한국 멸종위기 담수어종 열목어(Brachymystax lenok tsinlingensis) 개체군의 이주에 따른 새로운 서식처 환경 반응 생태적 분화 = Ecological Divergence in Response to Changing Habitat Environments in Translocated Populations of a Korean endangered freshwater fish, the Manchurian trout (Brachymystax lenok tsinlingensis)

다국어 초록 (Multilingual Abstract)

During recent years, indigenous freshwater fishes have profoundly decreased in population size, and a number of species are now under threat of extinction globally. To mitigate this breakdown of endemic fish populations, the use of translocation of animals to natural habitats to which they are not native as a conservation tool is a central issue under debate in conservation biologists, but may be the ‘unavoidable’ only choice where management augmentation of the target population is not possible naturally in practice. The Manchurian trout or lenok, Brachymystax lenok tsinlingensis (family Salmonidae), is a cold freshwater fish endemic to Northeast Asia. South Korea lenok populations that comprise the southern range edge of this species have recently decreased strikingly in size primarily due to anthropogenic pressure such as habitat destruction, agricultural run-off, water pollution and possibly climate change, and are now becoming critically endangered. To recover the number of individuals of B. lenok tsinlingensis, stocking or translocation programs have routinely been conducted by local governments since 1980s in South Korea. A local government research institute, for instance, introduced lenok individuals to the valleys at Mt. Chiaksan National Park in 1999, where they have never occurred naturally, but their source population was not recorded so remains unknown. Moreover, several local sites have been repopulated using stocking via the release of hatchery-reared or -bred fish or translocation from non-native habitats. However, whether and how these translocated populations have successfully been established in novel environmental conditions and have ecologically and/or genetically diverged from native populations remain untested. Our previous study found that South Korea lenok populations including natural and translocated populations were unarguably genetically divergent each other and also that the source population for the introduced Mt. Chiaksan National Park population might originate from Hongcheon. In the present study, we examine whether ecological divergence among two natural (Bangtae, Hongcheon) and three restored populations (translocated: Pyeongchang, Bonghwa; introduced: Mt. Chiaksan National Park) has resulted in during the past 20-35 years by comparing aspects of body shape using geometric morphometric analysis. By focusing on the source population of Hongcheon and the introduced population of Mt. Chiaksan National Park, we further investigate phenotypic characteristics of those populations, such as body shape, trophic niche, body length-weight relationship, condition factor and age frequency distribution to test whether recently introduced (recipient) lenok population has ecologically diverged in response to changing habitat environments from the native (source) population. We found that five South Korea lenok populations analyzed are morphologically significantly differentiated one another based on our geometric morphometric analysis (canonical variate analysis; CVA, P < 0.0001). However, there was no correlation detected between morphological similarity and different river basins (Cluster 1: Hongcheon and Mt. Chiaksan National Park; Cluster 2: Bangtae and Pyeonchang; Cluster 3: Bonghwa). Our CVA results showed some degrees of an overlap among individuals from different populations. CVA 1, which explains 47.3 % of the total morphological variance, clearly separated Cluster 1 and the residual groups (Clusters 2 and 3) by a change in the position of body shape related to shapes of mouth and caudal fin. On the other hand, CVA 2, which explains 27.7 % of the total variance, separated by body depth. Interestingly, for cross validation analysis among populations, Cluster 3 had generally more chubby body shape relative to Clusters 1 and 2. We also found there is divergence in trophic niche between the source (Hongcheon) and recipient (Mt. Chiaksan National Park) populations based on different levels of carbon and nitrogen isotopic signatures. The isotopic ranges of Hongcheon population (δ13C = －19.67 ‰, δ15N = 5.63 ‰) were significantly higher than Mt. Chiaksan National Park (δ13C = －21.67 ‰, δ15N = 4.25 ‰), suggesting that food sources differ substantially in these populations, and also that the trophic level of the introduced population might have shifted in novel feeding environments. Collectively, these findings imply that different environmental conditions facilitate a change in body shape and trophic niche during only few decades. Nevertheless, there were significant differences in neither body length-weight relationship nor condition factor between the source and recipient populations for multiple samples collected before and after breeding season. In both populations, age frequencies of the sampled individuals according to their body sizes was distributed mainly from one to three years old. We show that natural (source) and introduced (recipient) populations display ecological divergence with respect to body shape and trophic level, which is perhaps due to changing environmental conditions (e.g., water velocity, food source) between the two habitats. In the future, management of conservation for this lenok species through human- mediated translocation should consider not only the genetic characteristics, but also ecological features, which should help inform on the effective conservation and restoration plans for this highly cherished species in South Korea.