THE WORLD ACCORDING TO GARS: THE MOLECULAR SYSTEMATICS AND COMPARATIVE PHYLOGEOGRAPHY OF LIVING GARS (ACTINOPTERYGII: LEPISOSTEIDAE)

There are seven living species of gars in two genera (Lepisosteiformes: Actinopterygii). In my first chapter, I estimate phylogenetic relationships among six of them using DNA data generated from four complete mitochondrial loci (cytb, CR, 12S, and 16S) and a single, partial nuclear locus--recombination activating protein 1 (RAG1) intron. A single outgroup taxon, the bowfin (<italic>Amia calva<italic>), was included in my analyses. Regardless of optimality criterion (genetic distance, parsimony, maximum likelihood, and Bayesian inference), a single, well-supported phylogeny estimate emerged. Both sister genera (<italic>Atractosteus<italic> and <italic>Lepisosteus<italic>) were monophyletic. Within <italic>Atractosteus<italic>, <italic>A. spatula<italic> paired with <italic>A. tropicus<italic> in the absence of data from <italic>A. tristoechus<italic>. Within <italic>Lepisosteus<italic> I recovered two sister pairings of species: <italic>L. platyrhincus<italic> and <italic>L. oculatus<italic>; and <italic>L. ossues<italic> and <italic>L. platostomus<italic>. I estimated the phylogenetic position of the seventh gar species, <italic>A. tristoechus<italic>, using DNA data generated from several partial mitochondrial loci and 105 morphological characters. In this analysis, within a monophyletic <italic>Atractosteus<italic> I recovered a well-supported sister pairing between <italic>A. spatula<italic> and <italic>A. tristoechus<italic>, with <italic>A. tropicus<italic> sister to the pair. My molecular phylogenies largely agree with recent morphologically-based phylogenies aside from the positions of <italic>L. ossues<italic> and <italic>L. platostomus<italic>. Using dates associated with the best fossil data available (244 Ma minimal age of the node joining bowfins to gars, and 100 Ma for Lepisosteidae), I estimated divergence dates under a relaxed molecular clock model in a Bayesian framework. Estimated ages for lineages ranged from approximately 50 Ma for <italic>Lepisosteus<italic>, 23 Ma for the split between <italic>L. oculatus<italic> and <italic>L. platyrhincus<italic>, 28 Ma on the <italic>L. osseus<italic> and <italic>L. platostoms<italic> divergence, and 30 Ma for the node uniting <italic>A. spatula<italic> and <italic>A. tropicus<italic>--dates ranging from the Early Eocene to the Early Miocene. In my second chapter, I conducted basic phylogeographic investigations into the geographical structuring of gene genealogies built with mitochondrial D-loop sequences from 115 individual gars, belonging to five species (<italic>A. spatula, L. osseus, L. platostomus, L. platyrhincus<italic> and <italic>L. oculatus<italic>) and collected from a broad array of localities. Across species, across localities, I found some phylogeographic structuring in <italic>L. osseus<italic> and <italic>L. oculatus<italic>. I found one unique set of haplotypes confined to <italic>L. osseus<italic> in the Pee Dee River drainage of North Carolina. The level of molecular divergence between these and other <italic>L. osseus<italic> haplotypes was similar to that among gar species. I found evidence that there might be mixing of haplotypes across a contact zone between <italic>L. platyrhincus<italic> and <italic>L. oculatus<italic> in the Florida Panhandle. I found significant molecular divergence among populations of <italic>L. osseus<italic> and <italic>L. oculatus<italic> distributed among drainages to the Gulf of Mexico. However little genetic divergence was detected among populations of <italic>L. osseus<italic>, <italic>L. platostomus<italic> and <italic>L. oculatus<italic> within the Mississippi River basin. In my third chapter I present pilot work into characterizing the origins of a population of morphologically unusual gars in eastern Wisconsin. The longnose gar, <italic>Lepisosteus osseus<italic>, and the shortnose gar <italic>Lepisosteus platostomus<italic> are native to Wisconsin. In the Fox and Wolf River systems in eastern Wisconsin there is a third form that superficially resembles the spotted gar, <italic>L. oculatus<italic> (not previously reported to occur in Wisconsin) in that is exhibits heavy head and body pigmentation and a relatively short, broad snout. After initial molecular phylogenetic analyses showed that these gars did not belong to <italic>L. oculatus<italic>, results of more detailed molecular investigations, coupled with simple morphological findings, are consistent with the hypothesis that these unusual gars may be hybrids of <italic>L. platostomus<italic> and <italic>L. osseus<italic>. Further molecular and morphological investigations must be conducted to definitively infer hybrid status for these unusual gars.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Campus Only Dissertation

Discipline thesis:degree_discipline

Zoology

Year

2011

Author dc:creator

• Sipiorski, Justin Todd

Contributors dc:contributor

• Burr, Brooks
• Krajewski, Carey

• Gars
• Hybrid
• Lepisosteidae
• Molecular
• Phylogeography
• Systematics

Repository record dc:identifier

https://opensiuc.lib.siu.edu/dissertations/407

OAI identifier oai:identifier

oai:opensiuc.lib.siu.edu:dissertations-1407