Kenta Sugiura

Reproductive strategy is an important aspect of biological diversity. In tardigrades, several reproductive modes, including sexual reproduction, are known. However, tardigrade mating behavior has been observed only rarely in most species, and in some cases, especially in the freely ovipositing eutardigrades, remains entirely unknown. In the present study, we cultured two sexually reproducing tardigrade species that lay eggs freely, <i>Paramacrobiotus</i> sp. TYO strain and <i>Macrobiotus shonaic

The genus Paramacrobiotus was erected in 2009 from the genus Macrobiotus, and 43 Paramacrobiotus species have been described to date. Although the first genome sequence in the genus was reported for the TYO strain of Paramacrobiotus sp., which is a dioecious species and has five bivalent chromosomes, its precise taxonomic identification remained undetermined. Here, we report its morphology, confirming the presence of a microplacoid, cuticular bulge on the inner side of legs I–III, and granulatio

Presently, more than 40 species of the genus <i>Milnesium</i> Doyère, 1840 (Tardigrada: Eutardigrada: Apochela: Milnesiidae) have been described. In Japan, however, almost all records of milnesiid tardigrades should be re-examined with the current criteria on the taxonomy of this genus, except for one species, the recently described <i>Milnesium inceptum</i> Morek, Suzuki, Schill, Georgiev, Yankova, Marley, and Michalczyk, 2019. In this study, we found two species, <i>Milnesium pacificum</i> sp.

This study provides results for the first observations and analyses of individual spermatozoon motility in tardigrades. A comparison of the spermatozoon movements of the two tardigrades suggested that the motilities of the male gametes were affected by morphological differences, where the longer spermatozoa swam faster and the shorter ones showed more stable swimming. Swimming was mainly induced by tail movement, but the long head of Paramacrobiotus sp. spermatozoa might be especially important

To date, only seven species of Macrobiotidae (Parachela; Eutardigrada; Tardigrada) have been reported from Japan, including the recently described Macrobiotus shonaicus Stec et al., 2018 from the Shonai region of Japan. This species has flexible filaments on the egg processes and is known to proliferate only through sexual reproduction. Here, we report a multifaceted analysis of nine populations of M. shonaicus found on four Japanese islands. DNA sequencing of the cytochrome oxidase subunit I (C

The genus <i>Mesobiotus</i> was separated from the genus <i>Macrobiotus</i> in 2016 and the name referred to its phylogenetic position among the family Macrobiotidae; however, knowledge of the reproductive behavior of this genus is limited compared to those of <i>Paramacrobiotus</i> and <i>Macrobiotus</i>. This study comprehensively provides the reproductive traits, including the gamete morphologies and behavioral observations, of <i>Mesobiotus</i>. The morphology of its spermatozoon showed a le

Mating behaviours for two species of dioecious eutardigrades: a strain of Paramacrobiotus sp. and Macrobiotus shonaicus (Stec et al., 2018) have been recorded previously, and observations have indicated that spermatozoa of both species are first released into the environment, then swim through the cloaca of the females and into the spermatheca. The fusion of gamete nuclei has not yet occurred in a laid egg. Therefore, it has been suggested that fertilization is completed externally as the egg is

This study provides a comprehensive analysis for analyzing the genetic differences between sexes in tardigrades. The existence of male-biased, but not male-specific, genomic loci and identification of the family specific male-biased DMRT subfamily provides the foundation for understanding the sex determination cascade. In addition, sex-biased expression of several tardigrade-specific genes which are involved their stress tolerance suggests a potential role in protecting sex-specific tissue and g

Abstract Background Fertilization is an event at the beginning of ontogeny. Successful fertilization depends on strategies for uniting female and male gametes that developed throughout evolutionary history. In tardigrades, investigations of reproduction have revealed that released spermatozoa swim in the water to reach a female, after which the gametes are stored in her body. The morphology of the spermatozoa includes a coiled nucleus and a species-specific-length acrosome. Although the mating b

Sugiura, Kenta, Arakawa, Kazuharu, Matsumoto, Midori (2020): Distribution of Macrobiotus shonaicus Stec, Arakawa &amp; Michalczyk, 2018 (Tardigrada: Eutardigrada: Macrobiotidae) in Japan. Zootaxa 4778 (3): 600-600, DOI: https://doi.org/10.11646/zootaxa.4778.3.11

Additional file 4.

Abstract Background In gonochoristic animals, the sex determination pathway induces different morphological and behavioral features that can be observed between sexes, a condition known as sexual dimorphism. While many components of this sex differentiation cascade shows high levels of diversity, factors such as the Doublesex-Mab-3-related transcription factor (DMRT) are highly conserved throughout animals. Species of the phylum Tardigrada exhibits remarkable diversity in morphology and behavior

The order Apochela (Tardigrada: Eutardigrada) includes Milnesium and three monospecific genera Limmenius , Milnesioides , and Bergtrollus . These three genera have elongated buccal tubes and are found from limited areas in the world: Australia, New Zealand, and the Lyngen Alps in Norway, respectively. The existence of such milnesiids having elongated buccal tube in Japan was once reported at a conference but it has not been described further. We found the undescribed species again in summer 2023