研究者詳細 - 下地　博之

論文 - 下地　博之

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A potential risk and management of feces in the queenless ant

Y. Ishizuka, R. Yamashita, H. Itoh, Y. Matsuura, Y. Kikuchi, H. Shimoji

Insectes Sociaux ( Springer Science and Business Media LLC ) 2024年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Reproductive potentials of task-shifting workers in a queenless ant

Yasunari Tanaka, Kohei Oguchi, Satoshi Miyazaki, Kiyoto Maekawa, Hiroyuki Shimoji

Insectes Sociaux ( Springer Science and Business Media LLC ) 2024年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Protocol to obtain long movement trajectories of leaders and followers in ant tandem runs

Yasunari Tanaka, Gabriele Valentini, Stephen C. Pratt, Hiroyuki Shimoji, Nobuaki Mizumoto

STAR Protocols ( Elsevier BV ) 4 ( 4 ) 102769 - 102769 2023年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Maintenance mechanisms of the division of labor in social insects

Hiroyuki SHIMOJI, Yasunari TANAKA

Hikaku seiri seikagaku(Comparative Physiology and Biochemistry) ( The Japanese Society for Comparative Physiology and Biochemistry ) 40 ( 1 ) 54 - 61 2023年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Functional and mechanistic diversity in ant tandem communication

Nobuaki Mizumoto, Yasunari Tanaka, Gabriele Valentini, Thomas O. Richardson, Sumana Annagiri, Stephen C Pratt, Hiroyuki Shimoji

iScience ( Elsevier BV ) 106418 - 106418 2023年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Resilience of native ant community against invasion of exotic ants after anthropogenic disturbances of forest habitats

Hiroyuki Shimoji, Mayuko Suwabe, Tomonori Kikuchi, Hitoshi Ohnishi, Hirotaka Tanaka, Kengo Kawara, Yusuke Hidaka, Tsutomu Enoki, Kazuki Tsuji

Ecology and Evolution ( Wiley ) 12 ( 7 ) 2022年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Individual experience influences reconstruction of division of labour under colony disturbance in a queenless ant species

Yasunari Tanaka, Masaru K. Hojo, Hiroyuki Shimoji

Frontiers in Zoology ( Springer Science and Business Media LLC ) 19 ( 1 ) 2022年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Abstract Background Division of labour (DOL) is ubiquitous across biological hierarchies. In eusocial insects, DOL is often characterized by age-related task allocation, but workers can flexibly change their tasks, allowing for DOL reconstruction in fluctuating environments. Behavioural change driven by individual experience is regarded as a key to understanding this task flexibility. However, experimental evidence for the influence of individual experience is remains sparse. Here we tested the effect of individual experience on task choice in the queenless ponerine ant, Diacamma cf. indicum from Japan. Results We confirmed that both nurses and foragers shifted to vacant tasks when the colony composition was biased to one or the other. We also found that nurses which are induced to forage readily revert to nursing when reintroduced into balanced colonies. In contrast, foragers which are induced to revert to nursing very rarely return to a foraging role, even 19 days post reintroduction to their original colony. Conclusions Taken together, our results suggest that individual experience decreases the response threshold of original foragers, as they continue to be specialist nurses in a disturbed colony. However, original nurses do not appear strongly affected by having forager experience and revert to being nurses. Therefore, while individual experience does have an effect, other factors, such as reproductive ability, are clearly required to understand DOL maintenance in fluctuating environments.

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The build-up of dominance hierarchies in eusocial insects

Hiroyuki Shimoji, Shigeto Dobata

Philosophical Transactions of the Royal Society B: Biological Sciences ( The Royal Society ) 377 ( 1845 ) 2022年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Reproductive division of labour is a hallmark of eusocial insects. However, its stability can often be hampered by the potential for reproduction by otherwise sterile nest-mates. Dominance hierarchy has a crucial role in some species in regulating which individuals reproduce. Compared with those in vertebrates, the dominance hierarchies in eusocial insects tend to involve many more individuals, and should require additional selective forces unique to them. Here, we provide an overview of a series of studies on dominance hierarchies in eusocial insects. Although reported from diverse eusocial taxa, dominance hierarchies have been extensively studied in paper wasps and ponerine ants. Starting from molecular physiological attributes of individuals, we describe how the emergence of dominance hierarchies can be understood as a kind of self-organizing process through individual memory and local behavioural interactions. The resulting global structures can be captured by using network analyses. Lastly, we argue the adaptive significance of dominance hierarchies from the standpoint of sterile subordinates. Kin selection, underpinned by relatedness between nest-mates, is key to the subordinates' acceptance of their positions in the hierarchies. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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Worker-dependent gut symbiosis in an ant

