Joachim Moog

Two new myrmecophytic associations from the Malay Peninsula: Ants of the genusCladomyrma (Formicidae, Camponotinae) as partners ofSaraca thaipingensis (Caesalpiniaceae) andCrypteronia griffithii (Crypteroniaceae)

SummaryIn Peninsular Malaysia the treesSaraca thaipingensis (Caesalpiniaceae) andCrypteronia griffithii (Crypteroniaceae) are inhabited by ants. In the vicinity of Gombak, near Kuala Lumpur, the hollow internodes of youngSaraca thaipingensis plants are colonized mainly by twoCladomyrma species. In larger trees aCrematogaster sp. is also found.Crypteronia griffithii is inhabited by a third species ofCladomyrma. None of these species is conspecific with any of the threeCladomyrma taxa so far described. The colonies are founded by single mated queens, which have a conspicuous, sphecid wasp-like behaviour when searching for host plants and nest sites. They chew holes into the plant internodes and hollow them out to provide nest sites. Coccids and pseudococcids are cultivated within the internodes. The homopterans are not carried by queens on their nuptial flights. They apparently find their way by themselves into the cavities or are perhaps carried there by the worker ants. TheCladomyrma ants onCrypteronia are not aggressive, in contrast to those onSaraca thaipingensis.The relationship ofCrypteronia with ants seems to be obligatory, whereasSaraca was only partly colonized byCladomyrma. The interaction ofSaraca withCrematogaster sp. is loose and facultative, since theCrematogaster sp. also lives on other three species. Our studies have now revealed fourCladomyrma spp. which are regularly associated with plants. The genus therefore seems to have an entirely myrmecophytic way of life.

Ant-Plant Diversity in Peninsular Malaysia, with Special Reference to the Pasoh Forest Reserve

The overview of ant-plants in Peninsular Malaysia presented here covers: (i) diversity of participating ant and plant taxa; (ii) specificity of associations; (iii) morphological diversity of plant structures used for ant-housing; (iv) plant growth habit; and (v) food type of ants directly or indirectly derived from host plants. Included are unpublished observations both from field and herbarium studies and records of ant-plants obtained from a literature survey. It is the first comprehensive account of Malayan ant-plants on species level since many decades. At least 45 ‘true’ myrmecophytic species belonging to 20 genera and 14 families are recognized. Twenty-two additional species (from 17 genera) are looked upon as potential myrmecophytes but evidence is still anecdotal and incomplete. The review presented here allows a conservative estimate of ‘true’ ant-plants in Pasoh Forest Reserve (Pasoh FR). The reserve is home to at least one third of the known myrmecophytes occurring on the peninsula.

The triple alliance: how a plant-ant, living in an ant-plant, acquires the third partner, a scale insect

Summary.Mutualistic associations between ants and plants often involve a third partner, scale insects (Hemiptera, Coccoidea). In southeast Asia, plant-ants of the genus Cladomyrma live together with coccoids in hollowed twigs of a wide range of ant-plants (myrmecophytes). Established colonies never lack sap-sucking scale insects and the ants appear to be dependent on the honeydew excretions of their trophobionts. Acquisition of scale insects thus seems to be an important step in the successful establishment of a new colony on a host plant. Coccoids may either be transported by a foundress ant on her nuptial flight (vertical transmission via co-dispersal) or ant and coccoid disperse on their own and associate anew during colony initiation (horizontal transmission). Here we test the assumption that founding gynes of Cladomyrma do not transport scale insects during their dispersal flight, and we determine when and how trophobionts are acquired. The results obtained in this study show that although coccoids are not carried by foundresses, their numbers within founding chambers of Cladomyrma increased with the founding stage. In all Cladomyrma species, colony-founding is claustral and the entrance hole into the nest chamber is first plugged with pith debris and later grows over by wound callus. However, access of trophobionts into hollow twigs is facilitated either by additional small openings (‘secondary slits’) produced by the foundress ant after hollowing out a nest chamber or by the maintenance of an orifice at the entrance hole during the founding period. Immature pseudococcids experimentally placed onto twigs close to a Cladomyrma foundation readily entered these slits. Exclusion experiments suggest that foundresses of C. petalae are less successful in rearing their first offspring if entry of coccoids into founding chambers is prevented.

