Research


Approach

My research interest is pattern formed by animal behaviors. This includes animal swarms, nest structures, movement patterns or behavioral rhythm. I question the behavioral mechanisms and evolutionary processes of patterns observed in nature. What is the behavioral rule underlying pattern formation? How rules have evolved in nature?

I ask the above questions by combining the theoretical and empirical approaches. I often use termites as a model species. They are very fascinating because termites show a wide variety of behaviors across various group sizes: from a solitary animal during mate search to collective behaviors involving tens of thousands individuals. My work also includes behaviors of termites even apart from pattern formation.

Evolutionary process of collective building by termites

keywords: Self-organization, Evolutionary Convergence Termites

Structures created by social insects can largely vary in their shape and size within or among species, while their nests sometimes show a remarkable evolutionary convergence across phylogenetically distant species. To reveal the behavioral mechanism of these two contrasting phenomena, I am performing a comparative analysis of behavioral rules for collective building among termite species across the valleys in Arizona.

Mizumoto et al. in prep; Mizumoto and Bourguignon in prep.

Inferring collective behaviors from the fossilized records

keywords: Self-organization, Patterns, Trace fossils.

Fossils can be the only direct record of behaviors performed by animals extinct in the past. In this study, we found the evidence consistent with the interaction rules for coordinated collective motion in a fossilized group of the fish Erismatopterus levatus. By inferring the next moment of the fossilized conditions, we found the traces of two rules for social interaction: repulsion from close individuals, and attraction towards neighbors at a distance. This study highlights the possibility to explore the social communication of extinct animals, which may help the understanding of the evolution of collective behaviors.

Mizumoto et al. 2019 Proc. R. Soc. B

Movement patterns and search strategies of termites

keywords: Random walk; Tandem runs; Sexual selection; Social insects; Movement ecology

How should females and males move to search for partners whose exact location is unknown? Theory predicts that the answer depends on the searching conditions, specifically what they know about where targets can be found. We demonstrated that termites adaptively switch their search modes depending on the potential distance to their partners. We found that both sexes moved actively before finding partners that is the condition target locations are completely unpredictable. In stark contrast, when pairs were accidentally separated during tandem running, they showed distinct sexually dimorphic movements, where females paused for long periods while males paused only briefly and moved actively. Simulations confirmed that these movements increase the rate of successful encounters. The context-dependent switch of search modes is a key to enhance random encounters in animals.

Mizumoto and Dobata 2019 Science Advances

Optimal movement to search for mating partners

keywords: random walk, animal movements, sexual dimorphism, co-evolution

How can males and females enhance mating encounters when they have no idea of the locations of partners? Using simulations, we found that sexually dimorphic movements can achieve the highest encounter rates under some conditions, and demonstrated that this sexual dimorphism can evolve from an initial sexually monomorphic population. Our findings connect the evolutionary ecology of sex and the biophysics of movement, providing the novel mechanisms of how sexual dimorphism can evolve.

Mizumoto et al. 2017 J Roy Soc Interface, Mizumoto and Dobata 2018 Scientific Reports,

Poster: The 31th Annual Meeting of the Society of Population Ecology(Poster award)

Simulations

Circadian rhythm in mate search of termites

keywords: circadian rhythm, mate search, termites

Termites usually live within logs and underground with little light fluctuations, and thus they rarely show circadian rhythm in most of their life. However, in the mating period, termite dispersers must search for mates outside the nests at the correct time. We found that unpaired termites show daily search–rest cycles and restrict searching activity to a certain period of the day by responding to photic cycles. Termites also showed periodic search–rest patterns under constant darkness, indicating the involvement of internal oscillating clocks in their mate search rhythm.

Mizumoto et al. 2017 Popul Ecol

Termite search activity under photic cycles (LD) and constant darkness (DD).

