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Colony fission and intraspecific contests in Myrmica laevinodis NYL. (Hymenoptera, Formicidae)

Colony fission and intraspecific contests in Myrmica laevinodis NYL. (Hymenoptera, Formicidae)
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  POLSKA AKADEMIA NAUK  INSTYTUT ZOOLOGII ANNALES ZOOLOGICI Tom 38 Warszawa, 30 VIII 1984 Nr 4 Wojciech Czechowski Colony fission and intraspecific contests in  M yrmica laevinodis  Nyl.   (  Hymenoptera , Formicidae ) [With 1 text-figure]Abstract. In spring, large polygynic colonies of  M yrmica laevinodis   N yl . divide into smaller   units and mass contests occur between neighbouring colonies. In the paper the significance   of these phenomena as manifestations of foraging strategy and the mechanism of intraspecific   competition is suggested.INTRODUCTION Spring is a period when the activity of ants is particularly high. After the   winter interval workers carry out a reconnaissance of the area, renew the systems   of tracks, and territorial species establish the boundaries of their foraging areas   with regard to the existing abundance of the swarm and the potential of the   neighbouring colonies. Polycalic colonies extend their ranges through swarm   fission and founding filial nests. During this period the food requirements of    colonies are high while the food resources of the habitat are still low. Ants deal   with this situation by adjusting their foraging strategies —and the most frequent   is that of splitting large societies. Moreover, competition —both inter- and   intraspecific —between colonies is particularly fierce. Intraspecific conflicts   may be accompanied by different level of aggressiveness. In extreme cases   they take the form of cannibalistic predation, as is the case in Formica polyctena   Foerst. (de Bruyn and Mabelis 1972, Mabelis 1979a, b), or of ritualized   tournament contests, as in  Lasius niger    (L.) (Czechowski 1984). And seemingly   desperate combats, but with only a few victims, are an intermediate form.   Such spring conflicts have been recorded in Tetramorium caespitum  (L.)  100W. Czechowski (M c O ook    1879, W ilson   1971). The facts presented in this paper indicate that   they also occur in  Myrmica laevinodis   N yl .1 DESCRIPTION OF THE OBSERVATION'S Basic observations were carried out in 1980-1981 in Boża Wola near Sochaczew (the Skierniewice district). The same phenomenon had been recorded in   1978 in Celestynów near Otwock (the Warsaw province).In Boża Wola the studies were carried out from May to October, in a cottage   garden. Very numerous colonies of  Myrmica laevinodis  and  Lasius niger   occurred   there2. The local population of  M. laevinodis  must be regarded as exceptionally   abundant. In the part overgrown with grass (about 500 m2) the density of the   nests was about 0.2 /m2. Quite a lot of them were very large and, according to   a rough estimate —they included several thousand individuals. The nests,   in most cases entirely underground, were usually situated under tufts of grass.   Very frequently their presence was revealed only when the lawn was being   dug during some gardening activity. The density of workers penetrating the   surface of the soil was very high. In some places it was several dozen individuals   per 1 m2, even during summer broiling heat.Each year, in May, fissions of large 31. laevinodis  colonies took place. The   departing groups of workers with the brood and several queens founded new   nests at a distance of one or several metres from their maternal nest. The migrating swarm formed a loose column about 10 cm wide (sometimes even 30 cm   wide). The traffic was two-way. Workers carried pupae and young imagines   (lightly coloured) to the new nest and then returned for another “load”. They   very apparently moved along odour trails left by their predecessors. This type   of pheromonous signalization —usually applied in food recruitments —is well-   known in 31. laevinodis   (C ammaerts -T ricot   1974, C ammaerts -T iiicot   and   V eriiaeghe   1974, C ammaerts   1977b, 1978, D obrzańska   and D obrzański   1976). The queens migrated on their own, generally following the workers.   It gave the impression of tandem running. A queen that had suddenly found   itself without its guide (a distance of a few centimetres was sufficient) seemed   lost. It slowed down, often stopped, left the track, and occasionally went back.   