Hybridization, Isolation, and Low Genetic Diversity of Kirikuchi Char, the Southernmost Populations of the Genus Salvelinus

Abstract

The Kirikuchi char Salvelinus leucomaenis japonicus, which is endemic to the Kii Peninsula, central Honshu, Japan, is a relict nonanadromous char adapted to the southernmost habitats of the genus Salvelinus. As a result of anthropogenic disturbance, the distribution of the Kirikuchi char is now limited to the two upper drainages of the Totsu River system in the Kii Peninsula and this subspecies is now threatened with extinction. The present study determined the genetic population structure of the Kirikuchi char by using partial sequences of the mitochondrial cytochrome b gene, seven microsatellites, and a major histocompatibility complex (MHC) gene (exon 2 of MHC class II beta). The results indicated that native Kirikuchi char populations in both drainages have hybridized extensively with stocked S. leucomaenis pluvius or S. leucomaenis leucomaenis that were originally distributed in eastern Honshu. Native populations were restricted to isolated headwaters above natural falls or sediment control dams and showed very low genetic diversity: one mitochondrial DNA haplotype and average heterozygosity of 0.00–0.12 in microsatellites and 0.00–0.50 in the MHC gene. The distinct genetic differences between the Kirikuchi char populations in the two drainages suggest that these populations should be managed as separate conservation units. A high risk of hybridization with stocked nonnative subspecies widely distributed throughout the drainages has prevented the recovery of natural connections that permit gene flow between local populations of Kirikuchi char. Given the extremely low genetic diversity of the remaining Kirikuchi char populations, it is necessary to take proactive management measures, such as the promotion of artificial gene flow across local populations within each drainage and genetic restoration using the data presented here.

Hybridization and extinction

“…; Rubidge and Taylor ; Sato et al. ). Similarly, intentional releases of game birds for hunting may pose a risk for wild relatives, such as black ducks ( Anas rubripes ) in America (Mank et al.…”

“…Examples include widely stocked rainbow trout (Oncorhynchus mykiss) and charr (Salvelinus sp. ), which are eroding the genetic identities of native congeners (Rubidge et al 2001;Allendorf et al 2004;Rubidge and Taylor 2004;Sato et al 2010). Similarly, intentional releases of game birds for hunting may pose a risk for wild relatives, such as black ducks (Anas rubripes) in America (Mank et al 2004) and the endangered koloa (Anas wyvilliana) in Hawaii (Fowler et al 2009), which are threatened by worldwide introductions of mallard ducks (Anas platyrhynchos) and subsequent hybridization.…”

Isolation and characterization of tri‐ and tetra‐repeat microsatellite loci in the white‐spotted charr Salvelinus leucomaenis (Salmonidae)

“…This is of particular relevance because of the supplemental stocking activities. The current evidence suggests accelerated rate of hybridization between wild and hatchery fish within and among subspecies (Kubota et al , ; Kikko et al , ; Sato et al , ). In addition, habitat fragmentation by artificial damming is common on Japanese rivers.…”