Hiroyuki Shimoji, Hideomi Itoh, Yu Matsuura, Rio Yamashita, Tomoyuki Hori, Masaru K. Hojo, Yoshitomo Kikuchi

ISME Communications ( Springer Science and Business Media LLC ) 1 ( 1 ) 2021年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

<title>Abstract</title>The hallmark of eusocial insects, honeybees, ants, and termites, is division of labor between reproductive and non-reproductive worker castes. In addition, environmental adaption and ecological dominance are also underpinned by symbiotic associations with beneficial microorganisms. Microbial symbionts are generally considered to be maintained in an insect colony in two alternative ways: shared among all colony members or inherited only by a specific caste. Especially in ants, the reproductive caste plays a crucial role in transmission of the symbionts shared among colony members over generations. Here, we report an exceptional case, the worker-dependent microbiota in an ant, <italic>Diacamma</italic> cf. <italic>indicum</italic> from Japan. By collecting almost all the individuals from 22 colonies in the field, we revealed that microbiota of workers is characterized by a single dominant bacterium localized at the hindgut. The bacterium belonging to an unclassified member within the phylum Firmicutes, which is scarce or mostly absent in the reproductive castes. Furthermore, we show that the gut symbiont is acquired at the adult stage. Collectively, our findings strongly suggest that the specific symbiont is maintained by only workers, demonstrating a novel pattern of ant-associated bacterial symbiosis, and thus further our understanding of host-microbe interactions in the light of sociobiology.

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Social Evolution With Decoupling of Multiple Roles of Biogenic Amines Into Different Phenotypes in Hymenoptera

Ken Sasaki, Yasukazu Okada, Hiroyuki Shimoji, Hitoshi Aonuma, Toru Miura, Kazuki Tsuji

Frontiers in Ecology and Evolution ( Frontiers Media SA ) 9 2021年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Convergent evolution of eusociality with the division of reproduction and its plastic transition in Hymenoptera has long attracted the attention of researchers. To explain the evolutionary scenario of the reproductive division of labor, several hypotheses had been proposed. Among these, we focus on the most basic concepts, i.e., the ovarian ground plan hypothesis (OGPH) and the split-function hypothesis (SFH). The OGPH assumes the physiological decoupling of ovarian cycles and behavior into reproductive and non-reproductive individuals, whereas the SFH assumes that the ancestral reproductive function of juvenile hormone (JH) became split into a dual function. Here, we review recent progress in the understanding of the neurohormonal regulation of reproduction and social behavior in eusocial hymenopterans, with an emphasis on biogenic amines. Biogenic amines are key substances involved in the switching of reproductive physiology and modulation of social behaviors. Dopamine has a pivotal role in the formation of reproductive skew irrespective of the social system, whereas octopamine and serotonin contribute largely to non-reproductive social behaviors. These decoupling roles of biogenic amines are seen in the life cycle of a single female in a solitary species, supporting OGPH. JH promotes reproduction with dopamine function in primitively eusocial species, whereas it regulates non-reproductive social behaviors with octopamine function in advanced eusocial species. The signal transduction networks between JH and the biogenic amines have been rewired in advanced eusocial species, which could regulate reproduction in response to various social stimuli independently of JH action.

