Low Genetic Variation of Red-Crowned Cranes on Hokkaido Island, Japan, Over the Hundred Years

Abstract

The red-crowned crane (Grus japonensis) is recognized internationally as an endangered species. Migratory populations breed in eastern Russia and northeastern China, whereas the resident population inhabits the island of Hokkaido, Japan. Although the population inhabiting Hokkaido had experienced a severe bottleneck by the end of the 19th century, the population size has recovered to about 1500 and continues to increase now thanks to conservation efforts. A previous study reported that no marked genetic differences were seen in the island population, and that the genetic variation of the whole population on Hokkaido was lower than that of the continental population. However, the precise genetic structure of the island population in the past or near present remains unclear. To better understand the spatiotemporal changes in the genetic structure of the island population, we performed mitochondrial DNA (mtDNA) analyses using stuffed specimens (years 1878-2001) and tissue or blood samples (years 1970-2014). We found three haplotypes in the island population, one of which was a novel mtDNA haplotype in 1997 and 2007 samples. In addition, there was no clear difference in the haplotype frequency through the time span. These results suggest that the low genetic variation of the island population persisted for the last hundred years. It is thus nearly impossible for the island population to recover its genetic variation in isolation. Conservation plans for this species should therefore include the promotion of genetic exchanges between the continental and island populations, such as through artificial introduction to Hokkaido.

Conventional Gel Electrophoresis-Resolvable Insertion/Deletion Markers for Individual Identification and Analysis of Population Genetics in Red-Crowned Cranes in Eastern Hokkaido, Japan

“…Although the genetic markers used were different, notable differences in these heterozygosity indexes are additional evidence for scarce genetic diversity in the island population. Low genetic diversity in the island population has been frequently reported based on haplotype analysis [ 9 , 10 , 27 ] and microsatellite analysis [ 17 , 18 ]. It has been assumed that there was a high degree of inbreeding or genetic drift as the cause of scarce diversity in the island population [ 10 ].…”

“…Low genetic diversity in the island population has been frequently reported based on haplotype analysis [ 9 , 10 , 27 ] and microsatellite analysis [ 17 , 18 ]. It has been assumed that there was a high degree of inbreeding or genetic drift as the cause of scarce diversity in the island population [ 10 ]. In this study, the average of FIS of the 11 InDel markers as an inbreeding index was 0.095.…”

“…The mitochondrial haplotype (control region 2, CR2) [ 10 ] was conveniently determined with the amplification refractory mutation system (ARMS) PCR assay using the same DNA extracts from blood samples and a muscle as templates [ 27 ]. The ARMS method that can detect Gj1, Gj2, Gj13 and the other haplotypes is almost sufficient because all of the cranes in Hokkaido can be classified into these three haplotypes except very rare individuals of possibly continental origin [ 11 ].…”

“…The d-Loop, a non-coding region in the mitochondrial genome, showed a very high frequency of mutation, 5–10-times higher than that in somatic DNA, and it has been studied for genetic analyses such as analysis of genetic diversity within a species [ 5 ], including some crane species [ 6 , 7 , 8 ]. Haplotype analyses clearly suggested that the genetic diversity of red-crowned cranes in the island population is very poor, and only three haplotypes (Gj1, Gj2 and Gj3) were confirmed, whereas 14 haplotypes (Gj4-Gj6/18) were confirmed in the continental population [ 9 , 10 , 11 ]. It is speculated that this scarce diversity of red-crowned cranes in the island population might be caused by bottleneck effects since they were nearly extinct at the end of the 19th century [ 12 , 13 ].…”

Rectification of Abnormal Migration Recorded in Hand-reared Red-crowned Cranes (Grus japonensis)

“…Autopsy results showed that 3K1 died of eating seeds mixed with pesticide, which is a common form of poisoning reported (Zhou et al 2014). The sedentary Red-crowned Crane population is stable but with low genetic variation (Harris and Mirande 2013; Akiyama et al 2017). Researchers found that if migratory behavior was completely dominated by genetic factors, it was likely to persist, regardless of population size; however, for species relying mainly on learning for their first migration, small migratory populations may face strong "Allee effect (individual fitness tends to decline at low population density)'', which will ultimately lead to loss of migratory behavior (Stephens and Sutherland.…”