Summary Mammalian karyotypes (number and structure of chromosomes) can vary dramatically over short evolutionary time frames [1–3]. There are examples of massive karyotype conversion, from mostly telocentric (centromere terminal) to mostly metacentric (centromere internal), in 102–105 years [4, 5]. These changes typically reflect rapid fixation of Robertsonian (Rb) fusions, a common chromosomal rearrangement that joins two telocentric chromosomes at their centromeres to create one metacentric [5]. Fixation of Rb fusions can be explained by meiotic drive: biased chromosome segregation during female meiosis in violation of Mendel’s First Law [3, 6, 7]. However, there is no mechanistic explanation of why fusions would preferentially segregate to the egg in some populations, leading to fixation and karyotype change, while other populations preferentially eliminate the fusions and maintain a telocentric karyotype. Here we show, using both laboratory models and wild mice, that differences in centromere strength predict the direction of drive. Stronger centromeres, manifested by increased kinetochore protein levels and altered interactions with spindle microtubules, are preferentially retained in the egg. We find that fusions preferentially segregate to the polar body in laboratory mouse strains when the fusion centromeres are weaker than those of telocentrics. Conversely, fusion centromeres are stronger relative to telocentrics in natural house mouse populations that have changed karyotype by accumulating metacentric fusions. Our findings suggest that natural variation in centromere strength explains how the direction of drive can switch between populations. They also provide a cell biological basis of centromere drive and karyotype evolution.

Introduction: Morphological integration and modularity depend on genetic covariation between traits, which emerges from pleiotropic effects of single loci and genetic linkage between loci. Since chromosomal reorganizations alter meiotic recombination, they might modify groups of linked genes and entail the fixation of new alleles with new pleiotropic effects. As a result, they could contribute to the intraspecific variation of the covariance structure of morphological traits. Although the mouse mandible has long been studied in terms of development and evolution, little is known about how its covariance structure varies in natural populations with chromosomal reorganizations. Consequently, here we analyzed the magnitude and patterns of morphological covariation of mandible shape in groups of mice with different karyotypes from a Robertsonian system of Mus musculus domesticus. Results: The organization of the mouse mandible into two main modules was confirmed in all chromosomal groups, since RV coefficients for the corresponding subdivision of landmarks were always significant. However, substantial variation in the magnitude of integration was detected between groups, especially when the effect of allometry was not removed. A significant positive correlation between differences in magnitude of integration of the symmetric component of shape and karyotypic distances between groups was detected when not correcting for size. Moreover, the degree of dependence of symmetric shape variation on size showed a negative association with the chromosome number and a positive association with the magnitude of integration. All groups showed similar patterns of morphological integration of the mandible, especially regarding the symmetric component of shape. However, the display of landmark displacements and the computation of vector angles highlighted some differences. In addition, distances between groups in terms of covariation matrices of the symmetric component were positively correlated with geographic distance. Conclusions: Robertsonian translocations do not alter the organization of the mouse mandible into two main modules, but do affect the magnitude of integration between them. This effect is mainly due to changes in the allometric relationship. In the 'Barcelona' Robertsonian system, geographically structured sources of variation seem to affect the patterns of integration by producing parallel variation in separate developmental pathways. Overall, our results suggest that Robertsonian translocations could play a role in intraspecific differentiation processes by producing changes in the covariance structure of morphological traits.

P. (2017). Molecular data and ecological niche modelling reveal the evolutionary history of the common and Iberian blind moles (Talpidae) in Europe. -Zoologica Scripta, 46, 12-26. According to mitochondrial data, the common mole, Talpa europaea, is paraphyletic. This could be explained by either an ancient introgression of mtDNA from the Iberian blind mole T. occidentalis to T. europaea, or the existence of a differentiated taxonomic entity in northern Spain that needs to be described. In this study, we combined mitochondrial (Cytb) and nuclear (HDAC2) data to investigate these two alternative hypotheses. Based on both mitochondrial and nuclear data and an extensive geographical sampling (399 sequenced individuals), we show that the populations of T. europaea from Spain and south-western France (south of the Loire River) are phylogenetically closer to T. occidentalis than to T. europaea. The Spanish-French lineage has some morphological characters resembling more to T. occidentalis (e.g. eyes) and others resembling more to T. europaea (external measurements, mesostyle of the first upper molar). It also seems to have several distinctive dental characters, suggesting that it should be recognized as a new species. Within the three lineages, we found a marked phylogeographical pattern, with several allopatric or parapatric lineages, dating from the Pleistocene. Our genetic data combined with species distribution models support the presence of several putative glacial refugia during glacial maxima for each species.

Comparative information on the variation in the temporospatial patterning of mandible growth in wild and laboratory mice during early postnatal ontogeny is scarce but important to understand variation among wild rodent populations. Here, we compare mandible growth between two ontogenetic series from the second to the eighth week of postnatal life, corresponding to two different groups of mice reared under the same conditions: the classical inbred strain C57BL/6J, and Mus musculus domesticus. We characterize the ontogenetic patterns of bone remodeling of the mandibles belonging to these laboratory and wild mice by analyzing bone surface, as well as examine their ontogenetic form changes and bimodular organization using geometric morphometrics. Through ontogeny, the two mouse groups display similar directions of mandible growth, according to the temporospatial distribution of bone remodeling fields. The allometric shape variation of the mandibles of these mice entails the relative enlargement of the ascending ramus. The organization of the mandible into two modules is confirmed in both groups during the last postnatal weeks. However, especially after weaning, the mandibles of wild and laboratory mice differ in the timing and localization of several remodeling fields, in addition to exhibiting different patterns of shape variation and differences in size. The stimulation of dentary bone growth derived from the harder post-weaning diet might account for some features of postnatal mandible growth common to both groups. Nonetheless, a large component of the postnatal growth of the mouse mandible appears to be driven by the inherent genetic programs, which might explain between-group differences.

