外来植物セイタカアワダチソウの抵抗性の時間的な動態：原産地と侵入地における植物-植食者相互作用の地理的変異

京都大学0048新制・課程博士博士(理学)甲第19529号理博第4189号新制||理||1601(附属図書館)32565京都大学大学院理学研究科生物科学専攻(主査)教授 大串 隆之, 教授 中野 伸一, 教授 曽田 貞滋学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDGA

Geographic variations in phenotypic traits of the exotic herb Solidago altissima and abundance of recent established exotic herbivorous insects

Many invasive plants increase aggressiveness after introduction. Since evolutionary forces such as herbivore pressure may change over different time scales, understanding the changes in biotic interactions in invasive plants through time can clarify the mechanism of their evolution in aggressiveness. In this study, we examined the geographic variation in phenotypic traits of Solidago altissima and the abundance of two exotic herbivorous insect species (the aphid, Uroleucon nigrotuberculatum and the lacebug, Corythucha marmorata), which are recently expanding their habitat on S. altissima populations over Japan. The two exotic insects were present at high density on S. altissima throughout their range. No differences in growth traits (plant height and number of leaves) were found among populations, and all plants examined appear to be exclusively hexaploid. Future studies on population genetics and common garden experiments are necessary to evaluate the potential evolutionary dynamics of the S. altissima after introduction

An exotic herbivorous insect drives the evolution of resistance in the exotic perennial herb

Invasive plants often experience rapid changes in biological interactions by escaping from their original herbivores at their new habitats, and sometimes re-associating with those herbivores afterwards. However, little is known about whether the temporal changes in herbivorous impact work as a selective agent for defensive traits of invaded plants. Solidago altissima (goldenrod) is a North American perennial that has widely invaded abandoned fields in Japan. Recently, an herbivorous insect Corythucha marmorata (lace bug), an exotic insect also from North America, which was first recorded in 2000 in Japan, has been expanding its habitat on S. altissima populations in Japan. In this study, we investigated whether the invasion of C. marmorata had a selective impact on the defensive traits of S. altissima, by conducting a field survey, a common garden experiment and microsatellite analysis. We compared quantitative genetic differentiation of traits (resistance, growth, and reproduction) and neutral molecular differentiation among 16 S. altissima populations with different establishment years of C. marmorata. The common garden experiment, in which plants were grown in a greenhouse and treated to either C. marmorata herbivory or no herbivory, revealed the presence of higher resistance, sexual reproduction, and asexual (rhizome) reproduction in populations subjected to a longer history of C. marmorata pressure. Such phenotypic variability among establishment years of lace bugs was likely driven by natural selection rather than stochastic events such as genetic drift and founder effects. In addition, when plants were exposed to lace bug herbivory, resistance had a positive relationship with sexual and asexual reproduction, although no relationship was found when plants were free from herbivory. These findings suggest that defensive traits in S. altissima have evolved locally in the last decade in response to the selective pressure of C. marmorata

Fauna of nocturnal moth species collected in a semi-natural grassland at Kanpu-zan in northern Japan

Semi-natural grasslands, which house species-rich ecosystems, have rapidly declined since the twentieth century due to land-use practices, such as agricultural intensification and abandonment. Owing to their diversity and known habitat associations, nocturnal moths are considered as one of the most suitable organisms to be studied for assessing the dynamics of species composition as a result of changes in landscape management of semi-natural grasslands. The present study provides the foremost description of nocturnal moth fauna of the semi-natural grassland at Kanpu-zan, northern Japan. Moth population data from 1987 were compared to the data collected in 2018 to evaluate the impact of decline in grasslands on species-richness. During the field sampling in 2018, a total of 226 nocturnal moth species were detected, which was nearly two-thirds of the number of species recorded in 1987, i.e. 396 species. The values obtained in 2018 were found to be nearly constant for different sites. For both periods, it was evident that moth fauna in Kanpu-zan mainly consisted of species that relied on woody plants. Amongst the species which were only recorded in 1987, 107 species were generalists that fed on plants that are commonly distributed in Kanpu-zan. No moth species were recorded that depended upon endangered or extinct plant food sources. Thus, it is unlikely that the decline in the number of moth species in Kanpu-zan was due to the loss in plant food sources. Our results suggest that environmental factors other than food plants may have caused decline and changes in nocturnal moth fauna. More studies on various organism fauna are needed for understanding the conservation of semi-natural grassland, considering that the loss of semi-natural grasslands is one of the major threats to biodiversity

Deer overbrowsing on autumn-flowering plants causes bumblebee decline and impairs pollination service

Increased ungulate browsing has altered the composition of plant communities and food webs of forest ecosystems in many regions around the world. To evaluate the cascading impact of deer browsing on pollination and plant reproduction is critical to understand the roles of species interactions in maintaining plant populations and for conservation management. In this study, we investigated the relationships among floral resources of understory herbaceous plants, pollinator visitation, and fruit set of shrub species based on data accumulation over three years in six temperate deciduous forests with deer and without deer.We found that in deer browsed sites, the visitation rate of bumblebees had decreased due to severe reduction in the coverage of autumn-flowering herbaceous plants, while the effect varied between bumblebee species. On the other hand, other insect taxa showed no dependence on variation in autumn floral resources. The two genera of bumblebee-pollinated shrubs showed reduced fruit set due to severe decline in autumn-flowering herbaceous plants and bumblebee visitation (Weigela: -18.5% and Rhododendron: -21.9%). In contrast, the fruit set of shrubs pollinated by insects that did not show dependence on autumn floral resources were not negatively affected by deer browsing. Our results suggest that deer browsing have not only caused negative effects on herbaceous plants, but in addition have negative indirect effects on reproduction of woody plants through cascading effects of pollination linkages

Appendix A. Supplemental tables and a figure.

Supplemental tables and a figure

Multiple and mass introductions from limited origins: genetic diversity and structure of Solidago altissima in the native and invaded range.

Understanding the origins and diversity of invasive species can reveal introduction and invasion pathways, and inform an effective management of invasive species. Tall goldenrod, Solidago altissima, is a herbaceous perennial plant native to North America and it has become a widespread invasive weed in East Asian countries. We used microsatellite and chloroplast DNA markers to obtain information on neutral processes and on genetic diversity in native and invaded populations of S. altissima and to infer how it invaded and spread in Japan. We found that introduced (n = 12) and native (n = 20) populations had similar levels of genetic diversity at nuclear SSR loci. Genetic structure analysis indicated that at least two independent colonization events gave rise to current S. altissima populations in Japan. The majority (68%) of the Japanese S. altissima were genetically similar and likely shared a common origin from a single or a small number of populations from the southern USA populations, while the populations in Hokkaido were suggested to arise from a different source. Our results suggest that multiple and mass introductions have contributed to the persistence and rapid adaptation of S. altissima promoting its widespread establishment throughout Japan

Appendix B. A table of population collections of Solidago altissima used in this study.

A table of population collections of Solidago altissima used in this study