Yoh Iwasa

@kyudai.jp

Department of Biology
Kyushu University



                    

https://researchid.co/yohiwasa

Yoh Iwasa is a professor emeritus at Kyushu University, Japan. He received PhD from Kyoto University (Theoretical Biophysics) in 1980. After postdoctoral studies at Stanford and Cornell, he joined the faculty of Department of Biology, Kyushu University in 1985. Dr Yoh Iwasa started his carrier in the theoretical study of ecology, evolution, and animal behavior, including the evolution of mate preference, the dynamics of tropical forests, and social-ecological coupled dynamics for ecosystem management. More recently he has also been working on biological rhythm, cancer, development, and immune system, as well as cultural/social studies. He has repeatedly found that the same mathematical and computational methods are applicable to diverse branches of biology, and similar concepts are able to give insights in different subfields of life sciences. Director, Institute of Advanced Study Kyushu University (since 2010). FHM of American Academy of Arts and Sciences (since 2006).

EDUCATION

1975 B Sc Kyoto University, Japan
1980 Ph.D Kyoto University, Japan

RESEARCH INTERESTS

mathematical biology

374

Scopus Publications

28004

Scholar Citations

83

Scholar h-index

283

Scholar i10-index

Scopus Publications

  • Age-dependence of food allergy due to decreased supply of naïve T cells
    Yuna Kotsubo, Akane Hara, Rena Hayashi, and Yoh Iwasa
    Elsevier BV



  • Genetic diversity within a tree and alternative indexes for different evolutionary effects
    Yoh Iwasa, Sou Tomimoto, and Akiko Satake
    Cambridge University Press (CUP)
    Abstract Trees, living for centuries, accumulate somatic mutations in their growing trunks and branches, causing genetic divergence within a single tree. Stem cell lineages in a shoot apical meristem accumulate mutations independently and diverge from each other. In plants, somatic mutations can alter the genetic composition of reproductive organs and gametes, impacting future generations. To evaluate the genetic variation among a tree’s reproductive organs, we consider three indexes: mean pairwise phylogenetic distance ( $\\overline{D}$ ), phylogenetic diversity ( $PD$ ; sum of branch lengths in molecular phylogeny) and parent-offspring phylogenetic distance ( ${D}_{PO}$ ). The tissue architecture of trees facilitated the accumulation of somatic mutations, which have various evolutionary effects, including enhancing fitness under strong sib competition and intense host-pathogen interactions, efficiently eliminating deleterious mutations through epistasis and increasing genetic variance in the population. Choosing appropriate indexes for the genetic diversity of somatic mutations depends on the specific aspect of evolutionary influence being assessed.

  • Optimal seasonal schedule for the production of isoprene, a highly volatile biogenic VOC
    Yoh Iwasa, Rena Hayashi, and Akiko Satake
    Springer Science and Business Media LLC
    AbstractThe leaves of many trees emit volatile organic compounds (abbreviated as BVOCs), which protect them from various damages, such as herbivory, pathogens, and heat stress. For example, isoprene is highly volatile and is known to enhance the resistance to heat stress. In this study, we analyze the optimal seasonal schedule for producing isoprene in leaves to mitigate damage. We assume that photosynthetic rate, heat stress, and the stress-suppressing effect of isoprene may vary throughout the season. We seek the seasonal schedule of isoprene production that maximizes the total net photosynthesis using Pontryagin’s maximum principle. The isoprene production rate is determined by the changing balance between the cost and benefit of enhanced leaf protection over time. If heat stress peaks in midsummer, isoprene production can reach its highest levels during the summer. However, if a large portion of leaves is lost due to heat stress in a short period, the optimal schedule involves peaking isoprene production after the peak of heat stress. Both high photosynthetic rate and high isoprene volatility in midsummer make the peak of isoprene production in spring. These results can be clearly understood by distinguishing immediate impacts and the impacts of future expectations.

