Genetics and distribution of black spotting in Enoplognatha ovata (Araneae: Theridiidae), and the role of intermittent drift in population differentiation

Breeding studies have shown that the number of black spots on the dorsal surface of the opisthosoma of E. ovata is genetically determined, with a narrow heritability of about 0.7. There is, in addition, evidence that the presence and absence of spots might be under the control of a small number of major loci. Frequencies of spotted and non-spotted spiders in Nidderdale, Yorkshire, define the same three regions identified by previously studied variation at a regulatory locus. There are no correlations between sites in spotting and colour-morph frequencies. Variation in all three systems is independent of gross environmental factors. It is argued that the present-day patterns of genetic variation in these populations probably result from stochastic events during major environmental disturbance which is known to have occurred 40 years (generations) ago. Genetic drift, both continuous and intermittent, could be an important influence on morph frequencies in many E. ovata populations. Selection on conspicuous polymorphisms is not necessarily strong merely because the variation is conspicuous.