Biogeographic distribution of the Arachis (Leguminosae) karyotype variants

ROBLEDO, G; J. G. SEIJO

Bariloche,

Congreso; Southern Connections meeting; 2010

Biogeografic distribution of the Arachis (Leguminosae)  karyotype variants   Robledo, G.  & G. Seijo   Arachis is a South American genus of geocarpic and autogamous legumes. Section Arachis includes 29 diploid and two allotetraploid taxa. Three different genomes (A, B, D) have been described for the section based on karyotype morphology and cross compatibility. Geographically, the section extends southward of the Amazonian basin until La Plata River, and from the Andes mountains toward the Atlantic Ocean. The particular reproductive system of these species, autogamy and geocarpy, drastically reduces the chances of pollen and seed dispersion, and suggests that the karyotype variability should be geographically structured. To test this hypothesis, we conducted FISH analysis using rDNAs and heterochromatin detection in 29 species. We detected seven karyotype patterns, three for the A-genome, three for the B-genome, and one for the D genome. Each of the patterns detected within a particular genome was biogeographically segregated. Overlapping distributions of species having different karyotype patterns always correspond to species with different genomes. This non-random occurrence of karyotype variability is probably reflecting the biological constrains for gene flow and seed dispersion, and suggest independent species radiation of the A and B linages. Notoriously, most of the karyotype patterns are usually associated to a particular river basin, which strongly suggest that past and present dispersion through hydrochory may have determined the geographical structure of karyotypes.