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Phylogeny of the Weakly Electric Banded Knifefishes: Insights on Biogeography and Evolution in the Neotropical Genus Gymnotus (Pisces: Gymnotidae)

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Phylogeny of the Weakly Electric Banded Knifefishes: Insights on Biogeography and Evolution in the Neotropical Genus Gymnotus (Pisces: Gymnotidae) Phylogeny of the weakly electric banded knifefishes: Insights on biogeography and evolution in the Neotropical genus Gymnotus (Pisces: Gymnotidae). by K¡ìstie L. Lester A Thesis submitted to the Faculty of Graduate Studies of The University of Manitoba In partjal fulfillment ofthe requirements ofthe degree of MASTER OF SCIENCE Depadment ofZoology University of Manitoba Winnipeg, Manìtoba, Canada Copyright @ by Kristìe L. Lester THE UNIVERSITY OF MANITOBA FACULTY OF GRADUATE STUDIES * ***+ COPYRIGHT PERMISSION Phylogeny of the weakly electric banded knifefishes: Insights on biogeography and evolution in the Neotropical genus Gyrnaotas (Pisces: Gymnotidae). BY Kristie L. Lester A Thesis/Practicum submitted to the Faculty of Graduate Studies of The University of Manitobâ in partial fulfillment of the requirement of the degree of Master of Science Kristie L. Lester O 2007 Permission has been granted to the Library of the University of Manitoba fo lend or sell copies of this thesis/prâcticum' to the Nafional Library of Canada to microfrlm this thesis and to lend or sell copies of the film, and to University Microfilms Inc. to publish an âbstract of this thesis/prâcticum. This reproduction or copy of this thesis has been made available by authority of the copyright owner solely for the purpose of privâte study and research, and may only be reproduced and copied as perrnitted by copyright låws or rvith express \ryritten autborizatiotr from the copyright oryner. Abstract A total evidence hypothesis ofphylogenetic relationships is proposed for the weakly electric banded knifefishes ofthe genus Gymnotus based on data from the mitochondrial cytochrorne ó and l65 genes, the nuclear RAG-2 gene, and I l3 morphological characters. Maximum parsimony trees provide partial confrrmation of previous findings based on morphological data sets, wìth lhe ' carapo'species group intact, The South American assemblage of Gymnotus is shown to be paraphyletic, with Central American species rnost closely allied to lhe 'carapo' species group. This relationship has important implications for biogeography and the evolution of electric signals within the genus. Dating of the node connecting Central American Gymnotus to their South American congeners suggests that genetic divcrgence between the two assemblages took place during the Miocene, prior to the uplift of the Isthmus of panama. Acknowledgements I gratefully acknowledge the support of my supervisor Dr. N. Lovejoy and the remaining members of my examining committee, Dr. B. Ford and Dr. J. Hare. I also thank Dr. J.S. Albert for his hospitality and guidance while examining specimens at the University of Florida. I am indebted to both J.S. Albert and W.G.R. Crampton for access to unpublished data and ideas, paficularly during the early stages of the research. Collection of fish in the field was graciously arranged by S. Willis and C. Montaña and facilitated by W.G.R. Crampton and N. Lovejoy. Additional tissues were kindly provided by J. Armbruster, W.G.R. Crampton, F. Femandes, M. Sabaj, and K. Winemiller. DNA for some outgroup species was provided by J.S. Albert. Funding for this research was provided by grants to N. Lovejoy from the Natural Sciences and Engineering Research Council of Canada (NSERC). Lastly, I thank all those family and friends who provided me with financial and/or emotional support throughout the graduate school process. Table of Contents COPYRIGHT PERMISSION........... ,......,.........11 ,...,......................--l¡r LIST OF TÄBLES ----...--...,.........,Yu -..............--................,, lx CHAPTER 1: GENERAL INTRODUCTION. CHAPTER 2: MOLECIJ'LAR PFIÌ'LOGENY OF THE WEAKLY ELECTRIC BÀNDED KNIFEFISIIES: INSIGIITS ON BIOGEOGRAPHY AND THE EVOLUTION OF SIGNAL WAVEFORMS IN THE GENUS GYMNOT¿l,t (GYMÀTOTIFORMES: GYMNOTIDAI'). .................6 1.Introduction ..... 2. Materials and Methods ...... I2 2-l- Taxon sampling, DNA ertraction und sequencing.... 2.2. DNA aligntnent .. 2.3. Phylogenetic analysis.................... 2.4. Molecular clacks and divergence estimøtes.................. 2.5. Charøcter optùnizatio n.................... 3. Results--............. 3.1. Charøcterization of sequence data ..................,.......22 3-2. Trees, support values, ønd generøl biogeogrøphic patterns ................. .......................... 24 Toral Evidence....... ..........................24 R4G2........ J.4. Character cvo1utio,t.................. 1.1. Phylogenetic relationsltþs of Gymnotus species and comparison with prcvious studies..........32 4. 