ACTA NEUROBIOL. EXP. 1978, 38: 133-138 EVALUATION OF FUNCTIONAL DEGENERATION OF THE AMAZON-ANT POLYERGUS RUFESCENS LATR. UNDER AN INFLUENCE OF SOCIALLY PARASITIC WAY OF LIFE Janina DOBRZANSKA Department of Neurophysiology, Nencki Institute of Experimental Biology Warsaw, Poland Abstract. In certain, infrequently occurring, favorable circumstances the ants P. rufescens can display patterns of behavior which seem to be disappearing as a result of their parasitic way of life: the ability to food themselves, independently though ineffectively, elements of the offspring-protection behavior, transporting of nestmates, escape reaction. Similar events reinforce the infrequently used, latent reflexes, preventing their complete extinction. It is supposed that the characteristic in conventional parasitism disappearance of certain elements of behavior is inhibited by a social way of life. It may also be true of other, non-insect communities. The same one-sidedness of research which has influenced the opinion on the lack of plasticity in the behavior of slave-making ants (3) has also led to the widely held belief that, as a result of degeneration caused by a parasitic way of life, the slave-making ants have irrevocably lost all raid-unconnected abilities characteristic of their nonparasitic ancestors. However, during our studies on Polyergus rufescens' ,behavior we have collected observations, which contradict those assumptions and make us look anew at the problem of its functional degeneration. They lead to a new conclusion, namely, that some patterns of behavior which the slave-making ants do not normally display can manifest themselves in certain, atypical circumstances. Escape reaction. The normal reaction of the Formica fusca L. ants when their nest is attacked by the slave-making ants is flight and carrying off their offspring, the latter being the real object attack. Most frequently 4 - Acta Neurobiologiae Experimentalis the invaded F. fusca escape upwards, to the tops of surrounding grass blades. It was a most unusual occurrence when the army of P. rufescens attacked a nest situated 90 m from their own and also occupied by amazons. The events that followed were deciphered only because the two nests happened to be under observation from the beginning of their seasonal activity and a large number of individuals were marked with dye and wire rings. If it was not for that, this rare instance of intraspecific aggression 'in the P. rufescens could have remained illegible. There were large numbers of running ant-slaves F. fusca on the surface of the raided nest. They were carrying the offspring and the winged forms of the amazons out of the nests. A few of the workers woul'd take up the fight, which F. fusca ants never do in their independent nests, and they were getting killed in the unequal struggle with the attackers. As always in the case of attack, the escaping worker ants with the brood found refuge in great number on the tops of grass blades around the nest. Unexpected, however, was the reaction of the amazons, who ran from the attacked nest together with their slaves, climbing the grass blades to await the end of the attack. Others were simply running away in the direction opposite to the one from which the attackers had come, which was aLso most unusual for ants of that species. As it is not in the nature of the P. rufescens to hunt down the escaping enemy, running away should have saved the invaded ants. This was, however, made impossible by an obstacle - just one meter away in the direction of their escape route was positioned a nest belon- ging to Lasius niger. These small ants, absolutely defenseless individually, become a formidable force when defending their nest in great numbers, signalling rapidly to each other and fighting collectivelly. The irritation of the L. niger's nest has led to the destruction of the slave-making ants, their many-year-neighbors. The lethal mandibles of P. rufescens were a useless weapon against such small and numerous enemy: the slave- making ants were literally torn apart, each by 4 - 6 Lasius ants. The amazons' panicky escape observes consideration. Observations of typical P. rufescens' slave raids give an impression that those ants have completely lost the escape reflex, that fighting is their only reaction to aggression. And yet, the unusual circumstances have evoked the escape reaction in the amazons, attaoked in their own nest. What is more, the ants fled in an upward direction, at of the surrounding grass blades. This reaction is characteristic of the F. fusca slave-species which is etholog- ically opposite to the slave-making ant as, unable to defend itself actively and systematically raided in its own nest by numerous and stronger enemies. It is, however, impossible to exclude the possibility that the