Biogeography of the Weakly Electric Knifefish Gymnotus Carapo (Teleostei: Gymnotidae) in the Guianas
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Biogeography of the weakly electric knifefish Gymnotus carapo (Teleostei: Gymnotidae) in the Guianas by Emma S. Lehmberg A thesis submitted in conformity with the requirements for the degree of Master of Science Ecology and Evolutionary Biology University of Toronto © Copyright by Emma S. Lehmberg 2015 Biogeography of the weakly electric knifefish Gymnotus carapo (Teleostei: Gymnotidae) in the Guianas Emma S. Lehmberg Master of Science Ecology and Evolutionary Biology University of Toronto 2015 Abstract The electric knifefishes (Gymnotiformes) are widely distributed across South and Central America, with the highest species concentrations occurring in the Amazon and Orinoco basins. Riverine features such as waterfalls and rapids can cause disjunct populations to form between highland and lowland areas in these basins. The Guiana Shield provides a good model to study the genetic differences between populations precisely because it has upland and lowland areas with extant populations of Gymnotiformes. To examine genetic divergence between highlands and lowlands, mitochondrial (cytochrome b) and nuclear (S7) DNA was sequenced for members of the Gymnotus carapo species complex (Gymnotidae). Population and phylogenetic analysis indicate a distinct split between upland and lowland populations, with those species in the highlands showing greater genetic similarity to populations from the Amazon basin. ii Acknowledgements First and foremost, thank you to my advisor, Nathan Lovejoy. Always a well of information, he has been patient and supportive throughout the duration of this project. This past year has been a growing one, and I will carry the things he has taught me into the next stage of my research life. My timely completion of my thesis would also not have been possible without the support of the entire Lovejoy lab. I owe huge thanks to Dominik Halas, for being an endless source of information about all things phylogenetic and sharing that knowledge without hesitation; Ahmed Elbassiouny, who taught me so much in the lab and continues to be inspiring in more ways than one; Alex Van Nynatten, who taught me the “five minute” rule and always gave thought- provoking feedback; Charmaine Condy, who was always supportive and kind, especially when I needed it most; and to Matt Kolmann, who patiently answered my questions and aided in the quiet proliferation of office aquaria and their inhabitants. Thanks also to Megan McCusker, Thanara Rajakulendran, Frankie Janzen and Michael Dobrovetsky for all the office chats and thoughtful comments. Many people were responsible for the collections that made this project possible, not least among them Hernán López-Fernández, Devin Bloom, and William GR Crampton, as well as Matt Kolmann. Kristen Brochu and Gabrielle Malcolm provided additional sequences that helped round out the datasets. Thank you to my supervisory committee, Hernán López-Fernández and Maydianne Andrade. Your feedback was invaluable and helped a great deal. Thanks to my friends and family, who encouraged and supported me throughout my entire iii masters. This thesis is for three of them: my mother, who taught me how to look; my father, who taught me how to ask; and Noel, who first showed me the beauty of a fish. iv Table of Contents Abstract………………………………………………...………………………………………….ii Acknowledgments………………………………………………………..………………………iii Table of Contents……………………………………………………………………………...….v List of Tables…………………………………………………………………………………….vii List of Figures………………………………………………………………………………...…viii Chapter 1 Introduction…………………………………………………………………….……....1 1 Biogeography of the Guianas………………………...……………………………….…1 1.1 Riverine Barriers and Connectivity…………………………………………...……….2 1.2 Model Species: Gymnotus carapo……………………………………………….…....4 1.3 Objectives, Hypotheses, and Predictions………………………………………….…..7 1.4 Significance……………………………………………………………………..……..8 Chapter 2 Materials and Methods…………………………………………………………..……..9 2 Taxon Sampling………………………………...………………………………...……..9 2.1 Mapping and Elevational Division………………………………………………..…10 2.2 DNA Extraction………………………………………………………………..…….10 2.3 PCR and Sequencing………………………………………………………..………..11 2.4 Sequence Alignments and Matrices………………………………………..………...13 2.5 Phylogenetic Analyses………………………………………………………….……13 2.6 Sequence Divergence Calculations…………………………………………………..15 Chapter 3 Results……………………………………………………………...…………………16 v 3 Haplotype Sharing Between Upland and Lowland Guianas…………………...………16 3.1 Biogeographic Relationships Between Upland and Lowland Gymnotus carapo……17 3.2 Continent-wide Gymnotus carapo Relationships……………………………………19 Chapter 4 Discussion…………………………………………………………………………….21 4 Upland and Lowland Division of Guianas Gymnotus carapo…...