Hybridization and introgression appear more common in rapidly evolving groups, suggesting an important role in the evolutionary process. Detailed studies of how extrinsic or intrinsic forces regulate hybridization and introgression have the potential for broadening our understanding of mechanisms generating diversity. Species in the Fundulus notatus species complex have broad overlapping ranges and occur in replicated hybrid zones along predictable stream gradients. Typical hybrid zone structure has Fundulus olivaceus in headwaters,F. notatus downstream, and hybrid zones near confluences or abrupt shifts in habitat. Rarely, the typical upstream-downstream orientation is reversed raising questions as to how hybrid zones are formed and maintained. We used next-generation sequencing data to study hybridization and introgression in hybrid zones in neighboring drainages that differ in orientation (typical and reversed). We predicted extrinsic forces linked to stream gradients would result in noticeable differences between the two. Contrary to predictions, the data indicate the hybrid zones are remarkably similar. We used individual-based simulations to explore the potential role of intrinsic and extrinsic forces in generating and maintaining typical and reversed hybrid zones. Simulation results were consistent with reversed hybrid zones being formed from stochastic processes combined with strong intrinsic forces and weak extrinsic forces.

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The Evolution of Body Size in the Order Siluriformes (Undergraduate Thesis; Non-Peer Reviewed. In prep for publication 85% complete)

By Campbell, D.C., J. Schaefer, and W. Matamoros

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Abstract

The evolution of body size has long been a topic of interest to biologists due to the close link between size and various aspects of an organism’s biology. Adult body size is influenced by the underlying tradeoff in energy allocation between maintenance, somatic growth and reproduction. The evolution of a large group of globally distributed fishes (primarily freshwater with some marine forms) was studied to test some basic hypotheses about the evolution of adult body size. Catfish (Siluriformes) are an excellent group for this type of research as they represent approximately 11% of all fishes and species range in size from over three meters (family Pangasiidae) to a few centimeters (family Trichomycteridae). Due to how speciose this order is, the study was completed at the genera level to better manage the large amounts of data. The final dataset included data for 212 genera representing over 2,400 species. Tests for the strength of phylogenetic signal in body size were completed first before phylogenetic least squared methods were used to test for the effects of distribution (range size and latitude), habitat (freshwater vs. marine), trophic ecology and body shape on body size in catfish. Because the study was done at the genera level, patterns of variability in body shape within groups (coefficient of variation in size within a genera) were also quantified and analyzed. Results suggest that the greatest drivers of average body size evolution are body shape and habitat in catfishes.

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Lets Jump In: A Phylogeographic Study of the Great Basin Springfishes and Poolfishes, Crenichthys and Empetrichthys (Cyprinodontiformes: Goodeidae)

(In Prep for publication, 70% complete)

By Campbell, D.C., and K. Piller

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Abstract:
Crenichthys and Empetrichthys are two genera of goodeid fishes that are poorly studied and lack clear taxonomic distinction in terms of their species and subspecies status. Many of the members of these two genera are federally listed as endangered due to anthropogenic impacts and their disjunct distribution across the Great Basin. As a result, clarification of the taxonomy of these populations has been limited by the constraints on specimen acquisition due to conservation concerns. Most recently, with the cooperation of natural resources agencies, we obtained tissue samples for 18 different populations inclusive of nearly all species and subspecies. The objective of this study was to examine the phylogenetic relationships of the populations, subspecies, and species of Crenichthys and Empetrichthys using both mitochondrial and nuclear markers analyzed using Bayesian inference. We also examined genetic variation within and between populations, estimated divergence times, and generated haplotype networks. The results of this study represent a first step towards understanding the evolutionary history and taxonomic diversity of this understudied group of fishes.

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Larval Life History of the Southern Leopard Frog (Lithobates sphenocephalus) in Southeastern Louisiana (In prep for publication, 50% complete)

By Borgardt, T., D.C. Campbell, J. Donini, J.A. Erdmann, C.D. Godwin, C.E. Parker, M.A.J. Partin, A.E.E. Rupp, M.R.

Villalba-Guerra, and C.A. Weyand

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*Author order is alphabetical by last name, not by contribution effort.

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