A cytogenetic study of the leaf beetle genus Cyrtonus (Coleoptera, Chrysomelidae).

The chromosomes of ten species of Cyrtonus and the genome sizes of six are surveyed. Among the total of 15 chromosomally studied species, 11 have 2n = 28 chromosomes and a 13 + Xyp male meioformula, three have 2n = 40 and 19 + Xyp and one 2n = 46 and 22 + Xyp. All but one species with 28 chromosomes show only metacentric or submetacentric chromosomes, whereas the species with 40 and 46 chromosomes display some telocentrics or subtelocentrics, that are probably derived from the former by centric fissions. However, since the number of major chromosome arms is strikingly higher in these latter species (NF = 70 and 78) than in the 28-chromosome species (mostly NF = 56), other chromosomal rearrangements such as pericentric inversions or heterochromatin accretions could also be involved. The genome sizes display a narrow range, from 1C = 0.6-1.22 pg, and they are not significantly correlated with the chromosome numbers. Some possible factors implied in the rough chromosomal evolution of Cyrtonus are discussed in relation to a few other genera of the subfamily Chrysomelinae.

Satellite DNA in the elm leaf beetle, Xanthogaleruca luteola (Coleoptera, Chrysomelidae): characterization, interpopulation analysis, and chromosome location.

In this paper the satellite DNA (stDNA) of the phytophagous beetle Xanthogaleruca luteola is analyzed. It is organized in a tandem repeat of 149-bp-long monomers, has an AT content of 59%, and presents inverted internal repeats. Restriction analysis of the total DNA with methylation-sensitive enzymes suggests that this repetitive DNA is not methylated. Analysis of the electrophoretic mobility of stDNA on non-denaturing polyacrylamide gels showed that this stDNA is not curved. In situ hybridization with a biotinylated probe of the stDNA revealed a pericentromeric localization of these sequences in the majority of the meiotic bivalents. We have studied the stDNA of X. luteola from two populations with very distinct geographical origins. The sequence and phylogenetic analysis of monomers from these two populations showed that the repetitive element is conserved within the species. Putative gene conversion tracts are identified when the different monomers of the same population are compared. These results could indicate the existence of processes of homogenization that would extend these mutations to all the satellite repeats.

Characterization and chromosome location of satellite DNA in the leaf beetle Chrysolina americana (Coleoptera, Chrysomelidae).

This paper is the first record of the satellite DNA of the specialized phytophagous genus Chrysolina. The satellite DNA of Chrysolina americana is organized in a tandem repeat of monomers 189 bp long, has a A + T content of 59.6% and presents direct and inverted internal repeats. Restriction analysis of the total DNA with methylation sensitive enzymes suggests that this repetitive DNA is undermethylated. In siti hybridization with a biotinylated probe of the satellite DNA showed the pericentromeric localization of these sequences in all meiotic bivalents. The presence of this repetitive DNA in other species of the genus was also tested by Southern analysis. The results showed that this satellite DNA sequence is specific to the C. americana genome and has not been found in three other species of Chrysolina with a different choice of host plants than in the former.