Biology subjects

Ishii, N. I.

Publications and source records attributed to Ishii, N. I..

3 recordsLinked to original sources

bioRxiv2024

Genetic diversity and differentiation of a mycoheterotrophic orchid (Cymbidium macrorhizon) under urbanization

Urbanization exerts substantial pressures on genetic diversity of plant species. However, depending on species-specific life history, the direction/magnitude of urbanization impacts can vary. To elucidate relationships between life history and urbanization effects, there are needs to accumulate the knowledge on genetic diversity/differentiation along urban-rural gradients for species with unique traits. We examined these facets based on genome-wide single nucleotide polymorphisms of a mycoheterotrophic and vegetative-dormant orchid, Cymbidium macrorhizon, for eleven populations in remnant forests along an urban gradient within the Tokyo metropolitan area, Japan. The reduced inbreeding coefficient and increased genetic differentiation were observed with increased proportion of surrounding urban land-use 50 years ago rather than in recent years. This pattern might reflect lowest heterozygosity under intensive urbanization due to population bottleneck and genetic drift due to habitat shrinkage and fragmentation. The significant impacts of past landscape on the indices might indicate time lags of genetic erosion, namely intra-specific extinction debt, due to longevity and dormancy. Therefore, 30% increase of urban land-use since 1970s has not yet affected genetic erosion, resulting in its progression in the future. We emphasize the importance not only to assess genetic diversity but also to connect the assessments with life history and spatiotemporal urbanization impacts.

ecology↗

bioRxiv2022

Abrupt shifts in the plant species richness and community composition along an aridity gradient in the Mongolian grasslands

Aridity, edaphic variables related to aridity, and livestock grazing are major drivers of plant community composition across dryland grasslands. With accounting these factors, little is known about differences in determinants and changing patterns along aridity gradients with different average of aridity. Thus, the comparative investigations of communities without and with grazing in semi-arid and arid regions are suitable to clarify the difference in compositional responses along aridity gradients between potential vegetations and degraded ones with grazing. We investigated compositional changes of communities without/with grazing in semi-arid (north) /arid (south) regions across Mongolia. The compositional changes based on Bray-Curtis dissimilarity were investigated by generalized dissimilarity modeling, including geographic distance, aridity, soil pH, and sand and clay contents as independent variables. The determinants and changing patterns of community composition were compared among the four groups. Aridity had significant impacts on community composition regardless of the regions and the absence/presence of grazing. However, without the dependency on grazing, the difference in response patterns was observed between the regions. The compositional change was steeper especially at the upper edge of aridity rather than the lower edge in the arid region. This indicates the vulnerability of plant communities to aridity shifts due to future climate change in desert steppe of Mongolia. In addition, regardless of the regions, the effects of soil pH on community composition were eliminated by grazing. Because soil pH indirectly affected by aridity shifts can have impacts on community composition of potential vegetations without grazing, the long-term monitoring of vegetation dynamics needs observations of both of communities without and with grazing.

ecology↗

bioRxiv2022

Extremely low level of genetic diversity in Gentiana yakushimensis, an endangered species in Yakushima Island, Japan

Rare or endangered species largely contributing to global biodiversity are essential components of ecosystems. Because genetic diversity depends not only on apparent population size but also demographic processes, the conservation priority of endangered species based on population genetics needs to be assessed by comparison with common congeners and demographic events. In this study, we performed population genetic analysis for Gentiana yakushimensis Makino, a rare and endangered plant species with an isolated distribution on Yakushima Island, Japan. We performed comparison of genetic diversity with the congener (Gentiana triflora Pall. var. japonica (Kusn.) H.Hara), demographic inference, and bottleneck test based on genome-wide single nucleotide polymorphisms. The result was that G. yakushimensis had an extremely low genetic diversity level and a high inbreeding coefficient level compared to those of the congener. The population of G. yakushimensis was estimated to experience an expansion during the Last Glacial Maximum and a recent bottleneck by the demographic inference and the bottleneck test. Therefore, the low level of genetic diversity of this species might have resulted from the impact of the recent bottleneck and the long-term maintenance of a small population size. Due to the long lifespan of the genus Gentiana, the current level of genetic diversity probably does not reflect a large part of recent demographic events, which requires long-term monitoring of changes in genetic diversity to identify the time lag between the reduction in apparent population size and genetic diversity as a future outlook.

genetics↗