MEE Seminar

Mathematical Ecology & Evolution Seminar (MEE Seminar)

Everyone is welcome to attend the MEE seminar.

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MEE Seminar (No. 040) 

Date: Dec. 13. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A206
Campus map in Japanese   in English

Shigeki Nakagome, Kenji Fukumizu, Shuhei Mano
(The Institute of Statistical Mathematics)

Application of kernel approximate Bayesian computation
for population genetic study

Abstract:
Approximate Bayesian Computation (ABC), which is a likelihood-free approach for Bayesian inferences, is a rejection-based method that applies a tolerance of dissimilarity between summary statistics from observed and simulated data. The approximation to a posterior density given data can be improved by adding summary statistics. Acceptance rates, however, significantly decrease with increasing number of summary statistics in the limit of zero tolerance. Here, we apply a new kernel-based ABC proposed by Fukumizu et al. (2011) into population genetic study and evaluate the performance of demographic inferences using a large number of summary statistics.


MEE Seminar (No. 039) 

Date: Dec. 6. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A206
Campus map in Japanese   in English

Tomoko TAKEMURA
(Nara Women's University)

Brownian motion and a harmonic transform for one
dimensional diffusion processes

Abstract:
I introduce Brownian motion on a compact domain with the end points where the reflecting boundary is posed and I show its known results. I will mention my recent works, "a harmonic transform of one dimensional diffusion processes" and "Elementary solution of Bessel processes with boundary conditions".


MEE Seminar (No. 038) 

Date: Nov. 30. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A306
Campus map in Japanese   in English

Jun Nakabayashi
(Yokohama City University, Faculty of Medicine Department of Immunology)

Theoretical studies of the intracellular dynamics and
within host evolution of viruses.

Abstract:
Recently, the detailed mechanism of viral replication is revealed according to the development of the molecular biological technique. In addition to these microscopic findings, it is necessary to understand the viral replication from the dynamical aspect for the clarification of the whole picture of the viral infection. I constructed mathematical models to investigate the intracellular replication dynamics for viruses, HSV-1, HBV and HCV. Each virus has the unique life cycle, and its intracellular replication dynamics is then varied. The mechanisms of the viral replication are evaluated by using the mathematical model. I would like to show the characteristic regulatory mechanism to optimize the viral reproduction revealed through these theoretical studies of the intracellular viral replication and within host evolution of virus.


MEE Seminar (No. 037) 

Date: Nov. 22. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A206
Campus map in Japanese   in English

Ryusuke Kon (Faculty of Engineering, University of Miyazaki)

Population cycles induced by age-specific interactions

Abstract:
In animal (and insect) populations, regular multiannual cycles are often observed. To understand and explain the causes of the regular population cycles, several mechanisms have been proposed. In this talk, I will show a new mechanism that can produce population cycles. The mechanism can be found by examining an age-structured population model involving agespecific species interactions.


MEE Seminar (No. 036) 

Date: Jul 12. 2012 16:45~17:45
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207
Campus map in Japanese   in English

Shiro Horiuchi (Shibaura Institute of Technology)

Evolution of the sharing convention

Abstract:
In many animal species, including modern humans, individuals struggle for various resources, which sometimes leads to heavy damages for the participants. To avoid severe struggles, the convention of ownership often evolves among the individuals; she gains the resources if she finds them earlier, she gives up the resources if she finds them later. In modern humans, however, individuals sometimes share their resources even with strangers, neglecting their ownership; the convention of sharing can hardly be observed in other animals, including the great apes and the Neanderthals. To elucidate the conditions in which the convention of sharing evolves, I construct an Agent Based Model in which multiple individuals struggle for resources. In the model individuals select one of the four strategies, Hawk, Dove, Bourgeois and Sharing, to increase their total gains in a boundary limited plane. If more individuals select the Dove or the Sharing strategy, the convention of sharing more likely dominates the population. Computer simulations suggest that the convention of sharing expands in the population when (1) the costs of severe struggles are high, (2) resources are distributed around locally restricted region, and (3) individuals can move for wider ranges. Modern humans might have faced with such social environments at the era of the Replacement and have adopted their sharing strategy to release their risks.


MEE Seminar (No. 035) 

Date: Jul 5. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207
Campus map in Japanese   in English

Nen Saito (The University of Tokyo)

The role of phenotypic fluctuation in evolution:
Baldwin effect under multi-peaked landscape

Abstract:
Phenotypic fluctuations or phenotypic plasticity are common in various living organisms (e.g., stochasticity in cell or the solitary/gregarious phase of desert locust). Can phenotypic plasticity accelerate evolutionary rate? -Several studies addressed the question. At the first glance, phenotypic changes acquired during life cycle do not seem to affect evolutionary processes because only genotype, rather than phenotype, is heritable to the next generation. However, non-heritable phenotypes can be fixed into genotype through natural selection that acts on phenotypes, and thus can affect evolution. This process is called Baldwin effect [1,2]. However validity of this Baldwin effect is still controversial. Some of subsequent studies showed that phenotypic plasticity decelerates evolutionary rate [3,4], while others claimed that phenotypic plasticity accelerates evolution [5,6]. We study evolutionary population dynamics of a quantitative genetic model to evaluate the validity of the Baldwin effect under a multi-peaked fitness landscape. We provide analytical expressions of the evolutionary rate and of the average fitness over population. These results indicate that under a multi-peaked fitness landscape phenotypic fluctuation always accelerates evolutionary rate but decreases average fitness. We also show that as an extreme case of the trade-off relation, phenotypic fluctuation causes the error catastrophe, where population fails to concentrate a peak of fitness and thus to keep a high fitness value.

