Yakushima Island Research Articles

Maternal rejection but not protectiveness predicts juvenile Japanese macaque behavior without direct maternal influence.

Primates show large interindividual variability in the character and quantity of interactions between mothers and their immature offspring. Multiple studies have documented associations between maternal behavior and the occurrence or frequency of certain behaviors among offspring, but it remains unclear whether and how early maternal interactions generally affect behavioral development in offspring. We followed two wild groups of Japanese macaques on Yakushima island and investigated the relationship between maternal behavior and several types of behavior performed by 35 juvenile offspring. We further asked if the impact of maternal behavior on juvenile behavior persists regardless of the distance between mother and offspring, testing whether the influence extends beyond cases when the mother is nearby. We found that juveniles whose mothers frequently rejected them approached and played with others more often, independent of their mother's presence. Juveniles of more protective mothers were in proximity to fewer other individuals and played less, but only if their mothers were nearby. Maternal rejection appears to exert a generalized effect on offspring behavior that endures when mothers are absent. In contrast, effects of maternal protectiveness may be temporary and/or reflect direct maternal influences, such as active intervention in offspring interactions, or effects of the mother's own social relationships on offspring interactions. Our results suggest that understanding how maternal behavior affects offspring development requires paying attention to the context of juvenile behavior, including the mother's distance from her offspring.

Environmental DNA metabarcoding reveals the effect of river slope on diadromous fish communities in island rivers

Understanding the natural factors that influence diadromous fish communities in river ecosystems is crucial for effective biodiversity management. However, this remains an unexplored and challenging task. Here, the relationship between river morphology and diadromous fish communities within rivers was explored. We focused on river slope and estuary size, as these may constrain their upstream migration and affect the availability of important nursery grounds for some species. Using environmental DNA metabarcoding, we investigated the diadromous fish communities within 12 rivers of subtropical Yakushima Island, southern Japan, and compared the community differences among rivers with different river slopes and estuary sizes. Fewer diadromous fish species were detected in rivers with steeper slopes and smaller estuaries. Additionally, the community similarity was greater among rivers with analogous gradients and estuary sizes. These results indicate that river slopes exert a species-selective effect on diadromous fish communities by affecting their upstream migration and estuarine habitat availability, thereby playing a crucial role in shaping the composition of these communities within rivers. Conserving gentle-gradient rivers with large estuaries would be crucial for preserving the diversity of diadromous fish species, which play a crucial role in shaping biodiversity especially in rivers of subtropical and tropical oceanic islands.

Fish fauna and environmental factors in river estuaries of small and medium-sized rivers on islands significantly influenced by warm currents.

River estuaries are influenced by terrestrial and marine areas, and have a unique environment that is constantly fluctuating. They are also important habitats for biodiversity conservation. Tanegashima Island is significantly influenced by the Kuroshio Current. Although nearby Yakushima Island has been recognized as a World Natural Heritage site and information on many species has been collected, there is little information on species inhabiting the river estuaries of Tanegashima Island. In this study, the river estuarine ichthyofauna of 26 small and medium-sized rivers on Tanegashima Island was surveyed and a total of 2758 individuals of 29 species and one genus belonging to 15 families were collected. The fish fauna of the river estuaries of Tanegashima Island were classified into three groups, namely the river estuaries where coastal terraces are underdeveloped and drowned valleys are formed, the river group where the riverbed gradient at the mouth is high, and other river groups. Environmental factors selected as being important for ordination of fish fauna were the altitude of the headstreams at the watershed scale, the gradient of the river estuarine area, and the presence or absence of rapids in the estuary. The importance of the geohistorical factor of drowned valley formation, in addition to habitat and watershed scale environmental factors, as a factor on river estuarine fish fauna is an important finding for future conservation of local biota diversity.

