Diverse Heat Tolerance of the Yeast Symbionts of Platycerus Stag Beetles in Japan

Abstract

The genus Platycerus (Coleoptera: Lucanidae) is a small stag beetle group, which is adapted to cool-temperate deciduous broad-leaved forests in East Asia. Ten Platycerus species in Japan form a monophyletic clade endemic to Japan and inhabit species-specific climatic zones. They are reported to have co-evolutionary associations with their yeast symbionts of the genus Sheffersomyces based on host cytochrome oxidase subunit I (COI) and yeast intergenic spacer (IGS) phylogenies. Here we examined the heat tolerances of the yeast colonies isolated from the mycangia of 37 females belonging ten Japanese Platycerus species. The upper limits of growth and survival temperatures of each colony were decided by cultivating it at ten temperature levels between 17.5 and 40°C. Although both temperatures varied during 25.0–31.25°C, the maximum survival temperatures (MSTs) were a little higher than the maximum growth temperatures (MGTs) in 16 colonies. Pearson’s correlations between these temperatures and environmental factors (elevation and 19 bioclimatic variables from Worldclim database) of host beetle collection sites were calculated. These temperatures were significantly correlated with elevation negatively, the maximum temperature of the warmest month (Bio5) positively, and some precipitative variables, especially in the warm season (Bio12, 13, 16, 18) negatively. Sympatric Platycerus kawadai and Platycerus albisomni share the same lineage of yeast symbionts that exhibit the same heat tolerance, but the elevational lower range limit of P. kawadai is higher than that of P. albisomni. Based on the field survey in their sympatric site, the maximum temperature of host wood of P. kawadai larvae is higher about 2–3°C than that of P. albisomni larvae in the summer, which may restrict the elevational range of P. kawadai to higher area. In conclusion, it is suggested that the heat tolerance of yeast symbionts restricts the habitat range of their host Platycerus species or/and that the environmental condition that host Platycerus species prefers affect the heat tolerance of its yeast symbionts.

Accounting for dispersal and intraspecific variation in forecasts of species distribution under climate change

“…Zhang and Kubota (2021b) demonstrated the importance of intraspecific variation in the environmental space and assessed the predicted suitability differences at the species and subspecies levels, indicating that subspecies-based SDMs were more accurate. Here, we predicted distribution shifts under climatic change in consideration of both factors of two cold-adapted Platycerus species: Platycerus albisomni Kubota et al, 2008 andPlatycerus takakuwai Fujita, 1987. Both species live in cool-temperature deciduous broad-leaved forests and are particularly sensitive to climate change, as well as having limited dispersal ability (Zhang & Kubota, 2021a;Zhu et al, 2022). Future changes in the geographic distribution at the sub-specific level may thus affect the distribution at the species level because of their local adaptation and limited dispersal abilities.…”