Differential Diet Breadths and Species Coexistence in Leafroller-Hunting Eumenid Wasps

There are, at least, three possible ways in which similar species coexist; resource partitioning, interference competition, and exploitation competition. Here, I investigated which way contributed to the coexistence of leafroller-hunting eumenid wasp species. Resource partitioning and, in addition, differential diet breadths proved to promote species coexistence in this case. First, I analyze the prey records and diet overlap of four eumenid species in a local area. The larger two eumenids hunted similar-sized prey items and had similar potential taxonomic prey uses. But the diet breadth of the subsocial eumenid was much wider than that of the solitary one. As a result, the diet overlap between the two large eumenids decreased. This was because the solitary eumenid attend repeatedly to the same hunting site inhabited by one abundant prey species, while the subsocial one made random hunting. On the other hand, the two medium-sized eumenids partitioned resources according to prey size. Secondly, I related these results to prey choice by several other species of eumenid obtained from literature sources. Ten Japanese common eumenids were divided into four groups according to their prey size. In each of the four groups, 2 to 3 wasp species differentiated the habitat (1 group) or coexisted by means of differential diet breadths (parallel with differential sociality, 2 groups). 自然界における近似種の共存様式としては，資源分割，干渉型の競争，および先取り型の競争などが知られている．メイガ科やハマキガ科などの葉巻蛾を狩るドロバチ類の共存様式について，資源分割とともに餌種選択幅の広狭が種の共存をゆるす要因になっていることが示唆された．まず，野外におけるドロバチ類4種の餌種構成，および餌種選択の重複度について2年間のデータから検討した．大型の2種のドロバチは餌サイズと餌の分類群のいずれにおいても潜在的な選好性は類似していたが，実際に狩ってくる餌種の構成は，亜社会性ドロバチが単独性ドロバチよりも多様であった．この原因は，単独性種が主選好の餌種を集中的に狩るのに対し，亜社会性種は，ランダム採餌を行なっていることによる．この結果，両種ドロバチの餌種の重複度は低下していた．一方，中型の2種のドロバチ同士は，餌サイズの選好性をちがえていた．次に，日本産の普通種のドロバチ10種について，餌サイズ，餌の分類群，ハチの社会性の程度などを文献資料も用いて比較検討した． 10 種は餌サイズの違いによって 4 つのグループに分れた．各グループ内の種同士を比較すると，生息場所が異なっている場合（ 1 グループ）とともに，生息、場所は類似しているが，餌種選択幅が異なり，かつ社会性の程度が異なっている場合（ 2 グループ）が認められた（残りの1グループの共存機構は不明）．以上より，社会性の程度の差が採餌戦略および餌選択幅の相違をうみ，ひいては種の共存をゆるす一つの機構となっている可能性が示唆された．ArticleResearches on Population Ecology. 34(1):203-211 (1992)journal articl

The spatial patterns of parasitism of eumenid wasps,Anterhynchium flavomarginatum andOrancistrocerus drewseni by the miltogrammine flyAmobia distorta

寄生率の空間的密度依存性は，同じ寄主－寄生者の組み合わせであれば，場所や世代が違っても基本的には同じパターンを示すという研究がこれまでなされてきた．本研究ではこの点について，世代によって寄生率の空間的パターンが異なっていった事例を示す．合わせて，異なる2種の寄主に対する寄生の空間的パターンが基本的には類似していたことも報告する．京都市の広範囲にわたる地域 (10km x 10km) において 1980 年から 1984 年にかけて野外調査を行った．この地域にパッチ状に分布する 2 種のドロバチ，オオフタオビドロバチ (Anterhynchium flavomorginatum) とオオカパフスジドロバチ (OrancistrocCTUS drewsent) に対するドロバチャドリニクバエ (Amobia distorta) の寄生率の空間的パターンをオオフタオビでは 4 世代，オオカバフでは7世代について調べた．寄生率の空間的密度依存性は，両寄主とも世代によってそのパターンが変化した．平均寄生率が低い世代においては，寄主密度の高いパッチほど寄生率も高くなった．一方，平均寄生率が高い世代においては，寄生率はパッチ当たりの寄主密度の高低にかかわらずほぼ一定であった．これらの傾向は両寄主ともにみられ，寄生率の基本的な空間的パターンは 2 種の寄主間で類似していた．代によって寄生の空間的パターンが違っていた理由を理解するために，ニクバエ成虫がパッチ閣でどのように空間分布しているかを，平均寄生率が低い世代について調べた．エクパエが少なくともl頭発見される確率は，寄主密度の高いノミッチほど高く，寄主の多いパッチにニクバエが集まってくることがわかった，しかし， IWAO (1968)の m-m 法で解析するとニクバエ成虫は空間的に正の二項分布をしており，互いにある程度以上こみあわないようにパッチを選んで、いることがわかった．パッチ当たり最大収容数は 4.05 頭と推定された．平均寄生率の高い世代においては，寄主を探索するニクバエの個体数が多いため，寄主密度の高いパッチでニクバエ同士の相互干渉が頻繁におこると考えられる．この干渉を避けるためにニクバエが寄主密度の低いパッチへ分散することによって，寄生率がどのパッチでも同じレベルになったと結論づけた．ArticleResearches on Population Ecology. 30(1):1-12 (1988)journal articl