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Expressions of conventional vitellogenin and vitellogenin‐like A in worker brains are associated with a nursing task in a ponerine ant

S. Miyazaki, H. Shimoji, R. Suzuki, I. Chinushi, H. Takayanagi, H. Yaguchi, T. Miura, K. Maekawa

Insect Molecular Biology ( Wiley ) 30 ( 1 ) 113 - 121 2021年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In eusocial insect colonies, non-reproductive workers often perform different tasks. Tasks of an individual worker are shifted depending on various factors, e.g., age and colony demography. Although a vitellogenin (Vg) gene play regulatory roles in both reproductive and non-reproductive division of labours in a honeybee, it has been shown that the insect Vg underwent multiple gene duplications and sub-functionalisation, especially in apical ant lineages. The regulatory roles of duplicated Vgs were suggested to change evolutionarily among ants, whereas such roles in phylogenetically basal ants remain unclear. Here, we examined the expression patterns of conventional Vg (CVg), Vg-like A, Vg-like B and Vg-like C, as well as Vg receptor, during the task shift in an age-dependent manner and under experimental manipulation of colony demography in a primitive ant Diacamma sp. Expressions of CVg and Vg-like A in a brain were associated with a nursing task. It is suggested that associations of brain expressions of these Vgs with worker tasks were acquired in the basal ant lineage, and that such Vg functions could have sub-functionalised in the derived ant lineage.

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Male neotenic reproductives accelerate additional differentiation of female reproductives by lowering JH titer in termites

Kohei Oguchi, Yasuhiro Sugime, Hiroyuki Shimoji, Yoshinobu Hayashi, Toru Miura

Scientific Reports ( Springer Science and Business Media LLC ) 10 ( 1 ) 2020年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Eusocial insects exhibit reproductive division of labor, in which only a fraction of colony members differentiate into reproductives. In termites, reproductives of both sexes are present in a colony and constantly engaged in reproduction. It has been suggested that the sex ratio of reproductives is maintained by social interactions. The presence of reproductives is known to inhibit the additional differentiation of same-sex reproductives, while it promotes the differentiation of opposite-sex reproductives. In this study, using the damp-wood termite Hodotermopsis sjostedti, physiological effects of male/female reproductives on the differentiation of supplementary reproductives (neotenics) were examined. The results showed that the only male-neotenic condition, i.e., the presence of male neotenics in the absence of female neotenics, accelerated the neotenic differentiation from female workers (i.e., pseudergates). Under this condition, the rise of juvenile hormone (JH) titer was repressed in females, and the application of a JH analog inhibited the female neotenic differentiation, indicating that the low JH titer leads to rapid differentiation. Thus, the only male-neotenic condition that actively promotes reproductive differentiation by manipulating physiological condition of females is suggested to be a mechanism underlying sexual asymmetry in reproductive function, which may lead the female-biased sex allocation of reproductives.

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Worker propensity affects flexible task reversion in an ant

Hiroyuki Shimoji, Nana Kasutani, Shinya Ogawa, Masaru K Hojo

Behavioral Ecology and Sociobiology ( Springer Science and Business Media LLC ) 74 ( 7 ) 2020年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Caste-biased locomotor activities in isolated termites

Hiroyuki Shimoji, Nobuaki Mizumoto, Kohei Oguchi, Shigeto Dobata

Physiological Entomology ( WILEY ) 45 ( 1 ) 50 - 59 2020年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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-specific intrinsic behavioural characteristics might be masked by social interactions within colonies. The present study explores caste-specific intrinsic locomotive activities of termites by quantifying them in isolation. We track individual movement trajectories of the damp-wood termite Hodotermopsis sjostedti over 30 min and extract individual locomotion parameters. Multivariate statistical analyses reveal significant differences among castes: soldiers move more actively than workers and neotenic reproductives. The morphometric data of test individuals indicate that locomotor activities reflected caste identity more strongly compared with quantitative morphological variations among individuals. We find that the different locomotor activities of soldiers compared with those of neotenics and workers probably reflect their physiological differentiation. The present study provides a basis for a deeper understanding of the roles of individual locomotor activities in social behaviours.

