Biogeogrpahy and Diversity of Freshwater Mussels of the Southeast
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BIOGEOGRPAHY AND DIVERSITY OF FRESHWATER MUSSELS OF THE SOUTHEAST UNITED STATES by SCOTT THOMAS SMALL (Under the Direction of John P. Wares) ABSTRACT Biodiversity is the variation of life at all levels of biological organization (Gaston and Spicer 2004). However, it is rare that biodiversity is actually studied at all levels of organization. To form a more cohesive picture of biodiversity, this means that we must consider data ranging from genes to species (or even higher taxonomic units), and from various spatial scales. It is only with data from multiple spatial scales that we begin to understand how species are distributed in a region, how species diversity is generated and maintained, and how evolution within species shapes patterns in communities. Here we investigate patterns of species and genetic diversity in communities of freshwater mussels (Unionidae) in the southeast United States. We approach this problem by combining numerical models with empirical data from regional and community scales. My methods combine the fields of biogeography, community ecology, and population genetics to elucidate the driving forces that maintain biodiversity in freshwater communities. Our results provide evidence for a regional vicariant event that is responsible for structuring diversity in freshwater mussels and possibly other freshwater taxa. Numerical simulations provide evidence for the non-neutral structuring of mussel communities influenced by both positive and negative density dependence. Patterns of genetic diversity within populations support the contemporary formation of species within the Altamaha River in Georgia with moderate spatial structuring of populations. In conclusion we find that by collecting data on 2 aspects of biodiversity, species diversity and genetic diversity, we are able to form a complete picture of forces shaping diversity in the southeast United States. Future goals of our study are to test hypotheses of mechanisms structuring freshwater communities, providing valuable data for comparison across drainages and taxa. INDEX WORDS: Biodiversity, Genetic diversity, Species abundance, Population genetics, Freshwater Mussels, Unionids, Biogeography, Community ecology, BIOGEOGRAPHY AND DIVERSITY OF FRESHWATER MUSSELS OF THE SOUTHEAST UNITED STATES by SCOTT THOMAS SMALL BS, University of Wisconsin-Stevens Point, 2002 A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY ATHENS, GEORGIA 2009 © 2009 Scott Thomas Small All Rights Reserved BIOGEOGRAPHY AND DIVERSITY OF FRESHWATER MUSSELS OF THE SOUTHEAST UNITED STATES by SCOTT THOMAS SMALL Major Professor: John P. Wares Committee: David Hall James Hamrick James Peterson David Moeller Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2009 DEDICATION To Melissa, the constant in my life iv ACKNOWLEDGEMENTS There are many people and experiences throughout my life that have inspired my love of science. First and foremost are my parents whose encouragement to explore the world through inquiry and imagination has led to many mistakes. Thank you, Mom and Dad, for letting me make those mistakes and learn the valuable lessons that follow. Thank you to my family whose tolerance and acceptance has always given me strength. Thank you to all of my friends and adopted families who have always seen fit to care for me with infinite patience, nary a difference between myself and their own. To everyone else who has given me a chance and trusted me to find my own solutions, your faith in me has surely been tested but hopefully never lost. Finally to Melissa, who continues to teach me lessons of life far beyond science, reminding me what makes it all worthwhile. v TABLE OF CONTENTS Page DEDICATION...........................................................................................................................iv ACKNOWLEDGEMENTS ........................................................................................................v LIST OF TABLES...................................................................................................................viii LIST OF FIGURES ...................................................................................................................ix CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW ...................................................1 INTRODUCTION.................................................................................................1 COMPARATIVE PHYLOGEOGRAPHY ............................................................2 COMMUNITY ECOLOGY ..................................................................................3 POPULATION GENETICS..................................................................................4 LIFE HISTORY....................................................................................................5 SUMMARY..........................................................................................................6 2 COMPARATIVE PHYLOGEOGRAPHY OF FRESHWATER MUSSESL OF THE SOUTHEASTERN UNITED STATES .................................................................9 INTRODUCTION.................................................................................................9 MATERIALS AND METHODS.........................................................................12 RESULTS...........................................................................................................15 DISCUSSION.....................................................................................................18 vi 3 ABUNDANCE AND GENETIC DIVERSITY OF SESSILE ORGANISMS IN A NEUTRAL COMMUNITY.................................................................................35 INTRODUCTION...............................................................................................35 MODEL OVERVIEW.........................................................................................37 SIMULATIONS..................................................................................................45 RESULTS...........................................................................................................48 DISCUSSION.....................................................................................................50 4 POPULATION GENETICS OF MUSSELS (UNIONIDAE) IN THE ALTAMAHA RIVER DRAINAGE, GEORGIA........................................................................70 INTRODUCTION...............................................................................................70 MATERIALS AND METHODS.........................................................................73 RESULTS...........................................................................................................81 DISCUSSION.....................................................................................................86 5 CONCLUDING REMARKS ................................................................................. 113 SUMMARY...................................................................................................... 113 CONCLUSION.................................................................................................116 BIBLIOGRAPHY................................................................................................................... 118 APPENDICES........................................................................................................................141 A Sample accession numbers for Chapter 2............................................................... 142 vii LIST OF TABLES Page Table 1.1: Classification and distribution of freshwater mussels..................................................8 Table 2.1: Mussel taxa utilized for comparative phylogeography ..............................................25 Table 2.2: Summary of genetic data collected for freshwater mussels........................................26 Table 2.3: Estimated species ages .............................................................................................27 Table 2.4: Divergence time between the Atlantic Slope and Gulf Coast drainages.....................28 Table 3.1: List of parameters used in the model.........................................................................58 Table 3.2: Statistical comparison between different models.......................................................59 Table 4.1: Summary of genetic data ..........................................................................................97 Table 4.2: Abundance corrections on raw count data.................................................................98 Table 4.3: AMOVA results .......................................................................................................99 Table 4.4: Estimates of effective population size to census size............................................... 100 Table A.1: Museum Accession Numbers................................................................................. 142 Table A.2: GenBank Accession Numbers................................................................................ 146 viii LIST OF FIGURES Page Figure 2.1: Map of southeast United States detailing sampled drainages....................................29 Figure 2.2: Species trees and divergence times..........................................................................32 Figure 2.3: Median divergence time between the