[1] J. Baldwin, 1896. Am. Nat. 30: 441-451.
[2] G.G. Simpson, 1953 Evolution, 7(2):110-117
[3] L. Ancel, 2000. Theor. Popul. Biol. 58: 207-319.
[4] R. Anderson, 1995. J. Theor. Biol. 175: 89-101.
[5] G. Hinton. and S. Nowlan, 1987. Complex Systems 1: 495-502.
[6] I. Borenstein, et al., 2006 J. Evol. Biol. 19(5):1555-1570


MEE Seminar (No. 034) 

Date: Jun 28. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A304
Campus map in Japanese   in English

Sayaki Suzuki
(Division of Plant Protection, Agricultural Research Center (NARC),
National Agriculture and Food Research Organization (NARO))

Finite-size scaling analysis applied to evaluate spatially heterogeneous planting of crop genotypes

Abstract:
From the perspective of epidemic, there are several analytical methods and many factors embedded, such as spatial structures, transmission distance, stochasticity and heterogeneity. Every plant disease has its unique infection cycle and agricultural form, and therefore we should consider these aspects of diseases in defining an appropriate criterion. Here, if we assume spatially explicit plant epidemics with a strongly local interaction, the lattice model can help define the integrated criterion in the disease spread. I analyzed the lattice model by the approximations, such as mean field approximation, pair approximation, and percolation theory, and the computer simulations, which give us not only the estimated values of the epidemic magnitude, but also a theoretical idea to capture the essential features of differently spatial conditions. In this presentation, I’d like to show focus on an application of finite-size scaling analysis to a critical behavior of percolating cluster in a plant epidemic. The dynamics of disease spread is described by a basic SIR model (susceptible, infected, recovered or removed, without the host reproduction) in this study. With using the Monte Carlo simulations in the lattice space and several approximations such as mean field approximation, pair approximation, and finite scaling theory, we show that the different approximations can lead to the different thresholds of the initial resistant density which prevent an outbreak as agricultural criteria. Functional behaviors of these threshold fractions, depending on basic reproductive rate (R0) of infected crops, shaped zones between among their curves. This zoning suggests the different features of disease transmission in different crop diseases.


MEE Seminar (No. 033) 

Date: May 31. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A304
Campus map in Japanese   in English

Kenichi Aoki (The University of Tokyo)

Evolution of learning strategies in temporally and spatially variable environments

Abstract:
Individual learning (IL; learning by oneself, e.g., by trial-and-error) and social learning (SL; learning from others, e.g., by imitation) are alternative ways of acquiring and expressing the appropriate behavior (phenotype) in a given environment. The way in which an organism combines IL and SL and its relative dependence on each constitute a learning strategy. A learning strategy is a genetic adaptation to a variable environment and moreover constrains the possible pathways that culture can take. The simplest evolutionary situation involves competition between organisms that use IL or SL but not both. I review the various mathematical models of competition between obligate IL and SL in temporally variable environments with a digression on the so-called Rogers’ paradox. An analogous model with spatial heterogeneity of the environment is also considered. Next, I introduce a more realistic mixed strategy model which assumes that each organism is capable of both IL and SL, but with the probability of using each fixed throughout its lifetime. The evolutionarily stable strategy (ESS) in this model incorporates SL with positive probability when the periodicity of environmental change is sufficiently long. Finally, I consider the evolution of learning schedules, which are defined as the lifestage dependent application of IL and SL. Of special interest is the social-learner-explorer strategy in which an organism first uses SL and then IL. I argue that environmental change experienced in mid-life, either as a result of temporal change or of long-distance migration, favors the evolution of this strategy. Social-learner-explorer is one of the few plausible learning strategies supportive of cumulative culture as seen in modern humans.


MEE Seminar (No. 032) 

Date: Feb 23. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207
Campus map in Japanese   in English

Hideo Deguchi (Toyama University)

Spatial dominance in symmetric 3 × 3 games

Abstract:
The concept of Nash equilibrium has played a central role as a solution concept in game theory. However, when a game has multiple Nash equilibria, the players face a problem which equilibrium they should play. To deal with this problem, Hofbauer (1999) introduced the concept of spatial dominance using the stability of a constant stationary solution, which corresponds to a Nash equilibrium, of a reaction-diffusion system. That a Nash equilibrium is spatially dominant means that if it prevails initially on a large enough finite part of the space, then it eventually takes over the whole space. At most one equilibrium can be spatially dominant. Hence, if existence can be shown, spatial dominance can be used as an equilibrium selection criterion. He proved that the spatial dominance concept agrees with the risk-dominance concept by Harsanyi and Selten (1988) for 2 × 2 games with two strict equilibria. In this talk we consider symmetric 3 × 3 games. We first show the existence of solutions of the reaction-diffusion system. We then report on spatial dominance selection results. (This talk is based on joint work with Josef Hofbauer.)


MEE Seminar (No. 031) 

Date: Jan 19. 2012 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A305
Campus map in Japanese   in English

Koji Noshita (Kyushu University)

Theoretical morphological study on gastropod shell forms

Abstract:
Theoretical morphology is an approach with mathematical models that mimic organic forms, growing and morphogenetic process. Especially, a “morphospace” which is a set of parameterized biological forms is a helpful tool for understanding adaptation and evolution of organisms. However, in mathematical biology, there are few studies adopting the concept of the morphospace explicitly. Therefore, as a demonstration of theoretical morphological approaches, I would like to exhibit that a gastropod shell diversity of the coiling patterns and aperture inclination is described by a functional tradeoff. Firstly, it was revealed that the postural stability depending on the gravity and the efficiency of shell construction that means a relative soft-body volume against the shell are important in terms of functional constraints on morphological diversity and uniformity. Biometric analysis showed that actual shell forms tend to occupy optimal regions of the morphospace, which allows the animals to achieve both stable postures and sufficient space for soft body. Moreover, I report there are difference of aperture inclination between habitats, and attempt to explain it by the drag of fluid.


MEE Seminar (No. 030) 

Date: June 16. 2011 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207
Campus map in Japanese   in English

Ryusuke Kon (Meiji University)

Dynamics of age-structured predator-prey models

Abstract:
Motivated by a classical problem of periodical cicadas, a certainage-structured predator-prey model is constructed. In this talk, I will show how the age-structured model can be analyzed. The mathematical analysis involves two steps. The first step is to derive a Lotka-Volterra equation from the age-structured model. The Lotka-Volterra equation appears as a limit of the originalage-structured model. The second step is to analyze the derived Lotka-Volterra equation. Since Lotka-Volterra equations have been studied very well since Lotka (1925) and Volterra (1926), there areseveral useful theories. In fact, using a theory of average Liapunovfunctions, we can deal with the problem of permanence. We show that our Lokta-Volterra equation can be permanent if the life spans of twospecies are not coprime, while the equation cannot be permanent if the life spans are coprime.


MEE Seminar (No. 029) 

Date: May 19. 2011 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207
Campus map in Japanese   in English

Joe Yuichiro Wakano (Meiji University)

Mathematical expression of inclusive fitness theory

Abstract:
Recent developments have revealed that, by means of the inclusive fitness theory, the direction of evolution can be analytically predicted in a wider class of models than previously thought, such as those models dealing with network structure. However, understanding the inclusive fitness theory requires a deep intuition and hence mathematically explicit expression of the theory is required. We provide a general framework based on a Markov chain that can implement basic models of inclusive fitness. We show that key concepts of the theory, such as fitness, relatedness and inclusive fitness, are all derived from the probability distribution of an "offspring-to-parent map" in a straightforward manner. We prove theorems showing that inclusive fitness provides a correct prediction on which of two competing genes more frequently appears in the long run in the Markov chain. As an application of the theorems, we prove a general formula of the optimal dispersal rate in Wright's is land model. We also show the existence of the critical mutation rate, that does not depend on the number of islands, below which a positive dispersal rate evolves.
•This talk is prepared for the audience who are not familiar with inclusive fitness.


MEE Seminar (No. 028)  / GCOE colloquium 共催 

【CANCELLED】

Date: Mar 24. 2011 16:30~17:30
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A306

Sze-Bi Hsu (National Tsing-HuaUniversity)

SINGLE PHYTOPLANKTON SPECIES GROWTH WITH LIGHT AND ADVECTION IN A WATER COLUMN  - Joint work with Yuan Lou -

Abstract:
We investigate a nonlocal reaction-diffusion-advection equation which models the growth of a single phytoplankton species in a water column where the species depends solely on light for its metabolism. We study the combined effect of death rate, sinking or buoyant coefficient, water column depth and vertical turbulent diffusion rate on the persistence of a single phytoplankton species. Under a general reproductive rate which is an increasing function of light intensity, we establish the existence of a critical death rate; i.e., the phytoplankton survives if and only if its death rate is less than the critical death rate. The critical death rate is a strictly monotone decreasing function of sinking or buoyant coefficient and water column depth, and it is also a strictly monotone decreasing function of turbulent diffusion rate for buoyant species. In contrast to critical death rate, critical sinking or buoyant velocity, critical water column depth and critical turbulent diffusion rate may or may not exist. For instance, it is shown that if the death rate is suitably small with respect to the water column depth, the phytoplankton can persist for any sinking or buoyant velocity; i.e., there is no critical sinking or buoyant velocity under such situation. We further show that critical water column depth, critical sinking or buoyant velocity and critical turbulent diffusion rate for buoyant species can exist for some intermediate range of phytoplankton death rates and, whenever they exist, are always unique. In strong contrast, we show that there may exist two critical turbulent diffusion rates for sinking species. The phytoplankton forms a thin layer at the surface of the water column for sufficiently large buoyant rate, and it forms a thin layer at the bottom of the water column for sufficiently large sinking rate. Precise characterizations of these thin layers are also given.


