Taxonomic Revision of the Obligate Plant-Ants of the Genus Crematogaster Lund (Hymenoptera, Formicidae, Myrmicinae), Associated with Macaranga Thouars (Euphorbiaceae) on Borneo and the Malay Peninsula

The taxonomy and natural history of ants of the genus Crematogaster Lund, 1831 (Crematogaster borneensis-group of the former subgenus Decacrema) obligately associated with myrmecophytic host-plants of the euphorb genus Macaranga are reviewed. Within this group of ants Crematogaster borneensis André, 1896 (with five subspecies and four varieties), Crematogaster captiosa Forel, 1910 as well as Crematogaster decamera Forel, 1910 have previously been described from SE Asia. Here we synonymise C. borneensis subsp. capax Forel, 1911, C. borneensis subsp. hosei Forel, 1911, C. borneensis subsp. sembilana Forel, 1911, and C. borneensis var. macarangae Viehmeyer, 1916 with C. borneensis André, 1896. Crematogaster borneensis var. harpyia Forel, 1911, C. borneensis var. insulsa Forel, 1911, C. borneensis subsp. symbia Forel, 1911, and C. borneensis subsp. novem Forel, 1911 are synonymised with C. captiosa Forel, 1910. In addition we describe five new species: C. claudiae sp. nov., C. hullettii sp. nov., C. linsenmairi sp. nov., C. maryatii sp. nov., and C. roslihashimi sp. nov.. Seven of these eight species are placed into two informal species subgroups based on queen morphology, life-history characters and a formerly published molecular phylogeny. Keys are provided for the identification of queens and workers, as well as natural history information on the eight ant species. The morphology of these Macaranga-associated Crematogaster (formerly Decacrema) species is compared to the only other three species described for this former subgenus in SE Asia, i.e. C. angulosa André, 1896, C. biformis André, 1892 and C. cephalotes Smith, 1857

Phylogeography of three closely related myrmecophytic pioneer tree species in SE Asia: implications for species delimitation

Members of the Euphorbiaceae are ecologically important elements of Southeast Asian forests. Species of the pioneer tree genus Macaranga, which is also known for its association with ants, are often abundant in disturbed areas. Phylogenetic studies suggested a recent radiation of section Pachystemon which comprises the majority of obligate myrmecophytes within Macaranga. In the present study, we analyzed the genetic structure of three closely related species of this section (M. constricta, M. griffithiana, and M. motleyana) with the aim of resolving their controversial taxonomy and historical biogeography. Chloroplast DNA haplotypes proved to be species-specific and showed a strong phylogeographic pattern. Nuclear microsatellite data supported the taxonomic distinctness of M. griffithiana and M. motleyana, but gave ambiguous results for M. constricta. Genetic differentiation was stronger each within M. griffithiana and M. motleyana than between M. constricta and M. griffithiana, highlighting problems of defining species boundaries. We found no indication for introgression or hybridization events. The high intraspecific morphological variation of the Bornean endemic M. motleyana was partly reflected by similar patterns of genetic variation. The pronounced genetic structure indicates a comparatively long diversification for this species. In contrast, the weak genetic differentiation within M. griffithiana, as well as the widespread distribution of its most common chloroplast haplotype from peninsular Malaysia up to Indochina, indicates a recent expansion in this area. Despite their morphological similarity and close relatedness, all species possess their own specific ant-partners with a corresponding distribution pattern

Studies on the south east asian ant-plant association Crematogaster borneensis / Macaranga: adaptations of the ant partner.

