A living evolution experiment
In the arid scrublands of the Monte Desert, an extraordinary evolutionary process is unfolding beneath the surface. The protagonists are small, burrowing rodents called tuco-tucos, belonging to the genus Ctenomys. This group of over 60 species is undergoing rapid diversification, and the primary engine of this change is their chromosomes. Across the entire genus, the diploid chromosome number—the total count of chromosomes in a cell—ranges dramatically from 2n=10 in one species to 2n=70 in another. This is one of the largest ranges of chromosomal variation known in any mammal genus.
This genetic variability is more than a curiosity; a powerful mechanism for creating new species. When two populations of tuco-tucos with different chromosome numbers attempt to interbreed, their offspring are often infertile. The mismatched chromosomes fail to pair correctly during the formation of sperm and eggs, a process known as meiotic failure. This effectively creates a reproductive barrier, isolating the gene pools of the two populations. In the San Luis Province, this process can be observed over very short distances, where populations separated by only a few kilometers, or by a subtle shift in soil type, are already on distinct evolutionary paths. The primary mechanisms for these changes are thought to be Robertsonian translocations (the fusion or splitting of chromosomes) and other rearrangements.