Morphologic and allozymic analysis of microgeographic variation in the isopod Sphaeroma Quadridentatum



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The intertidal marine isopod Sphaeroma quadridentatum was scored for polymorphisms of color, carapace pattern and enzyme systems. Samples were collected at six sites in Galveston County, Texas, during three collection periods: August, 1976; December, 1976 and February, 1977. Possible microgeographic variation and population subdivision were evaluated by spatial and temporal analysis. Data for the morphologic characters and one allozyme locus were analyzed using GH tests and a non-parametric analysis of variance. Also, allozyme frequencies were used to calculate genetic measures of subdivision. Spatial analysis revealed no significant deviations from homogeneity either morphologically or allozymically. Temporal variation was not distinguishable allozymically, however, morphological analysis revealed an increase of the red and grey color classes. This change may be related to seasonality, however further work is necessary to make any definitive statement.