Hybridization in the Mexican and 13-lined ground squirrels, Spermophilus mexicanus and Spermophilus tridecemlineatus.

Evidence of hybridization between the ground squirrels, Spermophilus tridecemlineatus and S. mexicanus is presented on the basis of chromosomal and protein data. The hybrids produced appear to be completely interfertile. Based on the evidence of hybridization and the recent reestablishment of contact between these two species, they are considered to be semispecies.