Severe Enamel Defects in Wild Japanese Macaques

Plane-form enamel hypoplasia (PFEH) is a severe dental defect in which large areas of the crown are devoid of enamel. This condition is rare in humans and even rarer in wild primates. The etiology of PFEH has been linked to exposure to severe disease, malnutrition, and environmental toxins and associated with systemic conditions. In this study, we examined the prevalence of enamel hypoplasia in several populations of wild Japanese macaques (Macaca fuscata) with the aim of providing context for severe defects observed in macaques from Yakushima Island. We found that 10 of 21 individuals (48%) from Yakushima Island displayed uniform and significant PFEH; all 10 specimens were from two adjacent locations in the south of the island. In contrast, macaques from other islands and from mainland Japan have a low prevalence of the more common types of enamel hypoplasia and none exhibit PFEH. In Yakushima macaques, every tooth type was affected to varying degrees except for first molars and primary teeth, and the mineral content of the remaining enamel in teeth with PFEH was normal (i.e., no hypo- or hypermineralization). The aetiology of PFEH might be linked to extreme weather events or high rates of environmental fluoride-causing enamel breakdown. However, given that the affected individuals underwent dental development during a period of substantial human-related habitat change, an anthropogenic-related etiology seems most likely. Further research on living primate populations is needed to better understand the causes of PFEH in wild primates.

Influences of topography on nitrate export from forested watersheds on Yakushima Island, a Natural World Heritage site

Long-term monitoring of nitrate ions and topographical control of atmospheric nitrate in forest river waters of Yakushima Island, a Natural World Heritage site.

Changes in forest structure over 23 years under disturbances in a warm temperate rain forest on Yakushima Island, Japan

AbstractClarifying the influence of disturbances by biotic and abiotic agents on long‐term changes in forest structure and demographic rates is an important task of forest ecology. Here, we investigated changes in forest structure and demographic rates and the effects of biotic and abiotic factors (sika deer, ambrosia beetle, neighborhood trees, and indices of strong wind and wetness) in a 4‐ha long‐term ecological study plot in a lowland warm temperate rain forest on Yakushima Island, Japan, from 1996 to 2019 for three regeneration groups related to gap dynamics (gap demander: GD, light shade tolerant: LS, and strong shade tolerant: SS). GD had relatively lower recruitment and survival than LS and/or SS. Changes in demographic rates were not significantly correlated with those in the index of strong wind in any regeneration group. The effects of sika deer on demographic rates did not differ among groups. Stems of Fagaceae species belonging to LS attacked by ambrosia beetles recorded in 2013 did not significantly differ in RGR and survival rates. Our results indicate that despite the relatively long monitoring period of 23 years, we did not detect significant effects of strong winds on demographic rates among regeneration groups, and shade‐tolerant species (LS and SS) showed better demographic performance than light‐demanding species (GD) and an increase in total basal area over time. We need longer monitoring of forest dynamics to understand forest responses to disturbances considering several factors, including the time lag of demographic responses to disturbances and the long‐term effects of disturbances.

Community composition and diversity of land snails along an elevation gradient in the World Natural Heritage Site, Yakushima Island

Understanding alpine communities that form along elevation gradients is not only a major topic in community ecology but also provides biological conservation insights into recent environmental changes in alpine ecosystems. In this study, we investigated the community composition and diversity of land snails on Yakushima Island, Japan, which has steep mountainous areas and has been designated a World Natural Heritage Site. As a result of the survey, 3689 individuals of 42 species were recorded at 64 sites, and Bayesian hierarchical models were constructed using a species matrix and environmental data from remote sensing. We found that both land surface temperature, which correlated with elevation, and soil moisture index, which uncorrelated with elevation, altered community composition. Furthermore, species diversity was high at low elevations and decreased monotonically with increasing elevation. This diversity was related to the vegetation types. Thus, the results of these analyses imply that the land snail community on Yakushima Island varies along elevation. This study highlights the need to focus on changes in multiple environmental variables from a conservation perspective and the need to pay attention not only to alpine areas, but also to highly diverse low-elevation areas that are not legally designated as conservation areas.

Taxonomic study of the genus Dactylolabis Osten Sacken, 1860 of Japan (Diptera: Limoniidae).