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Context-dependent aggression toward non-nestmates in the ant Diacamma sp. from Japan

Jumpei Uematsu, Masayuki Hayashi, Hiroyuki Shimoji, Michel-Olivier Laurent Salazar, Kazuki Tsuji

Journal of Ethology ( SPRINGER JAPAN KK ) 37 ( 3 ) 259 - 264 2019年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Aggression toward competitors is a useful measure of resource ownership and defense in animals, but aggressive behavior is costly. Therefore, it is predicted that animals will display aggression only when the expected benefit to individual fitness exceeds the expected cost. In ants, when conspecific individuals belonging to different colonies encounter each other, fighting occurs, seemingly facultatively. However, the context that influences the expression of ants' aggressive behavior, especially in the field, is still largely unknown. We investigated the plasticity of aggressiveness toward non-nestmates in Diacamma sp. from Japan. Our field experiment clearly showed that the same foragers that were aggressive toward non-nestmates in the vicinity of their nest changed to be non-aggressive at greater distances from the nest. Furthermore, the size of the colony to which the foragers belonged weakly but significantly affected their aggressiveness: foragers belonging to larger colonies behaved more aggressively toward non-nestmates. We discuss the possible adaptive significance of the observed facultative aggression between conspecific non-nestmates.

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Social enforcement depending on the stage of colony growth in an ant

Hiroyuki Shimoji, Tomonori Kikuchi, Hitoshi Ohnishi, Noritsugu Kikuta, Kazuki Tsuji

Proceedings of the Royal Society B: Biological Sciences ( The Royal Society ) 285 ( 1875 ) 20172548 - 20172548 2018年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Altruism is a paradox in Darwinian evolution. Policing is an important mechanism of the evolution and maintenance of altruism. A recently developed dynamic game model incorporating colony demography and inclusive fitness predicts that, in hymenopteran social insects, policing behaviour enforcing reproductive altruism in group members depends strongly on the colony growth stage, with strong policing as the colony develops and a relaxation of policing during the reproductive phase. Here, we report clear evidence supporting this prediction. In the ant <italic>Diacamma</italic> sp., reproduction by workers was suppressed by worker policing when the colony was small, whereas in large, mature colonies worker policing was relaxed and worker-produced males emerged. Conditional expression of traits can provide strong empirical evidence for natural selection theory if the expression pattern is precisely predicted by the theory, and our results illustrate the importance of intracolony population dynamics in the evolution of social systems.

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Regulation of neotenic differentiation through direct physical contact in the damp-wood termite Hodotermopsis sjostedti

H. Shimoji, K. Oguchi, Y. Hayashi, M. K. Hojo, T. Miura

Insectes Sociaux ( Birkhauser Verlag AG ) 64 ( 3 ) 393 - 401 2017年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In cooperative societies such as those of ants, honey bees, and termites, the number of reproductives is often regulated by social interactions. In many termite species, helper individuals (i.e., larvae or workers) can potentially differentiate into a “neotenic” reproductive caste in the absence of reproductives. In some termite species, multiple neotenics coexist within a nest, often with female-biased sex ratios. However, although the presence of female neotenics can suppress neotenic differentiation of female workers, it is largely unknown how male neotenics affect the differentiation of female neotenics. Here, we show that male and female neotenics regulate the neotenic differentiation in a sex-specific manner in the damp-wood termite Hodotermopsis sjostedti, whose colonies are often headed by multiple male and female neotenics in the field. Our rearing experiments showed that the presence of female neotenics suppressed differentiation of female neotenics from fourth- to seventh-larvae, i.e., pseudergates (called as “workers” in this study), whereas male neotenics promoted the differentiation of female neotenics. Moreover, the results of rearing experiments that restricted physical contact between neotenics and workers suggested that these effects were not mediated by volatile chemicals, but rather by direct contact. We found that the male neotenics were frequently groomed by female workers, suggesting that these interactions promote the differentiation of female neotenics. Our results represent an empirical evidence that the neotenic differentiation from female and male workers is regulated by direct physical contact with the preexisting neotenics.

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Queen contact and among-worker interactions dually suppress worker brain dopamine as a potential regulator of reproduction in an ant

Hiroyuki Shimoji, Hitoshi Aonuma, Toru Miura, Kazuki Tsuji, Ken Sasaki, Yasukazu Okada

Behavioral Ecology and Sociobiology ( SPRINGER ) 71 ( 2 ) 2017年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