MEE Seminar (No. 027) 

Date: Feb 8. 2011 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A303

Yukiko Tanabe (National Institute of Polar Research)

Photophysiological responses and the structure are the key to the success of lush vegetation in Antarctic lakes

Abstract:
Unique phytobenthic communities in Antarctic freshwater lakes, are one of the most luxuriant vegetation across the lake and terrestrial ecosystems in continental Antarctica. During summer ice-free conditions, the phytobenthos were exposed to high levels of photosynthetically active radiation and UV, because of the low concentration of UV-absorbing materials and the continuous solar radiation. Almost lakes were oligotrophic, with transparent. The phytobenthoic communities were composed dominantly of cyanobacteria and green algae, and in a minority of mosses and diatoms, which form mat structures with vertically color pattern. Photosynthesis measurements of the phytobenthos showed that they might be in a stressed condition, however, they can grow slowly but positive activity. Photosynthetic pigments analyses revealed that, in addition to the high contents of pigments and protective-substances in the surface layer of the phytobenthos, the pigments changed the functions such as “photo-protection, light-harvesting, light-regulation” in response to changes in the light environment. With these strategy: photophysiological responses and formation of the mat structure, the phytobenthos allowed the growth and survival by using the possible light energy while preventing from death during a short but strong light summer, and were considered to lushly develop in Antarctica.


MEE Seminar (No. 026) 

Date: Sep 21. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A303

Andy Gardner (University of Oxford)

Group selection and group adaptation

Abstract:
There is currently huge interest in the role of group selection in social evolution, and in the possibility for this to drive the evolution of group adaptations, leading to social groups becoming "superorganisms" in their own right. First, I review the theories of group selection and kin selection, and emphasise that these are simply different ways of viewing the same evolutionary process. Second, I discuss the relative usefulness of these alternative approaches to social evolution theory. Third, I distinguish group adaptation from group selection, and provide the first formal theory of group adaptation and the superorganism.


MEE Seminar (No. 025) 

Date: Jun 22. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Shigeto Dobata (University of the Ryukyus)

Cooperation and cheating in an asexual ant society

Abstract:
Biological cooperation is vulnerable to cheaters that exploit the benefits of cooperation without contributing to these benefits, thus the control of cheating is important to maintain cooperative systems. The Japanese ant Pristomyrmexpunctatusis characterized by asexual reproduction and an extraordinary social structure: all females fulfill both reproduction and cooperative tasks in their colonies. We revealed that most colonies were genetically heterogeneous. Inclusive fitness theory predicts that the resulting lowered nestmaterelatedness allows the cheaters to evolve, and indeed we found that this ant society harbors cheaters, which lay more eggs and take little part in cooperative tasks. This results in a negative fitness effect on their nestmatecooperators, which we confirmed by rearing experiments. Although theory predicts that the cheaters are evolutionarily short-lived, population genetic analyses found that the cheater lineage persisted for 200-9200 generations, which is longer than any comparable example of disruptive cheaters in nature. We also found that the cheaters migrate and are thus horizontally transmitted between colonies. Using computer simulation, we show that the estimated rates of cheating and horizontal transmission are sufficient for the cheater lineage to avoid the immediate extinction.


MEE Seminar (No. 024) 

Date: Jun 15. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Daishin Ueyama (Meiji University)

A mathematical model of Liesegang type precipitation and its simulations

Abstract:
The so-called Liesegangbands (rings) give us varied interests and many researchers in several field of research have studied the phenomenon over 100 years. We have introduced a new type of reaction diffusion model for the Liesegangsystem and we will demonstrate the reproducibility of the patterns. The mechanism of the pattern formation processes can be relatively easy to understand due to the model is based on the phase-field type model. Moreover, we can have some phenomenological understanding for the mechanism of the transition between periodic patterns and tree-like complex patterns.


MEE Seminar (No. 023) 

Date: Jun 8. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Yoshimi Yoshino (The University of Tokyo)

Generating Functional Analysis on Asymmetric Random Replicators

Abstract:
The idea of Generating Functional (GF) was originally suggested by Martin, Siggia and Rose (1973). It is based on Path Integral and is widely referred in various research fields, mainly Quantum Mechanics. We applied the GF to Random Replicators model in order to consider the problem of stability and complexity in ecosystem. The Replicator model with random interacting species indicates that complexity tends to destabilize community dynamics (Gardner and Ashby (1970), May (1972)). The case under the detailed balance condition is discussed in Equilibrium statistical mechanics, especially Replica method is applied to the system with disordered interactions. GF includes Replica method to analyze in the framework of Non-equilibrium physics intrinsically without detailed balance, which is corresponding to general asymmetric interactions. In the seminar, we present a detailed discussion of GF method and its application to ecosystem using Random Replicators model (YY, Galla and Tokita, Phys. Rev. E 78, 031924 (2008)).


