Editor's Note: Some of the articles described below are not yet available at the PNAS site, but they are scheduled to be posted some time this week.
A hunter-gatherer population from Madagascar carries genetic ancestry from Austronesian and Bantu-speaking populations, similar to some other populations in the region, according to a study in the early, online edition of the Proceedings of the National Academy of Sciences. Researchers from France, the UK, and Madagascar compared genome-wide SNP patterns in 21 individuals from this population — known as the Mikea — with genotyping profiles in dozens of individuals from two other Malagasy populations and from populations in Indonesia. In each of the populations from Madagascar, the group saw evidence of admixture between Austronesian and Bantu-speaking populations, arguing against the notion that the Mikea are descended from a population present before the arrival of those agricultural groups.
Harvard University's Andrew Murray and colleagues did theoretical analyses and lab experiments with colonies of fluorescently labeled, cross-feeding budding yeast in an effort to explore the antagonistic processes of genetic drift and mutualism in populations expanding into new spatial areas. Their findings suggest that cooperation and genetic diversity may be maintained when that mutualism is strong. On the other hand, genetic drift appears to swamp out that effect, leading to de-mixing, when mutualism between different strains is weak or asymmetrical, they report.
In another study slated to appear online this week in PNAS, a team from Israel and the US looked at speciation patterns in spiny mice from the genus Acomys living on the ecologically distinct slopes of the so-called Evolution Canyon in Israel. Based on mitochondrial genome and amplified fragment length polymorphism assessments of mice from the canyon's hot, dry, "African"-like slope and from its more temperate, forested, "European"-like slope, the researchers determined that Acomys species in Evolution Canyon have undergone sympatric speciation — a form of new species diversification that occurs in populations that can interbreed with one another and are not isolated by a geographic barrier.