6533b837fe1ef96bd12a1d3c

RESEARCH PRODUCT

Radial and peripheral clines in northern polymorphic populations of Philaenus spumarius

subject

description

Geographic variability in the colour polymorphism of Philaenus spumarius (Homoptera) was investigated in the northern parts of Finland, Norway and Sweden. The investigation was directed mainly at peripheral populations south of the Baltic—Arctic divide. The colour phenotypes were found to differ in their “north tolerance”. The phenotypes typ (pt/pt) and lat (pt/pt) were the most, and the phenotype tri (pt/pT) the least tolerant to marginal conditions. Differences in “north tolerance” between the phenotypes cause radial clines to be present in allele frequencies. The radial clines may be caused by the combined effect of several different factors. These include shortness of the thermal growth period, random genetic drift, decreasing diversity of the food plant flora, and decreasing diversity of predators. These different explanations are discussed in the light of the ecology of Philaenus. Very clear clines perpendicular to the radial clines were observed in the frequencies of the phenotypes Ice (pt/pT) and lop (pt/pO). Both were found to increase in frequency in the west—east direction. These peripheral clines may be caused by increasing humidity from west to east. The frequency of typ (pt/pt) also seems to be a sensitive index of humidity conditions, or other factors parallelling humidity in distribution.