INCREASED GENETIC DIVERSITY IN MITOCHONDRIAL GENES IS CORRELATED WITHTHE EVOLUTION OF PARASITISM IN THE HYMENOPTERA

A higher AT content and rate of mtDNA sequence divergence was found in parasitic wasps (Apocrita) compared with nonparasitic wasps (Symphyta ). The compositional bias was reflected in extreme codon bias for a cy tochrome oxidase I protein coding gene fragment as well as in the type s of amino acid substitutions that have occurred during the evolution of this gene fragment. In some instances, compositional bias influence d the definition of a conservative amino acid change. The increased ra te of mtDNA sequence evolution probably arose during the early Jurassi c, coincident with the first appearance of parasitic wasps in the foss il record, Our results suggest a causal link between the rate of seque nce divergence and the parasitic lifestyle.