Evolution avoids a pathological stabilizing interaction in the immune protein S100A9.

Stability constrains evolution. While much is known about constraints on destabilizing mutations, less is known about the constraints on stabilizing mutations. We recently identified a mutation in the innate immune protein S100A9 that provides insight into such constraints.

RAPID, GEOGRAPHICALLY EXTENSIVE GENETIC INTROGRESSION AFTER SECONDARY CONTACT BETWEEN TWO PUPFISH SPECIES (CYPRINODON, CYPRINODONTIDAE).

Apparently between 1980 and 1984, Cyprinodon variegatus was introduced into an area of the Pecos River in Texas, where it hybridized with an endemic species, C. pecosensis. Protein electrophoresis indicated that, by 1985, panmictic admixtures of these two pupfishes occupied approximately 430 river-kilometers of the Pecos River, roughly one-half of the historic range of the endemic species.