MEE Seminar (No. 022) 

Date: Jun 1. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Ryo Oizumi (Hokkaido University)

The Optimal Control of Growth Process under Environmental Stochasticity

Abstract:
Organisms resist various risks (such as natural enemy, diseases, competition with other species, the variance of growth rate, etc) in terms of various manners of life history strategies. Above all, it is obtained with mathematical analysis (Tuljapurker, 1990)that variance of growth rate reduces fitness. In fact, it is known that sensitivity of the fitness to each parameter has negative correlation with its variance in some species, by using the transition matrix model (Pfister,1998). However, there are a few papers that the models include the control of the variance in the life-history strategy. Therefore, we directly derived a theoretical model, which is taken into account the control of the variance in their growth process, from typical demographic models (such as the transition matrix model and integration projection model (Zuidema, et al., 2010). Then, we present our analysis on the optimal control of variance in their growth process, based on our model.


MEE Seminar (No. 021) 

Date: May 25. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Tetsuya J. Kobayashi (The University of Tokyo)

Theoretical prediction of optimal intracellular kinetics for information extraction from noisy environmental signal

Abstract:
Decision-making in a noisy and dynamically changing environment is a fundamental task for a cell. To choose appropriate decisions over time, a cell must be equipped with intracellular kinetics that can conduct dynamic and efficient decision-making. But what kind of kinetics can do such an ingenious task? To solve this problem theoretically, I employed the theory of sequential inference, with which I demonstrate that a dynamic Bayesian decision-making can be implemented by an intracellular kinetics with dual positive feedback structure. I also show that the combination of linear instantaneous and nonlinear stationary sensitivities to the input dominantly contributes to decision making efficiency, and that the state-dependent sensitivity change further suppresses noisy response. The statistical principles underlying these two factors are further clarified to be log-likelihood-dependent quantification of the input information and uncertainty-dependent sensitivity control. The biological implications of this result will be discussed with several experimental evidences.


MEE Seminar (No. 020) 

Date: May 18. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Masahiro Yamaguchi (Meiji University)

Mathematical model of bone remodeling based on antagonistic adaptability

Abstract:
Bones are in a state of dynamic equilibrium with bone resorption and bone formation. It's called Bone Remodeling. Bone remodeling is intimately involved in the illness such as the osteoporosis. So it is a very important medical subject not only its kinetics. Therefore, based on accumulation of cytophysiological knowledge about it, various mathematical models have been suggested that incorporated detailed mechanism. Though, a lot existing model is far too complex to understand the core of its dynamics. The study aims to construct the interaction model based on antagonistic adaptability and capture the essential features of the dynamics.


MEE Seminar (No. 019) 

Date: May 11. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Shuhei Miyashita (The University of Tokyo)

Modeling dynamics of plant RNA viral population in a host plant

Abstract:
Most plant RNA viruses colonize host leaf tissues by moving from infected cells to uninfected cells through channels called “plasmodesmata”, which traverse the cell walls and connect cytoplasmsof adjacent cells. We recently found that only 5-6 genomes of a plant RNA virus can establish infection after cell-to-cell movement, by statistically analyzing our experimental data. This limitation on the number of viral genomes that establish infection was expected to work as genetic bottlenecks. Using the size of genetic bottlenecks as a variable, we developed a simple mathematical model that describes dynamics of viral population in a host plant. This model explained the possible important role of the bottlenecks in enhancing selection on variations in viral trans-acting genes, of which products are shared among viral intracellular population; it also indicated several possible requirements for maintenance of defective RNAs in a viral population in a host plant. Now we are trying to obtain means to modulate the size of bottlenecks, with the ultimate aim to establish effective systems to control and utilize plant RNA viruses basing on our mathematical model.


MEE Seminar (No. 018) 

Date: Mar 23. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Shiro Horiuchi (Meiji University)

Evolution of tourism in spirits-dancing (yokagura) festivals of Takachiho-cho, Miyazaki prefecture

Abstract:
Many mountainous areas have been under ageing and depopulation. In order to keep infrastructures and job opportunities, some mountainous areas have tried to invite tourists to their traditional festivals. However, mass tourism, or capitalism, likely damages traditional festivals. There is a dilemma between tourism (capitalism) and traditionalism. I did fieldwork study for spirits-dancing (yokagura) in Takachiho-cho, Miyazaki prefecture. I surveyed 19 areas of their dancing places. I also participated in 11 festivals and gained the data. The results were as follows. 19 areas could be divided into ‘festivals for tourists’ and ‘festivals for repeaters and local residents’ depending on their locations. The data of 11 festivals clearly showed significant differences between the two types. These suggest that mountainous people arranged their festivals into multi-layers. They thus can pursue tourism and traditionalism at the same time.


MEE Seminar (No. 017) 

Date: Feb 23. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Wataru Nakahashi (Meiji University)

Evolution of learning abilities

Abstract:
As is well known, the enlargement of the brain was achieved in genus Homo, and the improvement of (individual and social) learning abilities may be one of the reasons behind it. For example, more complex technologies (e.g., stone tools, bone tools, fire) emerged as the brain of genus Homo grew, and such technologies may not have been obtained innately but learned individually and socially. However, the reason the human acquired such high learning abilities (large brain) is uncertain. It is sometimes argued that bipedalism had caused the enlargement of the brain; however, the brain only started to grow (genus Homo emerged) a few million years after the advent of bipedalism. As such, bipedalism cannot be cited as the necessary and sufficient condition for the brain to enlarge. What brought on the enlargement of the brain (evolution of high learning ability)? In this talk, I will discuss this problem by analyzing a mathematical model to suggest that African climate change some 2-3 million years ago might have caused the improvement of learning abilities in genus Homo.


