N. Henriques-Gil

Evolution of a complex B-chromosome polymorphism in the grasshopper Eyprepocnemis plorans

B-chromosome systems in several Spanish natural populations of Eyprepocnemis plorans are reported. The geographical distributions of the fourteen types of B chromosomes, which were classified according to size, C-banding pattern, and meiotic behaviour, are described. The results indicate a common origin for most types and a possible independent origin for a few secondary B variants. The origin and mechanisms of evolution of this B chromosome polymorphism are discussed.

Spontaneous translocations between B chromosomes and the normal complement in the grasshopper Eyprepocnemis plorans

A translocation between a B chromosome and a medium-size autosome and a centric fusion between the B and the X chromosome were found in two different natural populations of Eyprepocnemis plorans. The cytological behaviour of both interchanges is described and discussed. These interchanges are highly asymmetrical and may be the beginning of an integration of B chromosomes into the genome of this species.

Mitochondrial DNA sequence variability in red-legged partridge, Alectoris rufa, Spanish populations and the origins of genetic contamination from A. chukar

The analysis of 135 mitochondrial D-loop sequences of the Iberian autochthonous red-legged partridge (Alectoris rufa) from wild population hunting bags from various locations and fowl runs in Spain yielded 37 different haplotypes. Among these, three haplotypes correspond to chukar partridges (Alectoris chukar), indicating genetic introgression from birds illegally introduced for restocking: three individuals carrying such haplotypes where found in natural populations, one appeared among those sampled on a mass reproduction farm and the remaining 10 in another fowl-run. The geographical origin of the contaminating chukar haplotypes could be assigned to the most easterly area of the chukar partridge geographical distribution in China. Molecular diversity parameters in the A. rufa samples indicate a considerable amount of genetic variation. ΦST showed significant differences among populations that are not explained by geographical distance alone. Particularly, one northern population (Palencia) shows a certain degree of genetic differentiation that could reflect a previously suggested subspecies division.

The effect of B chromosomes on mating success of the grasshopper Eyprepocnemis plorans

The mating ability of E. plorans was tested in laboratory conditions in six experimental units composed of ten males and fifteen females during 31 days. When significant differences were found (three from the six cages, and in totals) they involved a decrease of matings involving males with B chromosomes. The same tendency seems to exist in females, but to a lesser extent, so that a significant effect is only detected when the totals are considered. Accessory chromosomes also delay, in both sexes, the occurrence of the first mating. No mating preferences depending on the number of Bs were detected.

Centromere co-orientation in a spontaneous translocation heterozygote of Euchorthippus pulvinatus gallicus (Acrididae, Orthoptera)

The co-orientation of a quadrivalent in an individual of E. pulvinatus gallicus heterozygous for a reciprocal translocation is studied. The data agree with the hypothesis that the co-orientation behaviour of two adjacent centromeres in a quadrivalent depends on the relative distance between them at metaphase I, this distance being determined by chiasmata.

Sex-dependent meiotic behaviour of B chromosomes in the grasshopper Eyprepocnemis plorans

The meiotic behaviour of B chromosomes differs strongly between males and females of Eyprepocnemis plorans. In anaphase I of oogenesis the Bs always divide equationally though this segregation may become more or less aborted and a number of different secondary oocytes can be formed. In contrast, equational divisions of accessories in male meiosis are rare. This peculiar behaviour of B chromosomes in the females does not seem to be associated with accumulation or loss.

Interference relationships in grasshopper reciprocal translocation heterozygotes

Chiasma formation in four different reciprocal translocations in the grasshopper Eyprepocnemis plorans (2 n♂ =22+ X) is analysed using C-banding. A given chromosome involved in an interchange is sometimes identifiable in standard homozygotes so that changes in its formation of chiasmata may be estimated. The involvement of M9 chromosome in an interchange slightly reduces its mean chiasma frequency but interference is significatively reduced too. When interference relationships between arms are analysed in the interchanges, independence as well as interference may occur, the interference being positive between adjacent arms and negative between opposite arms. A parallel analysis at pachytene reveals synaptic failure affecting mainly small regions. These results are discussed under Sybengas (1970) model for interference relationships within quadrivalents.

The relationship between chiasma frequency and bivalent length: Effects of genotype and supernumerary chromosomes

In the grasshopper Eyprepocnemis plorans familial and individual genotypes have significant effects either on chiasma frequency or on bivalent length; the effect of B chromosomes depends on the particular family considered which derives in the absence of an overall effect of supernumeraries. This study confirms previous reports in that there is a significant positive correlation between chiasma frequency and bivalent length operating at a cellular rather than specific bivalent level. Nevertheless, the correlation between both variables is scarcely affected when the contributions of the different factors are eliminated. In addition, the effects of B chromosomes within the different families on chiasma frequencies are not parallel to the correspondent effects on bivalent length. These facts indicate that, despite such correlation, the influence of B chromosomes or familial and individual genotypes on chiasma frequency does not operate through changes in chromosome length at first meiotic prophase.

Orientation behaviour of interchanges forming chiasmata in interstitial regions: a cytological approach

The orientation behaviour of three different interchanges in the grasshopper Eyprepocnemis plorans is cytologically analysed by means of C-banding. The formation of chiasmata in interstitial regions produces metaphase I configurations different to those described in interchanges lacking such chiasmata, including frequent unbalanced orientations. Cytological evidence of undescribed orientations and segregations is presented. The structural effects of interstitial chiasmata and the validity of the rules governing the orientation of interchanges are discussed.