Tracking movement of individual insects with an omnidirectional treadmill

keywords: locomotion compensation, anomalous diffusion, random walk, tracking

Tracking free animal movements such as walking is an essential task for understanding how and why animals move. In this study, we applied an omnidirectional treadmill mechanism (OTM, a servosphere named ANTAM) that can provide the test animals with both a homogenous environment and a virtual infinite space. To validate the use of our tracking system for free-walking behavior, we compared walking patterns of individual pillbugs (Armadillidium vulgare) between on our OTM and on the classical experimental flat arenas. Our results revealed that the walking patterns of individuals on the servosphere show similar characteristics to that on the arena simulating an open space. Moreover, we showed that anomalous diffusion properties, including Lévy walk, can be detected from the freewalking behavior on our tracking system.

Nagaya, Mizumoto et al. 2017 PLOS ONE

Adaptive values of same sex pairing by termite males

keyword: same-sex pairing, coorperation, competition, termites

From insects to primates, various animal species show same-sex sexual behaviors such as courtship, copulation and pairing. However this provides the evolutionary paradox of selection because it cannot directly result in reproduction, and the occurrence of same-sex pairing is often explained by the mistaken identity of individuals. In this study, I found that termite males form homosexual pairs in a manner similar to that in monogamous colony foundation and demonstrated how this contributes to their fitness. We found that pairs of male adults stopped searching for females and cooperatively established nests without females, although single males rarely ceased searching for mates. Males in such male–male partnerships had much higher survival than single males. Then a male in a surviving homosexual pair invaded in an incipient colony, to kill the king and replace the colony. A mathematical model demonstrated that the observed strategy of establishing a male–male partnership instead of searching for females is advantageous when the risk of predation is high, even when colony fusion is very rare. Thus, we could demonstrate the adaptive significance of an apparently paradoxical interaction between same-sex individuals. Pairing with another male isn't the best option, but it gives mateless termites a chance to survive until they find a female, if that happens at all (Mizumoto et al. 2016 Anim Behav). Press release

Poster: The 32th Annual Meeting of the Society of Population Ecology(Best poster award)

A pair of males. They can survive more than 2 years by corperation.

Colony variation of shleter-tube construction by termites

keyword: self-organization, collective building, termites

Social insects build sophisticated and complex structures such as large nests and underground galleries. Construction is achieved by self-organization, whereby colony-level structures emerge from local interactions among members that elicit positive and negative feedback responses produced by interactions among individuals. Many studies have shown that this building rule can produce various strctures by changing the environmental conditions or group size. Then, under the same environmental conditions and with the same group size, will social insects construct the same structures? To test this idea, We focused on shelter-tube building by the termite: Reticulitermes speratus, and compared the patterns of shelter-tubes among multiple colonies.(Mizumoto and Matsuura 2013 Insect Soc).

Here, we found that termite termites show distinct colony-specificity. When we divided a colony into multiple groups of individuals, groups drawn from the same colony performed similar patterns of construction, whereas groups from different colonies exhibited different patterns. As the colony differences of structures are created under the same environmental conditions and with the same number of individuals, we can expect that termite workers differ among colonies in their responses. To explore the factors affect construction, we developed lattice model which mimicked the termite behavior (Mizumoto et al 2015 RSOS).

Termite workers carry a piece of wood to the end of the shelter tube and attach it one after another. This process continues again and again, and shelter tubes are constructed. Here termite workers share the information of under construction and locally interact each other indirectly using cement pheromone which is attached with materials. We mimick this behavioral algorithm in the lattice model. We analyzed the model by changing various factors which can affect the building process, and compared the simulation results with the results of emprican experiments.

As a result, we could recreate the similar patterns of colony variation by simply changing two behavioural parameters of group members, even with the same building algorithm. It was mainly attributed to the extent of positive feedback and the number of individuals engaged in building. Thus, single algorithm can create the variation within a species by tuning exogenous factors such as environment or group size and endogenous factors such as individual responses. By applying this mechanism to various ecological and evolutionary contexts, I'm now trying to figure out how termites exploit their behavioral algorithm in their society.

Shelter-tube patterns formed by fragment groups derived from the representative colonies. Termites constructed shelter tubes and/or covered the bottom of a container with mats consisting of particles of mixed sawdust and termite feces.
Shelter tube construction by termites. Termite workers carry pieces of wood to the end of the shelter tube and attach them one after another.
The scheme of simualations