Submitted to: Global Ecology and Biogeorgraphy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2007
Publication Date: 5/3/2007
Citation: Gavrilenko, T., Stephenson, S.A., Bamberg, J.B., Salas, A., Hijmans, R.J., Spooner, D.M. 2007. Geographical and environmental range expansion through polyploidy in wild potatoes (Solanum section Petota). Global Ecology and Biogeorgraphy. 16:485-495. Interpretive Summary: The cultivated potato of world commerce has about 190 wild species relatives distributed from Colorado (USA) to Chile and Uruguay, and are particularly diverse in the Central Mexican highlands and the Andes. There is great variation in the number of chromosomes in wild potatoes, with about 70% of the species having 24 chromosomes (technically called diploids), and the rest (polyploids) having higher numbers of 36 (triploids), 48 (tetraploids), 60 (pentaploids, and 72 (hexaploids). This study compiles, for the first time, all the reports of chromosome numbers of these wild potatoes and the cultivated potatoes. It then mapped the distribution of the different chromosome numbers and examines the different ecological factors where they occur. In total, we compiled a list of 7785 previous chromosome counts and here report for the first time 912 new counts. This list shows that all species except two have known chromosome numbers. More than one type of ploidy level has been documented in 22 species, with the most common combination being diploid triploid in different populations of a single species. The diploids are more common that polyploids, but the tetraploid and hexaploid species have on average a larger range size than the diploids. There are more polyploid species than diploid species in the area between N. Mexico to S. Ecuador. Compared to diploids, triploids tend to occur in warmer and drier areas, while higher level polyploids tend to occur in relatively cold and wet areas. There are no diploids from Costa Rica to S. Colombia, the wettest part of the range of the group. These results are useful for scientists studying the diversity and ecology of wild potatoes, and will aid potato breeders who wish to know the ecological conditions where wild species grow.
Technical Abstract: Wild potatoes (Solanum sect. Petota) are distributed from Colorado (USA) to Chile and Uruguay, and are particularly diverse in the Central Mexican highlands and the Andes. The 187 species of include diploids, triploids, tetraploids, pentaploids and hexaploids (n = 12 in all cases); the cultivated potato (Solanum tuberosum) has all these levels except hexaploid, but there is a single report of an octoploid. We summarize 7785 previous chromosome counts and 912 new counts (8697 total, 5548 for the wild species, 3028 for the cultivated species, and 121 for outgroup species). Ploidy levels are now documented for all but two of the species; we provide a first report for S. hintonii. Multiple ploidy levels have been observed in 22 species, the most common combination is of diploid and triploid populations (12 species) and diploid and tetraploid populations (five species), but given the low frequency of discovery of variant cytotypes within a species we suspect that they may in fact occur in many more species than is currently known. We mapped the distribution of ploidy levels and tested hypotheses of eco-geographic differences between the distribution of diploids and polyploids. Diploids are more common that polyploids, but the even-numbered (4x, 6x) polyploid species have on average a larger range size than diploids. There are more polyploid species than diploid species in the area between N. Mexico to S. Ecuador. Compared to diploids, triploids tend to occur in warmer and drier areas, while higher level polyploids tend to occur in relatively cold and wet areas. There are no diploids from Costa Rica to S. Colombia, the wettest part of the range of the group. The tetraploid cytotype of the cultivated species is much more frequent than the diploid. The hexaploid appears to be restricted to the cold and dry areas of S. Peru the Altiplano (Bolivia, Peru). These results are useful for diversity, evolutionary, and ecogeographical studies of section Petota and for potato breeders who wish to know the ecogeographical correlates to species they use in their breeding programs.