MEE Seminar (No. 016) 

Date: Feb 16. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Hisashi Ohtsuki (Tokyo Institute of Technology)

Evolution of cooperation by phenotypic similarity

Abstract:
The emergence of cooperation in populations of selfish individuals is a fascinating topic that has inspired much work in theoretical biology. Here, we study the evolution of cooperation in a model where individuals are characterized by phenotypic properties that are visible to others. The population is well mixed in the sense that everyone is equally likely to interact with everyone else, but the behavioral strategies can depend on distance in phenotype space. We study the interaction of cooperators and defectors. In our model, cooperators cooperate with those who are similar and defect otherwise. Defectors always defect. Individuals mutate to nearby phenotypes, which generates a random walk of the population in phenotype space. Our analysis brings together ideas from coalescence theory and evolutionary game dynamics. We obtain a precise condition for natural selection to favor cooperators over defectors. Cooperation is favored when the phenotypic mutation rate is large and the strategy mutation rate is small. In the optimal case for cooperators, in a one-dimensional phenotype space and for large population size, the critical benefit-to-cost ratio is given by b/c = 1 + 2/sqrt(3).


MEE Seminar (No. 015) 

Date: Jan 19. 2010 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Mariko Kimura (The University of Tokyo)

Replicator-dynamics models of sexual conflict

Abstract:
In many species, females prefer mates with extreme characteristics that are apparently useless or deleterious for survival, such as bright colors, elaborate ornaments and conspicuous songs. Although empirical evidence has shown that many male traits have evolved via sexual selection by female mate choice, our understanding of the adaptive value of female mating preferences is still very incomplete. It has recently been suggested that female mate choice may result from females evolving resistance rather than attraction to males. When the sexes are in conflict over mating rates, natural selection favors both males that induce higher mating rates and females that are more successful at resisting mating attempts. Such sexual conflict may result in an escalating coevolutionaryarms race between males and females. Here, we develop simple replicator-dynamics models of sexual conflict in order to investigate its evolutionary dynamics. For these models, we obtain the conditions for a coevolutionaryprocess to establish costly male and female traits and examine under what circumstances polymorphism is maintained at equilibrium. Then we discuss how assumptions in previous models of sexual conflict are translated to fit to our model framework and compare our results with those of the previous studies.


MEE Seminar (No. 014) 

Date: Dec 15. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Sepideh Mirrahimi (Paris 6 University)

Asymptotic dynamics of a population density under selection-mutation

Abstract:
We study the dynamics of a population density under selection and mutations between phenotipical traits. We model the dynamics by some equations of Lotka-Volterra type.
By studying the asymptotic behavior of these equations in large time, while mutations are rare, we prove that the density goes to a sum of Dirac masses that are traveling in time. In biological terms, at every moment one or several dominant traits survive while other traits go extinct. We describe the limit population density by a constrained Hamilton-Jacobi equation.


MEE Seminar (No. 013) 

Date: Dec 8. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Makoto Asaoka (The University of Tokyo)

Theoretical study of differences in the desire to learn, “Incentive divide”

Abstract:
Kariya(2001) argues that expansion of differences in the desire to learn is caused by the curriculum of education reform. He called the differences ‘incentive divide’. But education reform also occurred to reduce the differences of high education opportunity increasing high education school. This study tries to explain that social change influence differences in the desire to learn. To solve this question, I use mathematical model that social change connect with the desire to learn. In the right of the result of this study, as proportion of high educated decreases, differences in the desire to learn expands, and as proportion of upper class increases, differences in the desire to learn expands. We can find that the expansion of differences in desire to learn is possible event in the developed country where proportion of upper class is large some degree.


MEE Seminar (No. 012) 

Date: Nov 24. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Yasuo Ihara (The University of Tokyo)

Models of cultural evolution

Abstract:
Culture is a complex phenomenon. One way to conceptualize culture scientifically is to regard it as a kind of information that is transmitted between individuals via social learning. Basing on this premise, a quantitative framework has been developed in order to study cultural evolution and its possible impact on human genetic evolution (Cavalli-Sforza & Feldman, 1981; Boyd & Richerson, 1985; Odling-Smee et al., 2003). On the one hand, it is likely that humans, instead of being the "blank slate" (Pinker, 2002), have innate predispositions to acquire certain cultural traits more readily than their alternatives, and that cultural evolution consequently depends on such predispositions. On the other hand, the presence of culture may have modified the pressure of natural selection acting on human populations, the process referred to as cultural niche construction, and as a result played a crucial role in human evolution. Simple mathematical models have been utilized to investigate some of these issues. I will discuss such investigations taking the evolution of ingroup favoritism and the spread of costly prestige-seeking behavior as examples.


MEE Seminar (No. 011) 

Date: Nov 17. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Kohei Tamura (The University of Tokyo)

Evolutionary transition to cultural communication

Abstract:
Communication plays an important role in animal societies. In humans and some animals, cultural communication is of particular importance. In fact, MaynardSmithand Szathmary(1995) suggested that human language, which is the extreme form of cultural communication, is the eighth major transition in evolution because it is emergence of the second inheritance system. However, the requirements for this transition are not obvious. To investigate that, we construct and analyze mathematical models of cultural communication which is formalized as a kind of coordination game. As a result, it turned out that evolution of new communication system needs a non random interaction. We discuss about a relationship between the bias of interaction and who obtains benefits from communication.


