Trans-continental visible morph-frequency variation at homologous loci in two species of spider, Enoplognatha ovata s.s. & E. latimana

The spiders Enoplognatha ovata s.s. and E. latimana are sibling species which share a number of visible genetic polymorphisms. Data on colour and black-spotting morph frequencies in these species have been collected from 67 sites in western Europe. Sixty nine percent of the collections contained both species. In all adequately-sized samples, both species were polymorphic for colour and, in general, exhibited the same rank order of morphs lineata and redimita. (The top dominant morph, ovata, has not been found in E. latimana). Colour-morph frequencies are not correlated between species in sympatric populations from mainland Europe and from a previously studied area in Pembrokeshire, South Wales. Although associations with certain climatic variables are evident in E. ovata they are not consistent between transects, making their biological significance unclear. For black spotting, E. ovata s.s. is nearly fixed for spotting throughout mainland Europe but is highly variable in the Pembrokeshire populations. E. latimana is polymorphic in both areas. In Europe, spotting frequencies in E. latimana show significant associations with climatic factors but, again, their biological significance is not obvious. In E. ovata s.s. the variance in both colour and spotting frequencies among populations in Pembrokeshire is significantly greater than that in the whole of mainland Europe. The implications of these and previous results are considered in the context of the persistence of visible polymorphisms across species and the forces which determine morph frequencies in local populations.