C. borneensis (Myrmicinae) lives in dose association with several myrmecophytic species of the South East Asian pioneer tree genus Macaranga (Euphorbiaceae). The ants are adapted to the plants so dosely that they do not survive away from it. The only food they utilize is provided as food bodies by the plant and honeydew from specific scale insects kept inside the hollow internodes. The anatomy of the digestive tract is also adapted to life on the host plant: the crop is very sm all and can store only minute food quantities. C. borneensis exdusively colonizes certain Macaranga species. Queens as weIl as workers are able to recognize their host plant species, probably by chemical cues. Colony founding queens swarm throughout the year, mostly during darkness. There is strong competition among queens for host plants. Queens do not carry scale insects on their nuptial flight. Worker ants are active day and night. Most of them patrol and collect food bodies on the younger parts of the host plant. An important characteristic is their deaning behaviour, which results in removal of aIl foreign objects. Even though they are rather smalI, workers respond very aggressively to certain kinds of disturbance of the host plant. The ants attack most phytophagous insects and are especially effective in killing and removing smalI, softbodied herbivores (e.g. caterpillars). They do not possess a functional sting, but apply defensive secretion and-once biting an intruder-will not let go. Their effective alarm system results in a mass attack, which provides adequate defence for the colony and the host plant. A comparison with another Crematogaster species further illustrated the special adaptations of C. borneensis to its host plant.Untersuchungen über die südostasiatische Ameisen·Pflanzen-Vergesellschaftung Cremattogaster borneensis Maoaranga : Anpassungen des Ameisenpartners 213 C. borneensis (Myrmicinae) lebt in enger Gemeinschaft mit myrmekophytischen Arten der südostasiatischen Pionierbaumgattung Macaranga (Euphorbiaceae) . Die Ameise ist so eng an die Pflanze adaptiert, daß sie getrennt von ihr nicht lebensfähig ist. Die Nahrung bezieht C. borneensis in Form von Nährkörperchen ausschließlich von der Pflanze. Im Sproßachseninnern gehaltene spezifische Schildläuse bieten eine weitere Nahrungsquelle. Die Adaptationen erstrecken sich bis auf die Anatomie des Verdauungstraktes : Der Kropf ist sehr klein und kann nur geringe Nahrungsmengen speichern. C. borneensis besiedelt spezifisch nur Macaranga-Pflanzen. Sowohl Königinnen als auch Arbeiterinnen sind in der Lage, die Wirtspflanze zu erkennen, wobei offenbar chemische Reize eine Rolle spielen. Die koloniegründenden Königinnen schwärmen das gesamte Jahr über, das Schwärmen erfolgt überwiegend während der Dunkelheit. Um die besiedlungsfähigen Macaranga-Pflanzen herrscht ein starker Konkurrenzdruck. Die beteiligten Schildlausarten sind spezifisch für die Assoziation. Sie werden nicht von der Königin beim Hochzeitsflug mitgenommen. Die Arbeiterinnen sind tag- und nachtaktiv. Die meisten Tiere halten sich im jüngsten Drittel der Pflanze auf, wo sie patrouillieren und Nährkörperchen sammeln. Mittels eines spezifischen Säuberungsverhaltens entfernen die Arbeiterinnen alle Fremdobjekte von der Pflanze. Trotz ihrer geringen Größe attackieren die Ameisen eine Vielzahl phytophager Insekten und sind dabei besonders effektiv in der Abwehr kleiner, wenig sklerotisierter Tiere wie z.B. Raupen. Sie verfügen zwar nicht ' über einen funktionsfähigen Stachel, setzen aber Wehrsekrete ein und beißen sich hartnäckig fest . Mit Hilfe eines effektiven Alarmierungssystems, das einen Massenangriff ermöglicht, gewährleisten sie eine Verteidigung ihrer Kolonien und damit gleichzeitig ihrer Wirtspflanze. Eine Vergleich mit einer anderen Crematogaster-Art demonstriert die besonderen Adaptationen von C. borneensis an ihre Wirtspflanze

Food bodies and their significance for obligate ant-association in the tree genus Macaranga (Euphorbiaceae)

The production of extrafloral nectar and food bodies plays an important role in many tropical ant-plant mutualisms. In Malaysia, a close association exists between ants and some species of the pioneer tree genus Macaranga (Euphorbiaccac). Macaranga is a very diverse genus which exhibits all stages ofintcraction with ants, from facultative to obligatory associations. The ants nest inside the hollow inlcrnodes and reed mainly on food budies provided by the plants. Food body production had previously been reported only in myrrnecophytic Macaranga species, where it is usually coneentrated on protected parts or the plants such as recurved stipules. We found that non-myrmecophytic Macaranga species also produce food bodies on leaves and stems, where they are collected by a variety or ants. Levels of food body production differ between facultatively and obligatorily ant-associated species but also among the various non-myrmecophytes. This may he rdated to the degree of interaction with ants. Food body production starts at a younger age in the myrmccophytic species than in the transitional or non-myrmcccophytic Macaranga. Although food bodies of the non-inhabited Macaranga species are collected by a variety of ants, there is nu evidence of association with specific ant species. Our observations suggest that food bodies enhance the evolution of ant-plant interactions. Production of food bodies alone, however, does not appear to be the most important factor for the development of obligate myrmccopllytism in Macaranga

Domatia as most important adaptations in the evolution of myrmecophytes in the paleotropical tree genus Macaranga (Euphorbiacae)

