p53 gene discriminates two ecologically divergent sister species of pine voles.

Genes with relevant roles in the differentiation of closely-related species are likely to have diverged simultaneously with the species and more accurately reproduce the species tree. The Lusitanian (Microtus lusitanicus) and Mediterranean (M. duodecimcostatus) pine voles are two recently separated sister species with fossorial lifestyles whose different ecological, physiological and morphological phenotypes reflect the better adaptation of M. duodecimcostatus to the underground habitat. Here we asked whether the differentiation of M. lusitanicus and M. duodecimcostatus involved genetic variations within the tumour suppressor p53 gene, given its role in stress-associated responses. We performed a population-genetic analysis through sequencing of exons and introns of p53 in individuals from sympatric and allopatric populations of both the species in the Iberian Peninsula in which a unidirectional introgression of mitochondrial DNA was previously observed. We were able to discriminate the two species to a large extent. We show that M. duodecimcostatus is composed of one genetically unstructured group of populations sharing a P53 protein that carries a mutation in the DNA-binding region not observed in M. lusitanicus, raising the possibility that this mutation may have been central in the evolutionary history of M. duodecimcostatus. Our results provide suggestive evidence for the involvement of a master transcription factor in the separation of M. lusitanicus and M. duodecimcostatus during Microtus radiation in the Quaternary presumably via a differential adaptive role of the novel p53 in M. duodecimcostatus.

Response of antioxidant enzymes in freshwater fish populations (Leuciscus alburnoides complex) to inorganic pollutants exposure.

Evidence is accumulating indicating the importance of antioxidant enzyme activity measurements in eco-toxicological studies, as they may constitute markers for exposure to a large variety of pollutants. Variation of antioxidant enzymes, superoxide dismutase (SOD) and glutathione S-transferases (GST) and the effect of heavy metals and selenium exposure on these enzymes were investigated in the livers of Iberian endemic minnows (Leuciscus alburnoides complex) captured in a copper (Cu) mining area. Higher hepatic levels of copper and selenium were always observed in fish captured at the polluted site relative to the reference area population, reflecting the environmental monitoring results. A seasonal fluctuation in zinc and selenium levels for both populations was also observed which could be related to gonad maturation. The activity of SOD did not show significant regional alterations, but a seasonal variation occurred presumably associated with the Leuciscus life cycle. The GST activity was higher in the fish population from the polluted area (except in spring) and GST variability was associated with selenium and copper levels when both regions were compared. The increased GST activity was probably a metabolic adaptation to the continuous exposure to higher levels of those elements.