Masatsugu Yokota

Phylogenetic systematics of the monotypic genus Hayataella (Rubiaceae) endemic to Taiwan

Hayataella (Rubiaceae) is a monotypic genus endemic to Taiwan that comprises H. michelloides. In recent years, Hayataella was considered to be synonymous with Ophiorrhiza; however, no specific data have been reported, and the systematic treatment of Hayataella has been unclear. To elucidate the systematic treatment of Hayataella, molecular phylogenetic analyses based on ITS of nrDNA, atpB–rbcL, and trnK/matK of cpDNA were conducted with four Ophiorrhiza species. In the Bayesian and the most parsimonious trees, H. michelloides was included in the Ophiorrhiza clade. The monotypic status of Hayataella is, therefore, not considered appropriate, and the combination Ophiorrhiza michelloides (Masam.) H. S. Lo is supported.

Breakdown of distyly in a tetraploid variety of Ophiorrhiza japonica (Rubiaceae) and its phylogenetic analysis.

We examined the floral morph of tetraploid Ophiorrhizajaponica Blume var. amamiana Hatus. and diploid O. japonica var. japonica to elucidate the association of distyly and ploidy levels. Chloroplast DNA phylogeny was reconstructed to determine the number of tetraploidization events and floral morph shifts in O. japonica. All individuals of O. japonica var. amamiana proved to be long-homostylous, whereas O. japonica var. japonica was distylous with typical long- and short-styled flowers. Distyly is related to the ploidy level. The bagging treatment of flowers indicated that O. japonica var. amamiana is self-compatible and potentially automatically self-pollinating. In cpDNA sequencing analysis, no haplotype was shared between the two varieties. The cpDNA haplotype network displayed the monophyly of O. japonica var. amamiana, suggesting a single origin of this variety. Hence, both tetraploidization and the breakdown of distyly to homostyly in O. japonica var. amamiana likely occurred just once. Because O. japonica var. amamiana having the morphological and cytological entity is recognized as a single lineage and clearly separated from O. japonica var. japonica, this variety can be considered to be a distinct species. We therefore propose to raise O. japonica var. amamiana to the rank of species.

Cytogeography of Ixeris nakazonei (Asteraceae, Lactuceae) in the Ryukyu Archipelago of Japan and Taiwan

The cytogeographical structures of Ixeris nakazonei, a putative hybrid between I. debilis (6x) and I. repens (2x), were investigated in the Ryukyu Archipelago and Taiwan. In the Ryukyus, I. debilis occurs on Miyakojima Island of the southern Ryukyus and northward, while I. repens occurs on all islands except for Iriomotejima and Yonagunijima Islands. I. nakazonei, comprises six polyploid cytotypes, 3x, 4x, 5x, 6x, 7x and 8x, based on x=8. Four cytotypes from 3x to 6x occur in the central Ryukyus, while four cytotypes from 5x to 8x occur in the southern Ryukyus. The higher polyploids of I. nakazonei tend to be distributed in the more southerly area. Tetraploids of I. nakazonei always co-occur with I. debilis and I. repens, supporting the hybrid origin of this cytotype. Considering the chromosome number, octoploids, which predominate in the southern Ryukyus and Taiwan, may have derived directly from hybridization between I. debilis and I. repens. Odd-numbered polyploids of I. nakazonei, 3x, 5x and 7x, are relatively rare. Their chromosome numbers indicate that triploids and heptaploids are hybrids between the tetraploid of I. nakazonei and I. repens, and between the octoploid of I. nakazonei and I. debilis, respectively. Pentaploids of I. nakazonei in the central and southern Ryukyus are, respectively, hybrids between the tetraploid of I. nakazonei and I. debilis and between the octoploid of I. nakazonei and I. repens, indicating that pentaploids of I. nakazonei have at least two independent origins.

Phylogenetic position of Oxygyne shinzatoi (Burmanniaceae) inferred from 18S rDNA sequences.

