Biology subjects

Dobata, S.

Publications and source records attributed to Dobata, S..

11 recordsLinked to original sources

bioRxiv2026

Contrasting phylogeographic patterns between geographically restricted and widespread mitochondrial lineages of the water strider Aquarius paludum in the Japanese archipelago

Aim To investigate how repeated historical connections between continental islands and the mainland have shaped the phylogeographic structure and genetic diversity of populations, using the widespread water strider Aquarius paludum as a model. Location Japan Taxon Water strider Aquarius paludum (Insecta: Hemiptera: Gerridae) Methods We analysed mitochondrial (COI and COII) and nuclear (ITS1) DNA sequences from populations across the Japanese archipelago and the Eurasian continent. Phylogenetic and population genetic analyses were used to reconstruct phylogeographic structure and infer demographic history. Results Western Japanese populations exhibited nucleotide diversity comparable to that of continental populations despite their insular distribution. Bayesian phylogenetic analyses identified two major mitochondrial haplogroups (A and B) that frequently co-occurred across the Japanese archipelago. Haplogroup A, which is rare on the Eurasian continent, occurred at high frequency in Japan and showed pronounced isolation by distance, whereas haplogroup B showed only weak but significant isolation by distance and was significantly more frequent in populations closer to the coast. These contrasting spatial patterns within species indicate distinct demographic histories for the two mitochondrial lineages. Main conclusion Repeated colonization from the Eurasian continent and the long-term coexistence of mitochondrial lineages with different demographic histories have shaped the pattern of genetic diversity of A. paludum in the Japanese archipelago. Our findings exemplify how continental islands can accumulate genetic diversity through lineage accumulation and secondary contact, which produces an intraspecific phylogeographic pattern comparable to those observed during an early phase of the taxon cycle between species.

evolutionary biology↗

bioRxiv2026

AMADEUS: Annotation-free multi-animal direction estimation using self-supervised learning

Markerless multi-animal tracking has advanced rapidly, yet measuring social interactions among visually similar animals remains challenging during occlusion and crowding. Here we present AMADEUS (Annotation-free Multi-Animal Direction Estimation Using Self-supervised learning), a tracking system that requires neither manual training annotation nor physical marking. AMADEUS extracts masks representing single animals, uses movement direction to assign head direction, and then synthesizes interaction images using copy-paste augmentation. A detector trained on the synthetic dataset estimates oriented bounding boxes and head direction, from which center, front and rear keypoints are derived. For a video containing instances of almost complete occlusion, AMADEUS additionally uses contrastive learning for identity verification. Across benchmark videos of 10 mice, 10 fish, 32 beetles, 32 ants with one cricket, 60 flies, and 368 ants, AMADEUS outperformed state-of-the-art methods in identity tracking and keypoint localization. AMADEUS enables scalable quantification of interactions across diverse species.

animal behavior and cognition↗

bioRxiv2026

Walking alone to the north: The origin and historical expansion of the polyploid parthenogenetic lineage in a weevil

Polyploid parthenogenetic organisms are distributed nonrandomly with respect to their diploid sexual relatives, and this pattern has been well documented in plants. Comparable cases are rare in animals, and their origin has been reconstructed in only a few taxa. Separating general eco-evolutionary processes from taxonomic idiosyncrasy therefore requires further animal examples of independent origin. Here we studied the flightless weevil Catapionus nebulosus species group, in which polyploid females were reported by early karyological work. We surveyed the group across its Japanese range to reconstruct its phylogenomic background from mitochondrial DNA and genome-wide SNPs. The sex ratio shifted sharply toward females in northern Japan. The all-female lineage had a single origin, carried a signal of hybridization between two divergent sexual lineages, and experienced rapid expansion in range and population size. The lineage was polyploid, and unmated females reared in isolation produced fertile female offspring. The effective population size, as estimated by the larval density and genetic diversity of the sexual populations, both declined toward the northern margin of their distribution range, already south of the co-occurrence zone with the parthenogenetic lineage. Mate limitation offers the most plausible explanation for the northward spread of the parthenogen. This species group adds an animal example of polyploid parthenogenesis and offers a system for testing why such lineages persist beyond the range of their sexual relatives.

evolutionary biology↗

bioRxiv2024

Adaptive decision-making by ants in response to past, imminent, and predicted adversity

