Dialectometry and Genetic Demography of Cystic Fibrosis. When Results Converge: The Case of Western Brittany

This article was born out of two separate approaches carried out independently of one another. The first dealt with genetic demography and the second with variational linguistics, aiming to study the population and language of Brittany from a certain perspective. In their recent study of the genetic history of France, Saint Pierre et al. show that Brittany “is substantially closer to the population from north-west Europe than to the north of France, in spite of both being equally geographically close” (2020: 863). They propose that the Bretons’ earliest ancestors could be the descendants of early Neolithic pastoralist nomads from the Steppes (SP) who would have arrived in Brittany (i.e. the ‘NW cluster’) via north-western Europe. The second hypothesis would support the idea of a more recent migration from northern Europe with high SP proportion, i.e., Celtic and/or Anglo-Saxon. Our initial hypothesis is that the convergences in linguistics and genetics may be explained by a unique historical event, namely, the Brittonic settlement of the Armorican peninsula from the 4th through at least the 7th centuries and perhaps as late as the 8th century. The application of linguistic distance measurements in the study of vernacular Breton varieties by means of a dialectometric analysis made it possible to observe clear correspondences between levels of linguistic similarity and the distribution of the genetic pools linked to cystic fibrosis. The convergence of our collective findings is most clearly manifested in the radical opposition of the north-western and the south-eastern zones of Breton-speaking Brittany in terms of the linguistic and genetic data. In our view, the scientific approach inherent to genetic and dialectometric research and the concordance of these data appear to not only reinforce many of the hypotheses advanced previously but to open new avenues for future research.

The scales of coevolution: comparative phylogeography and genetic demography of a locally adapted venomous predator and its prey

Coevolutionary theory predicts that differences in the genetic demography of interacting species can influence patterns of local adaptation by affecting the potential of local populations to respond to selection. We conducted a comparative phylogeographical study of venomous rattlesnakes and their venom-resistant ground squirrel prey across California, and assessed how effective population size (Ne) estimates correspond with a previously documented pattern of rattlesnake local adaptation. Using RAD sequencing markers, we detected lineage relationships among both the rattlesnakes (Crotalus oreganus ssp.) and ground squirrels (Otospermophilus sp.) that are incongruent with previous phylogenetic hypotheses. Both rattlesnakes and squirrels share a deep divergence at the Sacramento–San Joaquin River Delta. At this broad phylogeographical scale, we found that the locally adapted rattlesnakes had higher Ne than squirrels. At the population scale, snakes also had larger Ne accompanied by larger values of several metrics of population genetic diversity. However, the specific magnitude of local adaptation of venom activity to ground squirrel venom resistance was not significantly correlated with local differences in Ne or other diversity statistics between predator and prey populations, suggesting that other factors in the geographic mosaic of coevolution contribute to the specific local-scale outcomes of this interaction. These results suggest an evolutionary mechanism that may explain some (but clearly not all) of rattlesnake local adaptation in this coevolutionary interaction – larger population sizes raise the adaptive potential of rattlesnakes compared to ground squirrels.