  • Human movement avoidance decisions during Coronavirus disease 2019 in Japan
    Ryosuke Omori, Koichi Ito, Shunsuke Kanemitsu, Ryusuke Kimura, and Yoh Iwasa
    Elsevier BV



  • Temporal Pattern of the Emergence of a Mutant Virus Escaping Cross-Immunity and Stochastic Extinction Within a Host
    Rena Hayashi and Yoh Iwasa
    Springer Science and Business Media LLC
    AbstractA high mutation rate of the RNA virus results in the emergence of novel mutants that may escape the immunity activated by the original (wild-type) strain. However, many of them go extinct because of the stochasticity due to the small initial number of infected cells. In a previous paper, we studied the probability of escaping stochastic extinction when the novel mutant has a faster rate of infection and when it is resistant to a drug that suppresses the wild-type virus. In this study, we examine the effect of escaping the immune reaction of the host. Based on a continuous-time branching process with time-dependent rates, we conclude the chance for a mutant strain to be established $$p\\left(t\\right)$$ p t decreases with time $$t$$ t since the wild-type infection when the mutant is produced. The number of novel mutants that can escape extinction risk has a peak soon after the wild-type infection. The number of novel escape mutations produced per patient in the early phase of host infection is small both for very strong and very weak immune responses, and it attains its maximum value when immune activity is of an intermediate strength.

  • Mathematical modeling for developmental processes
    Yoh Iwasa
    Wiley
    We review several mathematical models and concepts in developmental biology that have been established over the last decade. [1] Feedback vertex set: Ascidian embryos contain cells of seven types, and cell fate is controlled by approximately 100 interacting genes. "Feedback vertex set" of the directed graph of gene regulatory network consists of a small number of genes. By experimentally manipulating them, we can differentiate cells into any cell type. [2] Tissue deformation: Describing morphological changes in tissues and relating them to gene expression and other cellular processes is a key in understanding morphogenesis. Expansion and anisotropy of the tissue are described by "deformation tensor" at each location. A study on chick limb bud formation revealed that both the volume growth rate and anisotropy in deformation differed significantly between locations and stages. [3] Mechanobiology: Forces operating on each cell may alter cell shape and gene expression, which may subsequently exert forces on their surroundings. Measurements of force, tissue shape, and gene expression help us understand autonomous tissue deformation. [4] Adaptive design of development: An optimal growth schedule in fluctuating environments explains the growth response to starvation in Drosophila larvae. Adaptive placement of morphogen sources makes development robust to noises. This article is protected by copyright. All rights reserved.

  • The genetic structure within a single tree is determined by the behavior of the stem cells in the meristem
    Yoh Iwasa, Sou Tomimoto, and Akiko Satake
    Oxford University Press (OUP)
    Abstract Genomic sequencing revealed that somatic mutations cause a genetic differentiation of the cells in a single tree. We studied a mathematical model for stem cell proliferation in the shoot apical meristem (SAM). We evaluated the phylogenetic distance between cells sampled from different portions of a shoot, indicating their genetic difference due to mutations accumulated during shoot elongation. The plant tissue has cell walls that suppress the exchange of location between cells. This leads to the genetic differentiation of cells according to the angle around the shoot and a larger genetic variance among cells in the body. The assumptions are as follows: stem cells in the SAM normally undergo asymmetric cell division, producing successor stem cells and differentiated cells. Occasionally, a stem cell fails to leave its successor stem cell and the vacancy is filled by the duplication of one of the nearest neighbor stem cells. A mathematical analysis revealed the following: the genetic diversity of cells sampled at the same position along the shoot increases with the distance from the base of the shoot. Stem cells hold a larger variation if they are replaced only by the nearest neighbors. The coalescent length between two cells increases not only with the difference in the position along the shoot but also in the angle around the shoot axis. The dynamics of stem cells at the SAM determine the genetic pattern of the entire shoot.


  • Theoretical studies of diverse sexual patterns in marine animals
    Yoh Iwasa and Sachi Yamaguchi
    The Royal Society
    Marine animals show diverse and flexible sexual systems. Here, we review several advancements of theoretical studies made in the last decade. (i) Sex change in coral fishes is often accompanied by a long break in reproductive activity. The delay can be shortened by retaining the inactive gonad for the opposite sex. (ii) Barnacles adopt diverse sexual patterns. The game model was analysed assuming that newly settled larvae choose either growth or immediate reproduction and large individuals adjust male–female investments. (iii) Some parasitic barnacles produce larvae with sexual size dimorphism and others produce larvae with the sex determined after settlement on hosts. (iv) In some fish and many reptiles, sex is determined by the temperature experienced as eggs. The dynamics of sex hormones were studied when the enzymatic reaction rates were followed by the Arrhenius equation. The FMF pattern (male at intermediates temperature; female both at high and low temperatures) required some reactions with enhanced temperature dependence at higher temperatures. The game model provides a useful framework for understanding diverse sexual patterns if we incorporate various constraints, such as unpredictability, cost of trait change and social situations. For further developments, we need to consider constraints imposed by physiological and molecular mechanisms.

