An analysis of the taxonomic status of the Coregonus autumnalis species complex in North America, and An investigation of the life histories of whitefishes and ciscoes (Pisces; Coregoninae) in North America and Eurasia

Dillinger, Robert E. (1989) An analysis of the taxonomic status of the Coregonus autumnalis species complex in North America, and An investigation of the life histories of whitefishes and ciscoes (Pisces; Coregoninae) in North America and Eurasia. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Aspects of the biology and taxonomy of the Coregonus autumnalis species complex were investigated in this study. The taxonomic and zoogeographic relationship of Coregonus autumnalis and C. laurettae was examined using morphometric, meristic, and distribution data. The morphometric data, a series of head and body measurements, was analyzed using a discriminant function analysis. The percentage of fish misclassified in the analysis was found to be higher than what would be expected for two distinct species, and was more indicative of subspecies, or stocks. The only meristic variable found to be significantly different was gill raker counts for the lower branch of the first gill arch. This character was originally used to separate the two species. An examination of the distribution of gill raker counts between the sample sites along the Beaufort Sea coast revealed a consistent percentage of the fish from the Mackenzie River with gill raker counts representative of the Yukon River species. This percentage was maintained in the hypothesized area of sympatry between the two species. It was concluded, from this analysis, that the original description was incorrect in the establishment of two reproductively isolated species with a single area of sympatry, based on gill raker counts. The actual situation is more likely that of two allopatric subspecies, with no area of sympatry. The distribution data were also analyzed to determine the support for the original zoogeographic hypothesis proposed to explain the separation of the two forms. It was concluded that the Bering Land Bridge was probably not responsible for this, as the present-day distribution of the two populations does not reflect ranges that could have been fragmented by the uplifting of the land bridge. An alternative hypothesis, which better fits the current distribution patterns of each form, involves known stream captures and headwater transfers between the Mackenzie and Yukon Rivers. Insufficient information is presently available to determine the direction of the transfer, or through which river system the transfer was made. -- Life histories were investigated at a number of levels. Arctic and Bering cisco populations were investigated using one-way analysis of variance and multiple analysis of covariance. No significant differences were found within the populations for reproductive variables but the two populations differed significantly from each other. It was concluded that, based on the occurrence of alternate spawning and its relatively short life span, Arctic cisco populations appeared unable to compensate reproductively for the rigorous conditions encountered in northern latitudes. Least cisco (C. sardinella) populations were investigated at the same levels. Between latitude comparisons were made using Mackenzie and Yukon River populations. As with Arctic ciscoes, no significant differences were found within populations for reproductive variables, but significant differences were seen in between population comparisons. It was concluded that northern least ciscoes, by virtue of their longer lifespan, are better able to compensate reproductively for the poor conditions encountered in the north than Arctic ciscoes. A second analysis of a number of least cisco populations inhabiting the same latitude found that anadromous populations were larger and more fecund. However, analysis of covariance detected no significant difference in fecundity between populations. An analysis of gonad weight among sympatric coregonines along the Beaufort Sea coast was conducted using an analysis of covariance but again, no significant difference was detected. A principal components analysis was used to determine patterns of life history variation in members of the subfamily Coregoninae using populations from North America and Eurasia. The effects of both phylogeny and latitude were examined. No significant trends in life history traits associated with latitude were found, although the subgenus Coreaonus (coregonus) did show a non-significant increase in egg size and number of broods with latitude, the subgenus Coregonus (leucichthys) showed non-significant inverse relationship for these variables and the genus Prosopium showed a nonsignificant inverse relationship for age and growth related variables. A number of genera and species appeared to be constrained by phylogeny and were unable to adapt completely to the environmental constraints imposed by northern environments. It was concluded that, despite this apparent inability to adapt, the great deal of variability of life histories demonstrated a large degree of plasticity in the subfamily.

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