乾 陽子

林冠生物学は、生物多様性や生態系機能が局在する森林の林冠において、多様な生物の生態や相互作用、生態学的な機能やプロセスの理解を目指す学問である。林冠は高所に存在し複雑な構造を有するため、林冠生物学研究の飛躍的な進展は1980年代以降の林冠アクセス手段の発達に拠るところが大きい。様々な林冠アクセス手段の中でも、ロープテクニックを駆使して樹上にアクセスするツリークライミングは道具を手軽に持ち運べることから移動性に優れ、対象木に反復してアクセスすることが可能である。また、林冠クレーンや林冠ウォークウェイなどの大型アクセス設備に比べて経済的であるという利点が活かされ、林冠生物学研究に幅広く適用されてきた。近年では、ツリークライミングの技術や道具の発展によって安全性や作業効率の向上が図られており、今後ますます活用されることが期待されている。本稿では、ツリークライミングを用いた林冠生物学の研究例を紹介しつつ、樹上調査における林冠アクセス手段としてのツリークライミングの有用性を示す。さらに、ツリークライミングを用いた林冠生物学研究の今後の展望および課題について議論する。移動性、経済性、撹乱性に優れたツリークライミングは、場所の制限を受けないため、あらゆる森林での林冠生物学研究において今後も重要な役割を担うと考えられる。また、他の林冠アクセス手段や測定機器と併用することでさらなる進展が期待される。一方、安全かつ有効なツリークライミングが普及するためには、研究調査以外の領域も含めたツリークライミング・ネットワークの形成と情報共有のためのプラットフォームづくりが急務である。

Many plants have mutualistic relationships with ants, whereby plants provide food and/or nesting sites for the symbiotic ants, and in turn the ants protect the host plants by excluding herbivores. While the ants are useful as guards, they may negatively affect host reproduction by excluding pollinators. Here we studied this potential conflict in the myrmecophytic Macaranga winkleri pollinated by the thrips Dolichothrips fialae. Behavioural responses of ant guards to pollinator thrips and their chemicals, and related chemical analyses, provide evidence that thrips deter ant-guards by secreting droplets containing ant-repelling n-decanoic acid from their anuses. This is the first report of insect pollinators repelling their host's symbiotic guard ants to perform pollination. This is a novel strategy by which a plant host avoids interference with pollination by ant-guards in an ant-plant mutualism. The acquisition of a pollination system that is resistant to ant attacks may have facilitated the evolution of myrmecophytes in the genus Macaranga.

Macaranga myrmecophytes (ant-plants) are generally well protected from herbivore attacks by their symbiotic ants (plant-ants). However, larvae of Arhopala (Lepidoptera: Lycaenidae) species survive and develop on specific Macaranga ant-plant species without being attacked by the plant-ants of their host species. We hypothesized that Arhopala larvae chemically mimic or camouflage themselves with the ants on their host plant so that the larvae are accepted by the plant-ant species of their host. Chemical analyses of cuticular hydrocarbons showed that chemical congruency varied among Arhopala species; A. dajagaka matched well the host plant-ants, A. amphimuta did not match, and unexpectedly, A. zylda lacked hydrocarbons. Behaviorally, the larvae and dummies coated with cuticular chemicals of A. dajagaka were well attended by the plant-ants, especially by those of the host. A. amphimuta was often attacked by all plant-ants except for the host plant-ants toward the larvae, and those of A. zylda were ignored by all plant-ants. Our results suggested that conspicuous variations exist in the chemical strategies used by the myrmecophilous butterflies that allow them to avoid ant attack and be accepted by the plant-ant colonies.

