Philip S. Newey

Not one odour but two: A new model for nestmate recognition

Recognition systems play a key role in a range of biological processes, including mate choice, immune defence and altruistic behaviour. Social insects provide an excellent model for studying recognition systems because workers need to discriminate between nestmates and non-nestmates, enabling them to direct altruistic behaviour towards closer kin and to repel potential invaders. However, the level of aggression directed towards conspecific intruders can vary enormously, even among workers within the same colony. This is usually attributed to differences in the aggression thresholds of individuals or to workers having different roles within the colony. Recent evidence from the weaver ant Oecophylla smaragdina suggests that this does not tell the whole story. Here I propose a new model for nestmate recognition based on a vector template derived from both the individuals innate odour and the shared colony odour. This model accounts for the recent findings concerning weaver ants, and also provides an alternative explanation for why the level of aggression expressed by a colony decreases as the diversity within the colony increases, even when odour is well-mixed. The model makes additional predictions that are easily tested, and represents a significant advance in our conceptualisation of recognition systems.

Near-infrared spectroscopy identifies the colony and nest of origin of weaver ants, Oecophylla smaragdina

Abstract.The ability of social insects to differentiate between colony members and others is essential for the survival of the colony. It enables individuals to direct altruistic behavior towards colony mates, while protecting the colony from intruders. Colonies have a distinct chemical signature that facilitates colony-mate recognition. However, in large polydomous colonies, this signal is likely to be modified by factors unique to each nest. We demonstrate, using near-infrared spectroscopy (NIRS), that individual weaver ants, Oecophylla smaragdina, can be differentiated with respect to their colony and nest of origin. 76.5% of individuals from four colonies could be correctly assigned to their colony of origin; and 79.6% of individuals could be assigned to the correct nest (of two) within their colony. Despite the differences between nests within colonies, in most cases individuals from one nest were more similar to individuals from the other nest within the colony than they were to individuals from any nest outside the colony. Therefore, a distinctive colony identity is maintained despite differences between nests within colonies. We discuss the advantages of using NIRS as a faster and less expensive alternative to the analysis of cuticular hydrocarbons following extraction and identification with gas chromatography/mass spectroscopy.

Temporal variation in recognition cues: implications for the social life of weaver ants Oecophylla smaragdina

Recognition systems are involved in a range of evolutionary and biological processes, and animals use a variety of visual, auditory, tactile and olfactory cues to determine the status of others. The use of chemical cues is widespread, occurring among mammals, fish, reptiles and birds, but particularly among insects. Yet chemical cues may be influenced by diet and environment, and can change over time, potentially limiting their reliability as recognition cues. Nevertheless, they play a key role in colonymate recognition among social insects. We created colony isolates from large multinest colonies of weaver ants and asked (1) whether colony spectral profiles (determined using near-infrared spectroscopy) changed over time, (2) whether spectral profiles of colony isolates diverged from those of original colonies, and (3) whether the behaviour of original colonies towards colony isolates changed over time. Although we detected changes in the spectral profile of original colonies and colony isolates, they did not diverge significantly from each other. As far as we are aware, this is the first time that such parallel changes in colony odour have been observed. Aggression towards individuals from colony isolates did not increase, although levels of trophallaxis did. This demonstrates that colonymate recognition among weaver ants was unimpaired by temporal variation in recognition cues. We discuss the characteristics of weaver ants that might give rise to this system. We also discuss the implications for other organisms when, for example, ontogenetic changes in the expression of individual cues may hamper their usefulness as kin recognition cues.

Foraging behaviour of the Common Myna (Acridotheres tristis) in relation to vigilance and group size.

Abstract Foraging individuals allocate time to foraging behaviour or anti-predator vigilance, but rarely both at the same time. If we assume that foraging rate (that is, the number of foraging attempts per minute) decreases as a function of time spent vigilant, an individual can directly increase food intake by reducing time spent vigilant. Alternatively, it may increase food intake by increasing foraging effort, that is, making more foraging attempts in the time remaining after time devoted to anti-predator vigilance is excluded. I studied the foraging behaviour of the Common Myna (Acridotheres tristis) to determine foraging behaviour under different conditions of human disturbance (indirect predation risk), time of day and group size. The results showed that Mynas generally increased their food intake by increasing foraging effort, rather than decreasing vigilance behaviour. Although joining a group resulted in significantly lower levels of vigilance behaviour, it did not increase foraging rate or food intake. Despite being well adapted to the human environment, and having few natural predators, Mynas showed high levels of anti-predator vigilance, at least within the resource rich urban environment. These results are discussed in the light of possible management options to control this highly invasive bird.

Social Evolution: War of the Worms

The discovery of a non-reproductive soldier caste in a clonally reproducing trematode greatly extends the taxonomic distribution of eusociality and reaffirms the importance of relatedness in the evolution of reproductive altruism.

Nest and colony-specific spectra in the weaver ant Oecophylla smaragdina

Animals in social groups need to differentiate between group members and others. In very large groups, such as those formed by many ant species, it is not possible to rely on individually specific cues to identify colonymates. Instead, recognition must be based on the colony-specific cues. Individual ant colonies tend to have a specific chemical gestalt that is maintained by the continual exchange of chemicals between workers. In very large polydomous colonies, the exchange of chemicals may be limited between nests within the colony, resulting in inter-nest variation in colony odour that might hinder identification of colonymates or conspecific intruders. We used near-infrared spectroscopy to explore variation in the chemical profile between and within colonies of the weaver ant Oecophylla smaragdina. We found that differences between colonies were reflected in the position, amplitude and width of spectral peaks, while differences between nests within colonies were reflected mainly in amplitude. Furthermore, in the context of colonymate recognition, the behaviour of the ants themselves was positively correlated with colony-specific spectral characteristics, rather than with nest-specific characteristics. Thus, colony spectra have features that are not obscured by intra-colonial variation and may potentially encode the chemical characteristics used by workers to identify colonymates.