Natural selection and neutral evolution jointly drive population divergence between alpine and lowland ecotypes of the allopolyploid plant Anemone multifida (Ranunculaceae).

Population differentiation can be driven in large part by natural selection, but selectively neutral evolution can play a prominent role in shaping patters of population divergence. The decomposition of the evolutionary history of populations into the relative effects of natural selection and selectively neutral evolution enables an understanding of the causes of population divergence and adaptation. In this study, we examined heterogeneous genomic divergence between alpine and lowland ecotypes of the allopolyploid plant, Anemone multifida. Using peak height and dominant AFLP data, we quantified population differentiation at non-outlier (neutral) and outlier loci to determine the potential contribution of natural selection and selectively neutral evolution to population divergence. We found 13 candidate loci, corresponding to 2.7% of loci, with signatures of divergent natural selection between alpine and lowland populations and between alpine populations (Fst  = 0.074-0.445 at outlier loci), but neutral population differentiation was also evident between alpine populations (FST  = 0.041-0.095 at neutral loci). By examining population structure at both neutral and outlier loci, we determined that the combined effects of selection and neutral evolution are associated with the divergence of alpine populations, which may be linked to extreme abiotic conditions and isolation between alpine sites. The presence of outlier levels of genetic variation in structured populations underscores the importance of separately analyzing neutral and outlier loci to infer the relative role of divergent natural selection and neutral evolution in population divergence.

Rapid isolation and cross-amplification of microsatellite markers in Plectritis congesta (Valerianaceae) with 454 sequencing.

PREMISE OF THE STUDY: Microsatellite markers were isolated and characterized in Plectritis congesta for studying the evolution of this highly variable species. METHODS AND RESULTS: We used 454 sequencing of DNA enriched for microsatellite repeats to develop microsatellite markers. This produced 262079 reads with an average length of 324 bp, representing approximately 800 microsatellite regions from which 48 primers were tested. Eleven markers reliably amplified without optimization. These primer pairs showed a high degree of heterozygosity and allelic diversity. Unexpectedly, half of the markers contained multiple peaks, with up to four alleles per individual, which suggests that either polyploidy or isolated gene duplication has occurred within this clade. These primers successfully cross-amplified in P. macrocera, indicating the utility of these markers for the genus. CONCLUSIONS: With variation in mating system and habitat, a mix of duplicated and nonduplicated markers, and high genetic variance, Plectritis is an ideal candidate model genus for studying the ecological and evolutionary consequences of gene duplication.

Floral colour versus phylogeny in structuring subalpine flowering communities.

The relative number of seeds produced by competing species can influence the community structure; yet, traits that influence seed production, such as pollinator attraction and floral colour, have received little attention in community ecology. Here, we analyse floral colour using reflectance spectra that include near-UV and examined the phylogenetic signal of floral colour. We found that coflowering species within communities tended to be more divergent in floral colour than expected by chance. However, coflowering species were not phylogenetically dispersed, in part due to our finding that floral colour is a labile trait with a weak phylogenetic signal. Furthermore, while we found that locally rare and common species exhibited equivalent floral colour distances from their coflowering neighbours, frequent species (those found in more communities) exhibited higher colour distances from their coflowering neighbours. Our findings support recent studies, which have found that (i) plant lineages exhibit frequent floral colour transitions; and (ii) traits that influence local population dynamics contribute to community structure.