The workers passing by paid no attention to it. Usually, after some time the   queen managed to get into contact with one of them and afterwards it once   again proceeded unhesitatingly. In the course of fission of a particularly large   colony over a dozen migrating queens were recorded within one hour (a removal   usually took 1-3 hours). 1 In literature tlie species is often given the synonymous name of  M yrmica rubra  L.2 The intraspecific conflicts in  L. niger   recorded there have already been described   (C zechowski   1984) and the competitive relations between  L. niger   and  M. laevinodis  is   discussed in the nest paper (C zechowski   1985).  Colony fission and intraspecific contests101 Very often when a new swarm was settling in a new place there were combats   between the settlers and the conspecific residents of a given area that nested   nearby. They were mass combats, and involved dozens or hundreds (and occasionally even thousands) of ants scattered over a fairly large area. Neither   a particular front nor a definite battlefield could be defined. The war was fought   in simultaneous yet independent single combats. Hardly even was one ant attacked by 2 or 3 enemies. Workers from the same swarm never helped one   another in danger. During combats were demonstrated all elements of the aggressive behaviour of  M. laevinodis:  mandibles opening, seizing, gaster flexing   and dragging ( de  V hoey   1980). A single combat began when two workers met   and one of them (the stronger or the local one ?) began to feel the other with   its antennae, then, with its mandibles, snapped the other by the antenna, leg   or petiole and began to drag it (not necessarily towards its own nest). Generally,   at first, the ant attacked was absolutely passive —it stopped and clung to the   ground. Only when dragged, it fought actively (yet not always even then).   The combat became very fierce (or at least gave the impression of being so).   The locked ants either rolled over the ground with flexed abdomens or one of    them, with great effort, dragged the other in spite of its cliuging to the ground.   A combat between two ants could last even over an hour. It ended when one   of them ran away or both departed calmly. After a combat, the ants seemed to   have no major wounds. Instances of serious injuries or-even death were very rare   indeed. Combats lasted for 2-3 consecutive days and afterwards both swarms   penetrated the common area without further conflicts.Fissions and removals of colonies and combats of  M. laevinodis  were difficult to watch because nests were hidden in dense and tall grass. Generally,   it was possible to study a removal only when the track crossed an open area.   Thus, only one case of fission and removal of a swarm was studied in detail.   The whole process was carried out by stages and most probably it was, to a large   extent, influenced by the interference of neighbouring colonies of  Lasius niger.   Therefore, this particular case cannot be considered a typical representation   of the phenomenon, but it is worth describing.The  M. laevinodis  colony under study (denoted by the symbol Ml;   Fig. 1) was situated under a tuft of grass on a flower-bed, close to the steps   leading to the terrace. At the beginning of May (before the 10th) 1981, a big   group of workers with pupae and many queens left the colony. The new swarm   (Ml') settled under the steps (in the place nx) about 60 cm from the maternal   nest. On May 15, the swarm moved from under the steps to the flower-bed,   covering another 60 cm. Here the ants made their nest (n2) in the cracks of    newly spaded soil, without any building activities. They stayed there for one   week, and during that time ants from the Ml' swarm occasionally fought with   workers from another colony of  M. laevinodis  (M2) situated about, 1.5 m away.   Previously, before the Ml' swarm separated, workers from Ml and M2 colonies   had penetrated the area without any conflicts, which was found out when sugar  102W. Czechowski baits were put out. (The very experiments may have induced the Ml' swarm   to settle in that place). On May 20, the n2nest was surrounded by several dozen   individuals from the neighbouring  Lasius niger   colony (LI). During that siege    M. laevinodis  very nearly revealed their presence. Separate individuals that   appeared from time to time were caught and killed by  L. niger.  