MEE Seminar (No. 010) 

Date: Nov 10. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Jun Gojobori (Graduate University for Advanced Studies)

Adaptive evolution in humans revealed by the negative correlation between the two phases of molecular evolution: polymorphism and fixation

Abstract:
Selective forces on amino acid substitutions may be different in the two phases of molecular evolution; polymorphism and fixation. Negative selection and drift may dominate the first phase whereas positive selection may become much more significant in the second. However, the conventional dichotomy of synonymous vs. nonsynonymouschanges does not offer the resolution needed to correlate the two phases. We separated amino acid changes into 75 elementary types (1 bpsubstitution between their respective codons). The likelihood of each type of amino acid change to become polymorphic (PI, for polymorphic index), relative to synonymous changes, can then be calculated. Similarly, the likelihood of fixation (FI, for fixation index) conditional on common polymorphism is also calculated. Using Perlegenand HapMapdata on human polymorphisms and the chimpanzee sequences as the outgroup, we compared the evolutionary dynamics of the 75 elementary changes in the two phases. We found a strong and significant (p < 0.001) negative correlation between FI and PI. Furthermore, only those changes with low PIs show FI > 1, which is often a signature of adaptive evolution. These patterns suggest that negative and positive selection operate more effectively on the same set of amino acid changes.


MEE Seminar (No. 009) 

Date: Oct 20. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Chiaki Miura (The University of Tokyo)

On the asymptotic approximation of gene frequency distribution

Abstract:
The change of a gene frequency in a finite population along the time is expressed by the stochastic process. The density function that accompanies the stochastic process will be obtained by solving the Fokker-Planck equation corresponding to the process. Kimura (1955) gives strict solutions when alleles are neutral and when the process has linear pressure like migration or mutation. It is, however, difficult to solve the equation strictly in many cases. In this study, I invoke the small disturbance asymptotic theory (Yoshida 1992, Kunitomoand Takahashi 2003), to consider the asymptotic approximation of the density function of the diffusion process that appears in population genetics. This asymptotic method gives a good approximation when boundaries are entrance, though the speed of convergence may not be fast and it does not give good approximations in other cases. However, the generality of this method is so high that we can use this method in many cases.


MEE Seminar (No. 008) 

Date: Oct 13. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Mitsuru Kikkawa (Meiji University)

Option Market Analysis with Evolutionary Game Theory

Abstract:
This study discusses the financial market with evolutionary gametheory from the basics. This study analyzes the following situations: there are many buyers and sellers in this market and each player plays a game with a randomly matched player.
In detail, this study pays attention to the order book and constructs the market model (for example, option market, future market, etc.). This study analyzes the real market with evolutionary game theory and derives the payoff matrix. We can predict the next market states with the equilibrium stability condition.This study compares this model and Black and Sholes (1973) whichis the basic mathematical financial model. This study can interpret that this model gives a player's micro-foundation with Black and Sholes (1973).


MEE Seminar (No. 007) 

Date: Oct 6. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Zu Jian (Meiji University)

The evolution of phenotypic traits in a predator-prey system subject to Allee effect

Abstract:
Background:The outcomes of predator-prey interactions often depend on phenotypic traits which influence or indicate their interactive ability, such as body size, weight, and skin color. It is observed that natural selection by the prey on the predator favors predator phenotypes best able to consume the prey, whereas selection by the predator on the prey favors prey phenotypes least likely to be killed, which may lead to a cyclic type of ‘arms race’.

Question: How do the phenotypic traits of predator and prey evolve when prey population is subject to Alleeeffect?

Methods: We use the theory of Adaptive Dynamics and the evolutionary model is constructed from a deterministic approximation of the stochastic process of mutation and selection.

Results: Firstly, it is found that predator and prey will evolve to a continuously stable strategy if the Alleeeffect of prey is strong. However, if the Alleeeffect of prey is not strong enough, then prey population will undergo evolutionary branching. Secondly, we find that evolutionary suicide can occur deterministically on prey population if prey individuals undergo asymmetric competition and are subject to Alleeeffect. Thirdly, we show that the evolutionary model with symmetric interactions admits a stable limit cycle. Evolutionary cycle is a likely outcome of the process, which depends on the strength of Alleeeffect and the mutation rates of predator and prey.


MEE Seminar (No. 006) 

Date: Sep 29. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Joe Yuichiro Wakano (Meiji University)

Spatial dynamics of costly spite and cooperation by conformist transmission

Abstract:
Consider a population of players involved in a two-strategy multi-player game. Each player copies the behavior of another player more likely when its payoff is smaller (social learning). The learning is skewed so that they tend to conform to the majority (conformist transmission). Frequency dynamics of the strategy is derived as a generalized replicator equation. When the effect of conformism is strong, the fixation to either strategy is locally stable. We study the outcome of spatial game where players randomly migrate, play a game locally and perform learning locally, based on the theory of traveling wave solution in a scalar reaction diffusion equation. By applying the result to spatial public goods game, we show not only that cooperation is less adaptive evolve under stronger conformist transmission but also that spite behavior that decreases the other players' payoff by paying cost evolves. Such spite behavior does not evolve when conformism is weak or absent. The result suggests that conformism might decrease the population average payoff and even promote evolutionary suicide.


