Temporal and Spatial Patterns of Morph-Frequency Variation among Coastal Maine Populations of the Polymorphic Spider Enoplognatha ovata (Araneae: Theridiidae)

Abstract

The theridiid spider Enoplognatha ovata exhibits a conspicuous color polymorphism characterized by three distinct phenotypes: lineata (yellow abdomen), redimita (two red stripes on abdomen) and ovata (solid red shield on abdomen). Here we examine temporal and spatial morph-frequency patterns of E. ovata from 1985-1987 for many coastal Maine populations distributed from Boothbay to Acadia National Park. All populations censused showed the same rank order of morph frequencies: % lineata > % redimita > % ovata. Males and females exhibited similar phenotypic frequencies within populations. A latitudinal cline of increasing redimita and ovata frequencies with increasing latitude, as occurs in Europe, was not observed. However, Maine E. ovata populations did exhibit patterns of regional and local morph-frequency variation similar to those exhibited by the species in Europe. The southernmost Maine populations were unusual, with few redimita and ovata phenotypes. Morph frequencies for most populations were stable between yearly censuses. Frequencies among females did not change significantly during the summer season, suggesting an absence of selection on adult phenotypes. Enoplognatha ovata females cluster nonrandomly within vegetation, but we found no evidence for assortative grouping on the basis of phenotype. Observations of male-female pairs suggest that the color morphs experience similar mating success and mate randomly. Fecundity was correlated with female body size, and significant fecundity and size differences were detected between two of the populations sampled. Fecundity estimates for one of the populations in 1987 revealed significant fecundity differences among phenotypes, with ovata females producing more eggs than redimita or lineata females. Our survey of Maine Enoplognatha ovata populations identifies may parallels between European and North American patterns of temporal and spatial morph-frequency variation. Our data indicate that processes of population differentiation and mechanisms maintaining morph frequencies within populations may be similar on both continents.