MHC genotype predicts mate choice in the ring-necked pheasant Phasianus colchicus.

Females of several vertebrate species selectively mate with males on the basis of the major histocompatibility complex (MHC) genes. As androgen-mediated maternal effects have long-lasting consequences for the adult phenotype, both mating and reproductive success may depend on the combined effect of MHC genotype and exposure to androgens during early ontogeny. We studied how MHC-based mate choice in ring-necked pheasants (Phasianus colchicus) was influenced by an experimental in ovo testosterone (T) increase. There was no conclusive evidence of in ovo T treatment differentially affecting mate choice in relation to MHC genotype. However, females avoided mating with males with a wholly different MHC genotype compared with males sharing at least one MHC allele. Females also tended to avoid mating with MHC-identical males, though not significantly so. These findings suggest that female pheasants preferred males with intermediate MHC dissimilarity. Male MHC heterozygosity or diversity did not predict the expression of ornaments or male dominance rank. Thus, MHC-based mating preferences in the ring-necked pheasant do not seem to be mediated by ornaments' expression and may have evolved mainly to reduce the costs of high heterozygosity at MHC loci for the progeny, such as increased risk of autoimmune diseases or disruption of coadapted gene pools.

Force-velocity and unloaded shortening velocity during graded potassium contractures in frog skeletal muscle fibres.

Steady-state conditions of contraction, at maximal and submaximal forces, were produced in intact single muscle fibres, from Rana esculenta, using full tetani and graded K+-contractures. The uniformity in radial direction. of spreading of activation produced in K+-contractures, was checked in relation to the fibre diameters. The absolute isometric force was similar in tetani and maximal contractures, for fibres with diameters between 40 and 60 microm, but not for fibres with diameters greater than about 70 microm in which contracture force never reached tetanic force. The force [K+]o relation was similar for fibres with diameters between 40 and 60 microm. but it was right shifted and it had a minor slope for fibres with diameters greater than 65-70 microm. This suggests that only in the small diameter fibres (40-60 microm) the activation does not fail to penetrate uniformly from the surface towards the fibre core. For fibres selected in the diameter range between 40 and 60 microm, force-velocity relations and unloaded shortening velocities were determined in tetani and maximal and submaximal contractures. Data were obtained across a force range of 0.3 to 1 P0 (tetanic plateau force). Controlled velocity method was used to obtain force-velocity relations, and slack test to determine the unloaded shortening velocity (VU). The values of the parameters characterising the force velocity relation (V0 and a/P0) and VU as determined by the slack test did not differ significantly in tetani and contractures, independent of the activation level or absolute force developed by the fibre. These results show that. at least within the range of forces tested. crossbridge kinetics is independent of the number of cycling crossbridges, in agreement with the prediction of the 'recruitment' model of myofilament activation.

Genome flux in tomato cell clones cultured in vitro in different physiological equilibria. II. A RAPD analysis of variability.

An analysis of the effect of changing physiological conditions on genome evolution in tomato cell populations has been carried out on long-term in vitro cultured clones grown on different auxin-cytokinin equilibria or selected for low-high competence for active defense against Fusarium oxysporum f.sp. lycopersici. RAPD analysis, confirmed through pattern rehybridization, was used as a random tool to measure the genetic variability. Through the use of a modified ANOVA, variation was shown to depend on both the initial genotype and the physiological conditions. Pattern correlation analysis through a mutual information algorithm suggested the fixation of RAPD patterns specific to physiological equilibria. The results are discussed in view of the possible relevance for evolution at hierarchical levels higher than cell populations. Key words : tomato clones, somaclonal variation, RAPD, coadaptation.