Population Differences in Rainbow Smelt, Osmerus mordax: Multivariate Analysis of Mensural and Meristic Data

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Abstract
The phenetic relationships are investigated between 13 samples of sexually mature rainbow smelt, Osmerus mordax, from 12 collecting sites including representatives of anadromous and landlocked populations. Data on 32 mensural and meristic characters were obtained. Univariate and multivariate analyses revealed that the samples fell into three distinct groups composed of the anadromous, normal freshwater, and stunted freshwater populations. Mean values of the mensural and some meristic characters decreased across these three groups; some other meristics increased. It is doubtful whether the magnitude of the observed meristic variation represents solely a plastic environmental response.The two freshwater stunted samples were 100% separable from the freshwater normal and anadromous samples using all the data, and 92.5 and 97.5% separable using one (total gill rakers) and all meristics, respectively. The identification success and other published biological data indicate that they fulfill the criteria for species recognition.Between anadromous and normal freshwater groups 99.2% correct identification was achieved when all data were used. Using only one and two meristics (total gill rakers and total vertebrae), 89.1 and 91.4% correct identification was achieved, which suggests subspecific status for these two groups.When the freshwater normal and anadromous groups were analyzed separately, more variation was seen within the freshwater group. Evidence of year-to-year variation was seen from the analysis of the anadromous samples and evidence for a genetic basis is presented. Key words: Osmerus mordax, population, anadromous, freshwater stunted, variation, meristic, multivariate, taxonomy

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