The paleotropical tree genus Macaranga (Euphorbiaceae) comprises all stages of interaction with ants, from facultative associations to obligate myrmecophytes. In SE.-Asia food availability does not seem to be the limiting factor for the development of a close relationship since all species provide food for ants in form of extrafloral nectar and/or food bodies. Only myrmecophytic Macaranga species offer nesting space for ants (domatia) inside intern odes which become hollow due to degeneration of the pith. Non-myrmecophytic species have a solid stem with a compact and wet pith and many resin ducts. The stem interior of some transitional species remains solid, but the soft pith can be excavated. The role of different ant-attracting attributes for the development of obligate ant-plant interactions is discussed. In the genus Macaranga, the provision of nesting space seems to be the most important factor for the evolution of obligate myrmecophytism

Ant-attracting plant-structures: Food bodies of SE Asian Vitaceae

No abstract availabl

The association between Macaranga trees and ants in South-east Asia

No abstract availabl

Clerodendrum fistulosum (Verbenanceae), an unspecific myrmecophyte from Borneo with spontaneously opening domatia

Clerodendrumjistulosum Becc. is a true myrmecophyte as it offers nesting space for ants in hollow intemodes. In contrast to previous reports our investigations proved that these domatia open by themselves, thus providing cavities for a variety of different ant species. In Sarawak, Malaysia, we did not find an obligate relationship between C. jistulosum and a specific ant-partner. For comparison, studies on herbarium material of other Clerodendrum species were carried out a further species, C. deflexum from the Malay Peninsula and Sumatra presumably also is myrmecophytic

A new ant-tree from SE Asia: Zanthoxylum myriacanthum (Rutaceae), the Thorny Ivy-Rue

Zanthoxylum myriacanthum, a small Rutaceous tree growing mainly in secondary hill forests in SE Asia, is a true myrmecophyte. It possesses stem domatia in the form of hollow branches with slitlike openings. Branch hollows and entrance slits are produced by the plant itself through pith degene~.tion ?u.d growth proceSses. If the entrance is not kept open by ants it closes again by growth ol the surrounding tissue after some time. The domatia are colonized opportunistic ally by different arboreous ants, e.g. Crematogaster and Campono tus. Additionally many small extrafloral nectaries are found on the leaflets of Zanthoxylum myriacanthum. Judging from herbarium studies and literature records at least four more true ant trees are found in the genus Zanthoxylum namely Z. rhetsa in SE Asia, Z. conspersipunctatum, Z. pluviatile and Z. vinkii in New Guinea. We could not confirm ant inhabitation in Drypetes pendula (Euphorbiaceae) on the Malay Peninsula, which has also been recorded to be an anttree

Extrafloral nectaries in the genus Macaranga (Euphorbiaceae) in Malaysia: comparative studies of their possible significance as predispositions for myrmecophytism.

So me species of the paleotropical tree genus Macaranga (Euphorbiaceae) live in elose association with ants. Thc genus comprises the full range of species from those not regularly inhabited by ants to obligate myrmecophytes. In Malaysia (peninsular and Borneo) 23 ofthe 52 species areknown to be ant-associated (44%). The simplest structural adaptation of plants to attract ants are extrafloral nectaries. We studied the distribution of extraflural nectaries in the genus Macaranga to assess the significance of this character as a possible predisposition for the evolution of obligate myrmecophytism. All species have marginal glands on the leaves. However, only the glands of nonmyrmecophytic species function as nectaries, whereas liquids secreted by these glands in myrmecophytic species did not contain sugar. Some non-myrmecophytic Macaranga and transitional Macaranga species in addition have extrafloral nectaries on the leaf blade near the petiole insertion. All obligatorily myrmecophytic Macaranga species, however, lack additional glands on the lamina. The non-myrmecophytic species are visited by a variety of different ant species, whereas myrmecophytic Macaranga are associated only with one specific ant-partner. Since these ants keep scale insects in the hollow sterns, reduction of nectary production in ant-inhabited Macaranga seems to be biologically significant. We interpret this as a means of (a) saving the assimilates and (b) stabilization of maintenance of the association's specificity. Competition with other ant species for food rewards is avoided and thereby danger ofweakening the protective function ofthe obligate antpartner for the plant is reduced. A comparison with other euphorb species living in the same habitats as Macaranga showed that in genera in which extrafloral nectaries are widespread, no myrmecophytes have evolved. Possession of extrafloral nectaries does not appear to be essential for the development of symbiotic ant-plant interactions. Other predispositions such as nesting space might have played a more important role