The bug family Nabidae (Heteroptera) includes taxa showing either a low chromosome number 2n = 16 + XY or high chromosome numbers 2n = 26 or 32 + XY. In order to reveal the direction of karyotype evolution in the family, a molecular phylogeny of the family was created to reveal the taxon closest to the ancestral type and hence the ancestral karyotype. The phylogeny was based on a partial sequence of the 18S rDNA gene of both high and low chromosome number species belonging to the subfamilies Prostemmatinae and Nabinae. Phylogeny created by the Neighbour Joining method separated the subfamilies, Prostemmatinae and Nabinae, which form sister groups at the base of this phylogenetic tree, as well as within the Nabinae, tribes Nabini and Arachnocorini. Combining karyosystematic data with the phylogeny of the family indicated that the ancestral karyotype was a high chromosome number, consisting of 2n = 32 + XY. During the course of evolution changes have occurred both in meiotic behaviour of the sex chromosomes and in the number of autosomes. The direction of karyotype evolution was from a high to low autosome number. Abrupt decreases in the number of autosomes have occurred twice; firstly when the tribe Arachnocorini differentiated from the main stem in the subfamily Nabinae and secondly within the tribe Nabini, when within the genus Nabis 2n = 16 + XY species diverged from the 2n = 32 + XY species. A scheme of the sequence of events in karyotype evolution during the evolution of the Nabidae is presented.
The Galerucella nymphaeae species complex is a controversial group of leaf-consuming beetles with a Holarctic distribution. It includes several closely allied species or forms living in different habitats and utilizing different food plants. In northern Europe, two species are encountered, G. nymphaeae (L.) living on Nuphar, and G. sagittariae (Gyllenhal) living on semiaquatic or terrestrial plants, while all North American forms have been so far considered conspecific with the European G. nymphaeae. In the present study we have compared chorion polypeptides of the northern European G. nymphaeae and G. sagittariae with North American G. nymphaeae collected from Nuphar. The northern European G. nymphaeae was found to differ from both northern European G. sagittariae and North American G. nymphaeae, which were found to be virtually identical in respect to their chorion polypeptides. The present results, coupled with earlier data concerning e.g. egg morphology, structure of larval cuticle, and comparison of several life history traits, demonstrate that northern European G. nymphaeae and North American G. nymphaeae are not conspecific, and that the North American G. nymphaeae may be more closely allied to the northern European G. sagittariae.
As a part of ongoing cytogenetic studies on the bug family Nabidae (Heteroptera), the karyotypes and meiotic patterns of male Nabis (Aspilaspis) viridulus Spinola, 1837, N. (A.) indicus (Stål, 1873) (subfamily Nabinae) and Prostemma guttula (Fabricius, 1787) (subfamily Prostemmatinae) are described.
N. viridulus and N. indicus differ from P. guttula in their chromosome numbers, which are 2n = 32 + XY and 2n = 26 + XY, respectively, and behaviour of the sex chromosomes in male meiosis, which, respectively, show "distance pairing" and "touch-and-go pairing" in spermatocyte metaphase II. The karyotype of 2n = 34 and "touch-and-go pairing" are considered to be plesiomorphic characters in Nabidae. The evolutionary mechanisms that might underlie different chromosome numbers, the taxonomic significance of karyotype variation and the distribution of meiotic patterns in the family, are discussed.