  • On the role of eviction in group living sex changers
    Yoh Iwasa and Sachi Yamaguchi
    Springer Science and Business Media LLC
    Abstract In most sex-changing fishes in coral reefs, a dominant male and multiple females form a mating group (harem). In a few species, the subordinates are simultaneous hermaphrodites that may act as sneakers. In this paper, we ask whether the subordinates in most sex changers choose to be female or whether they are forced to give up their male function to avoid eviction by the harem holder. We consider a game model in which (1) the dominant male evicts some hermaphroditic subordinates if the risk of sperm competition in regard to fertilizing eggs is high, and (2) each subordinate individual chooses its own sex allocation considering the risk of being evicted. In the evolutionarily stable state, the dominant male evicts subordinates only when the subordinates vary greatly in their reproductive resources. All the subordinate individuals are female if the summed male function of the subordinates is smaller than that of the dominant male. Otherwise, all the subordinates are hermaphrodites, and the large individuals have the same male investment but a greatly different female investment, while small individuals have a reduced male investment to avoid eviction risk. We conclude that situations in which the sex allocation of subordinates is affected by the possibility of eviction by the harem holder are rather limited Significance statement We studied the role of eviction in social evolution. In most sex-changing fishes in coral reefs, a dominant male and multiple females form a mating group. In a few species, subordinates are simultaneous hermaphrodites. We asked whether the subordinates are forced to give up their male function to avoid eviction by the harem holder. We examined a game model in which the dominant male evicts hermaphroditic subordinates with a high risk of sperm competition, and each subordinate chooses its own sex allocation considering the eviction risk. We derived mathematical conditions for when subordinates are females or hermaphrodites in the ESS. The model demonstrated that the control by the dominant over subordinate reproductive decisions is rather limited.






  • The Great Oxygenation Event as a consequence of ecological dynamics modulated by planetary change
    Jason Olejarz, Yoh Iwasa, Andrew H. Knoll, and Martin A. Nowak
    Springer Science and Business Media LLC
    AbstractThe Great Oxygenation Event (GOE), ca. 2.4 billion years ago, transformed life and environments on Earth. Its causes, however, are debated. We mathematically analyze the GOE in terms of ecological dynamics coupled with a changing Earth. Anoxygenic photosynthetic bacteria initially dominate over cyanobacteria, but their success depends on the availability of suitable electron donors that are vulnerable to oxidation. The GOE is triggered when the difference between the influxes of relevant reductants and phosphate falls below a critical value that is an increasing function of the reproductive rate of cyanobacteria. The transition can be either gradual and reversible or sudden and irreversible, depending on sources and sinks of oxygen. Increasing sources and decreasing sinks of oxygen can also trigger the GOE, but this possibility depends strongly on migration of cyanobacteria from privileged sites. Our model links ecological dynamics to planetary change, with geophysical evolution determining the relevant time scales.

  • Evolution of life cycle dimorphism: An example of sacoglossan sea slugs
    Sachi Yamaguchi, Yoichi Yusa, and Yoh Iwasa
    Elsevier BV
    Many sea slugs of Sacoglossa (Mollusca: Heterobranchia) are sometimes called "solar-powered sea slugs" because they keep chloroplasts obtained from their food algae and receive photosynthetic products (termed kleptoplasty). Some species show life cycle dimorphism, in which a single species has some individuals with a complex life cycle (the mother produces planktotrophic larvae, which later settle in the adult habitat) and others with a simple life cycle (mothers produce benthic offspring by direct development or short-term nonfeeding larvae in which feeding planktonic stages are skipped). Life cycle dimorphism is not common among marine species. In this paper, we ask whether some aspects of the ecology of solar-powered sea slugs have promoted the evolution of life cycle dimorphism in them. We study the population dynamics of the two life-cycle types that differ in summer (one with planktonic life and the other with benthic life), but both have benthic life in other seasons. We obtain the conditions in which two types with different life cycles coexist stably or a single type generating offspring with different life cycles evolves. We conclude that the stable coexistence of two life cycles can evolve if benthic individuals in summer experience strongly density-dependent processes or if the between-year fluctuation of biomass growth in summer is very large. We discuss whether these results match the life cycles of solar-powered sea slugs with life cycle dimorphism.

