Background and Aims The biggest genus of Salicaceae sensu lato (s.l.) Salix L. has been shown to consist of two main clades: clade Salix, in which species have XY sex determination systems (SDSs) on chromosome 7, and clade Vetrix including species with ZW SDSs on chromosome 15. Here, we test the utility of whole genome re-sequencing (WGR) for phylogenomic reconstructions of willows to infer changes between different SDSs. Methods We used more than 1 TB of whole genome re-sequencing (WGR) data from 70 Salix taxa to ascertain SNPs on the autosomes, the sex-linked regions (SLRs), and the chloroplast genomes, for phylogenetic and species tree analyses. To avoid bias, we chose reference genomes from both groups, Salix dunnii from clade Salix and S. purpurea from clade Vetrix. Key Results Two main largely congruent groups were recovered: the paraphyletic Salix grade and the Vetrix clade. The autosome dataset trees resolved four subclades (C1-C4) in Vetrix. C1 and C2 comprise species from the Hengduan Mountains and adjacent areas and Eurasia, respectively. Section Longifoliae (C3) grouped within the Vetrix clade but fell into the Salix clade in trees based on the chloroplast dataset analysis. Salix triandra from Eurasia (C4) was revealed as sister to the remaining species of clade Vetrix. In Salix, polyploid group C5 is paraphyletic to clade Vetrix and subclade C6 is consistent with Argus’s subgenus Protitea. Chloroplast datasets separated both Vetrix and Salix as monophyletic, and yielded C5 embedded in Salix. Using only diploid species, the SLR and autosomal datasets both yielded trees with Vetrix and Salix as well supported clades. Conclusion WGR data are useful for phylogenomic analyses of willows. The different sex determining systems may contribute to the isolation of the two major groups, but the reproductive barrier between them needs to be studied.

Heterodichogamy is a form of sex expression in which protandrous and protogynous individuals coexist, and is considered to be a mechanism that avoids selfing and promotes disassortative mating. We examined mating patterns in a heterodichogamous maple, Acer mono, using microsatellite markers. Parentage analysis revealed a selfing rate of only 9.8%. Disassortative mating between flowering types significantly exceeded within-type mating, but the mating patterns were better explained by flowering phenology (i.e., the temporal overlap between the female and male stages). Heterodichogamy in A. mono thus appears to promote outcrossing without requiring obligate self-or cross-incompatibility systems, although it did not guarantee disassortative mating. Multiple-regression analysis suggested that successful reproduction of pollen parents significantly increased with increased flower production and reciprocal flowering synchrony, but decreased only marginally with mating distance, although the distribution of mating distances suggested leptokurtic dispersal of pollen.

Magnolia sieboldii ssp. japonica, distributed mainly in western Japan, is restricted to high elevation areas (1000-2000 m above sea level) and usually forms small isolated populations. Four microsatellite loci were assayed for 19 populations from six regions spanning the range of distribution, and the levels and distribution of genetic variation were estimated. All four loci were variable, with a total of 39 alleles, but the overall level of microsatellite genetic variation was low, especially compared with a related species, M. obovata. Genetic structure in M. sieboldii was characterised by low intrapopulational genetic variation (A = 3.74 and H o = 0.366 on average) and high genetic differentiation even among regional populations. Highly significant isolation-by-distance (IBD) models at the short distance were detected. Genetic drift and limited gene flow was considered to be important Keywords: Magnolia sieboldii; microsatellite: genetic diversity; population size; genetic drift; isolation-by-distance IntroductionWithin a species, the genetic structures of plant populations are determined by factors such as mutation, migration, selection and genetic drift. The effects of genetic drift are important when populations are small or isolated. Species consisting of such populations usually have small within-population genetic variation and large among-population differentiation (Loveless and Hamrick, 1984). Genetic information can be useful in the conservation of rare plant species, which usually consist of small and/or isolated populations. For example, the risk of extinction of a population or a species can be assessed, and the steps and priorities necessary to prevent extinction can be determined by estimating the level of genetic diversity, the effect of genetic drift, and the extent of genetic differentiation and gene flow, from genetic data (Ellstrand and Elam, 1993). However, the genetic variability of isolated or local endemic populations sometimes collapses because of severe genetic drift or historical bottlenecks; in such cases little or no genetic variation is detected in the population using genetic markers, such Correspondence: S Kikuchi, Department of Forest Genetics, Forestry and Forest Products Research Institute, Kukizaki, in determining the genetic structure within regions. Total genetic differentiation was remarkably high (F ST = 0.488 and R ST = 0.538), suggesting genetic barriers among regions. Neighbour-joining dendrograms relating the 19 populations, and further analysis on the IBD models, revealed that a stepwise mutation model was more suited than an infinite allele model to explain the genetic differentiation among regions. It is suggested that mutation at microsatellite loci might be influential in generating the genetic differentiation among regions. These results showed the potential of hypervariable microsatellite loci to evaluate the effects of genetic drift and population isolation within regions, and to detect genetic distinctiveness, in spite of the loss of overall genetic variati...

Salix hukaoana is an endangered riparian pioneer tree that is distributed within a restricted area of Japan. Microsatellite genetic variations and genetic structures were investigated in 80 subpopulations patchily distributed within five river basins with varying degrees of habitat fragmentation. The correlation between geographic distance and genetic distance based on the Bayesian assignment test was significant across relatively intact riparian habitats, with steeper slopes of regression for more densely grouped subpopulations, suggesting restricted gene flow. However, the correlation became less apparent with increasing spacing of the habitat patches. These contradictory results are attributed to the increased chance of long-distance dispersal of sexual propagules among more isolated habitat patches. The observed accumulation of genetic diversity with increasing distance downstream along a few, but not all, of the rivers and the results of assignment tests suggested a downstream directionality of gene flow. The results of this study illustrate the patterns of genetic diversity and contemporary dispersal of S. hukaoana, and provide important insights into understanding the gene dispersal of riparian trees and into the conservation of genetic resources for this species.