Visible morph-frequency variation in allopatric and sympatric populations of two species of enoplognatha (Araneae: Theridiidae)

Abstract

Samples were taken from single- and mixed-species populations of two spiders, Enoplognatha ovata and E. latimana, which share visible polymorphisms. The range of colour-morph frequencies was comparable between the species but E. latimana had a uniformly lower proportion of individuals with black spots. Spotted E. ovata females were more likely to have cocoons when collected than females without spots, although in spotted individuals there was no relationship between presence of cocoons and spot number. Colour-morph frequencies varied both within and between the seven study areas, sometimes over very short distances. A similar, though less marked, pattern was shown by the black spotting phenotype. This variation, on two geographical scales, was present in both species. No evidence was found for consistent shifts in morph frequencies between allopatric and sympatric populations, and morph frequencies were not correlated between species across sympatric populations. Thus, common selective agents acting on the polymorphisms could not be demonstrated, although species-specific factors cannot be eliminated. It is possible that stochastic processes influence local morph frequencies, as has been suggested for E. ovata elsewhere. © 1991 The Genetical Society of Great Britain.