A previously reported mitochondrial DNA (mtDNA) phylogeny of Crematogaster (subgenus Decacrema) ants inhabiting Macaranga myrmecophytes indicated that the partners diversified synchronously and their specific association has been maintained for 20 million years. However, the mtDNA clades did not exactly match morphological species, probably owing to introgressive hybridization among younger species. In this study, we determined the congruence between nuclear simple sequence repeat (SSR, also called microsatellite) genotyping and mtDNA phylogeny to confirm the suitability of the mtDNA phylogeny for inferring the evolutionary history of Decacrema ants. Analyses of ant samples from Lambir Hills National park, northeastern Borneo, showed overall congruence between the SSR and mtDNA groupings, indicating that mtDNA markers are useful for delimiting species, at least at the local level. We also found overall high host-plant specificity of the SSR genotypes of Decacrema ants, consistent with the specificity based on the mtDNA phylogeny. Further, we detected cryptic genetic assemblages exhibiting high specificity toward particular plant species within a single mtDNA clade. This finding, which may be evidence for rapid ecological and genetic differentiation following a host shift, is a new insight into the previously suggested long-term codiversification of Decacrema ants and Macaranga plants.

In protective ant-plant mutualisms, plants offer ants food (such as extrafloral nectar and/or food bodies) and ants protect plants from herbivores. However, ants often negatively affect plant reproduction by deterring pollinators. The aggressive protection that mutualistic ants provide to some myrmecophytes may enhance this negative effect in comparison to plant species that are facultatively protected by ants. Because little is known about the processes by which myrmecophytes are pollinated in the presence of ant guards, we examined ant interactions with herbivores and pollinators on plant reproductive organs. We examined eight myrmecophytic and three nonmyrmecophytic Macaranga species in Borneo. Most of the species studied are pollinated by thrips breeding in the inflorescences. Seven of eight myrmecophytic species produced food bodies on young inflorescences and/or immature fruits. Food body production was associated with increased ant abundance on inflorescences of the three species observed. The exclusion of ants from inflorescences of one species without food rewards resulted in increased herbivory damage. In contrast, ant exclusion had no effect on the number of pollinator thrips. The absence of thrips pollinator deterrence by ants may be due to the presence of protective bracteoles that limit ants, but not pollinators, from accessing flowers. This unique mechanism may account for simultaneous thrips pollination and ant defense of inflorescences.

Pycnotarsobrentus inuiae Maruyama & Bartolozzi, gen. nov. and sp. nov. (Brentinae: Eremoxenini) is described from the Lambir Hills National Park, Borneo (Sarawak, Malaysia) based on specimens collected from Crematogaster difformis F. Smith, 1857 ant nests in the myrmecophytic epiphytic ferns Platycerium crustacea Copel. and Lecanopteris ridleyi H. Christ. A second species of Pycnotarsobrentus is known from Malaysia but is represented by only one female and consequently not yet described pending discovery of a male. Pycnotarsobrentus belongs to the tribe Eremoxenini and shares some character states with the African genus Pericordus Kolbe, 1883. No species of Eremoxenini with similar morphological modifications are known from the Oriental region.

We observed the abundance of leaf shelters, aphids, other herbivores, and predators on willow trees, Salix eriocarpa, from May to October 2003. There was a positive correlation between the growth rate of aphids and the number of ants per shoot, suggesting ant attendance to aphids. Although the mean abundance of leaf shelters per shoot was rather low (1.7-2.2) throughout the observation period, aphids preferred to use shoots with leaf shelters compared with those without leaf shelters. The abundance of ants was positively influenced by the presence of leaf shelters and aphids from May to August. The abundance of other herbivores was positively influenced by leaf shelters, but negatively influenced by aphid presence from May to August. Furthermore, leaf shelters had a positive effect on the abundance of predators from July to October. These data suggest that a relatively low abundance of naturally occurring leaf shelters per shoot influenced the arthropod communities on S. eriocarpa, and the effect of those leaf shelters on each type of arthropod varied according to the season.