  • Spatial distribution of gut microbes along the intestinal duct
    Shintaro Hishida and Yoh Iwasa
    Elsevier BV
    We studied the spatial pattern of two microbial strains along the intestinal duct. Probiotic bacteria acidify the environment and suppress their competitors, non-probiotic bacteria. Food resources are supplied from the proximal end, and there exists a flow from the proximal end to the distal end. In the steady state, we observed three major patterns. In the "standard" pattern (ST), the abundance of probiotic bacteria was high in the proximal end, and it decreased toward the distal end; in contrast, the abundance of non-probiotic bacteria was low in the proximal end, and it increased toward the distal end. In the "proximal reversion" pattern (PR), non-probiotic bacteria were dominant and probiotic bacteria were suppressed in the proximal portion of the duct. Subsequently, the abundance values of the two competitors switched, followed by a spatial pattern similar to ST. In the "distal suppression" pattern (DS), the pattern was similar to ST in the proximal portion; however, toward the distal end, the abundance of probiotic bacteria remained at an intermediate level and suppressed the abundance of non-probiotic bacteria, resulting in a peak abundance of non-probiotic bacteria in the middle portion of the duct. We additionally discuss the nonmonotonic increase in the abundance of non-probiotic bacteria in ST and the transition of the spatial pattern from one type to another due to changes in the resource abundance in the influx.


  • Eco-evolutionary dynamics may show an irreversible regime shift, illustrated by salmonids facing climate change
    Junnosuke Horita, Yoh Iwasa, and Yuuya Tachiki
    Springer Science and Business Media LLC
    AbstractThe enhanced or reduced growth of juvenile masu salmon (Oncorhynchus masou masou) may result from climate changes to their environment and thus impact on the eco-evolutionary dynamics of their life-history choices. Male juveniles with status, i.e., if their body size is larger than a threshold, stay in the stream and become resident males reproducing for multiple years, while those with smaller status, i.e., their body size is below the threshold, migrate to the ocean and return to the stream one year later to reproduce only once. Since juvenile growth is suppressed by the density of resident males, the fraction of resident males may stay in equilibrium or fluctuate wildly over a 2-year period. When the threshold value evolves, the convergence stable strategy may generate either an equilibrium or large fluctuations of male residents. If environmental changes occur faster than the rate of evolutionary adaptation, the eco-evolutionary dynamics exhibit a qualitative shift in the population dynamics. We also investigated the relative assessment models, in which individual life-history choices are made based on the individual’s relative status within the juvenile population. The eco-evolutionary dynamics are very different from the absolute assessment model, demonstrating the importance of understanding the mechanisms of life history choices when predicting the impacts of climate change.

  • Recurrent speciation rates on islands decline with species number
    Ryo Yamaguchi, Yoh Iwasa, and Yuuya Tachiki
    The Royal Society
    In an archipelagic system, species diversity is maintained and determined by the balance among speciation, extinction and migration. As the number of species increases, the average population size of each species decreases, and the extinction likelihood of any given species grows. By contrast, the role of reduced population size in geographic speciation has received comparatively less research attention. Here, to study the rate of recurrent speciation, we adopted a simple multi-species two-island model and considered symmetric interspecific competition on each island. As the number of species increases on an island, the competition intensifies, and the size of the resident population decreases. By contrast, the number of migrants is likely to exhibit a weaker than proportional relationship with the size of the source population due to rare oceanic dispersal. If this is the case, as the number of species on the recipient island increases, the impact of migration strengthens and decelerates the occurrence of further speciation events. According to our analyses, the number of species can be stabilized at a finite level, even in the absence of extinction.