Many animals exhibit innate behaviours, which are often interpreted as hard-wired, reflex-like responses, particularly in insects. Among these behaviours, beacon-aiming--an approach towards dark areas or objects--is observed in many animals; however, its functional significance remains unclear, and some ant species do not exhibit it. Here we show that in one such species, Camponotus japonicus, the behaviour was triggered only under adverse substrate conditions, such as during the crossing of liquid-covered surfaces, regardless of the locomotor patterns like walking or swimming, or the mere presence of water, or when walking upside-down. Once initiated, beacon-aiming persists even under normal substrate conditions, as demonstrated by ants transitioning from water-covered to dry substrates suitable for comfortable walking. This behavioural flexibility indicates that the innate behaviour is not hard-wired but modulated by internal states. Furthermore, changes in internal states may serve adaptive decision-making, potentially allowing ants to prepare for future adverse conditions. The isolated ants on a water-surrounded platform gradually established an attraction to the direction of the beacon before ultimately swimming towards it. These findings suggest that beacon-aiming is regulated by internal states, especially anxiety-like states formed in response to past, imminent, and predicted adverse substrate conditions in ants.

animal behavior and cognition↗

bioRxiv2024

Nestmate discrimination expels intrusion of intraspecific cheaters in an ant

Social animals utilise various communication methods to organise their societies. In social insects, nestmate discrimination plays a crucial role in regulating colony membership. Counter to this system, socially parasitic species employ diverse behavioural and chemical strategies to bypass their hosts detection. In this study, we tested whether such parasitic adaptations could be detected in the incipient stage of social parasitism that is observed as intraspecific phenomena in some social insects. The Japanese parthenogenetic ant Pristomyrmex punctatus harbours a genetically distinct cheater lineage which infiltrates and exploits host colonies. We found that intrusion of this intraspecific social parasite was defended by nestmate discrimination of host colonies without any behavioural strategies specialised in social parasitism. Most of the cheaters were eliminated through aggressions by host workers that are typically observed against non-nestmates, resulting in a low intrusion success rate for the cheaters (6.7%). This result contrasts with the expectation from interspecific social parasitism but rather resembles the intraspecific counterpart reported in Cape honeybees (Apis mellifera capensis), illustrating the role of nestmate discrimination against the intrusion of intraspecific social parasites.

animal behavior and cognition↗

bioRxiv2021

Morphology of immatures of the thelytokous ant, Monomorium triviale Wheeler (Formicidae: Myrmicinae: Solenopsidini) with descriptions of the larval caste dimorphism

The ant genus Monomorium is one of the most species-rich but taxonomically problematic groups in the hyperdiverse subfamily Myrmicinae. An East Asian species, M. triviale Wheeler, produces both reproductive queens and sterile workers via obligate thelytokous parthenogenesis. Here, we describe the immature forms of M. triviale based on light and scanning electron microscopy observations, with a note on the striking caste dimorphism in the last larval instar. The last-instar queen larvae were easily recognized by their large size, "aphaenogastroid" body shape, and rows of doorknob-like tubercles on the lateral and dorsal body surface. This type of queen-specific structure has not been found in ants in general, let alone congeneric species found in Japan. In stark contrast to the queen larvae, worker larvae showed a "pheidoloid" body shape and a body surface similar to other ants. The worker larvae were estimated to have three instars, consistent with previously described congeners. The pupae of both castes had no cocoon, a characteristic commonly described in other Myrmicinae species. In total, the developmental period from egg to adult worker averaged 59 days under 25{degrees}C. We discuss possible functions of the tubercles of queen larvae based on previous studies.

zoology↗

bioRxiv2021

The complete mitochondrial genome of a parthenogenetic ant, Monomorium triviale (Hymenoptera: Formicidae)

Monomorium is one of the most species-rich yet taxonomically problematic ant genus. An East Asian species, M. triviale Wheeler, W.M., 1906, are reproduced by obligate thelytokous parthenogenesis and performs strict reproductive division of labor. We sequenced the M. triviale mitogenome using next-generation sequencing methods. The circular mitogenome of M. triviale was 16,290 bp in length, consisting of 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNAs, and a single non-coding region of 568 bp. The base composition was AT-biased (82%). Gene order rearrangements were detected and likely to be unique to the genus Monomorium. We announce the M. triviale mitogenome as additional genomic resources for elucidating phylogenetic and taxonomic problems of Monomorium and comparative genomics of parthenogenetic ant species.

genomics↗

bioRxiv2021

Comprehensive analysis of male-free reproduction in Monomorium triviale (Formicidae: Myrmicinae)