Une étude, basée sur le mtDNA, de la génétique des populations de taupes récemment capturées en France nous a permis de découvrir une espèce nouvelle, Talpa aquitania nov. sp. Nous donnons ici une description préliminaire de la nouvelle espèce et de sa distribution. Cette dernière couvre une région se situant au sud et à l'ouest du cours de la Loire et, au-delà des Pyrénées, dans le nord de la péninsule ibérique.Mots clefs : taupe, Talpa aquitania nov. sp., mtDNA, France, Espagne. Résumé(1) Institut de Systématique, Evolution, Biodiversité, ISYEB UMR 7205 -CNRS, MNHN, UPMC, EPHE, Muséum National d'Histoire Naturelle, Sorbonne Universités, Paris, France.(2) Departament de Biologia Animal, de Biologia Vegetal i d'Ecologia, Facultat de Biociències, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Cerdanyola del Vallès), Barcelona, Spain. A mtDNA based study of the population genetics of moles recently captured in France allowed us to discover a new species, Talpa aquitania nov. sp. We are giving here a preliminary description of the new species. Its distribution covers an area lying south and west of the course of the Loire river in France and beyond the Pyrenees, a part of Northern Spain.Key words: mole, Talpa aquitania nov. sp., mtDNA, France, Spain. AbstrAct INTRODUCTIONFrom March 2012 to March 2015, moles were collected in different localities in France for which we obtained at least partial mtDNA sequences. The Bayesian analysis of the Cytb-mtDNA sequences presented in a previous publication (Hugot et al., 2014) revealed that a part of the French and Spanish specimens of Talpa europaea (60 individuals: 21 males, 39 females) constituted a distinct lineage closely associated but divergent from the specimens of the Iberian mole T. occidentalis Cabrera, 1907, included in the analyses This result strongly suggested that these specimens may belong to a different and not yet described species. A further examination of the external morphology and characters of the upper M1 mesostyle confirmed this hypothesis. In this preliminary note we define this lineage as a new mole species: Talpa aquitania nov. sp. MATERIAL AND METHODSThe field collection numbers, name of the collectors, localities of collection and measurements of the specimens are given in table 3 (annex 1). The methods for collecting moles, mtDNA sequencing, alignment and phylogenetic analysis are described in details in Hugot et al., (2014). The study of the anatomical characters and the measurements of the skulls were performed using the "Microvu Vertex 251 HC" of the Morphometric Platform of the Museum National d'Histoire Naturelle of Paris. Habitat of holotype specimenSubterranean area close to a private garden. DistributionWest and south to the Loire river and extending to northern Spain Derivation nominisThis name is given in reference to the ancient Roman province of Aquitania, created by August in 27 BC. DiagnosisThe mitochondrial analysis (Hugot et al., 2014, Feuda et al., 2015 CONCLUSIONSWe consider that the results of our preliminar...

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Bicuspid aortic valve (BAV) is the most prevalent human congenital cardiac malformation. It may appear isolated, associated with other cardiovascular malformations, or forming part of syndromes. Cranial neural crest (NC) defects are supposed to be the cause of the spectrum of disorders associated with syndromic BAV. Experimental studies with an inbred hamster model of isolated BAV showed that alterations in the migration or differentiation of the cardiac NC cells in the embryonic cardiac outflow tract are most probably responsible for the development of this congenital valvular defect. We hypothesize that isolated BAV is not the result of local, but of early alterations in the behavior of the NC cells, thus also affecting other cranial NC-derived structures. Therefore, we tested whether morphological variation of the aortic valve is linked to phenotypic variation of the mandible and the thymus in the hamster model of isolated BAV, compared to a control strain. Our results show significant differences in the size and shape of the mandible as well as in the cellular composition of the thymus between the two strains, and in mandible shape regarding the morphology of the aortic valve. Given that both the mandible and the thymus are cranial NC derivatives, and that the cardiac NC belongs to the cephalic domain, we propose that the causal defect leading to isolated BAV during embryonic development is not restricted to local alterations of the cardiac NC cells in the cardiac outflow tract, but it is of pleiotropic or polytopic nature. Our results suggest that isolated BAV may be the forme fruste of a polytopic syndrome involving the cranial NC in the hamster model and in a proportion of affected patients.

Sperm morphology reflects a long process of adaptation to external conditions and the barriers encountered before ova fertilization can take place; however, not all morphological variation found in gametes can be explained by the effects of these selective forces, as the genetic component may also contribute to the establishment of different gametic features. In north-eastern Spain, there is a wide Robertsonian system of Mus musculus domesticus, where individuals with 2n ranging from 27 to 40 chromosomes have been described. To elucidate the effect of the karyotype on sperm head form, a comparative analysis between different chromosomal groups of mice from this zone was carried out. Sperm heads from eight St (2n = 40) and 24 Rb (2n = 30-39) males were processed for scanning electron microscopy and analysed using geometric morphometric techniques. Canonical variate analyses showed substantial shape differences between St and Rb mice in the ventral spur region and between Rb groups in the post-acrosomal region. Significant differences in sperm head size were also detected between chromosomal groups. Structural disorders related to spermatogenesis, genetic alterations, and epistatic interactions among loci are probably involved in the relationship between the phenotypic variation of the sperm head and Rb translocations.