Organizer: Gaku Takimoto (University of Tokyo)
6/Oct. | 15:00–18:00 | A会場
Speciation is a more-than-ever exciting field of study in evolutionary biology. Extensive molecular genetic data from advanced technologies and better conceptual understanding on the roles of natural selection in species formation under gene flow have started to unveil that speciation is not only past events, but actively forming current biodiversity. This plenary symposium features talks including up-to-date topics by researchers whose model systems of plants and invertebrate and vertebrate animals have led recent advances of speciation research. We hope to seek with audience future direction of speciation research and future of biodiversity.
A major challenge for evolutionary biologists is to explain the extraordinary species richness and diversity of organisms. We will discuss progress in our understanding of the key evolutionary process, speciation, with special reference to the radiation of Darwin’s Finches. We draw upon the results of a long-term field study of finch populations spanning four decades, combined with laboratory investigations of the molecular genetic basis of beak variation and development. The process of speciation in the finches has been inferred by comparing the ecology and phylogeny of the species, and has been studied directly on the small island of Daphne Major. Introgressive hybridization has been an important factor in two respects, enhancing the potential for adaptive change by increasing additive genetic variation, and in the formation of a new species.
One of the great surprises of the genomic revolution has been the frequency with which footprints of hybridization and introgression have been detected across the tree of life. Even the human lineage has not been exempt from introgression with its close relatives. While such widespread genetic exchange was predicted by Edgard Anderson in his classic 1949 monograph, Introgressive Hybridization, its evolutionary significance remains uncertain due to the difficulty of distinguishing between adaptive and neutral introgression. In this presentation, I will discuss two approaches my collaborators and I have taken in annual sunflowers to address this problem. First, I will describe a long-term field experiment, in which we have tracked genotypic and phenotypic evolution in four experimental hybrid populations for up to fourteen generations. This has allowed us to ask whether and how often introgressed alleles have increased in frequency relative to native alleles and whether such changes have been repeatable across populations. Second, I will present a large scale genome wide association study involving circa 1500 genotypes across three hybridizing wild species. With these data we can test how often selective sweeps take advantage of introgressed versus native alleles, and whether such introgression is an important cause of parallel evolution. Preliminary results offer support for Edgar Anderson’s prescient conjecture that “the wide dispersal of introgressive genes (perceptible only to the exquisitely precise techniques) would be a phenomenon of fundamental importance.”
Resilience is the capacity of a system to resist damage and recover quickly following a perturbation, thus returning to its former state. In biology, this concept is most often applied to ecosystems. However, it also applies to evolutionary systems of multiple, interconnected populations. For example, processes such as gene flow, recombination, and negative frequency-dependent selection can make populations ‘resilient’ such that they resist sustained directional change. Speciation thus occurs only when resilience breaks down, for example due to strong directional selection or geographic barriers to gene flow. I will illustrate these concepts using 25 years of field, experimental, and genomic data from Timema cristinae stick-insect populations. In turn, I will show how evolutionary dynamics within this insect species can have far-reaching consequences for communities and the ecosystem.
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This symposium is supported by Naito Foundation, Springer Japan, and the 140th Founding Anniversary Fund of the Graduate School of Agricultural and Life Sciences, The University of Tokyo (the following companies have generously donated a significant amount to the Fund: Asahi Group Holdings, Ltd., ASAHI INDUSTRIES CO., LTD, Kikkoman Corporation, Kewpie Corporation, Kirin Company Limited, Gurunavi, Inc., Suntory Holdings Limited, Nice Holdings, Inc., Nippon Paper Industries, Co., Ltd., The Norinchukin Bank, B.E. Marubishi Co., Ltd., Yanmar Co., Ltd, and Lotte Co., Ltd.)