Physiological Entomology (2019), DOI: 10.1111/phen.12315 Caste-biased locomotor activities in isolated termites HIROYUKI SHIMOJI 1, † , NOBUAKI MIZUMOTO 2, † , ‡ , KOHEI OGUCHI 3 and S H I G E T O D O B A T A 2 1 Department ofBioscience, School of Science and Technology, Kwansei Gakuin University, Sanda, Japan, 2 Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan and 3 Misaki Marine Biological Station, Graduate School of Science, The University of Tokyo, Miura, Japan Abstract. Eusocial insects are characterized by a well-developed division of labour among castes. Although the successful division of labour should stem from behavioural differentiation depending on caste identity, caste-specifc intrinsic behavioural character- istics might be masked by social interactions within colonies. The present study explores caste-specifc intrinsic locomotive activities of termites by quantifying them in isolation. We track individual movement trajectories of the damp-wood termite Hodotermopsis sjostedti over 30min and extract individual locomotion parameters. Multivariate statis- tical analyses reveal signifcant differences among castes: soldiers move more actively than workers and neotenic reproductives. The morphometric data of test individuals indicate that locomotor activities refected caste identity more strongly compared with quantitative morphological variations among individuals. We fnd that the different loco- motor activities of soldiers compared with those of neotenics and workers probably refect their physiological differentiation. The present study provides a basis for a deeper understanding of the roles of individual locomotor activities in social behaviours. Key words. Caste, locomotor patterns, social insect, termite, tracking. Introduction Collective behaviours are ubiquitous in biological systems and are driven by self-organization (Sumpter, 2010). Eusocial insect colonies show sophisticated forms of division of labour between reproductive and nonreproductive castes and even among nonreproductive castes (Wilson, 1971). Such division of labour is facilitated by the presence of caste polymorphism, in which a colony has morphologically distinct nonreproductive castes with specialized roles (Oster & Wilson, 1978). On the basis of the bottom-up viewpoint of self-organization, local interactions between individuals of different castes should be key to understanding the division of labour (Wilson, 1985). Local interactions can take various forms, ranging from indirect chemical cues to direct physical contacts. In the present study, we focus on locomotor activity as a regulator of inter- actions. Although simply defned as a change in the spatial Correspondence: Hiroyuki Shimoji, Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan. e-mail: shimojih@kwansei.ac.jp †These authors contributed equally to this work. ‡Present address: School of Life Sciences Arizona State University ISTB1, 423, East Mall, Tempe, Arizona 85287, U.S.A. location of individuals over time, locomotion plays a central role in determining the fate of individuals (Nathan et al., 2008) and arguably so do their local interactions. However, empirical investigations aimed at elucidating caste-specifc locomotion are often hindered by the behavioural plasticity that depends on social context (Tanner, 2008; Tanner & Adler, 2009; Ishikawa & Miura, 2012). In other words, caste-specifc behavioural prop- erties of individuals might be masked by social interactions. To detect individual behavioural and physiological properties, many studies apply tests in social isolation (Batson et al., 1992; Traniello et al., 2002; Miramontes et al., 2014; Koto et al., 2015; Norman & Hughes, 2016; Leitner et al., 2019). In accor- dance with these previous studies, we measure the locomotion of individual social insects in isolation to explore the intrinsic caste specifcity of their locomotor activities. Termites, comprising a large group of eusocial insects, are a typical example of caste polymorphism (Eggleton, 2010). For example, the soldier caste, a specialist in colony defence, has a distinctly larger body size and better developed mandibles compared with those of workers. All immature individuals basi- cally remain totipotent and can differentiate into the reproduc- tive caste or soldier caste, and this differentiation is regulated by social interactions, especially direct physical contact between individuals (Dong et al., 2009; Watanabe et al., 2011; Maekawa © 2019 The Royal Entomological Society 1