Fine-Scale Genetically Based Differentiation of Life-History Traits in the Perennial Shrub Lupinus Arboreus

Abstract

Across large spatial scales, plants often exhibit genetically based differentiation in traits that allow adaptation to local sites. At smaller spatial scales, sharp boundaries between edaphic conditions also can create strong gradients in selection that counteract gene flow and result in local adaptation. 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 the degree of genetically based differentiation in adaptive traits among bush lupine (Lupinus arboreus) from nearby dune and grassland sites (sites separated by <0.75 km) that formed part of a larger continuous population of L. arboreus. We also investigated the spatial genetic structure of bush lupine by examining how genetic structure differed between seeds and juvenile plants that were less than two years old. We calculated F‐statistics from gel electrophoresis of 10 polymorphic loci. We then used these values to infer levels of gene flow. To examine differentiation in adaptive traits, we created full‐sibling/half‐sibling families of lupine within each area and established reciprocal common gardens at each site. Across two years, we measured canopy volume, flowering time, seed set, and mortality of progeny planted in each garden. Spatial genetic structure among seeds was virtually nonexistent (FST= 0.002), suggesting that gene flow between the three areas could be quite high. However, genetic structure increased 20‐fold among juvenile plants (FST= 0.041). We found strong evidence for fine‐scale genetically based differentiation and local adaptation in adaptive traits such as plant size, flowering phenology, fecundity, and mortality. Thus, it is likely that strong but differing selection regimes within each area drive spatial differentiation in lupine life‐history traits.

Mating system and genetic diversity of a rare desert legume Ammopiptanthus nanus (Leguminosae)

“…Finally, the differences in the materials analyzed (seeds for allozymes and adult plant leaves for the AFLP and ISSR analyses) may have also contributed to the discrepancies. From seeds to adults, the level of differentiation may increase, as reported for Brongniartia vazquezii Dorado (F ST : 0.0705 for seedlings and 0.1013 for adults; González-Astorga & Núñez-Farfán, 2001) and Lupinus arboreus Sims (F ST : 0.002 for seeds and 0.041 for juvenile plants; Kittelson & Maron, 2001). Such increases in differentiation may be due to natural selection, which plays a significant role during development from seedlings to adults.…”

Variation in Lupinus arboreus alkaloid profiles and relationships with multiple herbivores

“…Such differentiation is somewhat surprising since other research at the same site suggested that gene flow is not restricted between these populations (Kittelson and Maron, 2001). Therefore, it seems likely that selection produced site-specific patterns in lupine traits, including alkaloids.…”

“…The selective agents responsible for producing the local differentiation that we observed remain to be identified, but may involve a combination of edaphic and biotic pressures unique to each area. Life history traits, including plant size and fecundity, also varied substantially across the Bodega Marine Reserve, among families from different origins, and among different maternal parents (Kittelson and Maron, 2001). Thus, selection may act on a suite of correlated traits that vary among populations and among parents.…”

“…Lupines in the dunes supported the lowest numbers of herbivores of Epinotia infuscana, Dasineura lupini, Dasineura lupinorum, Orgyia vetusta, Hepialus californicus and fungal lessions of the three sites (Kittelson, unpublished data). The three areas show fine-scale genetically based differentiation and local adaptation in life-history traits such as plant size, flowering time, fecundity and mortality (Kittelson and Maron, 2001). …”

The evolution of quantitative traits in complex environments

“…Multiyear field studies, in particular, have the distinct advantage of detecting general patterns of adaptation and/or plasticity at multiple life-history stages even when there is interannual variation in conditions (Kittelson and Maron, 2001;Mojica and Kelly, 2010;Å gren and Schemske, 2012). The extent and directionality of natural selection can change through ontogeny, and selection detected at one lifehistory stage may misrepresent selection integrated across the lifetime.…”