Genome evolution in mosquitoes: intraspecific and interspecific variation in repetitive DNA amounts and organization

Abstract

SummaryDNA reassociation kinetics were used to determine the amounts and organization of repetitive and unique DNA in four mosquito species:Anopheles quadrimaculatus(Say),Culex pipiens(L.),Aedes albopictus(Skuse) andAe. triseriatus(Say). Intraspecific variation in repetitive DNA amounts was examined in two geographic strains ofAe. albopictusfom Calcutta, India and the island of Mauritius. Repetitive and unique sequences inAn. quadrimaculatuswere distributed in a pattern of long period interspersion. Repetitive DNA in all other mosquito species exhibited a pattern of short period interspersion. The amounts of fold-back, middle repetitive, and highly repetitive sequences increased with genome size. The amount of foldback DNA increased at a much slower rate than the middle and highly repetitive sequences. Intraspecific variation in genome size inAe. albopictuswas due primarily to the amounts of highly repetitive DNA. S1 nuclease digestion of repetitive DNA in all species revealed a positive correlation between genome size and the proportion of the repetitive DNA consisting of short repeats. The amounts of long and short repeats increased with genome size but short repeats increased at a higher rate. The repetitive DNA of the Mauritius strain contained approximately 15% more short repeats than the Calcutta strain. These findings suggest that genome evolution in mosquitoes has resulted from changes in both the amounts and organization of repetitive elements.