Shell-band color polymorphism in Cepaea vindobonensis at the northern limit of its range

The distribution of black-, brown- and faint-banded morphs in populations of Cepaea vindobonensis (Ferussac) was established at the northwestern edge of the species' distribution. In the Czech Republic, the species was sampled at 132 localities in the Morava and Elbe river basins, between 48degrees45' and 50degrees15' N. Even in this narrow zone, there was a significant trend for increasing frequency of the black-banded morph with increasing geographic latitude and altitude. The variation paralleled the decreasing length of sunshine (April-August), which is > 10% shorter at the northern than at the southern localities. The habitats occupied by northern populations (grassy steppe-like stands) differed from those preferred by southern populations (synanthropic weed stands, mostly stinging nettle). Geographic trends and habitat differences in morph frequencies may be affected by climatic selection. Other possible causes of variation are discussed, comparisons are made with other species, and gaps in evidence are identified.