MEE Seminar (No. 005) 

Date: Aug 13. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

小林 豊 (京都大学)

無限集団の包括適応度理論

Abstract:
「包括適応度理論」は、形質に相関がある個体間の相互作用があるような集団の進化ゲームにおいて、均衡戦略を解析的に求めるための理論的手法であり、進化生態学、特に社会性進化の研究分野で重要な役割を担ってきた。本講演では、無限集団に対象を限定し、この理論の詳細な解説を行う。まず、プライス方程式と呼ばれる、自然選択の下での遺伝子頻度の変化量を算出するための公式を紹介し、ここから「包括適応度」と呼ばれる量を導出する。さらに、包括適応度を用いて、進化ゲームの均衡戦略を計算する方法を、具体例に基づいて説明する。


MEE Seminar (No. 004) 

Date: Jul 21. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Wataru Nakahashi (Meiji University)

Evolution of conformist transmission in social learning

Abstract:
One of the most unique characteristics of the human is culture, which is brought about by the ability of social learning. Social learning is a way to obtain information (behavior) from socially interacting organisms by teaching, imitation, local enhancement, and various other psychological processes. One interesting feature of social learning is the tendency of learning the majority or most common behavior, which is called conformity (conformist transmission). Conformity is thought to cause the variation of culture between communities, to result in group selection, to affect adoption dynamics, and to stabilize cooperation and punishment. In this talk, I will introduce mathematical studies of evolution of learning and show that conformity always evolves when selection is weak in the infinite environmental state model.


MEE Seminar (No. 003) 

Date: Jul 14. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Shiro Horiuchi (Meiji University)

Intraspecific variation of Japanese macaques; its social relation and group composition

Abstract:
Wild groups of Japanese macaques show a great intraspecific variation in their group composition among different habitats. The species is thus a good model to test the theory of socioecology, which tries to explain primate societies by ecological conditions. Particularly important ecological factor is the group density that directly affects the relation between neighboring groups, which in turn affects the relation within a group. I at first introduce my fieldwork studies in Yakushima Island and Shimokita Peninsula populations; the group density is significantly different between the two. Then I show how the group density affects group size and male-female ratio in the groups of Japanese macaques by mathematical models, which are tested by empirical data.


MEE Seminar (No. 002) 

Date: Jun 30. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Zu Jian (Meiji University)

Adaptive dynamics and its application to a predator-prey system

Abstract:
The theory of adaptive dynamics provides a framework for modeling evolution by natural selection in complex ecological systems, where fitness depends on the frequencies of the interacting phenotypes. This framework links population dynamics to evolutionary dynamics and extends the fundamental idea of frequency dependent selection from evolutionary game theory, with special emphasis on dynamical phenomena such as the origin and divergence of new lineages by evolutionary branching. The general theory of adaptive dynamics yields algorithms that can readily be applied to analyze concrete ecological settings. In my talk, I will firstly introduce some basic theory of adaptive dynamics, and then I will discuss the evolution of phenotypic traits in a community comprising the populations of predator and prey, where prey population is subject to Alleeeffect. Some intriguing phenomena, such as evolutionary branching, evolutionary suicide and evolutionary cycle will emerge in the predator-prey system subject to Alleeeffect.


MEE Seminar (No. 001) 

Date: Jun 16. 2009 14:40~16:10
Location: Meiji Univ. Ikuta Campus Build 2 Annex A Room A207

Joe Yuichiro Wakano(Meiji University)

Spatial dynamics of ecological public goods

Abstract:
Question: Does space stabilize or destabilize maintenance of cooperation ?

Background and Previous Models: The emergence and abundance of cooperation in nature poses a challenging puzzle to evolutionary biology. Traditional approaches to studying the problem of cooperation assumeconstant population sizes and thus neglect the ecology of the interacting individuals. Ecological public goods game considers dynamics of group size in public goods game. As multiplication rate(total return on investment) is fixed, cooperation is adaptive strategy when public goods game is played by fewer members (because the return is shared by fewer members). We assume the average number of players in each public goods game is determined by population density. Then, low density facilitates evolution of cooperation and high density facilitates evolution of defection. On the other hand, large ratio of cooperators to defectors results in effective population growth. Thus, the system has a tendency toward coexistence of cooperators and defectors.

Model: We allow cooperators and defectors to diffuse in two-dimensional space. The spatial ecological public goods game is denoted by reaction-diffusion equations.

Results: Coexistence region always expands when both extinction and coexistence are locally stable without space. Coexistence is sometimes achieved by spatially heterogeneous pattern. Furthermore, spatial coexistence is achieved for some parameters that do not allow coexistence without space. Such spatial effect is often achieved by spatially chaotic dynamics (Many interesting movies are shown in the talk). Coexistence is favored when defectors diffuse faster than cooperators. The underlying mechanism is partly understood by Turing instability.