Document: PAM-3-46-6

High levels of gene flow and genetically-based differentiation in life-history traits between local subpopulations of the perennial yellow bush lupine, Lupinus arboreus.

KITTELSON, P.M.* ^1,2 and J.L.MARON ^1,3

Bodega Marine Laboratory, Bodega Bay, CA 94923 U.S.A. ¹
Gustavus Adolphus College, St. Peter, MN 56082 U.S.A. ²
University of Washington, Seattle, WA 98195 U.S.A. ³

Abstract:
Across large spatial scales, plants often exhibit genetically based differentiation in traits that allow adaptation to local sites. At smaller spatial scales, similar results have been found in cases where sharp boundaries between edaphic conditions create strong gradients in selection that can overcome the high levels of gene flow. Few studies, however, have examined the degree to which continuous populations of perennial plants exhibit genetically based differentiation in life-history traits over small spatial scales. We quantified levels of gene flow and determined the degree of genetically based differentiation in adaptive traits between two grassland and one dune subpopulation of yellow bush lupine, Lupinus arboreus. Populations grew in close proximity to one another, and were part of a larger continuous population of L. arboreus. We calculated F_st statistics based on gel electrophoresis of 10 polymorphic loci from two age classes of L. arboreus: seeds from one year, and juvenile plants that were less than two years old. We created full-sib/half-sib families of lupine within each subpopulation, and established reciprocal common gardens at each site. Across 3 years, we measured canopy volume, mortality, flowering time, and seed set of progeny planted in each garden. Differentiation among subpopulations of seeds and juvenile plants was virtually non-existent (F_st= 0.002 and 0.041 respectively), suggesting that gene flow between the three subpopulations was quite high (estimated N_m ranged from 18 to >1000). Despite high levels of gene flow, we found strong evidence for local adaptation and genetically-based differentiation in adaptive traits such as plant size, flowering phenology, fecundity and mortality. Environmental factors within gardens also produced fitness related responses in growth, survival and seed production. Our results indicate that there is a surprising amount of divergence in life-history traits between local subpopulations of L. arboreus. Given the homogenizing influence of gene flow, it is likely that strong but differing selection regimes operating within each subpopulation drive spatial differentiation in lupine life history traits.

Keywords: Lupinus arboreus, gene flow, F_st, common gardens, selection, life history traits, local adaptation.

This abstract is being presented at: 3:45 PM in session:
Oral Session #63: Evolutionary Ecology.