…………………….21 4.1 Biogeographic Patterns of the Guiana Shield Gymnotus carapo…………………….23 4.2 The Gymnotus carapo Species Complex…………………………………………….25 References………………………………………………………………………………………..27 vi List of Tables Table 1: Members of the Gymnotus carapo species complex included in this study……………33 Table 2: Gymnotus carapo collected from the Guiana Shield, and included in this study..……..37 Table 3: Primers used for S7 and cytb in this study ……………….……………………………45 Table 4: Average pairwise distances between allopatric populations of the Gymnotus carapo species complex included in this study..........................................................................................45 vii List of Figures Figure 1: Profile of different elevational categories of the Guiana Shield. Altitude divisions taken from Hammond (2005)…………………………………………………..………………………40 Figure 2: The drainages and major rivers of the Guiana Shield in Guyana and Suriname………41 Figure 3: Fish assemblages found above and below the Kaieteur Falls and the Tumatumari Cataract of the Potaro River. Modified from Hardman et al (2002).……….……………………42 Figure 4: Proposed relationships between members of the Gymnotus carapo clade based on a maximum parsimony analysis of morphological and meristic characters. Figure adapted from Albert et al. (2005)……………………………..………………………………………………...43 Figure 5: Collection locations of Gymnotus carapo from the Guiana Shield.………………....44 Figure 6: Cytb gene tree showing relationships between allopatric populations of Gymnotus carapo and closely related species. …………………….…………………..……………………46 Figure 7: S7 gene tree showing relationships between populations of G. carapo and closely related species.…………………………………………………..……………………………….47 Figure 8: Tree showing relationships of G. carapo and closely related species when S7 and cytb are concatenated and run as a single dataset.…………………………….………………………48 Figure 9: *BEAST analysis of cytb and S7 data showing relationships between populations of Gymnotus carapo and closely related species included in this study……….…………………...49 viii 1 Chapter 1 Introduction 1 Biogeography of the Guianas South America is a continent of high ichthyofaunal diversity, and it is likely that physical changes in river connections and drainage patterns have contributed to the diversification of South American fishes (Lundberg et al. 1998). The Guiana Shield region (Guianas) of northwestern South America is famous for its striking topography. This region includes sheer- edged tabletop mountains (tepuis), which rise above a slightly lower main platform known as the pantepui, which itself is elevated above the coastal lowland river drainages (Lujan and Armbruster 2011; McConnell 1968; Rull 2005) (Figure 1). The high elevation regions of the Guianas exhibit considerable isolation, with resulting biological endemicity. The Guiana highlands and uplands are home to 42% of vascular plants and approximately 100 birds are exclusive to these highland areas (Berry and Riina 2005; Zyskowski et al. 2011). Throughout the upland Guianas, ichthyological sampling is sparse, but estimates of endemicity of the upper Mazaruni, an isolated pantepui river, are placed between 67 - 95% (Alofs et al. 2014). The Guianas region (Figure 2) is centered in northeast South America and encompasses parts of Venezuela, Guyana, Suriname, and French Guiana, covering approximately 2 288 000 km2 (Hammond 2005). The region is bounded to the north and east by the Orinoco River, to the south by the Amazon basin, and to the east by the Atlantic Ocean. Forty-seven major rivers currently contribute to the major Guiana drainages, with the largest basins being the Orinoco and Essequibo. The Orinoco is the second largest basin in South America, while the Essequibo basin encompasses a number of major highland rivers found in central Guyana, including the 2 Essequibo itself, the Cuyuni, the Mazaruni, and the Potaro. A number of smaller drainages that flow directly to the oceans have been collectively referred to as the Orinoco and Coastal drainage basins (Albert, Petry and Reis 2011). The Berbice, Commewijne, Coppename, Suriname and Marowijne drainages are included in this group of coastal basins (Figure 2). Geographically, the Guianas exhibit a gradient of altitudes from the tepui summits to the coastal floodplains of northeast South America. The highest peak, Pico Neblina, is approximately 3 000 meters above sea level (m-asl), with the average elevation of the pantepui at 1 000 m-asl, and the lowlands found at an average of 150 m-asl (Figure 1; Lujan and Armbruster 2011). As a result of this variation in altitude, many rivers of the Guiana Shield experience a numbers of abrupt changes in elevation (as rapids and waterfalls). With the exception of coastal drainage basins, most of the major rivers in the region originate in the highlands or uplands