Comparison of life tables between the solitary eumenid wasp Anterhynchium flavomarginatum and the subsocial eumenid wasp Orancistrocerus drewseni to evaluate the adaptive significance of maternal care

京都市において, 単独性のカリバチであるオオフタオビドロバチ Anterhynchium flavomarginatum と亜社会性のオオカパフスジドロバチ Orancistrocerus drewseni の野外調査を, 1980年から1983年まで行い, 生命表を種間で比較した. 乙の調査地においては亜社会性ドロバチは単為生殖を行っている. 単独性ドロバチでは, 9つの, 亜社会性ドロバチでは7つの死亡要因が識別できたが, そのうち6つは両穫に共通のものであった. 2種間の死亡率の大きな違いは卵期と幼虫期と前踊期にみられた. 卵期にはノミパエの1種が両種ドロバチの卵を捕食したが, これによる死亡率は単独性ドロバチ (15.0%) よりも亜社会性ドロバチ (1.4%) のほうがはるかに低かった. これは亜社会性ドロバチの母親による保護 (随時給食とそれに関連する諸行動) が捕食の機会を減少させたためと考えられた. 幼虫期にはニクバエの1種 Amobia distorta の捕食寄生率が, やはり単独性ドロバチ (23.8%) よりも亜社会性ドロバチ (8.1%) で低かったが, これも亜社会性ドロバチの母親による保護が原因と思われた. 安定で永続的な環境である自然営巣場所と一時的な環境である付加営巣場所で2種のドロバチの死亡率を比較したところ, ノミバエは羽化場所付近にとどまって産卵するため, 永続的な営巣場所のほうが捕食率が高いととがわかった. また, ニクバエは帰巣するドロバチを追跡することにより巣を発見し, また一度発見すると次々とまわりの巣を攻撃するので, 営巣密度の高い営巣場所での捕食寄生率がより高かった. 前虫雨期には不明死亡率が単独性ドロバチよりも亜社会性ドロバチで高かった.とれは単為生殖の悪影響と推定される. ハナノミによる死亡も亜社会性ドロバチのほうが多かったが, とれは亜社会性ドロバチのほうがより頻繁に訪花するためであると思われた. 亜社会性ドロバチの防衛機構について亜社会性の進化と関連づけて論議した.ArticleResearches on Population Ecology. 28(2):185-199 (1986)journal articl

The adaptation against soldier caste of a eusocial aphid: eggs are not attacked by soldiers in specialist predator Atkinsonia ignipicta (Lepidoptera: Stathmopodidae)

Predators generally have traits that enable them to efficiently capture their prey and thus improve their survival. Natural selection should also favor traits of predators that improve the survival rate of their eggs, which are immobile and incapable of active resistance. We hypothesized that eggs of Atkinsonia ignipicta, a specialist predator of the eusocial aphid Ceratovacuna japonica, exhibit a defensive trait against aphid soldiers. We found that the hatchability of A. ignipicta eggs did not differ significantly between the experimental treatments with and without soldiers, which suggests that the eggs have a defensive trait that protects them from soldier aphids. Moreover, although the soldiers occasionally exhibited attack behavior when they encountered an egg, they did not continue the attack. We have observed a similar interruption of attack behavior by soldiers that attacked their aphid siblings by mistake, suggesting that the eggs may chemically mimic the soldiers' siblings. This study thus provides evidence for adaptation in a specialist predator of a eusocial aphid.ArticleSOCIOBIOLOGY. 59(4):1315-1322 (2012)journal articl

Soldiers' armature changes seasonally and locally in an eusocial aphid (Homoptera : Aphididae)

Size-frequency distribution of social insect castes has been reported to change temporally and spatially, and be influenced by external factors Such as colony size. Here, we show for the first time that the sterile soldiers of eusocial aphids change the size and shape of their armatures, seasonally and locally. Evidence is presented that, in non-soldier individuals, the sizes of armatures were seasonally constant. Two potential mechanisms causing these morphological changes in the soldiers' armatures are discussed in relation to predation pressure on the aphid.ArticleSOCIOBIOLOGY. 52(2):429-436 (2008)journal articl

Congruence between pollination morphs and genotypes based on internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA in Cimicifuga simplex (Ranunculaceae)

Cimicifuga simplex (Ranunculaceae) has been classified into several morphs or races based on external morphology, pollinator guild, or genotype. However, no attempt has been made to elucidate whether the subdivisions based on the different characters are congruent or not. Here, we genotyped the three pollination morphs reported previously, and found that they were genetically differentiated and each morph consistently corresponds to one of the seven ITS genotypes described in a different study. The three morphs were distributed parapatrically or allopatrically along altitudinal gradients. In accordance with the genetic differentiation of the pollination morphs, the degree of pubescence of leaf margin was found to be a diagnostic external character to discriminate pollination morph II from morphs I and III.ArticleThe Journal of Japanese Botany. 88(3):176-181 (2013)journal articl

