A morphological approach to improving the conservation of Arizona's native chubs (genus:Gila)

The fields of function morphology and environmental physiology are based on the paradigm that there is a causal relationship between morphology, performance, and fitness. In Arizona many of the native fishes are imperiled as a result of reduced fitness in altered habitats. Because fitness can be significantly altered by morphology, this dissertation aims to use morphology to improve the management of Arizona's native chubs (Gila spp. ). First, I explored the biological species concept as it pertains to the Gila robusta complex. I found that the closely related and phenotypically similar Gila robusta, Gila nigra and Gila intermedia have comparable shapes and morphological features. We found that different species from the same location had similar body shapes suggesting that location may impact the morphology of these species. Second, I analyzed the locomotor morphology of the highly endangered bonytail chub (Gila elegans) with the aim of understanding the performance implications of their unique "bonytail". I found that G. elegans closely resembled the chub mackerel ( Scomber japonicus) (a high performance swimmer from the marine environment) suggesting that historical flow conditions in the Colorado River have selected for a locomotor morphology similar to that of a high performance steady swimmer. Third, I investigated the phenotypic responses to different rearing temperatures of the roundtail chub (Gila robusta). This study was aimed at describing morphological and performance changes that occur in response to temperature. In many fishes, rearing temperature has been shown to alter vertebral column morphology. I found that Gila robusta did not have a difference in total number of vertebrae in response to rearing temperature. However, temperature did significantly impact predator escape response performance. Fish reared at intermediate temperatures, similar temperatures to those historically found in the wild, performed better than fishes raised at higher and lower temperatures. Fourth, I investigated into the key anatomical features that enable invasive species to thrive in the now equilibrium habitats of the Colorado River. I found that the non-native species have larger eyes and larger gapes which aids them in predation on native fishes. These morphological advantages have facilitated the steady decline in native fish populations. The findings from this dissertation can be used for the management of these imperiled species. Native fish management can be improved by altering habitats to favor the morphology and performance of native fishes.