Search

International audience; The role of chromosomal rearrangements in disturbing reproduction in hybrids between karyotypically differentiated groups is fairly well documented. However, the effect of chromosomal changes at other phenotypic levels is rarely considered. In Tunisia, natural chromosomal hybrids of the house mouse exhibit developmental instability, suggesting that a high karyotypic heterozygosity might also affect developmental processes. If this is true, we predict that, in this species, developmental instability should arise in hybrids between any populations with a high chromosomal differentiation. To test this hypothesis, we compare the results obtained in Tunisian mice with those obtained in the present analysis on Madeiran mice. Both systems of races have similar levels of chromosomal differentiation (nine Robertsonian fusions). Unlike Tunisian mice, hybrids in Madeira display a similar level of developmental instability as parental groups. This indicates that structural heterozygosity per se does not necessarily impair developmental stability. It further suggests that chromosomal fusions are not all equivalent in their phenotypic effects, and that the identity of each fusion should be taken into account.

The divergence in reproductive features and hybrid fertility patterns between two chromosomal races (2 n = 40, 40St, and 2 n = 22, 22Rb) of the house mouse in Tunisia were re-assessed on a larger sample of wild and laboratory-bred individuals than studied hitherto. Results showed that litter sizes were significantly smaller in 40St than in 22Rb mice, contrary to previous analyses. This suggests that variation in litter size between the two chromosomal races is more likely related to selective and/or environmental factors acting locally than to interracial reproductive trait divergence. However, the significantly reduced litter size of F 1 hybrids compared with parental individuals was confirmed, and further highlighted a sex difference in hybrid infertility, as F 1 females produced fewer litters and of smaller size than males. Histological analyses of F 1 and backcrosses showed a breakdown of spermatogenesis in males and a significantly reduced primordial follicle pool in females. The degree of gametogenic dysfunction was not related to the level of chromosomal heterozygosity per se , but a significant effect of two Rb fusions on follicle number was observed in hybrid females. These results suggest that genetic incompatibilities contribute to primary gametogenic dysfunction in hybrids between the chromosomal races in Tunisia.

Gündüz, İslam (Balikesir Author), To study the colonization history of the house mouse (Mus musculus domesticus) on the Madeiran archipelago, complete mitochondrial D-loop sequences were obtained for 44 individuals from Madeira, Porto Santo and Ilhas Desertas. Altogether, 19 D-loop haplotypes were identified which formed part of a single clade in a phylogeny incorporating haplotypes from elsewhere in the range of M. m. domesticus, indicating that the Madeiras were colonized from a single source. Similarities between the sequences found in the Madeiras and those in Scandinavia and northern Germany suggest that northern Europe was the source area, and there is the intriguing possibility that the Vikings may have accidentally brought house mice to the archipelago. However, there is no record of Vikings visiting the Madeiras; on historical grounds, Portugal is the most likely source area for Madeiran mice and further molecular data from Portugal are needed to rule out that possibility.

International audience; The amplified esterase B gene responsible for resistance to organophosphorus insecticides in Culex mosquitoes is shown to form a DNA ''puff'' in salivary gland polytene chromosomes. This ''puff'' is absent in susceptible mosquitoes lacking the amplified gene, and unlike all puffs known today, it is neither related to development nor involved in protein synthesis. The ''puff'' therefore corresponds to a special arrangement of the very large number of copies (possibly up to 250,000) of the 25-30-kb DNA fragment encompassing the esterase B structural gene in polytene chromosomes. In addition, the amplified and nonamplified esterase B gene(s) were found to be localized on chromosome 2L, and flanked by identical banding patterns, indicating the absence of an important chromosome rearrangement before, during, or after gene amplification.

The ecological requirements of two species of shrews, the Greater Whitetoothed Shrew (Crocidura russula) and the Lesser White-toothed Shrew (Crocidura suaveolens) were compared in Southern France and Corsica. Both species are shown to differ in their ecophysiology. However, their fundamental niches are not fully realized when the two species coexist, which suggests some kind of competition between the two. This view is supported by the fact that the two shrew species are very seldom met together at a same traping site on the mainland, and by the larger size of C. suaveolens in Corsica, where C. russula does not occur., L’écologie comparée des populations de Crocidura russula et de Crocidura suaveolens dans le midi de la France et en Corse, a permis de mettre en évidence des besoins éco-physiologiques différents pour ces deux espèces. Toutefois, la comparaison de populations continentales et insulaires a montré que la niche potentielle de chacune d’entre elles était également limitée par la présence de l’autre. On en conclut qu’il existe une compétition interspécifique active. Cette hypothèse est renforcée par la quasi exclusion spatiale des deux espèces à l’échelle de la station et l’augmentation importante de la taille de l’espèce la plus petite (Crocidura suaveolens) en condition insulaire où cette compétition n’existe pas., Poitevin F.,Catalan Josette,Fons Roger,Croset Henri. Biologie évolutive des populations Ouest-Européennes de Crocidures (Mammalia, Insectivora). II. — Ecologie comparée de Crocidura russula Hermann, 1780 et de Crocidura suaveolens Pallas, 1811 dans le midi de la France et en Corse : rôle probable de la compétition dans le partage des milieux. In: Revue d'Écologie (La Terre et La Vie), tome 42, n°1, 1987. pp. 39-58.