Mitochondrial DNA Population Structure of the White-Spotted Charr (Salvelinus leucomaenis) in the Lake Biwa Water System

Abstract

A phylogeographic analysis of mitochondrial DNA sequences was performed in order to elucidate the origin, dispersal process, and genetic structure of white-spotted charr in the Lake Biwa water system. Two haplotypes were most common in the Lake Biwa water system, and were also common in the adjacent inlet rivers of the Sea of Japan. These results suggest that in the glacial periods of the Pleistocene, white-spotted charr dispersed into the northern inlet rivers of Lake Biwa from adjacent inlet rivers of the Sea of Japan by watershed exchanges, colonizing the whole of the Lake Biwa water system. Mitochondrial DNA diversity contrasted sharply between the western and eastern parts of the system, suggesting that the populations in the western part might be more reduced than those in the eastern part in relation to the smaller habitat size. The high overall FST estimate (0.50), together with pairwise comparisons of FST, indicated significant genetic divergence between populations due to isolation and small population size. Hierarchical analysis (AMOVA) also showed that genetic variation was more pronounced among regions (28.39%) and among populations within regions (47.24%) than within populations (24.37%). This suggests that each population in and around the Lake Biwa water system should be treated as a significant unit for conservation and management.

Relationships among tributary length, census population size, and genetic variability of white-spotted charr, Salvelinus leucomaenis, in the Lake Biwa water system

“…On the other hand, it has been reported that the mean annual temperature in Japan from 7,000 to 5,000 years ago was higher by 1-2°C than the current temperature (Yasuda 1997). This postglacial warming might have reduced the habitat size of white-spotted charr populations, and the level of habitat reduction would be higher in the western Lake Biwa populations than the eastern due to the smaller high altitude area (Kikko et al 2008c). Thus, the correlation between haplotype diversity and census population size in the eastern part of the system and monomorphic haplotype diversity in the western part of the system could be due to the different levels of bottlenecks related to the habitat size between the eastern and western parts of the system during the warmer postglacial period than today, although it appears to result partly from historical incidents such as range expansion as well as recent anthropogenic disturbances.…”

“…These results suggest that the low haplotype diversity of the western populations is mainly explained by historical bottlenecks rather than current reduction in population size. White-spotted charr populations in the Lake Biwa water system might have maintained the genetic variability at a similar level between the western and eastern parts until the end of the last glacial period because of the gene flow among the populations through the littoral waters of Lake Biwa (Yamamoto et al 2004a, b;Kikko et al 2008c). The current tributary length (a proxy for potential habitat size) populated by white-spotted charr between the eastern and western parts of the system were not significantly different (mean ± SD = 1,588 ± 1,273 m in the eastern part; 1,040 ± 594 m in the western part; Mann-Whitney U test, U = 4.0, P [ 0.05).…”

“…We used data on the genetic variability of the mitochondrial cytochrome b region from a previous study of the ten white-spotted charr populations in the Lake Biwa water system and the adjacent basins (Kikko et al 2008c). Genetic variability in each population was assessed by haplotype diversity (Frankham 1996).…”

“…This is because the distribution and abundance of whitespotted charr populations in the Lake Biwa water system has became drastically reduced since the 1970s as a result of several factors including hybridization with stocked hatchery-reared charr, habitat fragmentation by damming, and overharvesting, therefore at present in the inlet rivers of Lake Biwa native white-spotted charr populations persist only in small headwater tributaries isolated by erosion-control dams or waterfalls (Kikko et al 2007(Kikko et al , 2008a. Kikko et al (2008c) discussed the origin and dispersal processes of white-spotted charr in the Lake Biwa water system and the adjacent basins based on the sequence variations of mitochondrial DNA (mtDNA). In Kikko et al (2008c), they pointed out that the genetic diversity within populations in the Lake Biwa system and the adjacent basins was generally low; especially the genetic diversity in the western part of the study area was markedly lower than in the eastern.…”

“…Kikko et al (2008c) discussed the origin and dispersal processes of white-spotted charr in the Lake Biwa water system and the adjacent basins based on the sequence variations of mitochondrial DNA (mtDNA). In Kikko et al (2008c), they pointed out that the genetic diversity within populations in the Lake Biwa system and the adjacent basins was generally low; especially the genetic diversity in the western part of the study area was markedly lower than in the eastern. Genetic variability is related to population size within and across species (Frankham 1996); however, the relationship between genetic variability and population size in the fluvial whitespotted charr populations near the southern limit of the distribution range has remained unclear (see Yamamoto et al 2004b).…”