Spawning sites of the Japanese Forest Green Tree Frog (Zhangixalus arboreus: Rhacophoridae) in Central Japan

Abstract

We conducted field observations of spawning sites of the Japanese forest green tree frog (Zhangixalus arboreus: Rhacophoridae) at four ponds for two years. In 2019, a total of 50 foam nests were made on trees (77%), whereas 15 foam nests were made on the ground (23%). In 2020, 65 nests were arboreal (97%) and there were only two ground nests (3%). About 70% of all ground nests deteriorated or disappeared without their eggs hatching, mostly because of predation. In contrast, only about 4% of all arboreal nests died because of desiccation and 27% died mainly of outside spawning and disappearance before egg hatching for any reason. The relative proportions of arboreal versus ground spawning sites differed significantly between 2019 and 2020. Ground spawning was scarcely observed in 2020; in that year the amount of precipitation during the reproductive period was about 1.5 times that in 2019. Our field experiment using paper-clay models confirmed that arboreal nests were more susceptible to desiccation than ground nests. These results suggest that ground spawning may be of some advantage in resistance to desiccation, whereas arboreal spawning may be less susceptible to predation of foam nests.

Arboreal or terrestrial: Oviposition site of Zhangixalus frogs affects the thermal function of foam nests

“…Our research suggests that terrestrial foam nesting could contribute to protecting eggs from cold temperatures. This advantage seems to be related to the behavioural evolution of the genus Zhangixalus , which began nesting in terrestrial sites in response to global cooling (Dufresnes et al., 2022 ), despite its higher predation risk compared to arboreal nesting (Ichioka & Hijii, 2021 ). However, to fully elucidate the effect of the nesting site, additional aspects need to be considered.…”

“…Only fresh nests were collected, which were identified based on their appearance, specifically the presence or absence of a white surface colour, that gradually changes to yellowish (Herpetological Society of Japan, 2021 ). In the study area, Z. arboreus use both arboreal and terrestrial oviposition sites (Figure 2a,c : Ichioka & Hijii, 2021 ). However, for further experiments, we only used nests spawned arboreally.…”

“…Herein, we studied the effect of foam nest site, foam nest function and egg fate using the Japanese green tree frog, Zhangixalus arboreus . This is a relatively large frog endemic to Japan that shows plasticity in nesting site use that includes both trees and the ground (Figure 1 ; Ichioka & Hijii, 2021 ; Matsui & Maeda, 2018 ). Among Zhangixalus species, arboreal nest‐making is an ancestral behaviour, with terrestrial nest‐making having evolved during subsequent periods of global cooling (Dufresnes et al., 2022 ).…”