Hiroyuki Higashi

Molecular phylogeny of Shortia sensu lato (Diapensiaceae) based on multiple nuclear sequences

Molecular phylogenetics is commonly used to perform accurate taxonomic classification. Furthermore, nuclear multilocus sequences have been applied to resolve ambiguous phylogenetic relationships based on conventional markers such as chloroplast and nuclear ribosomal DNA. Here, we reconstructed the phylogenetic tree of Diapensiaceae to revise the traditional classification of the genus Shortia sensu lato (s.l.), which includes Shortia sensu stricto (s.s.) and Schizocodon; whether the latter taxon is treated as an independent genus or includes Shortia s.l. has been disputed since its first description. The phylogeny based on eight nuclear markers developed for this study indicated that Shortia s.l. is not a monophyletic group and that Schizocodon and Shortia s.s. are reciprocally monophyletic. In addition, Schizocodon would be sister to other genus Diapensia despite their morphological differentiation. Thus, our data suggest that Schizocodon represents an independent genus. Our study demonstrated that multiple nuclear loci can resolve obscure phylogenetic relationships determined using conventional markers.

Persistent history of the bird-dispersed arctic-alpine plant Vaccinium vitis-idaea L. (Ericaceae) in Japan.

AbstractArctic–alpine plants have expanded and contracted their ranges in response to the Pleistocene climate oscillations. Today, many arctic–alpine plants have vast distributions in the circumarctic region as well as marginal, isolated occurrences in high mountains at lower latitudes. These marginal populations may represent relict, long-standing populations that have persisted for several cycles of cold and warm climate during the Pleistocene, or recent occurrences that either result from southward step-wise migration during the last glacial period or from recent long-distance dispersal. In light of these hypotheses, we investigated the biogeographic history of the marginal Japanese populations of the widespread arctic–alpine plant Vaccinium vitis-idaea (Ericaceae), which is bird-dispersed, potentially over long distances. We sequenced three nuclear loci and one plastid DNA region in 130 individuals from 65 localities covering its entire geographic range, with a focus on its marginal populations in Japan. We found a homogenous genetic pattern across its enormous range based on the loci analysed, in contrast to the geographically structured variation found in a previous study of amplified fragment length polymorphisms in this species. However, we found several unique haplotypes in the Japanese populations, excluding the possibility that these marginal populations result from recent southward migration. Thus, even though V. vitis-idaea is efficiently dispersed via berries, our study suggests that its isolated populations in Japan have persisted during several cycles of cold and warm climate during the Pleistocene.

Distinct Phylogeographic Structures of Wild Radish (Raphanus sativus L. var. raphanistroides Makino) in Japan

Coastal plants with simple linear distribution ranges along coastlines provide a suitable system for improving our understanding of patterns of intra-specific distributional history and genetic variation. Due to the combination of high seed longevity and high dispersibility of seeds via seawater, we hypothesized that wild radish would poorly represent phylogeographic structure at the local scale. On the other hand, we also hypothesized that wild radish populations might be geographically differentiated, as has been exhibited by their considerable phenotypic variations along the islands of Japan. We conducted nuclear DNA microsatellite loci and chloroplast DNA haplotype analyses for 486 samples and 144 samples, respectively, from 18 populations to investigate the phylogeographic structure of wild radish in Japan. Cluster analysis supported the existence of differential genetic structures between the Ryukyu Islands and mainland Japan populations. A significant strong pattern of isolation by distance and significant evidence of a recent bottleneck were detected. The chloroplast marker analysis resulted in the generation of eight haplotypes, of which two haplotypes (A and B) were broadly distributed in most wild radish populations. High levels of variation in microsatellite loci were identified, whereas cpDNA displayed low levels of genetic diversity within populations. Our results indicate that the Kuroshio Current would have contributed to the sculpting of the phylogeographic structure by shaping genetic gaps between isolated populations. In addition, the Tokara Strait would have created a geographic barrier between the Ryukyu Islands and mainland Japan. Finally, extant habitat disturbances (coastal erosion), migration patterns (linear expansion), and geographic characteristics (small islands and sea currents) have influenced the expansion and historical population dynamics of wild radish. Our study is the first to record the robust phylogeographic structure in wild radish between the Ryukyu Islands and mainland Japan, and might provide new insight into the genetic differentiation of coastal plants across islands.

Development of Polymorphic Microsatellite Loci in the Perennial Herb Hepatica nobilis var. japonica (Ranunculaceae)

Premise of the study: Microsatellite markers were developed and characterized in the vulnerable plant Hepatica nobilis var. japonica (Ranunculaceae) to investigate its genetic diversity, population structure, and gene flow. Methods and Results: Fourteen microsatellite markers were developed. The number of alleles per locus ranged from one to 12, and the expected heterozygosity per locus ranged from 0.043 to 0.855. Eleven markers were successfully amplified in the cultivar ‘Mego’ from Japan. Conclusions: These microsatellite markers can be used to investigate the genetic diversity, population structure, and gene flow of H. nobilis var. japonica.

Isolation and characterization of microsatellite loci in Patrinia triloba var. takeuchiana (Valerianaceae)

Patrinia triloba var. takeuchiana is an endangered plant endemic to Japan, and conservation activities on its behalf have begun recently. Fourteen polymorphic microsatellite loci were successfully isolated from P. triloba var. takeuchiana. The range of expected heterozygosity was 0.139–0.666 in the wild population. Four loci showed significant deviations from Hardy–Weinberg equilibrium. Two markers merit caution due to their significant linkage disequilibrium with other markers. The markers described here will be useful for conservation genetics and development of effective conservation programs for P. triloba var. takeuchiana.

Erratum to: Population fragmentation causes randomly fixed genotypes in populations of Arabidopsis kamchatica in the Japanese Archipelago (J Plant Res, 10.1007/s10265-011-0436-8)

Populations of arctic alpine plants likely disappeared and re-colonised several times at the southern edge of their distributions during glacial and interglacial cycles throughout the Quaternary. Range shift and population fragmentation after a glacial period would affect the genetic structure of such plants in southernmost populations. We aimed to elucidate how climatic oscillations influenced the population subsistence of alpine plants in the Japanese Archipelago as one of the southernmost populations, by inferring the genetic structure of Arabidopsis kamchatica subsp. kamchatica and the intraspecific littoral taxon, subsp. kawasakiana. We identified genotypes based on the haplotypes of five nuclear genes and two chloroplast DNA spacers for 164 individuals from 24 populations. Most populations harboured only one private genotype, whereas few polymorphisms were found in each population. Two genetic genealogies were found, suggesting that northern Japanese populations of alpine subsp. kamchatica, subsp. kawasakiana and the northerly subsp. kamchatica in eastern Russia and Alaska clustered and differentiated from populations in central Honshu, western Japan and Taiwan. During climatic oscillations, the genetic structure of extant southernmost populations would have been shaped by strong genetic drift under population fragmentation and randomly fixed to a single genotype among their ancestral polymorphisms.