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Comparative analyses of separate data sources in a systematic study of the genus Myoxocephalus (Pisces; Cottidae) Cowan, Garry Ian McTaggart


The purpose of this study was to compare the systematic relationships within the genus Myoxocephalus (Pisces; Cottidae) suggested by separate conventional morphological and "bio-chemical"=protein evidence and to compare the effects of numerical and conventional systematic analyses of this evidence on the relationships. About 5000 specimens representing 13 nominal species of the genus Myoxocephalus provided the source for morphological investigation. An additional 157 fresh-frozen specimens representing 11 nominal species were used in the determination of biochemical differences. Protein data consisted of electrophoretic characteristics of muscle protein, malic dehydrogenase, and lactic dehydrogenase. No sexual variation in banding patterns of any of the characters employed was detected. In each species examined the myogen pattern was constant and unique. In only two nominal species were samples obtained from wide geographic range. One of these (M. scorpioides) had a constant pattern, the other, M. "M. scorpius" revealed the presence of two species types within the currently recognized taxon. There were two electrophoretic patterns in the malic dehydrogenase isozymes, 10 species possessed one pattern, two the second. Eleven species had identical isozyme patterns of lactic dehydrogenase. One other species (M. scorpioides) was biphasic. Within the 7 meristic characters examined, both latitudinal and longitudinal clines were exhibited. Latitudinal clines generally increased northward. Longitudinal trends increased eastward across the Arctic of North America, while in the transpacific species values increased westward. In cases where there was a response in the number of pectoral rays, it was in a direction opposite to the response in the other meristic features. Meristic characters were rich in differences between species. Morphological data excluding morphometric characters were derived from 20 major conventional features as well as from squamation, cephalic lateral line system, lateral line ossicles, olfactory rosettes, and the coiling pattern of the gut, all of them features not previously used in systematic studies of this genus. Twenty body features were measured and gave rise to 190 character combinations. When analyzed these did not yield any natural groupings. Separate phenetic dendrograms based on "biochemical" and morphological data were derived as well as dendrograms based on numerical taxonomic analyses of biochemical, morphological and the combined data. No similarities were exhibited upon comparison of the numerical analyses of "biochemical" and morphological data. However, patterns of relationships from both "biochemical" and morphological sources using the conventional phenetic treatment were similar. The conventional and numerical treatments of the morphological data yielded almost identical patterns of relationship between the species. Analyses of the "biochemical" data using the same two approaches produced completely different results. Speculations are included on the probable sources of the differences arising from the latter comparison. A new diagnosis of the genus Myoxocephalus was given as well as a synopsis of the species attributed to it. Two unrecognized species were revealed through the analysis.

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