Ecological Developmental Adaptability Life Sciences :
Ecological Dynamics


Associate Professor SAKAI Satoki
Campus Aobayama campus
Laboratory Ecological Integration
Tel +81-22-795-6697
E-mail sakai@tohoku.ac.jp

I specialize in the evolutionary ecology of plants. Our purpose is to investigate the ultimate cause as to why the ecological characteristics of plants evolved. We engage in theoretical analysis using mathematical models and the empirical research thereof.
Outside of the lab, I enjoy soccer. I am a big fan of Vegalta Sendai and the Japan national team.


Graduated, Faculty of Science, Kyoto University
Completed botany doctoral program (Doctor of Science), Graduate School of Science, University of Tokyo
Achieved current position after serving as a Researcher; Grassland Laboratory, Ministry of Agriculture, Forestry and Fisheries

Selected Publications
  1. Matsuhashi, S., Kudoh, H., Maki, M., Cartolano, M., Tsiantis, M., Itagaki, T., and Sakai, S.  (2016) Invasion history of Cardamine hirsuta in Japan inferred from genetic analyses of herbarium specimens and current populations.  Biological  Invasions 18:1939-1951.
  2. Sakai, S.  (2016) How have self-incompatibility haplotypes diversified? Generation of new haplotypes during the evolution of self-incompatibility from self-compatibility.  American Naturalist 188:163-174.
  3. Itagaki, T., Kimura, M. K., Maki, M. and Sakai, S.  (2016) Differential self-fertilization rates in response to variation in floral traits within inflorescences of Aquilegia buergerianavar. oxysepala (Ranunculaceae).  Botanical Journal of the Linnean Society 181:294-304.
  4. Oka, C., Itagaki, T., and Sakai, S.  (2016) Effect of the number of embryos in a seed and of seed size on seedling emergence and growth in polyembryonic Ophiopogon japonicusvar. umbrosus (Asparagaceae).  Botany 94:261-268.
  5. Matsubara, Y. and Sakai, S.  (2016) The role of flood regime on invasive success of exotic species growing in riparian environments.  Biological Invasions 18: 793-808.
  6. Fusato, Y., Itagaki, T., Oguro, M., and Sakai, S.  (2015) Effect of change in floral openness with floral age on floral display and reproduction in Gentiana.  Acta Oecologica 67:17-23.
  7. Itagaki, T., Kimura, M. K., Lian, L., and Sakai, S. (2015) Development of microsatellite markers for Aquilegia buergeriana var. oxysepala (Ranunculaceae), a vulnerable Japanese herb.  Plant Species Biology 30:159-162.
  8. Oguro, M. and Sakai, S.  (2015) Relation between flower head traits and florivory in Asteraceae: A phylogenetically controlled approach.  American Journal of Botany 102:407-416.
  9. Onodera, H., Oguro, M., and Sakai, S.  (2014) Effects of nutrient contents and defense compounds on herbivory in reproductive organs and leaves of Iris gracilipes.  Plant Ecology 215:1025-1035.
  10. Sakai, S. and Wakoh, H.  (2014) Initial invasion of gametophytic self-incompatibility alleles in the absence of tight linkage between pollen and pistil S alleles.  American Naturalist 184:248-257.
  11. Oguro, M. and Sakai, S. (2014) Difference in defense strategy in flower heads and leaves of Asteraceae: multiple species approach.  Oecologia 174:227-239.
  12. Sakai, S. (2013) Evolutionarily stable size of a megagametophyte: evolution of tiny megagametophytes of angiosperms from large ones of gymnosperms.  Evolution 67:539-547.
  13. Matsuhashi, S., Sakai, S., and Kudo, H.  (2012) Temperature-dependent fluctuation of stamen number in Cardamine hirsuta (Brassicaceae).  International Journal of Plant Sciences 173:391-398.

See the following.

Activities in Academic Societies

Ecological Society of Japan
Ecological Society of America
Society for the Study of Evolution
Botanical Society of America


Plant Evolutionary Ecology (5th semester)

Recent Activities

We are engaged in analysis using mathematical models and the verification thereof, concerning tradeoffs between seed size and number as well as optimum seed size The problem of how many seeds to create and of what size by using a fixed amount of resources is one that contributes significantly to life cycle strategies in plants. The bigger a seed that is made, the higher the germination rate needs to be of each individual seed. However, the number of seeds that can be produced decreases. Conversely, the smaller the seed that is created, the lower the individual germination rate, but the number of seeds that can be produced increases. So, what are the optimum size and number? Until now, research concerning this problem has hypothesized a tradeoff relationship in which seed size equals the amount of resources invested in seed production divided by the number of seeds. Essentially, the hypothesis is the size and number of seeds are an inverse proportion. The total amount of seed substance (seed size multiplied by seed number) does not change regardless of the number of seeds. However, we have shown theoretically that this inverse proportion tradeoff relationship is not feasible (Sakai and Harada 2001, Evolution 55: 467-476; American Naturalist 157: 348-359). We predict that even if you decrease the number of seeds, the seed size does not increase to the extent of a true inverse proportion (figure). The total amount of seed substance decreases the more you decrease the number of seeds. This occurs because resources decrease in value during seed production due to maintenance respiration (see our papers for details). Under Sakai and Harada’s tradeoff, sacrificing seed size to increase the number of seeds is advantageous, and, as such, optimum seed size is smaller than optimum seed size under the inverse proportion tradeoff. These predictions are backed by testing using Cardiocrinum cordatum (Sakai and Sakai 2005, Oikos 108:105-114).

Message to Students

The ecological characteristics of plants are truly diverse. For example, flower color and shape differ greatly between species, groups, and individuals. Seed size can range from big like the coconut to being like dust as are those of orchids. Our laboratory is attempting to understand why this diversity of ecological characteristics evolved. We are attempting to discover the reasons why these characteristics evolved from the perspective that having such characteristics was advantageous for survival and reproduction. Our research methods are centered on field research and theoretical analysis. Each student sets research themes and engages in research based on their own individual interests. Those who see the diversity of plants and are struck by the wonder of this, those who wish to understand why such diversity has evolved; why not research plant evolutionary ecology with us?