Haploid nuclear DNA of 23 species of Aedes, as determined by Feulgen cytophotometry, was found to vary 3-fold. This was accompanied by a 2-fold variation in total chromosomal length. There was a significant correlation (r = 9765, P< 0.001) between these two parameters. Genome size varied from 0-87 pg to 1-3 pg among 10 strains of Aedes albopictus, from wide geographic regions. Large scale differences in chromosomal DNA amounts have accompanied speclation and evolution in aedine mosquitoes.

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SUMMARYIntraspecific variation in nuclear DNA amount was found among 12 field populations of Collinsia verna (Scrophulariaceae). Nearly a four fold difference in DNA amount was found among populations collected from a 300 mile area of the mid-west United States. Genetic isolation and microhabitat differences are suggested causes of this high degree of genetic differentiation, and possible incipient speciation.

A restriction map was constructed of the ribosomal cistron in a mosquito, Aedes albopictus (Skuse). The 18s, 28s and nontranscribed spacer (NTS) regions were subcloned and used to probe for intraspecific variation. Seventeen populations were examined throughout the world range of the species. No variation was detected in the coding regions but extensive and continuous variation existed in the NTS. The NTS consisted of two nonhomologous regions. The first region contained multiple 190-bp AluI repeats nested within larger XhoI repeats of various sizes. There was a large number of length variants in the AluI repeat region of the NTS. No repeats were found in the second region and it gave rise to relatively fewer variants. An analysis of NTS diversity in individual mosquitoes indicated that most of the diversity arose at the population level. Discriminant analysis was performed on spacer types in individual mosquitoes and demonstrated that individuals within a population carried a unique set of spacers. In contrast with studies of the NTS in Drosophila populations, there seems to be little conservation of spacers in a population. The importance of molecular drive relative to drift and selection in the generation of local population differentiation is discussed.

Two types of duplication-deficiency heterozygotes have been discovered from a translocation stock of Aedes ae&ypti. The structural interchange involved one arm of chromosome 2 with chromosome 1 and the other arm with chromosome 3. Both types of dp-dfheterozygotes were deficient for a part of chromosome 2. But in one case a part of chromosome 1 and, in the other, a part of chromosome 3 was duplicated. During meiosis, chromosomes with a duplication usually formed homomorphic ring bivalents in a variable frequency. The remaining four chromosomes formed chain multiples. Ring multiples were never observed. In one heterozygote where chromosome 3 was involved in duplication, approximately 91 per cent of the cells showed a chiasma in one of the interstitial regions. The frequency of the interstitial chiasma corresponded with the expected equational segregation during first anaphase of meiosis.