RECENT SCHOLAR PUBLICATIONS

  • Branching architecture affects genetic diversity within an individual tree
    Y Iwasa, S Tomimoto, A Satake
    Journal of Theoretical Biology, in press; Available at biRxiv 2025

  • Age-dependence of food allergy due to decreased supply of naive T cells
    Y Kotsubo, A Hara, R Hayashi, Y Iwasa.
    Journal of Theoretical Biology 602 (112060), doi.org/10.1016/j.jtbi.2025.112060 2025

  • Optimal seasonal schedule for producing biogenic volatile organic compounds for tree defense
    Y Iwasa, R Hayashi, S Akiko
    Journal of Theoretical Biology 596 (111986), doi.org/10.1016/j.jtbi.2024.111986 2025

  • Modeling innate immunity causing chronic inflammation and tissue damage
    K Matsuo, Y Iwasa
    Bulletin of Mathematical Biology 87 (art 34), doi.org/10.1007/s11538-024-01410-0 2025

  • Thymic involution as an adaptive schedule for combating diverse pathogens
    Y Iwasa, K Matsuo
    bioRxiv, 2024.12. 21.629868 2024

  • Genetic diversity within a tree and alternative indexes for different evolutionary effects
    Y Iwasa, S Tomimoto, A Satake
    Quantitative Plant Biology 5 (e11, 1-9.), https://dx.doi.org/10.1017/qpb.2024.9 2024

  • Optimal seasonal schedule for the production of isoprene, a highly volatile biogenic VOC
    Y Iwasa, R Hayashi, A Satake
    Scientific Reports 14 (12311), doi.org/10.1038/s41598-024-62975-3 2024

  • Human movement avoidance decisions during Coronavirus disease 2019 in Japan
    R Omori, K Ito, S Kanemitsu, R Kimura, Y Iwasa
    Journal of Theoretical Biology 585, 111795 2024

  • Viral rebound occurrence immediately after drug discontinuation involving neither drug resistance nor latent reservoir
    R Hayashi, A Hara, Y Iwasa
    Journal of Theoretical Biology 582, 111767 2024

  • Branching architecture affects genetic diversity within an individual tree
    S Tomimoto, Y Iwasa, A Satake
    bioRxiv, 2023.10. 02.560431 2023

  • Multiple colonies of cancer involved in mutual suppression with the immune system
    K Matsuo, R Hayashi, Y Iwasa
    Journal of Theoretical Biology 572, 111577 2023

  • Temporal pattern of the emergence of a mutant virus escaping cross-immunity and stochastic extinction within a host.
    R Hayashi, Y Iwasa
    Bulletin of Mathematical Biology 85, 81 (doi: 10.1007/s11538-023-01184) 2023

  • Mathematical modeling for developmental processes
    Y Iwasa
    Development Growth and Differentiation 2023, 1-10. doi: 10.1111/dgd.12856 2023

  • The genetic structure within a single tree is determined by the behavior of the stem cells in the meristem
    Y Iwasa, S Tomimoto, A Satake
    Genetics 223, iyad020 doi:10.1093/genetics/iyad020 2023

  • Waves of infection emerging from coupled social and epidemiological dynamics
    Y Iwasa, R Hayashi
    Journal of Theoretical Biology 558, 111366 2023

  • Theoretical studies of diverse sexual patterns in marine animals
    Y Iwasa, S Yamaguchi
    Proceedings of the Royal Society B 290 (1990), 20222229 2023

  • On the role of eviction in group living sex changers
    Y Iwasa, S Yamaguchi
    Behavioral Ecology and Sociobiology 76 (4), 49 2022

  • Escaping stochastic extinction of mutant virus: temporal pattern of emergence of drug resistance within a host
    R Hayashi, S Iwami, Y Iwasa
    Journal of Theoretical Biology 537, 111029 2022

  • Evolutionary game of life-cycle types in marine benthic invertebrates: feeding larvae versus nonfeeding larvae versus direct development
    Y Iwasa, Y Yusa, S Yamaguchi
    Journal of Theoretical Biology 537, 111019 2022

