Genetic divergence among populations of two closely related species of Cicada Linnaeus (Hemiptera : Cicadoidea) in Portugal

Portuguese populations from localities of sympatry and allopatry of Cicada orni Linnaeus and C, barbara (Stal), a pair of closely related cicada speci es, were screened electrophoretically to clarify their genetic relationship s. Thirteen enzyme systems coded by 19 presumptive loci were analysed. Seve n loci were polymorphic on the 0.95 criterion. Data on within- and between- species variation, based on several genetic estimates (number of alleles pe r locus, amount of polymorphism, heterozygosity and genetic divergence) are presented. A dendrogram was constructed based on the Cavalli-Sforza & Edwa rds chord distance, using the UPGMA clustering method. Two groups were prod uced, one clustering the populations of C. orni and a second one clustering C. barbara. The former cicada species was much more variable genetically t han C. barbara, this latter being a very homogeneous species. The high leve l of genetic similarity might suggest that C. barbara is a relatively recen t immigrant to the Iberian Peninsula from its origin in North Africa. Alter natively, the present populations of C. barbara in Portugal might originate from small relict populations having survived the climatic cooling during the ice ages in a few warm refugia. Moreover, the present results suggest t hat reproductive isolation and therefore speciation in these cicadas may ha ve occurred at a smaller genetic divergence level than in some other insect s.