Date of Award:

1968

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Department name when degree awarded

Fishery Biology

Advisor/Chair:

Clair Stalnaker

Co-Advisor/Chair:

Donald R. Franklin

Abstract

Three Hundred and nine specimens of Gila from the Colorado River basin were studied. A form of numerical taxonomy, taximetrics, was used to help classify the specimens. The data from these fish indicate that many of the present hypotheses concerning their taxonomy are not valid. The concept of ecosubspecies or ecological subspecies does not fit the Colorado basin Gila. The roundtail and bonytail chubs, G. robusta Baird and Girard and G. elegans Baird and Girard respectively, currently treated as subspecies, are well separated morphologically, ecologically and reproductively and therefore are better considered two valid species. The relationship between G. cypha Miller and G. elegans is clouded by the presence of what appear to be intergrade forms. Future investigations are needed to piece together the puzzle surrounding these two fish. The subspecies name seminuda (Cope and Yarrow), presently attributed to fish from throughout the Colorado basin, more correctly is allied to the robusta of the Virgin River. Preliminary study indicates this population may be sufficiently different to warrent subspecies recognition. No specimens of G. robusta intermedia (Girard) were examined but the literature suggests this form may also be a valid species.

Comments

Three Hundred and nine specimens of Gila from the Colorado River basin were studied. A form of numerical taxonomy, taximetrics, was used to help classify the specimens. The data from these fish indicate that many of the present hypotheses concerning their taxonomy are not valid. The concept of ecosubspecies or ecological subspecies does not fit the Colorado basin Gila. The roundtail and bonytail chubs, G. robusta Baird and Girard and G. elegans Baird and Girard respectively, currently treated as subspecies, are well separated morphologically, ecologically and reproductively and therefore are better considered two valid species. The relationship between G. cypha Miller and G. elegans is clouded by the presence of what appear to be intergrade forms. Future investigations are needed to piece together the puzzle surrounding these two fish. The subspecies name seminuda (Cope and Yarrow), presently attributed to fish from throughout the Colorado basin, more correctly is allied to the robusta of the Virgin River. Preliminary study indicates this population may be sufficiently different to warrent subspecies recognition. No specimens of G. robusta intermedia (Girard) were examined but the literature suggests this form may also be a valid species.

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