Gene flow in colonizing Hippodamia variegata ladybird beetle populations

Abstract

Genetic diversity and gene flow at allozyme loci was investigated in natural and laboratory-reared populations of the predatory ladybird species Hippodamia variegata, a recently naturalized beetle from the Palaearctic. Gene diversity was 24.9 ± 4.9% at 28 resolved loci and 31.6 ± 5.5% at 22 polymorphic loci. Average gene diversity at nine polymorphic loci was only slightly greater among field-collected beetles than among laboratory-cultured beetles. There were five alleles in cultured beetles not found in natural U.S. population samples. Wright's F statistics showed modest genetic differentiation among two field collections from the northeastern United States and one from Europe (F(ST) = 0.107 ± 0.077). Analysis of variance in gene frequencies in these feral ladybirds showed that about 97% of the variance existed within populations of this colonizing species. A substantial level of genetic differentiation was detected among 10 laboratory populations descended from collections made in Europe, Asia, North Africa, and Chile (F(ST) = 0.191 ± 0.021). Drift is the most likely explanation for this differentiation.