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Stream habitat is distributed discontinuously, which restricts the dispersal of animals among streams. Freshwater decapod crustaceans have poor dispersal ability and thus may suffer high extinction risk in the face of habitat destruction and other forces. Here, the ecological characteristics of two freshwater decapods, the threatened crayfish Cambaroides japonicus (de Haan, 1841) and the widespread crab Geothelphusa dehaani (White, 1847), were compared. The objective of the study was to determine which characteristics are most likely to limit the distribution of C. japonicus.Environmental DNA sampling was conducted to detect C. japonicus and G. dehaani populations, and environmental characteristics were measured to identify suitable stream habitat. Phylogenetic divergence and genetic differentiation among populations were examined. Using species distribution modelling, the future distributions of both species under climate change were predicted.Stream habitats harbouring C. japonicus tended to be supplied with more beech leaves and fewer cedar leaves, whereas those of G. dehaani were relatively wide, indicating that C. japonicus favours upstream areas in natural broad‐leaved forest. The results also showed greater genetic divergence among populations of C. japonicus than those of G. dehaani. Modelling indicated that most areas within the current distribution of C. japonicus were predicted to be areas with low distribution probability under a future climate scenario.To protect C. japonicus, further loss of local populations should be prevented to allow for the maintenance of high genetic diversity among populations, which may provide the evolutionary capability of surviving under future climate conditions. To prevent further loss of C. japonicus populations, natural deciduous forests in mountainous areas need to be preserved. C. japonicus can be the indicator species within the freshwater environment in these forests. Conservation measures for C. japonicus should also be effective for the conservation of the other freshwater invertebrates in upstream areas. [ABSTRACT FROM AUTHOR]

Aim: As climate change presents a major threat to biodiversity in the next decades, it is critical to assess its impact on species habitat suitability to inform biodiversity conservation. Species distribution models (SDMs) are a widely used tool to assess climate change impacts on species' geographical distributions. As the name of these models suggests, the species level is the most commonly used taxonomic unit in SDMs. However, recently it has been demonstrated that SDMs considering taxonomic resolution below (or above) the species level can make more reliable predictions of biodiversity change when different populations exhibit local adaptation. Here, we tested this idea using the Japanese crayfish (Cambaroides japonicus), a threatened species encompassing two geographically structured and phylogenetically distinct genetic lineages. Location: Northern Japan. Methods: We first estimated niche differentiation between the two lineages of C. japonicus using n‐dimensional hypervolumes and then made climate change predictions of habitat suitability using SDMs constructed at two phylogenetic levels: species and intraspecific lineage. Results: Our results showed only intermediate niche overlap, demonstrating measurable niche differences between the two lineages. The species‐level SDM made future predictions that predicted much broader and severe impacts of climate change. However, the lineage‐level SDMs led to reduced climate change impacts overall and also suggested that the eastern lineage may be more resilient to climate change than the western one. Main conclusions: The two lineages of C. japonicus occupy different niche spaces. Compared with lineage‐level models, species‐level models can overestimate climate change impacts. These results not only have important implications for designing future conservation strategies for this threatened species, but also highlight the need for incorporating genetic information into SDMs to obtain realistic predictions of biodiversity change. [ABSTRACT FROM AUTHOR]

During a visit to the Musée des Confluences in Lyon, France, specimens of the branchiobdellidan Cirrodrilus cirratus were discovered on four endemic Japanese crayfish, Cambaroides japonicus, that had been donated to the museum in 1889. This discovery was placed in context with a review of the early international researchers involved with studying Japanese branchiobdellidans. Concomitantly, investigations on Cirrodrilus inukaii, including morphological variations, led to a reassessment of the taxonomic status of Branchiobdella digitata Pierantoni, 1906. This resulted in B. digitata being transferred to the genus Cirrodrilus as C. digitatus (Pierantoni, 1906) comb. n. and C. inukaii (Yamaguchi, 1934) recognised as a junior synonym of C. digitatus (new synonymy). These studies have demonstrated the importance of good preservation practices and particularly the need in future decapod collections so as to conserve the present diversity of their delicate ectosymbionts. [ABSTRACT FROM AUTHOR]