  • Optimal composition of chloride cells for osmoregulation in a randomly fluctuating environment
    Y Uchiyama, Y Iwasa, S Yamaguchi
    Journal of Theoretical Biology 537, 111016 2022

MOST CITED SCHOLAR PUBLICATIONS

  • Influence of nonlinear incidence rates upon the behavior of SIRS epidemiological models
    W Liu, SA Levin, Y Iwasa
    Journal of mathematical biology 23, 187-204 1986
    Citations: 1077

  • Dynamics of chronic myeloid leukaemia
    F Michor, TP Hughes, Y Iwasa, S Branford, NP Shah, CL Sawyers, ...
    Nature 435 (7046), 1267-1270 2005
    Citations: 1001

  • Sexual selection
    M Andersson, Y Iwasa
    Trends in ecology & evolution 11 (2), 53-58 1996
    Citations: 955

  • The evolution of costly mate preferences II. The “handicap” principle
    Y Iwasa, A Pomiankowski, S Nee
    Evolution 45 (6), 1431-1442 1991
    Citations: 948

  • Demographic theory for an open marine population with space‐limited recruitment
    J Roughgarden, Y Iwasa, C Baxter
    Ecology 66 (1), 54-67 1985
    Citations: 703

  • Prey distribution as a factor determining the choice of optimal foraging strategy
    Y Iwasa, M Higashi, N Yamamura
    The American Naturalist 117 (5), 710-723 1981
    Citations: 672

  • Dynamics of cancer progression
    F Michor, Y Iwasa, MA Nowak
    Nature reviews cancer 4 (3), 197-205 2004
    Citations: 649

  • How should we define goodness?—reputation dynamics in indirect reciprocity
    H Ohtsuki, Y Iwasa
    Journal of theoretical biology 231 (1), 107-120 2004
    Citations: 553

  • The leading eight: social norms that can maintain cooperation by indirect reciprocity
    H Ohtsuki, Y Iwasa
    Journal of theoretical biology 239 (4), 435-444 2006
    Citations: 548

  • The evolution of costly mate preferences I. Fisher and biased mutation
    A Pomiankowski, Y Iwasa, S Nee
    Evolution 45 (6), 1422-1430 1991
    Citations: 500

  • Indirect reciprocity provides only a narrow margin of efficiency for costly punishment
    H Ohtsuki, Y Iwasa, MA Nowak
    Nature 457 (7225), 79-82 2009
    Citations: 404

  • The evolution of cooperation in a lattice-structured population
    M Nakamaru, H Matsuda, Y Iwasa
    Journal of theoretical Biology 184 (1), 65-81 1997
    Citations: 389

  • Theory of oviposition strategy of parasitoids. I. Effect of mortality and limited egg number
    Y Iwasa, Y Suzuki, H Matsuda
    Theoretical population biology 26 (2), 205-227 1984
    Citations: 358

  • The evolution of mate preferences for multiple sexual ornaments
    Y Iwasa, A Pomiankowski
    Evolution 48 (3), 853-867 1994
    Citations: 348

  • Onymity promotes cooperation in social dilemma experiments
    Z Wang, M Jusup, RW Wang, L Shi, Y Iwasa, Y Moreno, J Kurths
    Science advances 3 (3), e1601444 2017
    Citations: 332

  • Shoot/root balance of plants: optimal growth of a system with many vegetative organs
    Y Iwasa, J Roughgarden
    Theoretical population biology 25 (1), 78-105 1984
    Citations: 329

  • Aggregation in model ecosystems. I. Perfect aggregation
    Y Iwasa, V Andreasen, S Levin
    Ecological Modelling 37 (3-4), 287-302 1987
    Citations: 311

  • Stochastic tunnels in evolutionary dynamics
    Y Iwasa, F Michor, MA Nowak
    Genetics 166 (3), 1571-1579 2004
    Citations: 297

  • Exploiting a cognitive bias promotes cooperation in social dilemma experiments
    Z Wang, M Jusup, L Shi, JH Lee, Y Iwasa, S Boccaletti
    Nature communications 9 (1), 2954 2018
    Citations: 294

  • Evolution of resistance during clonal expansion
    Y Iwasa, MA Nowak, F Michor
    Genetics 172 (4), 2557-2566 2006
    Citations: 289