Geometric Morphometrics and Phylogeny of the Catfish genus Mystus Scopoli (Siluriformes:Bagridae) and North American Cyprinids (Cypriniformes)
Type of Degreedissertation
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Understanding the evolution of organismal form is a primary concern of comparative biology, and inferring the phylogenetic history of shape change is, therefore, a central concern. Shape is one of the most important and easily measured elements of phenotype, and shape is the result of the interaction of many, if not most, genes. The evolution of morphological traits may be tightly linked to the phylogeny of the group. Thus, it is important to test the phylogenetic dependence of traits to study the relationship between traits and phylogeny. My dissertation research has focused on the study of body shape evolution using geometric morphometrics and the ability of geometric morphometrics to infer or inform phylogeny. For this I have studied shape change in Mystus (Siluriformes: Bagridae) and North American cyprinids. Mystus Scopoli 1771 is a diverse catfish group within Bagridae with small- to medium-sized fishes. Out of the 44 nominal species worldwide, only 30 are considered to be part of Mystus. Mystus is distributed in Turkey, Syria, Iraq, Iran, Afghanistan, Pakistan, India, Nepal, Sri Lanka, Bangladesh, Myanmar, Thailand, Malay Peninsula, Vietnam, Sumatra, Java and Borneo. Species of Mystus are morphologically similar and diagnostic characteristics are usually subtle. The group is poorly diagnosed and is not likely monophyletic. Their classification has remained in disarray and there has been no phylogenetic study done on the genus Mystus. Among the 44 species of Mystus, M. gulio remains even a more problematic group. At least nine species have been named that are now all considered to be synonyms of M. gulio. Mystus gulio is morphologically distinct among Mystus species. So it is very important to resolve the taxonomy of the M. gulio species complex. For Mystus, I first examined the molecular phylogeny using the mitochondrial cytochrome b gene for about half of the recognized species of Mystus (Chapter 2). With few monophyletic clades, M. gulio came as a monophyletic clade in this analysis. In addition to phylogenetic relationship of Mystus species, I was also able estimate the timing of the divergence of Mystus. Using this molecular phylogeny I tried to test if shape has evolved phylogenetically across the genus Mystus using geometric morphometrics (Chapter 3). A Principal Component Analysis (PCA) shows considerable dispersion between species and species groups within Mystus. Species were split between those with long adipose fins (adipose starts immediately after dorsal fin), medium dorsal fins (a small to relatively large gap is present between the dorsal and start of the adipose), and small adipose fins (adipose taller than long). Geometric Morphometrics show promise in being able to separate species within each of the adipose fin groupings. I also studied the taxonomy of Mystus gulio using traditional morphometrics (Chapter 4) which found M. gulio as one single species. Lastly, I combined all of the approaches I used on Mystus, and have additionally added a test of a method to construct a phylogeny using geometric morphometric data on a much more morphologically and taxonomically diverse group, the North American cyprinids of the subfamily Leuciscinae. I used the cyprinids to study whether shape is evolving phylogenetically across cyprinids and if shape data can be used to elucidate phylogeny (Chapter5).