Japanese species of the genus Dactylolabis Osten Sacken, 1860 are revised. One new species, D. kyororo sp. nov. is described and the two other species of the genus, D. diluta Alexander, 1922 and D. longicauda Alexander, 1922, are redescribed, with images of the habitus and wings, and drawings of the terminalia. A subspecies of D. longicauda Alexander, 1922 described from Yakushima Island, D. longicauda megastylata Alexander, 1930, is synonymized with the nominotypical subspecies. A key to the species is provided.

Distribution and characterization of nematodes in above-ground microhabitats in a natural pristine cedar forest in Yakushima Island, Japan

Nematode communities in natural pristine forests composed of trees aged over 1000 years have not been thoroughly studied. Old-growth forests can provide diverse microhabitats for nematodes such as fallen trees with mossy conditions. This study aimed to characterize the community and trophic compositions of nematodes in relation to different microhabitats in old-growth Japanese cedar ( Cryptomeria japonica (L. f.) D. Don) forests in Yakushima Island, Japan. To this aim, nematodes retrieved from four different types of microhabitats were morphologically identified at the family/genus level and divided into five trophic groups. A nonmetric multidimensional scaling scatterplot showed that nematode communities clustered significantly in each microhabitat and their community compositions were significantly affected by C/N ratio. With respect to nematode trophic composition, bacterivorous nematodes dominated decaying barks of fallen trees, with a relative abundance of 45%, while fungivorous nematodes were dominant in living barks of cedar trunks (61%). Predatory–omnivorous nematodes predominated in mosses of fallen trees (51%). These results showed that nematode community and trophic composition were different among microhabitats characterized by nutrient conditions. The predatory–omnivorous nematodes were abundant in mosses with N-rich conditions. In contrast, fungivorous nematodes were abundant in cedar trunks with high C/N conditions. Thus, old-growth natural forests can provide diverse microhabitats where various nematode taxa coexist due to the presence of fallen trees and mosses.

Integrative taxonomic revision of the genera Nesticella and Howaia in Japan with the description of five new species (Araneae, Nesticidae, Nesticellini).

The Japanese species of the genera Nesticella Lehtinen & Saaristo, 1980 and Howaia Lehtinen & Saaristo, 1980 (Araneae, Nesticidae, Nesticellini) are revised using an integrative taxonomic approach. Their morphology, phylogenetic position within the genera, assignment to species groups, and distribution in mainland Japan and the Ryukyu islands are discussed herein. A phylogenetic and species delimitation analysis was conducted to confirm the boundaries between the putative species that were initially discriminated based on external and genital morphology. As a result of the present study, six species of Nesticella and three species of Howaia are proposed for the fauna of Japan based on the combined results of morphology and molecular analyses. Male and female of the previously known species H.mogera (Yaginuma, 1972), N.brevipes (Yaginuma, 1970), and N.okinawaensis (Yaginuma, 1979) are redescribed and illustrated using type specimens or specimens collected at the type locality. Nesticellaterrestris (Yaginuma, 1970) is resurrected as a valid species and distinguished from the closely related N.brevipes based on morphological and molecular evidence. The male of N.terrestris is described for the first time. We herein describe three new species of Nesticella and two new species of Howaia from different islands in the Ryukyu Archipelago, southwest Japan: N.insulanasp. nov. (♂, ♀) from Yonaguni-jima Island, N.occultasp. nov. (♀) from Ishigaki-jima Island, N.silvicolasp. nov. (♂, ♀) from Yakushima Island, H.albasp. nov. (♂, ♀) from Miyako-jima Island and H.subterraneasp. nov. (♀) from Okinoerabu-jima Island. Nesticellaoccultasp. nov., H.albasp. nov. and H.subterraneasp. nov. dwell exclusively in caves and show extensive morphological adaptation to subterranean life.

