談話会 ユスップ マルコ「How do mutualisms evolve? Evolutionary game dynamics under an asymmetric strategy setup」、西浦廉政「On the interplay between intrinsic and extrinsic instabilities of spatially localized patterns」

開催日時
2016年   12月 21日 15時 30分 ~ 2016年   12月 21日 18時 00分
場所
北海道大学理学部3号館309号室
講演者
ユスップ マルコ先生(北大)、西浦廉政(東北大)
 
スケジュール:
15:30〜16:30 ユスップ マルコ先生(北大)
16:30〜17:00 お茶会
17:00〜18:00 西浦 廉政先生(東北大)

ユスップ マルコ先生(北大)
タイトル:How do mutualisms evolve? Evolutionary game dynamics under an asymmetric strategy setup
概要:Asymmetries in nature arise when individuals of one species, called hosts, are in a position to reward cooperative and/or punish non-cooperative partners of another species, called symbionts. The use of reward and punishment conditional on the symbiont's action is called a carrot-stick (CS) strategy. We examine the evolution of mutualistic relationships by setting up an evolutionary game model wherein a host species can choose between cooperation and CS strategy, while a symbiont species is restricted to cooperation and defection. Analytical and numerical approaches alike indicate that (incomplete) mutual cooperation is possible only through cycles over a very limited domain in the phase space. Applying the CS strategy, by contrast, ensures the symbiont's cooperativeness over a much wider domain in the phase space. These theoretical results are consistent with existing empirical evidence that the ability of host species to reward and/or sanction symbionts may disentangle conflicting incentives in mutualistic relationships. We discuss the results in the context of concrete mutualisms in nature as exhibited by, for example, figs and fig wasps or cleaner fish and their clients.

西浦 廉政先生(東北大)
タイトル: On the interplay between intrinsic and extrinsic instabilities of spatially localized patterns
概要: Spatially localized dissipative structures are observed in various fields, such as neural signaling, chemical reactions, discharge patterns, granular materials, vegetated landscapes and binary convection. These patterns are much simpler than single living cells, however they seem to inherit several characteristic “living state” features, such as self-replication, self-healing and robustness as a system. Adaptive switching of dynamics can also be observed when these structures collide with each other, or when they encounter environmental changes in the media. These behaviors stem from an interplay between the intrinsic instability of each localized pattern and the strength of external signals. To understand such an interplay, we explore the global geometric interrelation amongst all relevant solution branches of a corresponding system with approximate unfolding parameters. For instance, it has been uncovered that large deformation at strong collision is mapped into the network of unstable patterns called scattors, and that an organizing center for 1D pulse generators is a double homoclinic orbit of butterfly type. We will illustrate the impact of this approach by presenting its application in relation to the decision making process of amoeboid locomotion and hierarchical structures of ordered patterns arising in reaction diffusion systems and binary fluids.

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