Distribution of genetic variance and isolation by distance in two leaf beetle species: Oreina cacaliae and Oreina speciosissima

The distribution of genetic variance was investigated in two closely related <i>Oreina</i> leaf beetle species, <i>Oreina cacaliae</i> and <i>Oreina speciosissima</i>, Populations of these alpine beetles were sampled in mountainous areas of Western Europe, the total sampling area ranging from the Pyrenees to the Czech Republic. Allozyme electrophoresis of 21 (<i>O. cacaliae</i>) and 16 (<i>O. speciosissima</i>) loci revealed high genetic variability as expressed in a high percentage of polymorphic loci (only one monomorphic locus was found in each species) and high heterozygosities. No overall linkage disequilibrium was found in either species. Extensive heterozygote deficits were observed in several samples as reflected by high <i>F</i>_IS-values and high overall inbreeding coefficients (<i>F</i>_IT) of 0.349 (<i>O. cacaliae</i>) and 0.503 (<i>O. speciosissima</i>). The overall inbreeding coefficient was mainly attributable to within-population differentiation. The high heterozygote deficits are explained by a combination of inbreeding resulting in kinship groups and a sampling effect over several such kinship groups. No explanation of the observed patterns could be found in the host plant use or altitudinal location of the samples. For <i>O. cacaliae</i>, isolation by distance was found, but not for <i>O. speciosissima</i>. Gene flow estimates were in the range of <i>Nm</i> = 0.8 to 1.5.