Plant-ants, i.e. those symbiotic with myrmecophyte plants, defend their hosts against herbivores. Plant-ants are expected to affect the host-plant ranges of herbivores that feed on myrmecophytes. This study aimed to experimentally determine whether anti-herbivore defences by plant-ants restrict the larval host-plant ranges of four Arhopala (Lycaenidae) butterflies that feed on Macaranga (Euphorbiaceae) trees, some of which are myrmecophytes. We fed Arhopala larvae with the leaves of five Macaranga species under ant-excluded conditions to examine their potential host-plant ranges. Under ant-excluded conditions, three Arhopala species survived to the pupal stage when fed species not used in the field as well as their normal host species. Our data suggested that the aggressive behaviours of plant-ants towards leaf-feeding insects restrict the potential host-plant ranges of some Macaranga-feeding Arhopala butterflies.

Some species in the tree genus Macaranga (Euphorbiaceae) in the Southeast Asian tropics are myrmecophytic they have highly species-specific mutualisms with symbiotic ants (plant-ants), which defend them from herbivores. However, larvae of some Arhopala (Lycaenidae, Lycaeninae) species can elude the ants. Here we demonstrated that Arhopala zylda larvae showed myrmecoxeny on their myrmecophytic Macaranga host plants they had no stable association with the plant-ants. Despite the presence of many plant-ants, A. zylda larvae were rarely attended or attacked by ants on their host plants. The plant-ants of three other myrmecophytic Macaranga species (non-hosts to A. zylda) also paid little attention to experimentally introduced A. zylda larvae. The myrmecoxeny seen in A. zylda is notable among lycaenid larvae that feed on myrmecophytes, because almost all are obligate intimate myrmecophiles.

In the Southeast Asian tropics, Arhopala lycaenid butterflies feed on Macaranga ant-plants inhabited by Crematogaster (subgenus Decacrema) ants tending Coccus-scale insects. A recent phylogenetic study showed that (1) the plants and ants have been codiversifying for the past 20-16 million years (Myr), and that (2) the tripartite symbiosis was formed 9-7 Myr ago, when the scale insects became involved in the plant-ant mutualism. To determine when the lycaenids first parasitized the Macaranga tripartite symbiosis, we constructed a molecular phylogeny of the lycaenids that feed on Macaranga by using mitochondrial and nuclear DNA sequence data and estimated their divergence times based on the cytochrome oxidase I molecular clock. The minimum age of the lycaenids was estimated by the time-calibrated phylogeny to be 2.05 Myr, about one-tenth the age of the plant-ant association, suggesting that the lycaenids are latecomers that associated themselves with the pre-existing symbiosis of plant, ant, and scale insects.

Several species of nocturnal gecko are known for their acoustic behavior in social contexts. The nocturnal house gecko, Gekko japonicus, was believed to be mute, except when threatened. We conducted behavioral encounter experiments involving same-sex and heterosexual pairs of G. japonicus. We also conducted two control experiments, chemical and blank, to confirm that acoustic behaviors are induced in the presence of conspecifics. Characteristic calls emitted by this gecko were recorded, providing the first evidence that G. japonicus uses acoustic signals for social communication. Geckos tended to call more frequently after the first physical contact with an opponent than before contact. In both control experiments, no gecko emitted calls. Whereas most characteristics of calls were similar to those reported for other gekkonid species, call intensity in this experiment was low. Males emitted calls toward both males and females, whereas females emitted calls almost exclusively toward other females. Several call variables differed significantly between intra- and intersexual calls. Our study demonstrated that G. japonicus uses acoustic signals in social contexts over short distances.

