Since the 1990s, increasing populations of a blood feeding land leech (Haemadipsa japonica) have become a serious issue in several Japanese prefectures, and it may be caused by the increases in sika deer (Cervus nippon) populations seen over the last quarter of the century. Therefore, this study aimed to reveal the host animal species of H. japonica using iDNA (vertebrate DNA isolated from invertebrates) and to test the hypothesis that the increasingly widespread distribution of sika deer results in increased H. japonica populations through changes to the host–parasite interface. We amplified mitochondrial DNA 16S ribosome RNA fragments from iDNA isolated from the blood clots of H. japonica collected across Japan. We identified 17 host animal species, including four orders of Mammalia (Carnivora, Artiodactyla, Rodentia, and Lagomorpha) and two orders of Amphibia (Caudata and Anura). The sika deer was the dominant host species of H. japonica. Additionally, the host animal species composition of H. japonica differed according to the presence or absence of sika deer. In the sites where sika deer were not found, Anura (frog) species were the most commonly identified hosts of H. japonica. These results suggest that the increases in H. japonica populations might have occurred via a change in host preference to sika deer. This change might be driven by the increases in sika deer populations and subsequent increase in the frequency that H. japonica uses the sika deer as easy prey, as well as by sika deer providing more reproductive energy per blood meal than blood meal from frog species. The present study suggests that a more widespread distribution of sika deer resulted in an increase in H. japonica through a change in the host–parasite interface. Therefore, management that focuses on decreasing sika deer populations would likely be an effective method for the reduction of H. japonica populations.
The development of an efficient and cost‐effective method for monitoring animal populations or biodiversity is urgently needed, and invertebrate‐derived DNA (iDNA) may offer a promising tool for assessing the diversity and other ecological information of vertebrates. We studied the host species of a hematophagous leech (Haemadipsa japonica) in Yakushima by genetic barcoding and compared the results with those for mammal composition revealed by camera trapping. We analyzed 119 samples using two sets of primers by Sanger sequencing and one set of primer by next generation sequencing. The proportion of the samples that were successfully sequenced and identified to at least one species was 11.8–24.3%, depending on the three different methods. In all of these three methods, most of the samples were identified as sika deer (18/20, 6/15 and 16/29) or human (2/20, 7/15 and 21/29). The nonhuman mammal host species composition was significantly different from that estimated by camera trapping. Sika deer was the main host, which may be related with their high abundance, large body size and terrestriality. Ten samples included DNA derived from multiple species of vertebrates. This may be due to the contamination of human DNA, but we also found DNA from deer, Japanese macaque and a frog in the same samples, suggesting the mixture of the two meals in the gut of the leech. Using H. japonica‐derived iDNA would not be suitable to make an inventory of species, but it may be useful to collect genetic information on the targeted species, due to their high host selectivity.
Recent molecular studies have indicated that phylogeographical history of Japanese biota is likely shaped by geohistory along with biological events, such as distribution shifts, isolation, and divergence of populations. However, the genetic structure and phylogeographical history of terrestrial Annelida species, including leech species, are poorly understood. Therefore, we aimed to understand the genetic structure and phylogeographical history across the natural range of Haemadipsa japonica , a sanguivorous land leech species endemic to Japan, by using nine polymorphic nuclear microsatellites (nSSR) and cytochrome oxidase subunit one (COI) sequences of mitochondrial DNA (mtDNA). Analyses using nSSR revealed that H . japonica exhibited a stronger regional genetic differentiation among populations ( G ' ST = 0.77) than other animal species, probably because of the low mobility of land leech. Analyses using mtDNA indicated that H . japonica exhibited two distinct lineages (A and B), which were estimated to have diverged in the middle Pleistocene and probably because of range fragmentation resulting from climatic change and glacial and interglacial cycles. Lineage A was widely distributed across Japan, and lineage B was found in southwestern Japan. Analyses using nSSR revealed that lineage A was roughly divided into two population groups (i.e., northeastern and southwestern Japan); these analyses also revealed a gradual decrease in genetic diversity with increasing latitude in lineage A and a strong genetic drift in populations of northeastern Japan. Combined with the largely unresolved shallow polytomies from the mtDNA phylogeny, these results implied that lineage A may have undergone a rapid northward migration, probably during the Holocene. Then, the regional genetic structure with local unique gene pools may have been formed within each lineage because of the low mobility of this leech species.
Since the 1990s, the range of the land leech Haemadipsa japonica has expanded to include areas of human activity, possibly due to increases in mammalian populations, which has become a problem in several Japanese prefectures. Knowledge of the origins and past distributions of the currently expanding populations of H. japonica is imperative to the successful implementation of countermeasures. Although previous studies have examined past distributions, much knowledge is still lacking, especially prior to 1945. Here, we surveyed past distributions of H. japonica based on academic and mountaineering literature in addition to travelersʼ journals published between the mid-Edo era (the 1770s) and the 1980s, prior to their range expansion. We reconstructed the distributions of this species for two periods: between the 1770s and 1945 and between 1946 and the 1980s, and compared the reconstructed distributions to the present distribution. Our results showed that H. japonica has been found in mountainous areas in parts of Tohoku, Chubu, Kii peninsula, and Kyushu since before 1945. In contrast, populations from Mt. Hikosan, Kyushu, and Mt. Amagi, Izu, may have disappeared before the mid-Meiji era.
Haemadipsa japonica is a Japanese land leech that feeds on the blood of host animals, mainly the sika deer (Cervus nippon). The distribution of H. japonica has expanded since the 1990s, possibly due to sika deer population increases.Haemadipsa japonica populations were found in the northern and southern regions of Tochigi Prefecture, central Japan. Previous investigations reported that these populations are genetically differentiated between the north and south, although the sika deer distribution extends throughout the northern and southern regions. We hypothesized that the migration of sika deer might be limited, thus maintaining the two H. japonica genetic groups and restricting its range expansion. We evaluated this hypothesis by investigating the genetic structure of the mitochondrial DNA (mtDNA) and nuclear microsatellites (nSSR) of sika deer samples collected from Tochigi Prefecture and from H. japonica bloodmeal samples (invertebrate-derived DNA; iDNA). The sika deer mtDNA presented two haplotypes (G-and A-haplotypes) without a clear genetic structure. Conversely, the sika deer nSSR analysis indicated clear genetic differentiation between deer in the northern and southern regions, corresponding to the two H. japonica genetic groups. This indicates that sika deer movement is restricted to narrow regions in Tochigi Prefecture. Therefore, we conclude that the current H. japonica expansion in the prefecture likely depends on the migration of sika deer, only occurring within the northern and southern regions, even though this is driven by sika deer migration.
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