How individual organisms whose behavior is potentially driven by selfish interests cooperate to form a society is a central question in evolutionary biology. Worker reproduction and its suppression in eusocial insects provide an illuminating model of such a conflict resolution. Although many theoretical and empirical studies focus on the nature and evolutionary consequences of this reproductive conflict, little is known about its physiological underpinnings. Here, we hypothesized that the dopaminergic system, which has a gonadotropic function in eusocial Hymenoptera, is controlled by social suppression via the queen presence signal and the worker-worker dominance interactions. In Diacamma sp. from Japan, the queen presence signal is transferred to workers by direct contact, and worker-worker dominance interaction occurs commonly in large colonies, even when a queen is present. Using the ant Diacamma sp., we showed that the aggressive interactions among workers suppressed brain dopamine levels of the workers. Moreover, our data suggest that the queen presence signal transmitted by direct contact suppresses the brain dopamine level and the transcription of dopamine synthetic enzyme (ddc) of workers. Our data provide clear empirical evidence that worker brain dopamine is suppressed by both social stimuli directed from dominant workers and the queen.Significance statementIn eusocial Hymenoptera, worker reproduction is suppressed by social interactions such as queen presence information and dominance interaction. Dopamine, one of the biogenic amines, is a well-known gonadotropic neurohormone in eusocial Hymenoptera. Honeybee studies revealed that the queen presence information regulated dopamine levels in worker brains. In an ant, the dominance interaction also controlled dopamine levels of workers. In a queenless ant Diacamma sp., queen presence information and dominance interaction are known to dually suppress worker reproduction. Given the above examples, dopaminergic signaling is predicted to be a general mechanism that can suppress worker reproduction in multiple ways. We here test whether both the queen-and worker-originated signals (i.e., queen presence information and dominance interaction) affect the worker dopamine level. We show that dopaminergic signaling is affected by dual social factors, suggesting the general role of dopaminergic signaling in mediating social interaction and reproductive suppression.

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Reproductive organ development along the caste differentiation pathways in the dampwood termite Hodotermopsis sjostedti

K. Oguchi, H. Shimoji, Y. Hayashi, T. Miura

Insectes Sociaux ( Birkhauser Verlag AG ) 63 ( 4 ) 519 - 529 2016年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

One of the principal features of eusocial insect societies is the reproductive division of labor, which involves developmental regulation of the reproductive organs. However, although the regulation of caste development is important for establishing social structure in termites, one of the major eusocial insect groups, little is known about reproductive organ development during caste differentiation. Therefore, in this study, we investigated the anatomy and histology of the reproductive organs at various developmental stages during caste differentiation in the dampwood termite Hodotermopsis sjostedti, in which the differentiation of reproductive and non-reproductive castes occurs in late larval instars. We found that the reproductive organs gradually developed during the younger instars in both sexes. However, in females, there were larger variations in ovarian development between individuals in the seventh-instar larvae (i.e., pseudergates), which may reflect variability in their caste fates. By contrast, the testis size did not show such heterogeneity in male pseudergates. Interestingly, presoldiers and soldiers possessed relatively well-developed ovaries or testes containing sperm. When differentiating into the two types of reproductives, i.e., alates and neotenics, the reproductive organs developed rapidly, but the developmental timing of organ growth differed between these as well as between the sexes. Thus, reproductive organ development along the caste differentiation pathways appears to be regulated in a caste- and sex-specific manner.

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Variation in the coat-color-controlling genes, Mc1r and Asip, in the house mouse Mus musculus from Madagascar

Yuki Sakuma, Marie C. Ranorosoa, Gohta Kinoshita, Hiroyuki Shimoji, Kimiyuki Tsuchiya, Satoshi D. Ohdachi, Satoru Arai, Chihiro Tanaka, Hajanirina Ramino, Hitoshi Suzuki

Mammal Study ( MAMMALOGICAL SOC JAPAN ) 41 ( 3 ) 131 - 140 2016年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Variability in the coat color of the house mouse, Mus musculus, provides an opportunity to study the evolution of phenotypes in this species. Here we associated genetic variations with coat color in seven mice from Madagascar that had identical M. m. gentilulus mitochondrial DNA sequences. The entire coding region of the 948-base pair (bp) coat-color-related gene, Mc1r, was shown to have no nonsynonymous changes. However, analyses of the two exon-1 promoter regions-termed 1A (317 bp) and 1B (499 bp)-from a second gene, Asip, which is also involved in the evolution of coat color, revealed two distinct haplotypes in each region. Associations between Asip promoter regions and dorsal color were ambiguous; however, two ventral color types-light and dark gray-were associated with the haplotypes of 1A, as determined by clustering analysis. Notably, the haplotype of the light gray animals was identical to the Asip A(w) allele that is associated with white bellies.