The genus Oxygyne comprises three species disjunctly distributed in Africa and Japan and is the least examined genus of the Burmanniaceae due to the scarcity of living material. We obtained living samples of Oxygyne shinzatoi and examined the phylogenetic position of this species on the basis on the 18S rDNA sequence. Oxygne shinzatoi was consistently found to belong to the monophyletic group of tribe Thismieae, but its position in the tribe differed depending on the criteria applied (maximum parsimony, maximum likelihood, Bayesian inference). Distance analysis from the most recent common ancestor indicated that O. shinzatoi had the lowest substitution rate among the species of tribe Thismieae. Combined with recent knowledge of basic chromosome numbers and substitution rate characteristics, O. shinzatoi can be considered to be one of the basal taxon of tribe Thismieae.

Crisis of Japanese vascular flora shown by quantifying extinction risks for 1618 taxa

Although many people have expressed alarm that we are witnessing a mass extinction, few projections have been quantified, owing to limited availability of time-series data on threatened organisms, especially plants. To quantify the risk of extinction, we need to monitor changes in population size over time for as many species as possible. Here, we present the worlds first quantitative projection of plant species loss at a national level, with stochastic simulations based on the results of population censuses of 1618 threatened plant taxa in 3574 map cells of ca. 100 km2. More than 500 lay botanists helped monitor those taxa in 1994–1995 and in 2003–2004. We projected that between 370 and 561 vascular plant taxa will go extinct in Japan during the next century if past trends of population decline continue. This extinction rate is approximately two to three times the global rate. Using time-series data, we show that existing national protected areas (PAs) covering ca. 7% of Japan will not adequately prevent population declines: even core PAs can protect at best <60% of local populations from decline. Thus, the Aichi Biodiversity Target to expand PAs to 17% of land (and inland water) areas, as committed to by many national governments, is not enough: only 29.2% of currently threatened species will become non-threatened under the assumption that probability of protection success by PAs is 0.5, which our assessment shows is realistic. In countries where volunteers can be organized to monitor threatened taxa, censuses using our method should be able to quantify how fast we are losing species and to assess how effective current conservation measures such as PAs are in preventing species extinction.

Distribution patterns of rDNAs and telomeres and chromosomal rearrangement between two cytotypes of Lysimachia mauritiana L. (Primulaceae)

Abstract Two cytotypes of Lysimachia mauritiana collected from Japanese mainland (JM-type) and the Sakishima group (SR-type), located in the southernmost of the Ryukyu Archipelago of Japan, were cytogenetically analyzed. JM- and SR-types showed karyotype formulae of 2n=20(4m)=4m+2sm+4st+10t and 2n=18(6m)=6m+2sm+10t, respectively. In FISH analysis, a signal of 5S rDNA was observed at the interstitial region of long arm on a pair of t-chromosome in both cytotypes. On the other hand, different sizes of 45S rDNA signals were observed on the distal and proximal regions of m-, sm-, st- and t-chromosomes in JM-type, and of m- and t-chromosomes in SR-type. Also in SR-type, a tiny 45S rDNA signal was shown at the interstitial region of long arm on sm-chromosome. Telomere signals in two cytotypes appeared at both ends of all chromosomes, and at internal sites of certain chromosomes. The big telomere sequence signal at the proximal region coincided with the small 45S rDNA signal in JM-type. These results gave us a fusion/fission hypothesis with two st- or one m-chromosome(s) for new intraspecific karyotype formation of JM-type or SR-type.