The siege lasted   about 2 hours. When it was over  M. laevinodis  ants resumed penetration.On   May 23, the Ml' swarm moved once again, this time over 2 m from the previous   place. The new nest (n3) was founded near the kerb of a concrete pavement. w a l l o f b u i l d i n gt e r r a c es t e p sb e d M2 b e d Ml p a v e m e n tg r a s sg r a s s M3 Fig. 1. Situational plan of the area (a bird’s-eye view) and the course of the removal of the  M . laevinodis  swarm (Boża Wola, May 1981; the symbols explained in the text). In the closest vicinity, also under the pavement was a  L. niger   nest (L2). For   a few days ants of the two species paid no attention to one another. Mass intraspecific combats of 31. laevinodis  began on May 25. Ants from the Ml' swarm   got simultaneously involved in fights with the M2 colony and also with the M3   colony situated about 6 m away. The number of struggling pairs reached several   dozen per 1 m2. The conflict was over on May 27. But the following day  M.   laevinodis  from the Ml' swarm attacked the neighbouring  L. niger   nest (L2)   and forced its inhabitants to withdraw from a part of the area occupied under   the pavement.1It was possible to find that out because the nest entrances of    the  L. niger   colony were situated along a crack between concrete flag-stones.   A violent counter-attack of  L. niger   took place on May 29. After several hours of    combat the Ml' swarm began its successive removal, this time settling in the place 1 Tbe course of the conflicts between  M. laevinodis   and  L. niger    (and also the manner   of fighting) is discussed in the paper on competition between these species (C zechowski 1985).  Colony fission and intraspecifio contests103 n4, situated beyond the reach of the colonies M2, M3, LI and L2. Meanwhile,   ill. laevinodis  workers form the colonies Ml and M2 utilized, without conflict   and until the end of the season, the common area around the former n2nest   of the Ml' swarm. Whether the Ml' swarm returned to its maternal nest in   autumn or not is not known; until mid-October it was not recorded there.Spring combats of ants from the genus  Myrmica   L atr  . sometimes take   place over a very large area. A particularly impressive phenomenon was recorded in Celestynów, in a pine wood. Unfortunately, the ant species was not   determined. Most probably they were  M. laevinodis  ants, too. The combat   took place over a 30-metre stretch of a sandy forest road and along the edges   of the forest on both sides of the road (thus the strip was about 4 m wide).   All over this area pairs of clenched ants were found every ten centimetres   or so. Undoubtedly the combat involved a lot of colonies. Just as in Boża Wola,   the combat was recorded in May. DISCUSSION Before the discussion begins it must be pointed out that the  M. laevinodis   population studied was exceptionally abundant. Generally the abundance of    colonies of this species is from several hundred to about 2 thousand individuals.   Larger colonies (3-5 thousand individuals) are rare (B rian   1972, P ętał   1972,   1980, E lmes   1973, 1974a, C ammaerts   1977a, S meeton   1982). The high abundance of the colonies in Boża Wola was indirectly indicated by a considerable   number of queens recorded during spring removals. In  M. laevinodis  the number   of queens in a nest is proportionate to the abundance of the swarm (S meeton   1982). According to literature data, the average number of queens in a nest   is 15-20 (very seldom it exceeds 50), and the average number of workers per   one queen is over 70 (B rian   1967, 1972, E lmes   1973, 1974a, b, C ammaerts   1977a). The density of nests is also generally lower than that in the area studied.   For instance, in different meadows in Poland it is 0.01-0.16/m2 (P ętał   1967,   1980). It seems that the srcin of the phenomena described must be attributed to the enormous abundance of particular colonies and of the entire population inhabiting the area, studied.In habitats with temporarily or permanently deteriorating conditions   polygynic colonies of many ant species have a tendency to divide into smaller   units. This phenomenon has been studied thoroughly in ants from the genus   Formica  L. (subgenera: Formica  s. str.; W ellenstein   1967, B osengren   1971,   B osengren   and P amilo   1979, Y epsalainen   and W uorenrinne   1978 and   Coptoformica   M ull .; C zechowski   1975, 1976, 1978). The splitting of a large   society into many small independent colonies increases the probability of its   survival under critical conditions (Y epsalainen   and W uorenrinne   1978).   However, it can also be assumed that the basis for changes in the structure of 
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