We report comprehensive evidence for obligatory thelytokous parthenogenesis in an ant Monomorium triviale. This species is characterized by distinct queen-worker dimorphism with strict reproductive division of labor: queens produce both workers and new queens without mating, whereas workers are completely sterile. We collected 333 nests of this species from 14 localities and three laboratory-reared populations in Japan. All wild queens dissected had no sperm in their spermathecae. Laboratory observation confirmed that virgin queens produced workers without mating. Furthermore, microsatellite genotyping showed identical heterozygous genotypes between mothers and their respective daughters, suggesting an extremely low probability of sexual reproduction. Microbial analysis detected no bacterial genera that are known to induce thelytokous parthenogenesis in Hymenoptera. Finally, the lack of variation in partial sequences of mitochondrial DNA among individuals sampled from across Japan suggests recent rapid spread or selective sweep. M. triviale would be a promising model system of superorganism-like adaptation through comparative analysis with well-studied sexual congeners, including the pharaoh ant M. pharaonis.

zoology↗

bioRxiv2018

Regulatory mechanism predates the evolution of ant-like swarm intelligence in simulated robots

The evolution of complexity is one of the prime features of life on Earth. Although well accepted as the product of adaptation, the dynamics underlying the evolutionary build-up of complex adaptive systems remains poorly resolved. Using simulated robot swarms that exhibit ant-like group foraging with trail pheromones, we show that their swarm intelligence paradoxically involves regulatory behavior that arises in advance. We focused on a \"traffic rule\" on their foraging trail as a regulatory trait. We allowed the simulated robot swarms to evolve pheromone responsiveness and behaviors simultaneously. In most cases, the traffic rule, initially arising as selectively neutral component behaviors, assisted the group foraging system to bypass a fitness valley caused by overcrowding on the trail. Our study reveals a hitherto underappreciated role of regulatory mechanisms in the origin of swarm intelligence, as well as highlights the importance of embodiment in the study of their evolution.

evolutionary biology↗

bioRxiv2018

Adaptive switch to sexually dimorphic movements by partner-seeking termites

When searching for targets whose location is not known, animals should benefit by adopting movement patterns that promote random encounters. During mate search, theory predicts that the optimal search pattern depends on the expected distance to potential partners. A key question is whether actual males and females update their mate search patterns to increase encounter probability when conditions change. Here we show that two termite species, Reticulitermes speratus and Coptoterines formosanus, adaptively alternate between sexually monomorphic and dimorphic movements during mate search. After leaving their nests in a synchronized manner, termites begin to search for a mate. The resulting pairs perform tandem runs toward potential nest sites. We found that both sexes moved faster and in straight lines before finding partners, which is known to improve encounter rates when targets have completely unpredictable positions. 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. Data-based simulations demonstrated that such sexually dimorphic movements are advantageous when a mate is located nearby but its exact location is unknown. These results emphasize the importance of biological details to evaluate the efficiency of random search in animals. By extending the concept of mutual search beyond the context of mating, the dimorphic movements between partners represent a remarkable convergence between termites and other animals including humans.\n\nSignificance StatementHow should females and males move to search for partners whose exact location is unknown? Theory predicts that the answer depends on what they know about where targets can be found, indicating that the question doesnt make sense until the searching context is clarified. We demonstrated that termites adaptively switch their search modes depending on the potential distance to their partners. When the location of potential mates was completely unpredictable, both sexes moved in straight lines to explore widely. In contrast, when the stray partner was at least nearby, males moved while females paused. 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.

animal behavior and cognition↗

bioRxiv2017

Caste-biased movements by termites in isolation

The caste system of termites is an example of phenotypic plasticity. The castes differ not only in morphology and physiology, but also in behavior. As most of their behaviors within colonies involve nestmates, it is difficult to extract innate differences among castes. In this study, we focused on movement patterns of isolated individuals of Hodotermopsis sjostedti. We observed distinct clusters in movement patterns over 30 min, which indicates that termites have multiple innate modes of movement. The use of these modes is biased among castes, among which neotenics had a caste-specific mode and soldiers moved more actively than workers or neotenics. These caste biases may reflect different adaptive responses to social isolation. Our study provides a basis for a deeper understanding of the roles of individual movements in social behaviors.\n\nSummary StatementMovement patterns of termites in isolation were described for different castes. We proposed movements as a novel caste-specific characteristics in social insects.

animal behavior and cognition↗