Antitropical distribution of Lobelia species (Campanulaceae) between the Ryukyu Archipelago of Japan and Oceania as indicated by molecular data

We tested the antitropical distribution of Lobelia loochooensis, endemic to the Ryukyu Archipelago of Japan, and its putative sister species of the same section Hypsela in Oceania (Australia and New Zealand). Molecular phylogenetic analyses based on cpDNA sequences were conducted for 41 Lobelia species of 11 sections including all the species of sect. Hypsela investigated in Asia and Malesia and 32 species of 16 allied genera of family Campanulaceae, because the genus Lobelia is known to be polyphyletic. In the result, L. loochooensis and an Australian endemic L. fluviatilis formed a clade, and this clade was sister to a clade of four New Zealand endemics: L. carens, L. fatiscens, L. fugax and L. ionantha. These two clades were nested in a clade with two other Australian congeners. We conclude that: (1) the lineage of L. loochooensis and the five Lobelia species occurring in Oceania demonstrate an antitropical distribution pattern; and (2) L. loochooensis has likely originated from a dispersal event from Australia to the Ryukyu Archipelago.

Evidence of three parallel evolutions of leaf dwarfism and phytogeography in Lysimachia sect. Nummularia in Japan and Taiwan

Phylogenetic analyses were performed using nrITS variations of eight species including one variety of the genus Lysimachia sect. Nummularia in Japan and Taiwan, with another 34 Lysimachia species and Glaux maritime obtained from a DNA database. Among the four dwarf-leaf taxa in Japan and Taiwan, L. japonica var. minutissima of Japan and two Taiwanese species were placed into two different clades; and L. liukiuensis of Japan, was positioned outside of these two clades. These results suggest that three independent dwarfism events generated the four dwarf-leaf taxa; and that there were likely multiple migration events from China to Japan and Taiwan.

Cassytha pubescens and C. glabella (Lauraceae) are not disjunctly distributed between Australia and the Ryukyu Archipelago of Japan: evidence from morphological and molecular data

Abstract. Morphological comparisons and molecular phylogenetic analyses were conducted to resolve taxonomic confusion in Cassytha glabella and C. pubescens, both of which were first described from Australia and subsequently considered to be disjunctly distributed between Australia and the Ryukyu Archipelago of Japan. In the morphological comparisons, plants considered as C. pubescens in the Ryukyus differ from C. pubescens in Australia in the presence or absence of hairs on the petals, and those considered as C. glabella in the Ryukyus differ from the C. glabella in Australia in bract and peduncle morphology. The molecular analyses indicated that plants attributed to C. pubescens in the Ryukyus were not closely related to C. pubescens in Australia, and were nested in a clade of populations of a Pan-Western Pacific species C. filiformis. Plants attributed to C. glabella in the Ryukyus were distantly related to C. glabella in Australia. We concluded that plants considered as C. pubescens and C. glabella in the Ryukyus are to be respectively treated as C. filiformis and the Ryukyu endemic species C. pergracilis.

Canopy Multilayering and Woody Species Diversity of a Subtropical Evergreen Broadleaf Forest, Okinawa Island.

ABSTRACT Woody species diversity and the spatial distribution of trees in a subtropical evergreen broadleaf forest on a silicate substrate, Okinawa Island, were investigated to determine the forests architectural stratification. The forest stand consisted of four architectural layers. The values of Shannons index H′ and Pielous index J′ tended to increase from the top layer downward, except for the bottom layer. The lower layers contained many species relative to their smaller height ranges. High woody species diversity of the forest depended on small trees. This trend of species diversity was different from that of forest on a limestone substrate on Okinawa Island, where high woody species diversity depended on large trees. Conservation of small trees in the lower layers, especially the bottom layer, is indispensable to maintain diversity in Okinawan evergreen broadleaf forests. Castanopsis sieboldii (Mak.) Hatusima had the highest importance value in all layers, indicating that it is typically a facultative shade species as well as a climax species. The spatial distribution patterns of trees were found to be random in the lower three layers, but in the top layer clumping seemed to occur at three spatial scales. A high degree of overlapping in spatial distributions of trees among the layers suggested that light cannot penetrate easily into the lower layers. As a result, most species in the lower layers must be shade-tolerant. Mean weight index decreased from the top toward the bottom layer, and tree density increased from the top downward. This trend resembled the mean weight-density trajectory of self-thinning plant populations.