The Japanese crayfish ( Cambaroides japonicus), the only native crayfish in Japan, is endangered and has experienced rapid population declines. We surveyed the habitat requirements of Japanese crayfish at the reach and microhabitat scales in semi-natural low-gradient streams. Habitat use by Japanese crayfish differed between the spatial scales. Reach-scale analysis revealed that the bed slope was the only positive predictor of crayfish density. This finding indicates that relatively high-gradient reaches, such as headwater reaches, are an important habitat for the conservation of Japanese crayfish in low-gradient streams. Microhabitat-scale analysis showed that crayfish density was positively affected by substrate coarseness and the presence of instream vegetation cover (bank vegetation, woody debris, and leaf patches), whereas it was negatively affected by distance from the stream edge. Coarse substrates and vegetation cover may function as shelters from water flows and predators during low flow periods. The use of stream-edge areas may allow quick access to refugia and enable the crayfish to avoid unexpected flood disturbance and predation. These habitat characteristics should therefore be preserved for the conservation of Japanese crayfish, and scale-dependent habitat characteristics should be considered in future conservation plans. [ABSTRACT FROM AUTHOR]

Lethal limits of high temperature were studied to clarify the effects on the survival of the endangered Japanese crayfish species Cambaroides japonicus and the alien species Pacifastacus leniusculus . After the acclimation period for 2 weeks at 16°C, the temperature was raised at a rate of 1°C per week. As a result, the ultimate upper lethal temperatures of C. japonicus and P. leniusculus were 27.0 and 31.1°C, respectively, and the lethal temperature for P. leniusculus was significantly higher than for C. japonicus . The natural distributions of these two species are discussed in terms of the temperature tolerance. [ABSTRACT FROM AUTHOR]

SUMMARY: Preference for artificial burrows by the endangered Japanese crayfish species Cambaroides japonicus was studied to improve its cultivation. The occupation of artificial burrows, which were made from straight polyvinyl chloride pipes of different internal diameters (Y, mm), by crayfishes of different total lengths (X, mm) was significantly (P < 0.001, n = 56) described by a linear regression: Y = 0.49X + 3.42 (19.0 ≤ X ≤ 70.2). Among burrows of different lengths [crayfish total length (TL) × 1, × 2, × 3, and × 4], crayfishes significantly preferred burrows that were greater than TL × 3 (P < 0.001, n = 588). [ABSTRACT FROM AUTHOR]

In eastern Hokkaidô, Japan, the native crayfish Cambaroides japonicus de Haan has been declining rapidly while the exotic crayfish Pacifastacus leniusculus Dana has been expanding its range. We speculated that the observed displacement of Cambaroides by Pacifastacus is partly due to an interference interaction for shelter between the two species. We studied the impacts of Pacifastacus on Cambaroides by testing experimentally whether intensity of interference, the outcome of dominance order and shelter occupancy differed between single- and mixed-species combinations of the two species. Pacifastacus showed less defensive behaviours towards Cambaroides than to conspecifics. In contrast, Cambaroides exhibited more defensive behaviours towards Pacifastacus than to conspecifics. Pairwise comparison of agonistic behaviours in mixed species groups revealed that Pacifastacus exhibiting frequently more aggressive attacks while Camaboides showing more defensive behaviours to their respective counterparts. Dominance in aggressive encounter generally dictated shelter occupancy in mixed-species and Pacifastacus pairs but not in Cambaroides pairs. Because shelter utilization, when these are not limited in supply, was much more frequent in Cambaroides than Pacifastacus, Cambaroides suffered interference from both conspecifics and heterospecifics when they competed for a single shelter. Pacifastacus, however, did not show any change in shelter occupancy in the presence or absence of conspecics or heterospecifics. Inferiority in aggressive interactions and shelter occupancy can therefore be a critical disadvantage for Cambaroides if shelters are limited in natural situations. [ABSTRACT FROM AUTHOR]