Moth caterpillar solicits for homopteran honeydew

A life-history in which an organism depends on ants is called myrmecophily. Among Lepidoptera (moths and butterflies), many species of lycaenid butterflies are known to show myrmecophily at the larval stage. Descriptions of myrmecophily among moth species, however, are very few and fragmentary. Here, we report the ant-associated behaviour of the tiny Japanese arctiid moth, Nudina artaxidia. Field observations revealed that the moth larvae associate with the jet black ant, Lasius (Dendrolasius) spp. The larvae, which we observed only near ant trails, showed an ability to follow the trails. Further, they solicit honeydew from ant-attended scale insects, without suffering attacks by the ants protecting the scale insects. These suggest that N. artaxidia is a myrmecophilous moth wholly dependent on ants and ant-attended homopterans. Considering the overwhelmingly plant-feeding habits of moth caterpillars, this discovery ranks in novelty with the discovery of the Hawaiian carnivorous moth larvae that stalk snails.ArticleSCIENTIFIC REPORTS. 4:3922 (2014)journal articl

Larger Seeds are Dispersed Farther: the Long-Distance Seed Disperser ant Aphaenogaster famelica Prefers Larger Seeds

Seed dispersal by ants (myrmecochory) is an important life phase in flowering herbs of temperate deciduous forests, and long dispersal is basically preferable in terms of plant fitness. Although it is known that larger ants transport seeds farther, previous studies conflicted whether larger seeds are preferred by large ants. We examine how seed size and ant body size influence removal rate of seeds and their dispersal distance by ants. The obligate myrmecochorous, large-seed bearing Viola hondoensis and ant-ballistic diplochorous, small-seed bearing Viola spp. and Corydalis pallida were comparatively investigated. 1) Ant preference: attraction rate and transportation rate of large V hondoensis seeds by ants were consistently high regardless of the disperser ant size whilst those rates of small diplochorous seeds were conspicuously lower for large Aphaenogaster ants than for small Pheidole ants, suggesting small seeds are not adapted to be carried by large ants. 2) Dispersal distance: large V hondoensis seeds were transported for a long distance because they were carried by both large and small ants while the small diplochorous seeds were transported for a short distance because they were carried only by small ants. These results suggest that large seeds are advantageous to attract large ants and to be farther dispersed as far as ant-mediated dispersal is concerned. On the other hand, the diplochorous small seeds do not attract large ants, and so are transported short by ants although they disperse their seeds by ballistic dispersal.ArticleSOCIOBIOLOGY. 59(4):1401-1411 (2012)journal articl

Multiple Factors Maintaining High Species-Specificity in Macaranga-Crematogaster (Hymenoptera: Formicidae) Myrmecophytism: Higher Mortality in Mismatched Ant-Seedling Pairs

Myrmecophytism, a type of mutualistic symbiosis, occurs between certain species of Macaranga trees and Crematogaster ants in the tropics of Southeast Asia. Several recent studies have revealed that myrmecophytism in Macaranga-Crematogaster involves a highly species-specific partnership, but there is less specificity at the beginning of the symbiosis when ant foundress queens settle into host seedlings. However, how 'mis-matched' species combinations of ants and plants are selected against in the field has not yet been investigated. We therefore experimentally swapped foundress queens among three sympatric species of myrmecophytic Macaranga and subsequently examined growth and survival of the ants and recipient plants. Our results suggest that severe mortality occurs among ants and seedlings of unmatched pairs throughout multiple processes, such as initial worker production, early colony growth after initial worker appearance, and defense by ants against herbivores. This contributes to the maintenance of high species-specificity in Macaranga-Crematogaster myrmecophytism.ArticleSOCIOBIOLOGY. 55(3):883-898 (2010)journal articl

Larger Seeds are Dispersed Farther: the Long-Distance Seed Disperser ant Aphaenogaster famelica Prefers Larger Seeds

Seed dispersal by ants (myrmecochory) is an important life phase in flowering herbs of temperate deciduous forests, and long dispersal is basically preferable in terms of plant fitness. Although it is known that larger ants transport seeds farther, previous studies conflicted whether larger seeds are preferred by large ants. We examine how seed size and ant body size influence removal rate of seeds and their dispersal distance by ants. The obligate myrmecochorous, large-seed bearing Viola hondoensis and ant-ballistic diplochorous, small-seed bearing Viola spp. and Corydalis pallida were comparatively investigated. 1) Ant preference: attraction rate and transportation rate of large V. hondoensis seeds by ants were consistently high regardless of the disperser ant size whilst those rates of small diplochorous seeds were conspicuously lower for large Aphaenogaster ants than for small Pheidole ants, suggesting small seeds are not adapted to be carried by large ants. 2) Dispersal distance: large V. hondoensis seeds were transported for a long distance because they were carried by both large and small ants while the small diplochorous seeds were transported for a short distance because they were carried only by small ants. These results suggest that large seeds are advantageous to attract large ants and to be farther dispersed as far as ant-mediated dispersal is concerned. On the other hand, the diplochorous small seeds do not attract large ants, and so are transported short by ants although they disperse their seeds by ballistic dispersal