character states 52 Figure 4. Phylogeny of the Rosaceae showing Bayesian Posterior Probabilities 55 Figure 5. Phylogeny of 61 Rosaceae species used in all analyses with character states 56 Figure 6. Flow diagrams representing the most likely evolutionary models based on Bayesian Discrete analysis 57 Figure 7. Flow diagrams representing the most likely evolutionary models based on Bayesian Discrete analysi 58 VI Abstract The purpose of this study was to determine whether mating system co-evolves with life span, chromosome number or both in the Rosaceae and the Asteraceae. Maximum likelihood and Bayesian methods as implemented in BayesMultistate and BayesDiscrete were used. It was hypothesized that: (I) SI will break down in the presence of polyploidy in the Rosaceae (which has a GSI system), (II) SI will not break down in the presence of polyploidy in the Asteraceae (which has an SSI system), (III) Herbs will be associated with SC in the Rosaceae and (IV) Annuals will be associated with SC in the Asteraceae. The analyses show that co-evolutionary relationships were supported in all analyses. Results show that mating system co-evolves with lifespan and chromosome number in both families. However, the strong relationship between polyploidy and chromosome number in the Rosaceae may be causing spurious conclusions. Vll Acknowledgements I would like to take this opportunity to thank the many people who helped during the course of my Masters. First Sara, thank you for all your help and the more than extra work you put in and thanks for never giving up on me. I would like to thank Sara, Acadia, NSERC, ACGCER and the AAFC for their funding. Thanks to my committee members Steve Mockford and Rodger Evans for their assistance and guidance. Elena Zamlynny, without whom I never would have accomplished any lab work, and Sergey Yegerov and Audrey for all the work they did for me. Thanks to everyone from the lab who helped, Amy, Beth, Jennie, Carrie, Miriam, Sam and German and thanks to my friends who listened, Cristina, Cody and Katie. I would like to thank Theresa Staratt for helping make sure I could actually graduate and Wayne Maddison for his correspondence and assistance. Finally I would like to thank the triangle for their support and team cut and paste for their late night assistance and sprinkler dodging adventuers. Vlll Introduction Self-incompatibility (SI) refers to the inability of a fertile hermaphroditic plant to set seed after self-fertilization. Self-incompatibility is achieved in angiosperms by the presence of genetically based self-recognition systems that allow female and male reproductive tissues to recognize each other as self versus non-self and thereby prevent inbreeding. Two main types of homomorphic SI systems are recognized in angiosperms called sporophytic SI (SSI) and gametophytic SI (GSI). They differ in the physiological and genetic basis of their SI reaction (de Nettancourt, 2001). In SSI the incompatibility reaction is determined by the genotype of the diploid pollen parent (therefore expressing two S-alleles) while in GSI the reaction is dependent on the haplotype of the male gametophyte (pollen tube) and males only express a single S-allele (de Nettancourt, 2001). Thirty nine percent of angiosperm species are estimated to harbor some form of SI (Igic et al. 2008). Since the presence of SI forces species to outcross, the gain and loss of SI would be expected to be associated with known correlates of outcrossing such as life history characteristics and polyploidy. For example, agriculturists have noted that many crop species lose SI when forced to become polyploid, especially in species with GSI (Venable and Miller, 2000; Mable 2004). Two main hypotheses have been proposed to explain the breakdown of SI after polyploidization. 1) It has been hypothesized that the reason polyploids are more likely to be self-compatible in species with either GSI or SSI is due to the advantage of reproductive assurance in recently formed polyploids (as it eliminates the problem of finding a mate of the same ploidy level) and the reduction in inbreeding depression associated with having multiple copies of the same gene (Lande and Schemske, 1985). This hypothesis has recently been given further support in a study by Barringer (2007) who collected data regarding outcrossing rates and polyploidy in 235 1 species and then used phylogenetically independent contrasts and cross-species analyses to show that polyploids have statistically higher rates of self-fertilization than diploids 2) It has also been suggested that the breakdown of GSI after polyploidization is caused by competition between S-alleles in hetero-allelic pollen (Lewis, 1947). Hetero-allelic pollen bypasses the SI response because both alleles compete for dominance and neither is fully functional as suggested by Lewis (1947) and shown experimentally by Golz, et al. (2001). Competition between 5-alleles hetero-allelic pollen is not an issue in species with SSI systems because they function with multiple alleles in diploid systems, and the additional ^-alleles in polyploids do not cause the system to breakdown. Mable (2004) found support for this in a meta-analysis study, which suggested that SI tends to break down in species with GSI but not SSI. There are also several hypotheses to explain the association between SI and both out-crossing rates and growth habit in plants. The most prevalent hypothesis is that annual plants are more likely to be self-compatible because it provides reproductive assurance, which is beneficial to species with short life spans (Stebbins, 1957). Lloyd (1992) and Morgan, et al. (1997) suggested another reason for the observation that perennials are more likely to be self-incompatible. Instead of focusing on the advantages of being a self-compatible annual they suggested that SC would be disadvantageous to perennials. Morgan, et al. (1997) developed a life history model that demonstrated that self-fertilization is disadvantageous to perennials if self- fertilization usurps energy from future (subsequent year) opportunities to produce higher fit cross-fertilized offspring, i.e. the cost of between year seed discounting. In a later paper, Morgan (2001) found that this was not always the case, because inbreeding depression can be lower in perennials than annuals given the same mating system and an absence of substantial mitotic mutation (Morgan, 2001). More recently, Scofield and 2 Schultz (2006) developed a model to include the correlation between somatic mutations and rates of self-fertilization in small (herbs) versus large (trees) statured plants and found convincing evidence that rates of somatic mutation are too high in large statured plants to allow for the high rates of self-fertilization. These theoretical predictions are borne out by several studies that have found support for the relationship between SI and outcrossing rates, growth habit (herb, shrub or tree) or lifespan (annual, biennial, perennial) in natural populations (Bena, et ah, 1998, Bullock, 1985, Hamrick, et ah, 1992 and Barrett, et ah 1996). Evolutionary biologists have long used methods in comparative biology to ask questions about why or whether groups of taxa share common patterns of evolutionary change. Although many important correlations have been detected using the comparative method (which was an essential tool for the development of Darwin's ideas in the Origin of Species), prior to the inclusion of phylogenetic information spurious conclusions were sometimes made because correlations among traits can arise in a group of taxa simply because they share a common evolutionary history (Felsensten, 1985, Harvey and Pagel, 1991). To avoid spurious conclusions, the rapidly expanding field of phylogenetic comparative methods (PCM) uses an independent estimate of the phylogenetic relationship (topology plus branch lengths) among taxa.