Abstract
The Asian black bear Ursus thibetanus is widely distributed in Asia and is adapted to broad-leaved deciduous forests, playing an important ecological role in the natural environment. Several subspecies of U. thibetanus have been recognized, one of which, the Japanese black bear, is distributed in the Japanese archipelago. Recent molecular phylogeographic studies clarified that this subspecies is genetically distantly related to continental subspecies, suggesting an earlier origin. However, the evolutionary relationship between the Japanese and continental subspecies remained unclear. To understand the evolution of the Asian black bear in relation to geological events such as climatic and transgression-regression cycles, a reliable time estimation is also essential. To address these issues, we determined and analyzed the mt-genome of the Japanese subspecies. This indicates that the Japanese subspecies initially diverged from other Asian black bears in around 1.46Ma. The Northern continental population (northeast China, Russia, Korean peninsula) subsequently evolved, relatively recently, from the Southern continental population (southern China and Southeast Asia). While the Japanese black bear has an early origin, the tMRCAs and the dynamics of population sizes suggest that it dispersed relatively recently in the main Japanese islands: during the late Middle and Late Pleistocene, probably during or soon after the extinction of the brown bear in Honshu in the same period. Our estimation that the population size of the Japanese subspecies increased rapidly during the Late Pleistocene is the first evidential signal of a niche exchange between brown bears and black bears in the Japanese main islands.This interpretation seems plausible but was not corroborated by paleontological evidence that fossil record of the Japanese subspecies limited after the Late Pleistocene. We also report here a new fossil record of the oldest Japanese black bear from the Middle Pleistocene, and it supports our new evolutionary hypothesis of the Japanese black bear.
Highlights
The Asian black bear (Ursus thibetanus) is a middle-sized bear that is widely distributed in Asia, from Japan in the east to Iran in the west
The divergence time between the Japanese and continental population has been estimated as around 0.5 Ma (Mega annum) [9] and 1.4– 2.6 Ma [8]. Both studies used divergence times at the genus (Ursus) level as calibration points: Yasukochi et al [9] assumed that the split between U. arctos and U. spelaeus was 1.2 Ma based on the estimate in a previous study [11] using D-loop sequences, while Ohnishi et al [8] assumed that the split between U. thibetanus and U. americanus occurred at 2.0 to 3.5 Ma, based on fossil records [12]
Since the strict molecular clock model could not be rejected by a likelihood ratio test, we carried out a new calculation of the evolutionary rate of the D-loop based on 61 Asian black bears including individuals from the continental population and Japanese population, assuming the split of U. t. formosanus and others (e.g., U.t. thibetanus, U.t. ussuricus) as 0.51 Ma
Summary
The Asian black bear (Ursus thibetanus) is a middle-sized bear that is widely distributed in Asia, from Japan in the east to Iran in the west. Their resulting tree indicated that the north continental population and the Japanese population evolved relatively recently from the south continental population Despite these studies, evolutionary time estimates for Asian black bear populations are still controversial. The divergence time between the Japanese and continental population (both north and south) has been estimated as around 0.5 Ma (Mega annum) [9] and 1.4– 2.6 Ma [8] Both studies used divergence times at the genus (Ursus) level as calibration points: Yasukochi et al [9] assumed that the split between U. arctos and U. spelaeus was 1.2 Ma based on the estimate in a previous study [11] using D-loop sequences, while Ohnishi et al [8] assumed that the split between U. thibetanus and U. americanus occurred at 2.0 to 3.5 Ma, based on fossil records [12]. We estimate the coalescent times among U. thibetanus as well as the behavior of the population size over time, through its history on a geological timescale
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
