The winner takes it all, the loser standing small!

A blog post highlighting the article written by Bang and Gadagkar in Insectes Sociaux

Written by Alok Bang

Remember the song by ABBA, ‘The winner takes it all’? In a nutshell, the fate of the dejected lover ABBA portrays can be extended to any conflict. Winners keep winning, and monopolise resources and opportunities. Losers keep losing and forego everything. Or, do they really?

But before coming to that, let’s discuss conflict in animal societies. Why is conflict of utmost interest and importance? For the simple reason, that it is omnipresent. Think of societies most harmonious and in unison, such as those of paper wasps, honey bees, ants and termites – where tens to hundreds and sometimes millions of individuals live and work together – are strewn with conflict. Individuals in these seemingly cooperative societies fight with each other often, over food, mates, territories and other opportunities. Who wins and who loses, thus, has a direct impact on an individual’s survival and reproduction, thereby affecting its evolutionary fitness.

Classically, researchers have focussed on role of individual characteristics such as age, size, weight, hormones and genes, in making winners and losers. While this approach has been important, it has excluded the role an individual’s social environment might play. Environment may influence fighting behaviour, fighting abilities, strength, and finally self-assessment of one’s strength, but this has been largely ignored.

Take the case of self-assessment of one’s fighting ability. When individuals fight, are they winning or losing merely based on their strengths, or does self-assessment of strength influence the outcome of a contest? Human history is laden with examples of an underdog, who is physically average or even weak, defeating a stronger opponent, because of a heightened perception of her strength. Similarly, a strong individual is known to lose a contest if she has a diminished self-assessment of her strength. Self-assessment can thus be influential – as much if not more – than the actual strength, in deciding the outcome of a fight.

In the past two decades, the phenomenon of winner-loser effects have come to the forefront of such enquiries into external determinants of fighting abilities and contest outcome. Simply put, they refer to an increased probability of winning or losing a contest based on prior experience of winning or losing, respectively, even if everything else is randomised. A prior experience of winning may enhance and a prior experience of losing may diminish an individual’s perception of its own fighting ability; thereby, affecting the contest outcome. Such studies have been mostly performed in vertebrates and research on the role the environment plays in conflict outcome in invertebrates is severely lacking.


A typical Ropalidia marginata colony. R. marginata is found abundantly in peninsular India. Photo credit: Thresiamma Varghese.

In the first study of its kind that investigated the role of prior experience on current contest outcome in a eusocial species, we chose the primitively eusocial Indian paper wasp, Ropalidia marginata as the model system. To control for a wasp’s environmental experience, the focal individuals to be included in the experiments had to be devoid of any prior fighting related experience. This was achieved by bringing adult-less colonies of R. marginata into a controlled environment, keeping thorough census records of all individuals being born on a colony, and isolating these individuals as soon as they were born.

The other important step was the method of choosing focal individuals for winner and loser effect experiments. We achieved random-selection by giving pre-decided contest outcomes to random focal individuals in the first contest, independent of their intrinsic strengths. We chose this method because these experiments aim to investigate the effect of experience, and not strength, on the contest outcome.


A lone R. marginata female. R. marginata females, like in many other paper wasp societies, can found new colonies individually as well as in a group. Photo credit: Alok Bang

In experiments performed to investigate winner effects, a pre-decided winning experience was given to a random focal individual by pairing it with an extremely weak individual (termed habitual loser) of the population. This ensured that the pool of focal individuals used for testing winner effects did not include only strong individuals, but included individuals with a wide range of intrinsic strengths. