Characterizing Japanese Giant Salamanders (Andrias japonicus) in Overlooked Habitats Highlights the Need for Connectivity Conservation

Résumé fourni par la source

Preserving different habitat types and their connectivity is essential for conserving species that migrate or disperse over heterogeneous habitats. These aspects are poorly understood for fully aquatic, often secretive amphibians, including imperiled Japanese Giant Salamanders (Andrias japonicus). A recent eDNA study found that A. japonicus inhabits small headwater tributaries, which have been overlooked as habitats for giant salamanders in the family Cryptobranchidae because such streams, susceptible to contraction and disconnection, appear too small for large aquatic salamanders. To evaluate the value of headwater tributaries as habitats, I explored the hypothesis that they would serve as suboptimal refugia for smaller adults, especially males, to avoid mate competition in the mainstem. Males compete, often via biting, to establish and guard nesting sites, resulting in injuries such as missing toes and limbs. Analyzing long-term monitoring data from the Ichi River, Hyogo, I tested the predictions: (1) tributary adults would have fewer injuries than the mainstem adults; (2) tributary adults would have poorer body conditions; and (3) the sexual dimorphism in body size would be more pronounced in the mainstem, with males being larger. I found that tributary males were as injury-prone as mainstem males, while tributary females had fewer injuries than mainstem females. Tributary adults were significantly smaller, but body condition and the body-size sexual dimorphism were similar between the two habitats. I also found that relatively large adults migrate between the mainstem and tributaries. These results rejected the hypothesis. Rather than suboptimal refugia, headwater tributaries serve as essential habitats where smaller adults can maintain body conditions comparable to their mainstem counterparts, and males are actively engaged in mate competition. These findings highlight the urgent need to conserve habitat connectivity throughout the river system for this species and, potentially, for other cryptobranchids that have suffered severe habitat fragmentation due to dams constructed across their distribution ranges.

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