Scavenging on a Carcass of Sika Deer by Introduced Raccoon Dogs (Nyctereutes procyonoides) in Spring: A Case Report in the World Heritage Site of Yakushima Island, Japan

Scavenging on a Carcass of Sika Deer by Introduced Raccoon Dogs (Nyctereutes procyonoides) in Spring: A Case Report in the World Heritage Site of Yakushima Island, Japan

The trait‐mediated trade‐off between growth and survival depends on tree sizes and environmental conditions

Abstract Interspecific relationships between growth and survival are critical determinants of tree species diversity maintenance in forests. The trade‐offs between growth and survival in co‐occurring tree species are believed to arise along a continuum of life‐history strategies. For example, co‐occurring species range from those that grow slowly and survive well in resource‐poor environments to those that grow quickly but have low survival rates in resource‐rich environments. However, uncertainties remain regarding how growth–survival trade‐offs are related to species traits, tree sizes or environmental conditions. We examined how the relationships between species traits and growth–survival relationships shift in response to changes in stem sizes and across census periods with different climate conditions (frequency of strong winds, drought intensity) across 45 co‐occurring tree species based on 23 years of growth and survival records in a warm temperate rainforest on Yakushima Island, Japan. We developed hierarchical Bayesian models of relative growth and survival rates, including leaf traits, wood density and 95‐percentile maximum stem diameter as explanatory variables. We tested the relationships between estimated trait‐mediated growth–survival relationships and the indices of climate events during five census periods. Each trait's effects on growth–survival relationships differed across the five census periods in response to climate conditions. Interspecific growth–survival relationships affected by a single trait axis for leaves or wood tended to be negative. In contrast, those affected by the maximum stem diameter tended to be positive. Such trends increased with more frequent strong winds or more intense droughts. The single‐trait effects on growth–survival relationships were stronger for smaller sizes than for larger sizes. For all traits combined, we found a significant growth–survival trade‐off only for small‐sized stems in three of five census periods. Synthesis. Our results indicate that the effect of species traits on the growth–survival relationships depended on tree sizes, the census periods or both in response to the frequency or intensity of climate events. We argue the importance of incorporating spatial and temporal variations in environmental conditions into long‐term data from tree census to predict forest dynamics.

Review of the species of Sorolopha Lower (Lepidoptera: Tortricidae) in Japan, with descriptions of three new species.

In this study, the genus Sorolopha Lower, 1901 in Japan was reviewed with five species including three that are described herein as new: S. sugiurai Sakagami, sp. nov., S. viridis Sakagami, sp. nov., and S. baribaris Sakagami, sp. nov. Adults of S. sugiurai and S. baribaris emerged from leaf shelters of Actinodaphne acuminata (Lauraceae). Larvae of S. viridis feed on young leaves of Illicium anisatum (Schisandraceae). S. viridis is known from Honshu and Yakushima Island, S. baribaris from Honshu and Kyushu, and S. sugiurai only from Honshu (Wakayama Prefecture). Diagnoses, biological information, and images of the adults, and male and female genitalia are provided.

Assessment of myxomycete species diversity on twig litter on Yakushima Island, World Natural Heritage site, Japan

Assessment of myxomycete species diversity on twig litter on Yakushima Island, World Natural Heritage site, Japan

Records of 15 fresh and brackish water fishes from Tanega-shima and Yaku-shima islands, Osumi Islands, Satsunan Islands, Kagoshima Prefecture, Japan

Records of 15 fresh and brackish water fishes from Tanega-shima and Yaku-shima islands, Osumi Islands, Satsunan Islands, Kagoshima Prefecture, Japan

Dynamics of rumen microbiome in sika deer (Cervus nippon yakushimae) from unique subtropical ecosystem in Yakushima Island, Japan

