Abstract
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 phy- logeny 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 subfami- lies 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 Arach- nocorini. Combining karyosystematic data with the phylogeny of the family indicated that the ancestral karyotype was a high chro- mosome 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.
Highlights
Nabidae is a relatively small bug family with 20 genera and approximately 400 species
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
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
Summary
Nabidae is a relatively small bug family with 20 genera and approximately 400 species. The representatives of this family are distributed throughout the world. According to Kerzhner (1981, 1996), the family Nabidae consists of four subfamilies: Velocipedinae, Medocostinae, Prostemmatinae (two tribes), and Nabinae (four tribes). The Nabinae and Prostemmatinae are sister groups. In contrast to Kerzhner, Schuh & Štys (1991) consider the first two subfamilies to be separate families. They based this concept on labial and membrane venation characters and the presence of Ekblom’s organ in nabids
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