We sequenced the envelope (E) genes of 59 DEN-2 isolates collected from ten Caribbean islands, six South American countries, and two Central American countries between 1981 and 2000, a period characterized by hyperendemicity and increased incidence of severe dengue. Fifty-two isolates belonged to "American/Asian" subtype IIIb, possessing a characteristic polar residue at envelope aa position 390 (N [n = 48] or S [n = 4]) common to that group. Six isolates from Trinidad (1981), Honduras (1991 [4]), and El Salvador (1987) fell into the "Native American" subtype V (D at aa 390), and one from Honduras (1986) belonged to "Asian" subtype I. The data suggest that after its first isolation in the Caribbean in 1981, genotype IIIb spread throughout the Americas and effectively replaced subtype V throughout the Caribbean basin. The strain also evolved into several distinct lineages, based on substitutions in the E glycoprotein (amino acids 91 and 131), two of which were still in circulation in 2000. Interestingly, a molecular clock did not fit the data well, suggesting that other sources of rate variation, such as differential selection or differences in effective population sizes, may exist among lineages. Our results indicate the importance of large temporal- and geographical-scale phylogenetic studies in understanding disease dynamics, particularly where replacements between regions can occur.

The organization and behaviour of nucleolar-organizer regions (NOR) of Scilla autumnalis were studied in two diploid races, their allotetraploid and autoallohexaploid derivatives and hybrids between them. The diploids of genome constitution AA and B7B7 each have a pair of nucleolarorganizer chromosomes while the polyploids A14 B7 B7 and AAB7 B7 B7 B7 only carry visible organizers on the B7 chromosomes. In situ hybridization using ribosomal probe pTA71 was used to localize ribosomal cistrons. In polyploids the sites of hybridization are limited to the B7-derived nucleolar-organizer chromosomes and ribosomal cistrons have thus been deleted from the A genome. A NOR-associated C-band has also been deleted.

We sequenced the E gene and adjacent prM/M and NS1 junctions (1940 bp) of 48 Dengue-4 (DEN-4) isolates collected between 1981 and 1999 from 8 Caribbean islands and from 7 South and Central American countries. Phylogenetic analysis confirms a single introduction in the early 1980s and a high degree of gene flow resulting in a pattern of evolution defined more by time period than geographic origin, especially within the Caribbean basin. A modern Caribbean clade consisting of four distinct lineages has arisen, comprised of isolates from Caribbean islands and nearby regions of South America. This clade is defined by three amino acid substitutions in the E (aa 163 and 351) and NS1 (aa 52) proteins. These findings highlight the importance of migration and gene flow in dengue viral change and suggest that efforts to understand disease dynamics in the Caribbean basin need to focus at regional, rather than local scales.

Scilla autumnalis, a bulbaceous perennial member of the Liliaceae, is widespread throughout much of Europe and North Africa. So far it has been classified as a single species, primarily on morphological grounds. This paper reports 10 cytologically distinct races of the plant present over the range of distribution, and hypothesizes the existence, at least at some stage of the evolution of the complex, of two additional races. At least five distinct genornes are described, involving chromosomal rearrangements, changes in DNA amount and three levels of ploidy. A picture of the evolutionary relationships of the cytotypes is suggested.

There is growing evidence that the integration of mitochondrial DNA sequences into nuclear and chloroplast genomes of higher organisms may be widespread rather than exceptional. We report the localization of 18S-25S rDNA and mitochondrial DNA sequences to meiotic chromosomes of several orthopteran species using in situ hybridisation. The cytochrome oxidase I (COI) sequence localizes to the centromeric and two telomeric regions of the eight bivalents of Chorthippus parallelus, the telomeric regions in Schistocerca gregaria and is present throughout the genome of Italopodisma sp. (Orthoptera: Acrididae). The control region of the mitochondrion and COI localize to similar chromosomal regions in S. gregaria. These data explain sequencing data that are inconsistent with the COI sequence being solely mitochondrial. The different nuclear locations of mtDNA in the different genera studied suggest that grasshopper mtDNA-like sequences have been inserted into the nuclear genome more than once in Acridid history, and there may have been different mechanisms involved when these events occurred in each of these species.Key words: Schistocerca gregaria, Italopodisma spp., Chorthippus parallelus, in situ hybridisation, mitochondrial DNA, genome organization.