Despite the recognition of the functional role of Hymenoptera (ants, bees and wasps) and Isoptera (termites) in tropical ecosystems, their detailed feeding habits are not well known. To examine the feeding habits of these groups, we measured nitrogen (N) and carbon (C) stable isotope ratios (delta(15)N and delta(13)C) of hymenopterans (12 families, a parts per thousand yen16 genera and a parts per thousand yen32 species) and isopterans (one family and 10 species) collected in a tropical rain forest, Sarawak, Malaysia. We compared the isotopic signatures of these insects to those previously reported for other consumers collected in the same forest. The delta(15)N and delta(13)C values of these insects overlapped with those of the other consumers, indicating that they have access to diverse C and N sources in the forest. The delta(15)N values of ants and termites indicated that their feeding habits range along a continuum from herbivory (i.e. dependent on honeydew and nectar) to predation and from wood-feeders to soil-feeders, respectively. In addition, the delta(15)N values of wasps varied greatly from -0.1aEuro degrees (Braconidae sp.) to 8.6aEuro degrees (Bembix sp.), suggesting that their feeding habits also range from omnivory to predation. The ant species Camponotus gigas had delta(13)C values similar to those of invertebrate detritivores and omnivores rather than to those of invertebrate herbivores, although the diet of this species consists mostly of honeydew. This discrepancy suggests that the ant uses carbohydrates as an energy source, the isotopic signatures of which are not well retained in the body tissues. Values of both delta(15)N and delta(13)C of the predatory army ant Leptogenys diminuta and the soil-feeding termite Dicuspiditermes nemorosus did not differ significantly, indicating that both trophic level and the humification of feeding substrates can increase the isotopic signatures of terrestrial consumers.

Ants are believed to regulate herbivorous insects in the canopy of tropical rainforests, but few studies have empirically investigated the anti-herbivore effects of the ants there. We examined the anti-herbivore effects of the ant species Crematogaster difformis, which territorializes a large area of the crown of emergent canopy trees and inhabits the myrmecophytic epiphytes, Lecanopteris sp. and Platycerium sp., which grow in the crown, by performing an ant-exclusion experiment in the field. The average proportion of leaf area loss, the proportion of damaged leaves, and the proportion of leaves with a parts per thousand yen50% leaf area loss were all significantly higher on experimentally ant-excluded branches than on ant-attended branches at 3 months from the beginning of the ant-exclusion treatment. These results suggest that C. difformis regulates not only herbivorous insects that potentially feed on its host epiphytes but also those that could feed on leaves of emergent canopy trees that harbor the epiphytes.

Many epiphytic ferns in tropical forest canopies have domatia that provide habitat for arboreal arthropods such as ants. Two species of fern that were predominantly occupied by Crematogaster difformis ants were collected from the canopy of a forest in Borneo. In the fern domatia, two cockroach species, Pseudoanaplectinia yumotoi and Blatta sp., were found to live with C. difformis. Pseudoanaplectinia yumotoi were found in large numbers and accounted for approximately 20% of the total arthropod population, while Blatta sp. comprised only 1% of the arthropods living in the domatia. Behavioural experiments were conducted to evaluate the response of C. difformis workers to newly introduced cockroaches of each species and to allospecific ant workers. Crematogaster difformis workers were highly aggressive and quickly attacked allospecific workers. Both cockroach species could fend off ant attacks; however, dead Blatta sp. were often attacked by the ants while dead P. yumotoi were infrequently bothered.

Macaranga myrmecophytes harbor species-specific Crematogaster ants that defend host trees from herbivores. We examined ant aggressive behaviors when artificially damaged leaf pieces from another tree were offered to four sympatric species of obligate Macaranga myrmecophytes. The ants showed aggressive behavior in response to leaf pieces regardless of the leaf species; however, aggressiveness was higher when conspecific leaf pieces were offered than when nonhost species were offered. Thus, ants can recognize leaf damage and distinguish among damaged leaf species. Chemical analyses of volatile compounds emitted from damaged leaves that may induce ant defense showed that the composition of the minor compounds differed among the four Macaranga species, although there were many compounds in common.

Plants produce volatile compounds known to influence insect preferences for oviposition and feeding. To examine whether volatile leaf compounds are correlated with the herbivorous insect community, we analyzed volatile compounds in leaves from three co-occurring willow species, Salix serissaefolia, S. eriocarpa, and S. integra, and investigated their associated insect communities in 3 months across different years. The gas chromatographic profiles of volatile compounds were highly specific to each willow species and remained constant in the study months. In a comparison between the chemical composition of the volatile compounds and the taxon composition of the insect communities, dissimilarity patterns in chemical composition among the three willow species were very close to those in herbivorous insect communities. These findings indicate that willow leaves produce specific volatiles that are highly correlated with the community structure of herbivorous insects associated with them.