2. H i s t ori c a l B i o g e o gra p h y................... CHAPTER 3: CONCLUSION.... TABLES..... .....98 List of Tables Table 1. Gymnotus species formally recognized in scientific literahrre. .......... .................... 60 Table 2. List of specimens included for study detailing tissue lots, held collection numbers, and collection localjty. ...............,.,..,6l Table 3. Priurers used for amplification and sequencing ofthe cyt å, l6S and RAG2 genes. ......... 64 Table 4. l6S clustalX alignment. Shaded sections represcnt ambiguously aligned portions of loop structu¡es excluded from phylogenetic analysis...,............... .................65 Tabie 5. Mean nucleotide frequencies for each gene and p-values for chi-square test ofbase frequency homogeneibr across taxa... ......................71 Table ó. U¡cor¡ected pairwise sequence divergence for the cytochrome ó data partition. Shaded a¡eas indicate distances between the Centual Amcrican sp ecies G. cylíndricus and other lal{a,.......,...,........... .................,...72 Table 7. Uncor¡ected pairwise sequence divergence for the RAG2 data partition. Shaded areas indicate distances between the Cent¡al American species G. cylindric¿¿J and other taxa. .. 74 Table 8. Average patristic distances (tree-based divergence) among Gymnotus species derived from the cytochrome å dataset using ACCTRAN optimization. Shaded pofions indicate distances used to estimate divergence dates between the Eleclrophorus-Gymnotus clades and the G. cylindricus-G. cørapo clades (r.e. the divergence between Central and South Table 9. Divergence date estimates (dates oforigins) for the cylindricus-carapo clade and E I ec t rop h oru s - Gym no tus clades. (assumrng B rac hy h yp o p o mu s p a I en q u e- ..................................._. 77 Table 10. Average patristic distances (tree-based divergence) among Gymnolís species derived from the RAG2 dataset using ACCTRAN optimization. Shaded portions indicate vtÌ distances used to estimate divergence dates between the tlech.ophorus-Gymnof¿l.r clades and the G. cylindricus-G. carapo clades (i.e. the divergence between Central and South American cìades).. ... .. ................ 7 8 List of Figures Figure 1. Phylogenetic hypothesis of Gymnotus relationships based on the morphological analysis Figure 2. Map of Middle and South America depicting nine drainage areas (MA:Middle America, PS:Pacific Slope, NW:Northwest, OR:Orinoco, GU:Guianas, Vy'A:Western Amazon, EA=Eastem Amazon, PA:Paraguay/Parana, SE:Southeastem, NE=Northeastem). ... 80 Figure 3. Paleogeographic map depicting the positions of postulated land bridges connecting the North and South American continents during the Late Cretaceous-Early Tertiary (-65mya) (adapted from Gayet et al. 1992 and Pindell er al. 1988). .,.................._.............. 8l Figure 4. Paleogeographic rnap showing the absence ofland bridges during the Early Tertiary (Paeleocene,60 mya) (adapted from Smith et al. 1994). Gray areas represent the limits of Figure 5. Paleogeographic map depicting quasi-land bridge connections comprising proto- Carribean land masses duri¡g the Eocene (35 mya) (adapted from lturralde-Vinent and MacPhee 1999)...................... ................,..................83 Figure 6. Expected tree topologies for Gl,mnolus based \poî (A) the Old Southem,/LateCreataceous-Ea¡ly Tertiary hypothesis ofBussing (1985) and (B) the Pliocene/Pleistocene hypothesis of Miller (1966) and Meyers (1966). SA:South America Figure 7. Shape ofmonophasic and multiphasic electric organ discharges as exhibited respectivcly by Cent¡al American (G. cylindricus) ald some South American foms of Gymnotus.............. .....................85 Figure 8. Saturation plot of cytochrome å third position transitions veßus pairwise sequence divergcnce for all pairwise comparisons amongst all Gymnotus species (black dots), and between all Gymnofus specres and the outgroups.. .,..........................,,.. 86 Figure 9. Single most parsimonious tree demonstrating Gymnotus phylogenetic relationships based on the combined analysis ofnuclear (BÀG2), mitochondrial (cytochrome b + l65), and morphological data (2894 characters, 3256 steps, CI:0.48, Rl:0.81). Numbers above nodes denote bootst¡ap support values based on 1000 replicates. + indicates terminal branches supported by 100% bootstrap values. Numbe¡s below nodes or indicated using arrows denote Partitioned Bremer Support values (decay indices) for the ntDNA, RAG2, and morphology partitions respectively. Biogeographjc abbreviations: CA : Cent¡al Amazon; WA = Westem Amazon, OR = Orinoco, GU: Guyana...................................... 8? Figure 10. Single most parsimonious t¡ee demonsttatiîg Gymnotus phylogenetic relationships based on the combined analysis ofnuclear (RAG2), mitochondrial (cytochrome å + l6S), and morphological data (2894 chaîaçters, 3256 steps, CI=48, RI:0.81). Excess taxa included in the analysis were pruned from th€ tlee. Numbers above nodes denote bootstrap support values based
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