DNA sequence variation of wild barley Hordeum spontaneum (L.) across environmental gradients in Israel.

Wild barley Hordeum spontaneum (L.) shows a wide geographic distribution and ecological diversity. A key question concerns the spatial scale at which genetic differentiation occurs and to what extent it is driven by natural selection. The Levant region exhibits a strong ecological gradient along the North-South axis, with numerous small canyons in an East-West direction and with small-scale environmental gradients on the opposing North- and South-facing slopes. We sequenced 34 short genomic regions in 54 accessions of wild barley collected throughout Israel and from the opposing slopes of two canyons. The nucleotide diversity of the total sample is 0.0042, which is about two-thirds of a sample from the whole species range (0.0060). Thirty accessions collected at 'Evolution Canyon' (EC) at Nahal Oren, close to Haifa, have a nucleotide diversity of 0.0036, and therefore harbor a large proportion of the genetic diversity. There is a high level of genetic clustering throughout Israel and within EC, which roughly differentiates the slopes. Accessions from the hot and dry South-facing slope have significantly reduced genetic diversity and are genetically more distinct from accessions from the North-facing slope, which are more similar to accessions from other regions in Northern Israel. Statistical population models indicate that wild barley within the EC consist of three separate genetic clusters with substantial gene flow. The data indicate a high level of population structure at large and small geographic scales that shows isolation-by-distance, and is also consistent with ongoing natural selection contributing to genetic differentiation at a small geographic scale.

Two postglacial immigration lineages of the polyploid Cerastium alpinum (Caryophyllaceae).

The plant cover of Fennoscandia is young because of the recent glaciation. This study covers the early stages of diversification and the genetic consequences of postglacial migration of a hermaphroditic polyploid plant. Cerastium alpinum. It has a continuous distribution in the alpine region, where it grows on alpine heaths and serpentine soils that are rich in heavy metals. Within the boreal forest C. alpinum has a scattered distribution on serpentine, dolomite and steep slopes. Plants from 31 populations in Norway, Sweden and Finland were subjected to enzyme electrophoresis. Analyses of the enzyme phenotypes suggest that C. alpinum has colonized Fennoscandia through two postglacial immigration events resulting in a southeastern and a southwestern lineage. These two lineages seem to meet in a hybrid zone in northern Sweden. Large genetic differences were found among most populations in both the southeastern and the southwestern lineages. This suggests that the populations are effectively isolated from each other.