Evolution at a geographic scale: Spatial variation in natural selection of floral traits in Anarthrophyllum desideratum.

PAIARO, V.; SÉRSIC, A. N.; COCUCCI, A. A.; OLIVA, G.

Bariloche, Río Negro, Argentina

Congreso; VI Southern Connection Congress. Gondwana reunited: A Southern perspective for a changing world.; 2010

The strength and direction of natural selection on floral traits can vary spatially because of variation in the biotic and abiotic selective scenarios. In the absence of plasticity, variation in selection among populations should lead to genetically based phenotypic differences in the traits under selection. Previous studies on the Southern Patagonia endemic shrub Anarthrophyllum desideratum have shown significant geographic patterns in floral variation and different pollinator assemblages among conspecific populations. To determine the importance of natural selection on spatial variation of flowers in this species, we measured phenotypic selection on different floral traits (morphometric, color and nectar traits, and floral display) in four distant populations with distinct pollinator assemblages. Flower number, corolla area, petal width and length, style exertion, nectar volume and concentration showed significant patterns of selection. While flower number was positively selected in all sites, the identity of the other floral traits under selection and/or the selection gradients (strength and/or the direction of the selection) varied among populations. Our results showed a geographic mosaic of phenotypic selection, and suggest that natural selection mediated by the abiotic environment and/or pollinators would be at least partly responsible for the evolution of flower variation in natural populations of A. desideratum.