Biomedical subjects

Jean-Christophe Auffray

Publications and source records attributed to Jean-Christophe Auffray.

7 recordsLinked to original sources

PubMed2006

Conserved phenotypic variation patterns, evolution along lines of least resistance, and departure due to selection in fossil rodents.

Within a group of organisms, some morphologies are more readily generated than others due to internal developmental constraints. Such constraints can channel evolutionary changes into directions corresponding to the greatest intraspecific variation. Long-term evolutionary outputs, however, depend on the stability of these intraspecific patterns of variation over time and from the interplay between internal constraints and selective regimes. To address these questions, the relationship between the structure of phenotypic variance covariance matrices and direction of morphological evolution was investigated using teeth of fossil rodents. One lineage considered here leads to Stephanomys, a highly specialized genus characterized by a dental pattern supposedly favoring grass eating. Stephanomys evolved in the context of directional selection related to the climatic trend of global cooling causing an increasing proportion of grasslands in southwestern Europe. The initial divergence (up to approximately 6.5 mya) was channeled along the direction of greatest intraspecific variation, whereas after 6.5 mya, morphological evolution departed from the direction favored by internal constraints. This departure from the "lines of least resistance" was likely the consequence of an environmental degradation causing a selective gradient strong enough to overwhelm the constraints to phenotypic evolution. However, in a context of stabilizing selection, these constraints actually channel evolution, as exemplified by the lineage of Apodemus. This lineage retained a primitive diet and dental pattern over the last 10 myr. Limited morphological changes occurred nevertheless in accordance with the main patterns of intraspecific variation. The importance of these lines of least resistance directing long-term morphological evolution may explain parallel evolution of some dental patterns in murine evolution.

Animals↗

PubMed2005

Chromosomal phylogeny of Robertsonian races of the house mouse on the island of Madeira: testing between alternative mutational processes.

The ancestral karyotype of the house mouse (Mus musculus) consists of 40 acrocentric chromosomes, but numerous races exist within the domesticus subspecies characterized by different metacentric chromosomes formed by the joining at the centromere of two acrocentrics. An exemplary case is present on the island of Madeira where six highly divergent chromosomal races have accumulated different combinations of 20 metacentrics in 500-1000 years. Chromosomal cladistic phylogenies were performed to test the relative performance of Robertsonian (Rb) fusions, Rb fissions and whole-arm reciprocal translocations (WARTs) in resolving relationships between the chromosomal races. The different trees yielded roughly similar topologies, but varied in the number of steps and branch support. The analyses using Rb fusions/fissions as characters resulted in poorly supported trees requiring six to eight homoplasious events. Allowance for WARTs considerably increased nodal support and yielded the most parsimonious trees since homoplasy was reduced to a single event. The WART-based trees required five to nine WARTs and 12 to 16 Rb fusions. These analyses provide support for the role of WARTs in generating the extensive chromosomal diversification observed in house mice. The repeated occurrence of Rb fusions and WARTs highlights the contribution of centromere-related rearrangements to accelerated rates of chromosomal change in the house mouse.

Animals↗

PubMed2005

Morphological evolution, ecological diversification and climate change in rodents.

Among rodents, the lineage from Progonomys hispanicus to Stephanomys documents a case of increasing size and dental specialization during an approximately 9 Myr time-interval. On the contrary, some contemporaneous generalist lineages like Apodemus show a limited morphological evolution. Dental shape can be related to diet and can be used to assess the ecological changes along the lineages. Consequently, size and shape of the first upper molar were measured in order to quantify the patterns of morphological evolution along both lineages and compare them to environmental trends. Climatic changes do not have a direct influence on evolution, but they open new ecological opportunities by changing vegetation and allow the evolution of a specialist like Stephanomys. On the other hand, environmental changes are not dramatic enough to destroy the habitat of a long-term generalist like Apodemus. Hence, our results exemplify a case of an influence of climate on the evolution of specialist species, although a generalist species may persist without change.

