Geographic genetic structure of Iberian columbines (gen. Aquilegia)

Southern European columbines (genus Aquilegia)are involved in active processes of diversification, and the Iberian Peninsula offers a privileged observatory to witness the process. Studies on Iberian columbines have provided significant advances on species diversification,but we still lack a complete perspective of the genetic diversification in the Iberian scenario. This work explores how genetic diversity of the genus Aquilegia is geographically structured across the Iberian Peninsula. We used Bayesian clustering methods, principal coordinates analyses, and NJ phenograms to assess the genetic relationships among 285 individuals from 62 locations and detect the main lineages. Genetic diversity of Iberian columbines consists of five geographically structured lineages, corresponding to different Iberian taxa. Differentiation among lineages shows particularly complex admixture patterns at Northeast and highly homogeneous toward Northwest and Southeast. This geographic genetic structure suggests the existence of incomplete lineage sorting and interspecific hybridization as could be expected in recent processes of diversification under the influence of quaternary postglacial migrations. This scenario is consistent with what is proposed by the most recent studies on European and Iberian columbines, which point to geographic isolation and divergent selection by habitat specialization as the main diversification drivers of the Iberian Aquilegia complex

Chloroplast DNA and isozyme evidence on the evolution of <em>Senecio vulgaris</em> (Asteraceae)

Chloroplast DNA (cpDNA) and isozyme variation were analyzed over a range of populations of two infraspecific taxa of the tetraploid Senecio vulgaris. The isozyme data were supportive of the hypothesis that the weedy and cosmopolitan S. vulgaris var. vulgaris is an evolutionary derivative of S. vulgaris subsp. denticulatus from the coasts of W Europe and montane altitudes in S Spain and Sicily. The two taxa exhibited a very high genetic identity with subsp. denticulatus containing slightly more isozyme diversity than was found in var. vulgaris. - Three cpDNA haplotypes (A, B, C) already known from other Mediterranean diploid species of Senecio were resolved in var. vulgaris, and an additional fourth haplotype (E) was found in subsp. denticulatus. Two alternative hypotheses were chosen to account for the origin and maintenance of the observed cpDNA composition of S. vulgaris. It either reflects (1) the retention of an ancestral polymorphism which stems from the recurrent and polytopic formation of ancestral tetraploid lineages; or (2) S. vulgaris originally was characterized by haplotype E, and haplotypes A, B and C were acquired through repeated introgressive hybridization with related diploid species. The finding that very low levels of nuclear (isozyme) diversity were present in both taxa of S. vulgaris examined supports the second of these two hypotheses; however, more detailed analysis of nuclear genetic diversity is required before a firm conclusion can be reached on this matter.</p

Chloroplast DNA and isozyme analysis of the progenitor-derivative species relationship between <em>Senecio nebrodensis</em> L. and <em>S. viscosus</em> L.

A comparison of chloroplast DNA (cpDNA) and isozyme diversity in Senecio nebrodensis L., a species restricted to certain mountain ranges in Spain, and S. viscosus L., a widespread ruderal species in Europe, revealed that S. viscosus possessed the more common of two cpDNA haplotypes resolved in S. nebrodensis and contained only a small subset of the alleles found in S. nebrodensis at enzyme coding loci. The two species shared one restriction length mutation and one site mutation in their cpDNA, which distinguished them from other European Senecio species examined previously. Taken overall, these results support the hypothesis that S. nebrodensis and S. viscosus are related as a progenitor-derivative pair of species. The fact that no novel alleles were found in S. viscosus would suggest a relatively recent origin of the species, most probably in late glacial or postglacial times.</p