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Expansion of presoldier cuticle contributes to head elongation during soldier differentiation in termites

Yasuhiro Sugime, Kota Ogawa, Dai Watanabe, Hiroyuki Shimoji, Shigeyuki Koshikawa, Toru Miura

Science of Nature ( SPRINGER HEIDELBERG ) 102 ( 11-12 ) 71 - 71 2015年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In termites, the soldier caste possesses morphological features suitable for colony defence, despite some exceptions. Soldiers are differentiated via two moultings through a presoldier stage with dramatic morphogenesis. While a number of morphological modifications are known to occur during the presoldier moult, growth and morphogenesis seem to continue even after the moult. The present study, using the damp-wood termite Hodotermopsis sjostedti, carried out morphological and histological investigations on the developmental processes during the presoldier stage that is artificially induced by the application of a juvenile hormone analogue. Measurements of five body parameters indicated that head length significantly increased during the 14-day period after the presoldier moult, while it did not increase subsequently to the stationary moult (pseudergate moult as control). Histological observations also showed that the cuticular development played a role in the presoldier head elongation, suggesting that the soft and flexible presoldier cuticle contributed to the soldier morphogenesis in termites.

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Social dominance and reproductive differentiation mediated by dopaminergic signaling in a queenless ant.

Yasukazu Okada, Ken Sasaki, Satoshi Miyazaki, Hiroyuki Shimoji, Kazuki Tsuji, Toru Miura

The Journal of experimental biology 218 ( Pt 7 ) 1091 - 8 2015年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In social Hymenoptera with no morphological caste, a dominant female becomes an egg layer, whereas subordinates become sterile helpers. The physiological mechanism that links dominance rank and fecundity is an essential part of the emergence of sterile females, which reflects the primitive phase of eusociality. Recent studies suggest that brain biogenic amines are correlated with the ranks in dominance hierarchy. However, the actual causality between aminergic systems and phenotype (i.e. fecundity and aggressiveness) is largely unknown due to the pleiotropic functions of amines (e.g. age-dependent polyethism) and the scarcity of manipulation experiments. To clarify the causality among dominance ranks, amine levels and phenotypes, we examined the dynamics of the aminergic system during the ontogeny of dominance hierarchy in the queenless ant Diacamma sp., which undergoes rapid physiological differentiation based on dominance interactions. Brain dopamine levels differed between dominants and subordinates at day 7 after eclosion, although they did not differ at day 1, reflecting fecundity but not aggressiveness. Topical applications of dopamine to the subordinate workers induced oocyte growth but did not induce aggressiveness, suggesting the gonadotropic effect of dopamine. Additionally, dopamine receptor transcripts (dopr1 and dopr2) were elevated in the gaster fat body of dominant females, suggesting that the fat body is a potential target of neurohormonal dopamine. Based on this evidence, we suggest that brain dopamine levels are elevated in dominants as a result of hierarchy formation, and differences in dopamine levels cause the reproductive differentiation, probably via stimulation of the fat body.

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Global network structure of dominance hierarchy of ant workers.

Hiroyuki Shimoji, Masato S Abe, Kazuki Tsuji, Naoki Masuda

Journal of the Royal Society, Interface 11 ( 99 ) 2014年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Dominance hierarchy among animals is widespread in various species and believed to serve to regulate resource allocation within an animal group. Unlike small groups, however, detection and quantification of linear hierarchy in large groups of animals are a difficult task. Here, we analyse aggression-based dominance hierarchies formed by worker ants in Diacamma sp. as large directed networks. We show that the observed dominance networks are perfect or approximate directed acyclic graphs, which are consistent with perfect linear hierarchy. The observed networks are also sparse and random but significantly different from networks generated through thinning of the perfect linear tournament (i.e. all individuals are linearly ranked and dominance relationship exists between every pair of individuals). These results pertain to global structure of the networks, which contrasts with the previous studies inspecting frequencies of different types of triads. In addition, the distribution of the out-degree (i.e. number of workers that the focal worker attacks), not in-degree (i.e. number of workers that attack the focal worker), of each observed network is right-skewed. Those having excessively large out-degrees are located near the top, but not the top, of the hierarchy. We also discuss evolutionary implications of the discovered properties of dominance networks.

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Egg discrimination by workers in Diacamma sp. from Japan

H. Shimoji, Y. Fujiki, R. Yamaoka, K. Tsuji

Insectes Sociaux ( Springer Science and Business Media LLC ) 59 ( 2 ) 201 - 206 2012年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In eusocial Hymenoptera, workers usually cannot mate but can lay male-destined haploid eggs. In contrast, in many species, worker reproduction is regulated by means of worker policing, which consists of two behavioral categories: aggression towards workers that have developed ovaries, and the destruction of worker-laid eggs. We focused on the latter behavior in the ant Diacamma sp. from Japan, in which a mated worker (gamergate) serves as the functional queen in each colony. An experiment in which we introduced both worker-laid eggs and gamergate-laid eggs from foreign colonies showed that workers preferentially destroyed the worker-laid eggs. This indicates that workers can discriminate worker-laid eggs from gamergate-laid eggs. In contrast, gamergates destroyed all introduced eggs that they discovered. Our chemical analysis of egg surface substances revealed that the worker-laid eggs clearly differed from gamergate-laid eggs in their surface hydrocarbons (SHCs), with the former containing more long-chain components. However, a bioassay to test whether specific components of the SHCs trigger the observed discrimination behavior by workers remains to be done. © International Union for the Study of Social Insects (IUSSI) 2011.

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Paternally inherited alleles in male body parts of an ant (Diacamma sp.) sex mosaic: Implication for androgenetic male production in the Hymenoptera

S. Dobata, H. Shimoji, H. Ohnishi, E. Hasegawa, K. Tsuji

Insectes Sociaux ( Springer Science and Business Media LLC ) 59 ( 1 ) 55 - 59 2012年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Sex mosaicism, also called gynandromorphism, refers to an accidental phenomenon in dioecious organisms (mainly animals) in which an individual phenotype includes both female and male characteristics. Despite the rarity of this phenomenon, elucidating the mechanisms of naturally occurring sex mosaicism should deepen our understanding of diverse sex determination and differentiation systems in nature. We report the results of a genetic study of a sex mosaic individual of the ant Diacamma sp. from Japan's Okinawa Island. Parentage analysis using microsatellite markers revealed that the female and male parts of the sex mosaic showed different inheritance patterns: female parts had alleles consistent with their biparental inheritance, whereas most of the male parts had alleles consistent with their paternal inheritance (i. e., androgenesis). We discuss plausible cytogenetic mechanisms that gave rise to the male parts of this individual: polyspermy and the subsequent independent cleavage by a surplus sperm pronucleus, and maternal genome elimination after fertilization of an ovule. Moreover, we hypothesize that the androgenetically produced males found in some Hymenoptera might share the same underlying cytogenetic mechanism with hymenopteran sex mosaicism. © 2011 International Union for the Study of Social Insects (IUSSI).

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Do eggs convey information on gamergate presence in Diacamma sp. from Japan?

H. Shimoji, Y. Fujiki, K. Tsuji, R. Yamaoka

Insectes Sociaux ( Springer Science and Business Media LLC ) 58 ( 1 ) 3 - 7 2011年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In eusocial Hymenoptera, information on the presence of a queen is considered to play an important role in regulating worker reproduction. We examined the mode of transmission of this putative queen information to workers. Previous studies have reported that, in Diacamma sp. from Japan, unmated helper workers perceive the presence of a gamergate (functional queen) only through direct physical contact with her. In contrary to this conclusion, we showed, by an experiment that exposed workers either to the gamergate or to the eggs laid by the gamergate, that the presence of eggs laid by the gamergate to some extent suppressed the workers' dominance interaction, a behavior that is associated with self-reproduction by unmated workers. We discuss the relative importance of direct and indirect transmission of gamergate-presence information under natural conditions in this ant. © 2010 International Union for the Study of Social Insects (IUSSI).

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