白神山地世界遺産核心地域に分布する典型的でかつ構造の異なる3つのタイプのブナ林について,動態と更新に関するモニタリングを4年間継続した。3つのブナ林は,種組成,密度,胸高直径分布,胸高断面積などの構造パラメータ,死亡率・新規加入率などの動態パラメータ,種子生産量・実生発生量などの更新パラメータに違いが見られ,主として林分の発達過程や地形による成立条件が異なっていることが示唆された。また,結果をもとにモニタリングを行う上で考慮すべき点などについて考察した。

Previous studies have demonstrated that the obligate myrmecophytism between Macaranga ant-plants and Crematogaster plant-ants is highly species specific, although multiple Macaranga species can coexist in a microhabitat. However, the species specificity has been described based on the study of trees with established plant-ant colonies. We studied how the process of settling into the partner Macaranga seedlings by single foundress Crematogaster queens contributes to species specificity. By sampling seedlings of three sympatric Macaranga myrmecophytes species in the field. we tested two hypotheses. The first is that foundresses correctly select their specific partner plant species when they settle into seedlings. The second hypothesis is that the seasons in which seedlings available for settling by foundresses appear are segregated among the Macaranga species, and the seasons in which foundress queens settle are synchronized to the appearance of seedlings of specific partner species: thus species specificity is consequently generated. Our results support the former hypothesis but not the latter: we always observed foundresses settling species-specific host plants, and seedlings suitable for settling were always available in each Macaranga species.

The partnership in the Crematogaster-Macaranga ant-plant interaction is highly species-specific. Because a mutualistic relationship on a Macaranga plant starts with colonization by a foundress queen of a partner Crematogaster species, we hypothesized that the foundress queens select their partner plant species by chemical recognition. We tested this hypothesis with four sympatric Macaranga species and their Crematogaster plant-ant species. We demonstrated that foundress Crematogaster queen, can recognize their partner Macaranga by contact with the surface of the seedlings, that they can recognize compounds from the stem surface of seedlings of their partner plant species, and that the gas chromatographic profiles are characteristic of the plant species. These findings support the hypothesis that foundress queens of the Crematogaster plant-ant species select their partner Macaranga species by recognizing nonvolatile chemical characteristics of the stem surfaces of seedlings.

To examine interspecific variation in the intensity of ant defense among three sympatric species of obligate myrmecophytes of Macaranga (Euphorbiaceae), we measured the ratio of ant biomass to plant biomass, ant aggressiveness to artificial damage on host plants, and increase in herbivore damage on host plants when symbiont ants were removed. increase in herbivore damage from two- and four-week ant exclusion varied significantly among the three species. The decreasing order of vulnerability to herbivory was M. winkleri, M. trachyphylla, and M. beccariana. The ant/plant biomass ratio (= rate of the dry weight of whole ant colonies to the dry weight of whole aboveground plant parts) and ant agressiveness also varied significantly among the three species; the orders of both the ant/plant biomass ratio and ant aggressiveness were the same as in the herbivory increase. These results indicated that the intensity of ant defense differs predictably among sympatric species of obligate myrmecophytes on Macaranga. In addition to the interspecific difference in the total intensity of ant defense, when symbiont ants were excluded, both patterns of within-plant variation in the amount of herbivore damage and compositions of herbivore species that caused the damage differed among species. This suggests that the three Macaranga species have different systems of ant defense with reference to what parts of plant tissue are protected and what herbivorous species are avoided by ant defense. Thus, it is important to consider the interspecific variation in ant defense among Macaranga species to understand the herbivore community on Macaranga plants and the mechanisms that promote the coexistence of multiple Macaranga myrmecophytes.