Postnatal ontogeny of the femur in fossorial and semiaquatic water voles in the 3D-shape space.

Water voles of the genus Arvicola constitute an excellent subject to investigate to which extent function affects postnatal developmental growth of limb structures in phylogenetically close species. We performed a comparative analysis of postweaning femur form changes between Arvicola sapidus (semiaquatic) and Arvicola scherman (fossorial) using three-dimensional landmark-based geometric morphometrics. In both species, we observed greater femur robustness in juvenile individuals than in adult ones, probably due to the accommodation of high loads on the bone during initial locomotor efforts. Significant interspecific differences were also found in the femur size and shape of adult specimens, as well as in the postnatal allometric and phenotypic trajectories. In terms of phenotypic variation, fossorial water voles show relatively wider third and lesser trochanters, and greater femur robustness than A. sapidus, characters associated to the digging activity. In contrast, A. sapidus displays a slight increase of the greater trochanter in comparison with A. scherman, which is seemingly an adaptive response for enhancing propulsion through the water. Results evidence that certain morphological traits and differences between A. sapidus and A. scherman in the allometric and phenotypic trajectories of the femur are associated with their different locomotor mode.

Evidence of micro-evolution in Crocidura russula from two abandoned heavy metal mines: potential use of Cytb, CYP1A1, and p53 as gene biomarkers.

Heavy metals accumulated in the environment due to the mining industry may impact on the health of exposed wild animals with consequences at the population level via survival and selection of the most resistant individuals. The detection and quantification of shifts in gene frequencies or in the genetic structure in populations inhabiting polluted sites may be used as early indicators of environmental stress and reveal potential 'candidate gene biomarkers' for environmental health assessment. We had previously observed that specimens of the Greater white-toothed shrew (Crocidura russula) from two heavy metal mines in Southern Portugal (the Aljustrel and the Preguiça mines) carried physiological alterations compared to shrews from an unpolluted site. Here, we further investigated whether these populations showed genetic differences in genes relevant for physiological homeostasis and/or that are associated with pathways altered in animals living under chronic exposure to pollution, and which could be used as biomarkers. We analysed the mitochondrial cytochrome b (Cytb) gene and intronic and/or exonic regions of four nuclear genes: CYP1A1, LCAT, PRPF31, and p53. We observed (1) population differences in allele frequencies, types of variation, and diversity parameters in the Cytb, CYP1A1, and p53 genes; (2) purifying selection of Cytb in the mine populations; (3) genetic differentiation of the two mine populations from the reference by the p53 gene. Adding to our previous observations with Mus spretus, we provide unequivocal evidence of a population effect exerted by the contaminated environment of the mines on the local species of small mammals.

Population effects of heavy metal pollution in wild Algerian mice (Mus spretus).

Heavy metal mining is one of the largest sources of environmental pollution. The analysis of different types of biomarkers in sentinel species living in contaminated areas provides a measure of the degree of the ecological impact of pollution and is thus a valuable tool for human and environmental risk assessments. In previous studies we found that specimens from two populations of the Algerian mice (Mus spretus) living in two abandoned heavy metal mines (Aljustrel and Preguiça, Portugal) had higher body burdens of heavy metals, which led to alterations in enzymatic activities and in haematological, histological and genotoxic parameters, than mice from a nearby reference population. We have now analysed individuals from the same sites at the biometric and genetic levels to get a broader portrayal of the impact of heavy metal pollution on biodiversity, from molecules to populations. Size and shape variations of the mouse mandible were searched by implementing the geometric morphometric method. Population genetic differentiation and diversity parameters (φST estimates; nucleotide and haplotype diversities) were studied using the mitochondrial cytochrome b gene (Cytb) and the control region (CR). The morphometric analyses revealed that animals from the three sites differed significantly in the shape of the mandible, but mandibular shape varied in a more resembling way within individuals of both mine sites, which is highly suggestive for an effect of environmental quality on normal development pathways in Algerian mice. Also, antisymmetry in mandible size and shape was detected in all populations, making these traits not reliable indicators of developmental instability. Overall little genetic differentiation was found among the three populations, although pairwise φST comparisons revealed that the Aljustrel and the Preguiça populations were each differentiated from the other two populations in Cytb and in CR, respectively. Genetic diversity parameters revealed higher genetic diversity for Cytb in the population from Aljustrel, while in the population from Preguiça diversity of the two markers changed in opposite directions, higher genetic diversity in CR and lower in Cytb, compared to the reference population. Demographic changes and increased mutation rates may explain these findings. We show that developmental patterns and genetic composition of wild populations of a small mammal can be affected by chronic heavy metal exposure within a relatively short time. Anthropogenic stress may thus influence the evolutionary path of natural populations, with largely unpredictable ecological costs.