Low genetic variation and high differentiation across sky island populations of Lupinus alopecuroides (Fabaceae) in the northern Andes

The tropical alpine flora in the northern Andes has caught the attention of evolutionary biologists and conservationists because of the extent of its diversity and its vulnerability. Although population genetics studies are essential to understand how diversity arises and how it can be maintained, plant populations occurring above 4100 m a.s.l. in the so-called super-páramo have rarely been studied at the molecular level. Here, we use 11 microsatellite DNA markers to examine genetic structure in populations of Lupinus alopecuroides, a long-lived semelparous giant rosette known from only 10 geographically isolated populations. Each population is located on a different mountain top, of which three are in Colombia and seven in Ecuador. We analysed 220 individuals from all the ten known populations. We find low genetic variation in all but one of the populations. Four populations are completely monomorphic, and another five show only one polymorphic locus each. On the other hand, we find extremely high genetic differentiation between populations. We discuss the mechanisms that might cause this pattern, and we suggest that it is related to founder effects, lack of gene flow, and autogamy. The genetic relationships among the populations, and the lack of correlation between the genetic and geographic distances also point to the importance of founder effects and colonization history in driving differentiation among the populations.