Yaku sika deer (Cervus nippon yakushimae) are endemic to Yakushima Island, whose landscape covered with primary evergreen forest is recognized as a World Heritage Site. In this study, the rumen bacterial microbiota (RBM) of wild Yaku sika was characterized using high throughput sequencing of bacterial 16S rRNA genes combined with targeted cultivation and functional analyses. Comparative analyses of RBM datasets from other ruminant animals revealed distinct community structure among domesticated and wild ruminants. Wild Yaku sika RBM exhibited higher species richness than other sika deer (i.e. wild Ezo sika and domesticated sika deer), likely reflecting their dietary variations associated with unique ecosystem in the island. The Yaku sika RBM of high deer population density samples exhibited higher diversity and contained higher proportion of Firmicutes than those of lower density samples. Moreover, the highest abundance of tannase gene were observed in individuals from the highest population density area, consistent with the previous observation that Yaku sika in the high density areas expanded their feed to include tannin-rich unpalatable plants. This study indicated that RBM of unique wild Yaku sika contribute to the flexibility of dietary shift and thus maintaining nutritional status of Yaku sika under high density conditions.

Review: Vegetation history of Cryptomeria japonica in Japan since the last interglacial period

AbstractThe natural distribution of Japanese cedar (Cryptomeria japonica) has been disturbed by human activities, owing mainly to its value as timber; thus, its position in the vegetation zone of Japan is not clear. Therefore, it is important to determine the history of C. japonica forests before human influence. We reviewed the transitions in distribution and abundance of C. japonica in the Japanese Archipelago since the last interglacial period by using published pollen data. During the last interglacial, temperate deciduous broadleaf forests developed on northeastern Honshu Island, whereas on southwestern Honshu Island C. japonica populations increased, accompanied by warm‐temperate evergreen broadleaf trees. During the first half of the last glacial period, C. japonica forests developed throughout the Japanese Archipelago except on Hokkaido. Thereafter, 60,000–30,000 years ago, C. japonica covered the area around Lake Biwa and the Izu Peninsula. During the Last Glacial Maximum, C. japonica was most abundant on the Izu Peninsula, and small refugial populations were located along the coast of the Sea of Japan from southwestern to northeastern Honshu, and along the Pacific coast of Shikoku Island. During the Middle Holocene, C. japonica populations increased rapidly in southwestern Honshu. Two thousand years ago, before the intensification of human activities, C. japonica was widespread in warm‐ to cool‐temperate zones on the Sea of Japan side of Honshu, the Izu Peninsula, the Pacific coast of Shikoku Island, and Yakushima Island. This evidence indicates that C. japonica is one of the major tree species in the Japanese vegetation zone.

High-throughput sequencing covers greater nematode diversity than conventional morphotyping on natural cedar forests in Yakushima Island, Japan

Massive sequence reads obtained via high-throughput sequencing (HTS) methods have provided opportunities to extensively identify nematodes in certain habitats, thereby enabling the generation of assemblage patterns depicting nematode communities in natural ecosystems. However, we do not know whether HTS analysis yields assemblage patterns for nematode communities that are similar to those generated by conventional morphological analyses. We compared the community structures of soil nematodes determined by HTS and morphological analyses in natural Japanese cedar (Cryptomeria japonica) forests more than 1,000 years old on Yakushima Island, South Japan. Soil nematodes were collected at two sites, namely, Shiratani (SR) and Arakawa (AR), and identified to the genus level under a compound light microscope. Nematodes were also subjected to DNA sequence analysis, focusing on partial small subunit rRNA. Morphological analysis divided the nematodes into 9 orders, 34 families, and 42 genera. The 509 amplicon sequence variants were assigned to 11 orders, 45 families, and 76 genera. Based on the phylogenetic analysis of Aphelenchoides, our sequences were divided into 12 independent clades with bootstrap values greater than 70%. From both morphological and HTS analyses, 77 and 72 genera were identified for SR and AR, respectively, and HTS analysis covered 88% and 85% of the total nematode genera in samples from SR and AR, respectively. The nematode abundance obtained via HTS analysis was significantly correlated with the morphological abundance of Acrobeloides, Aphelenchoides, Helicotylenchus, Rhabdolaimus, and Wilsonema. The non-metric multidimensional scaling scatter plot indices showed that nematode community structures were significantly different between SR and AR, regardless of the methodology. Thus, HTS analysis is more useful than morphological analysis for identifying the nematode communities of natural ecosystems to uncover hidden diversity.

