Mono- and oligophagous Phyllotreta (Coleoptera : Chrysomelidae) species: the relation between host plant range and genetic diversity

The niche-width variation hypothesis predicts a positive correlation between niche width and genetic variability. Here we evaluated this hypothesis by comparing genetic variability in four monophagous (narrow niche) and six oligophagous (broad niche) species of the beetle genus Phyllotreta Chevrolat, 1837 (Coleoptera: Chrysomelidae: Alticinae). The results, obtained over a similar geographic range, demonstrate that for all genetic variability measures used (average number of alleles per locus, percentage of loci polymorphic, observed heterozygosity and expected heterozygosity under Hardy-Weinberg conditions) the monophagous species showed a significantly higher genetic variability compared to the oligophagous species. This result is at variance with the niche-width variation hypothesis.