Analysis of Variance↗

PubMed2004

[A new species of wild mice on the Island of Cyprus].

A mitochondrial and nuclear gene analysis allowed us to precise the taxonomical position of the two sympatric species of mice known to be present on Cyprus. One of them is the commensal house mouse M. m. domesticus, and the other revealed to be a new taxon that is a sister species of M. spicilegus and M. macedonicus. The new species is equidistant from each of these, the divergence dating around 0.5-1 Myr. Its origin either results from an ancient accidental colonisation of the island or from a recent transportation by the first epipalaeolithic settlers. In this last eventuality, the new species would also exist somewhere else in Asia Minor.

Animals↗

PubMed2004

Ecological correlates and evolutionary divergence in the skull of turtles: a geometric morphometric assessment.

Resource use and phylogeny are often correlated with morphological variation. Moreover, because biological shapes are often complex and evolve depending on several internal constraints, they must be assessed using integrative methods. We analyzed the morphological variation of the turtle skull in the context of an adaptive radiation. Our focus are turtles of the superfamily Testudinoidea, which are remarkably diverse, both in number of species and in ecology. In this study, we depict morphological variation in the turtle skull in three dimensions with respect to diet, phylogeny, and habitat using modern geometric morphometrics. Our study revealed that morphological specialization was related to both diet and habitat. Morphological variation is decomposed in regard of both resource use (habitat and diet) and phylogeny. Feeding mode depending on environment was suggested as a key factor determining morphological evolution and diversification of turtle skulls. Diet (especially durophagy) leads to parallel morphologies in different clades. Phylogeny seemed to constrain only localized features of the skull and remained of minor influence, because overall morphotypes, closely correlated with ecological factors, occurred in both clades. In conclusion, the adaptive radiation of the Testudinoidea is revealed to demonstrate a clear relationship between the skull shape and life style.

Adaptation, Physiological↗

PubMed2003

The non-random occurrence of Robertsonian fusion in the house mouse.

Chromosomal rearrangements such as Robertsonian (Rb) fusions constitute a major phenomenon in the evolution of genome organization in a wide range of organisms. Although proximate mechanisms for the formation of Rb fusion are now well identified, the evolutionary forces that drive chromosomal evolution remain poorly understood. In the house mouse, numerous chromosomal races occur in nature, each defined by a unique combination of Rb fusions. Among the 106 different Rb fusions that were reported from natural populations, the low involvement of chromosome 19 in Rb fusions is striking, prompting the question of the randomness of chromosomal involvement in Rb fusions. We uncover a significant quadratic relationship between chromosome size and probability of fusing, which has never previously been in this species. It appears that fusions involving chromosome 19 are not particularly infrequent, given the expected low fusion probability associated with the chromosome's size. The results are discussed, assessing selective processes or constraints that may operate on chromosome size.

Animals↗

PubMedDate not supplied

Developmental integration in a complex morphological structure: how distinct are the modules in the mouse mandible?

The mouse mandible has long served as a model system for studying the development and evolution of complex morphological structures. We used the methods of geometric morphometrics to reassess the hypothesis that the mandible consists of two separate modules: an anterior part bearing the teeth and a posterior part with muscle attachment surfaces and articulating with the skull. The analyses particularly focused on covariation of fluctuating asymmetry, because such covariation is due exclusively to direct interactions between the developmental processes that produce the traits of interest, whereas variation of traits among individuals also reflects other factors. The patterns of fluctuating asymmetry and individual variation were only partly consistent, indicating that developmental processes contribute differentially to variation at different levels. The results were in agreement with the hypothesis that the anterior and posterior parts of the mandible are separate develop-mental modules. Comparison of all alternative partitions of the landmarks into two contiguous subsets confirmed the hypothesis for the location of the boundary between modules but also underscored that the separation between them is not complete. Modularity is therefore manifest as the relative independence of parts within the framework of overall integration of the mandible as a whole-it is a matter of degrees, not all or nothing.

Analysis of Variance↗