Phylogenetic position of the enigmatic genus Atherospio and description of Atherospio aestuarii sp. nov. (Annelida: Spionidae) from Japan.

BackgroundThere are currently two species within the small enigmatic genus Atherospio Mackie & Duff, 1986, which belongs to the Pygospiopsis-Atherospio group in the family Spionidae Grube, 1850. The taxonomic relationship of the genus Atherospio with other spionid or spioniform genera is currently not well understood due to its unusual morphological characteristics.MethodsHere, we describe a new Atherospio species, Atherospio aestuarii sp. nov., based on materials collected from three localities in Japan: Hirota Bay (Iwate Prefecture), Ago Bay (Mie Prefecture), and Yakushima Island (Kagoshima Prefecture). We have also evaluated the possible systematic position of this new species by conducting molecular phylogenetic analyses using the nuclear 18S, 28S, and mitochondrial 16S rRNA gene sequences.ResultsThe morphology of A. aestuarii sp. nov. resembles that of A. disticha Mackie & Duff, 1986 and A. guillei (Laubier & Ramos, 1974) in having branchiae fused to the notopodial lamellae on a restricted number of segments from chaetiger 7, modified neurochaetae on chaetiger 5, and at least some bidentate neuropodial hooks with the secondary tooth below the main fang. The form and arrangement of the modified aristate neurochaetae in double vertical rows closely resemble those found on chaetigers 4 and 5 of A. disticha. The new species lacks the occipital antenna present in A. disticha. In this respect it resembles A. guillei, however, that species differs in having robust neuropodial spines on chaetiger 5 and peristomial papillae, and a preponderance of unidentate neurochaetae. Both A. guillei and the new species have slender needle-like notochaetae in their posteriormost chaetigers. Atherospio aestuarii sp. nov. is distinguished from both congeneric species by its branchial and neuropodial hook distributions. The new species is also unique in that it was recorded at relatively shallow depths, which included intertidal zones. The results of our molecular phylogenetic analysis indicate that the new species was included in a clade that included the genera of the Polydora complex, Pygospio Claparède, 1863, Glandulospio Meißner, Bick, Guggolz, Götting, 2014, Spio Fabricius, 1785, Microspio Mesnil, 1896, Marenzelleria Mesnil, 1896, Rhynchospio Hartman, 1936, Scolelepis Blainville, 1828, Dispio Hartman, 1951, and Malacoceros Quatrefages, 1843 with robust statistical support. The new species formed a clade with Dispio and Scolelepis, however, statistical support for the node was not significant.

Extremely low level of genetic diversity in Gentiana yakushimensis, an endangered species in Yakushima Island, Japan

AbstractRare or endangered species largely contributing to global biodiversity are essential components of ecosystems. Because genetic diversity depends not only on apparent population size but also demographic processes, the conservation priority of endangered species based on population genetics needs to be assessed by comparison with common congeners and demographic events. In this study, we performed population genetic analysis for Gentiana yakushimensis Makino, a rare and endangered plant species with an isolated distribution on Yakushima Island, Japan. We performed comparison of genetic diversity with the congener (Gentiana triflora Pall. var. japonica [Kusn.] H.Hara), demographic inference, and bottleneck test based on genome‐wide single nucleotide polymorphisms. The result was that G. yakushimensis had an extremely low genetic diversity level and a high inbreeding coefficient level compared with those of the congener. The population of G. yakushimensis was estimated to experience an expansion during the Last Glacial Maximum and a recent bottleneck by the demographic inference and the bottleneck test. Therefore, the low level of genetic diversity of this species might have resulted from the impact of the recent bottleneck and the long‐term maintenance of a small population size. Due to the long lifespan of the genus Gentiana, the current level of genetic diversity probably does not reflect a large part of recent demographic events, which requires long‐term monitoring of changes in genetic diversity to identify the time lag between the reduction in apparent population size and genetic diversity as a future outlook.