slave-making ants imitated the behavior of their slaves. Yet, in other numerous situations the amazons' behavior was not dependent on the reaction of their slaves. Even supposing that in the unique situation described here the ants could have been imitating the behavior of their slaves, it could be explained only by the consistence of such behavior with the latent, inborn reflexes of the amazons. The protective behavior. It happens sporadically that beside the pupae the slave-making ants bring back from the raids very young workers of, the slave species, with chitin still colorless. Since the number of those very young, white ants that are brought along with the prey from each particular raid may reach a dozen or so, the fact cannot be dismissed as accidental. The young ant is carried by the slave-making ant with the same care and attention as a pipa, although-in contrast to the pupa - it has a tendency to struggle and .try to run away. In such a difficult situation, the amazon still does not clench its powerful mandibles, easily capable of piercing the chitin of a mature insect. On the contrary, the ant keeps the mandibles open and lets them slip over the soft chitin of the young ant. The ant in a protective way allows the limbs and antennae of the escaping ant to pass freely between the sharp ends of its mandibles, adapted to fighting. Under such circumstances the attempts to escape would be always successful, if it was not for the fact that the struggle usually takes place near the P. rufescens' nest, at the point when the slave-ants go into action. This is because the young ants usually do not object to being carried all the way and it is not till they reach the slave-making ants' nest that they begin to make attempts to free them- selves and run away. One of the inborn reflexes of the young ant is that of submission to a nestmate which catches and carries it. Furthemore, it is 'known that a newly hatched ant has poorly developed senses (7) and thus probably cannot distinguish the scent of a iingle amazon, when the latter seizes it in its own nest and subsequently carries away. It may be assumed, therefore that it is only the strong smell of the slave-making ants' nest that can reach the abducted ant's senses an'd trigger off the escape reaction. Then, however, it is too late. The slaves, aroused by the arrival of their trophy-carrying nestmates, run around, treating the fugitives in a manner completely ldifferent from that of the slave-making ants. They pull them brutally, sometimes drapping them along by one leg. Still, they never seem to injure the yet delicate bodies. It seems that the experienced nurses - in contrast to the amazons - how very well the biologically permissible and necessary means of taming the insubor- dinate young individuals. The young ant, even when eventually pulled by force inside the nest, still tries to run away, with the entry-guarding slave-making ants attempting clumsily to stop it. It could always manage to escape if it was not for the slave-ants who drag it back. With the function of offspring-protection having fallen out of the P. rufescens' behavior, their attitude to the sporadically abducted young slave-ants is somewhat unexpected. Of special interest is the comparison of the behavior of two slave-making species: P. rufescens and Formica sanguinea Latr. The amazons seldom kill defenders of the invaded nests and do it only in self-defence. They have lost the hunting-instinct to such a degree that even an extreme situation when the prey is struggling to escape, does not evoke their aggressive behavior, but triggers off, unexpectedly, manifestations of protective behavior. In contrast, F. sun- guinea regularly devour the captured pupae, kill the defending workers and bring them back as quarry (4, 11). Their aggression against potential slaves and a complete lack of social instincts towards them, which distin- guish F. sanguinea very sharply from the P. rufescens, is one more argument in support of Dobrzanski's (5) statement that F. sanguinea is in an early, initial stage of slavery. A through review of literature reveals a few references relevant to the subject under discussion: Huber (9) - writes about an amazon extracting a young ant from a cocoon and Wasmann (10) - about cleaning of freshly hatched ants by the amazons present in the nest. Unfortunately, both authors do not mention to what species the young individuals belonged. Transportation of nestmates. To all species of ants, removal is a complicated and important activity which is carried out by very active workers, moving not only offspring and sexual individuals, but also the more passive nestmates. For this reason the observed active parti- cipation of P. rufescens soldiers in the transportation of their F, cinerea slaves - acquires great importance.