CONICET | Buscador de Institutos y Recursos Humanos

Tuco-tucos, South American rodents of the genusCtenomys represent an interesting model of speciation.Their strict territorial and solitary life under the earth,vast but highly fragmented habitats, low migrationactivity were the causes of their very fast radiation.About 60 species of this genus have been described.They are found in a variety of habitats, from themountains of the Andes to the coastal dunes ofthe Atlantic, from humid steppes of Pampas to drydeserts of Chaco. Tuco-tucos have a very high levelof chromosomal polymorphism and polytypismbased on Robertsonian and whole-arm reciprocaltranslocations and inversions, and can thereforebe used to test di erent versions of chromosomalspeciation hypothesis. The classic version of this hypo-thesis emphasizes the sterility of the hybrids, due toincorrect or incomplete chromosome synapsis inheterozygotes for rearrangements, germ cells death,chromosome nondisjunction and the generationof unbalanced gametes. The modern version of chro-mosomal speciation hypothesis suggests that thereduction of gene ow across chromosomal hybridzones is due to the suppression of recombinationin hybrids around the break points of rearrangementsdistinguishing the parental species. Field studies havenot revealed strong negative e ects of chromosomalheterozygosity on the tness of the carriers. Theseresults cast doubt on the validity of the classic versionof the hypothesis. Analysis of chromosome behaviorin the meiotic prophase in the chromosomal hetero-zygotes revealed signi cant changes in the frequencyand distribution of recombination: crossingoversuppression around the breakpoint and chiasmadistalization. These changes can modulate the owof genes between chromosomal races and amplifythe divergence which has arisen due to spatial isola-tion. These data con rm the recombinational modelof chromosomal speciation.