Flood Control by Ants: Water-Bailing Behaviour in the Southeast Asian Plant-Ant Genus Cladomyrma Wheeler (Formicidae, Formicinae)

Strong and frequent rain is essentialfor the existence of tropical rain for-ests. Heavy showers, however, pose athreat especially for arboreal insectswhich can be washed down fromtrees or even be drowned in theirshelters. Queens of the plant-antgenus Cladomyrma, which must bitenest chambers into their host plantstems for colony foundation, fre-quently disappear during heavy rainand are sometimes drowned whenseeking refuge in their unfinished,still unclosed chambers due to runoffwater which collects in the hollow in-ternodes via the entrance holes. Ma-ture colonies of these ant species facethe same problem of intruding rain-water endangering ant brood and tro-phobiotic mealybugs, but they re-spond with an unusual behaviour onlyonce previously reported for ants: theworkers ingest the liquid and regurgi-tate it to the outside until no standingwater remains. This behaviour can bereadily provoked by injecting smallamounts of liquid into inhabited inter-nodes. The ability of Cladomyrma toremove water from its nest site ap-pears to be an adaptation to their obli-gate colonization of myrmecophytes(ant-plants).Cladomyrma is a formicine genuswhose species live exclusively in avariety of trees and vines from Bor-neo and the Malay Peninsula. To ourpresent knowledge Cladomyrma inha-bits 18 host plant species from 9 gen-era and 8families ([1–4], unpublishedresults). These ants protect their hostplants against herbivores ([4, 5], un-published results) and prune (at leastin part) encroaching vegetation. Theants gnaw open the host plant inter-nodes and hollow them out by remov-ing the pith. With both increasingplant and colony size other internodesare colonized successively. Eventuallythe nest chambers run through stem,branches and every twig of the host.These hollows contain brood and tro-phobiotic pseudococcids which arecultivated by the ants. As a rule onenest entrance per internode is found.In regard to nest structure the hostNeonauclea Merr. (Rubiaceae) differsfrom other host plants of Cladomyr-ma. Here only internodes which areswollen ( = myrmecodomatia) are hol-lowed out and colonized by the ants.The number of entrance holes per do-matium varies greatly, on averageabout 4–6 are found, depending onboth domatium and colony size.In all host plants the entrances are si-tuated more or less at the lateral sidesof the internodes. Thus the risk ofgetting runoff-water into the nestchambers is reduced (exept for thevertical stem). However, rainwatermay still be able to collect in the nest.We dissected longitudinally several in-habited internodes of the trees Sara-ca, Ryparosa, Neonauclea, Cryptero-nia, and the woody climber Spatholo-bus. By watering the outer walls ofthe internodes we could check frominside that small amounts of water dointrude into the nest. Most of the run-off water, however, passes the en-trances due to very small callus ridgesaround the holes. Rain water mayalso penetrate into the nest hollowsthrough openings of damaged twigs,the latter being torn open by predatorsof ants and brood.To test how Cladomyrma ants react tothe intrusion of water we injected be-tween 0.2 and 6 ml artificially co-loured liquid into nest entrances witha syringe. Table 1 summarizes the re-sults. In total we performed 16 testswith nine colonies of three Cladomyr-ma species, C. near andrei (Emery; 1colony, 3 tests), C. maschwitzi Agosti(4 colonies, 6 tests), C. petalae Agosti(4 colonies, 7 tests); and in nine hostplants of five various other species:Saraca thaipingensis Cantley ex Prain(n = 2), Ryparosa fasciculata King(n = 1), Spatholobus bracteolatusPrain (n = 1), Crypteronia griffithiiClarke (n = 4), and Neonauclea gigan-tea (Valeton) Merr. (n = 1). On eachplant we fixed the experimental twigsin a horizontal position to prevent theinjected water from draining away in-side the nest channels. Prior to the in-jection of coloured liquid we fixed asmall filter paper (4 ×4 cm) beneatheach experimental entrance hole(n = 16). Within minutes after flood-ing the internodes (1–15 min, median4, mean 5.38 ± 4.76) the number ofworkers increased noticeably (at leastthree-fold the activity level prior to in-jection) around the affected areas.Shortly afterwards the first workerswith distended gasters, containing co-loured liquid (tested by squashingworkers on filter paper), appeared onthe plant surface (3–65 min, median5, mean 12.08 ± 17.52). There alwayspassed a considerable period of timebefore the first appearance of thewater-ejection behaviour (3–41 min,median 27, mean 24.92 ± 13.18).The results are highly variable andmay be due to (a) different amountused of injected liquid, (b) the num-ber of workers involved, i.e., colonysize, (c) incomparability of risk levels,i.e., different number of larvae orpseudococcids inside the affected in-ternodes, and (d) species-specific dif-ferences in behavioural response.

Überlebensstrategien von Regenwaldameisen

Die heftigen Regenfälle in den feuchten Tropen stellen Pflanzen und Tiere vor besondere Herausforderungen. Ameisen haben unterschiedliche Anpassungen gegen Überflutungen entwickelt. Von der Floßbildung bis zu verschiedenen Methoden der Nestentwässerung reichen die Maßnahmen gegen Hochwasser. In der Gezeitenzone werden Nester wasserdicht verschlossen, dabei reagieren die Ameisen mit physiologischen Anpassungen auf den Sauerstoffmangel. In einer obligaten Symbiose zwischen einer carnivoren Kannenpflanze und einer Rossameise hat sich ein einzigartiges Zusammenleben entwickelt, bei der die Partnerameise unbeschadet in dem enzymhaltigen Kannenwasser schwimmt und nach Mückenlarven und ertrunkenen Beutetieren taucht.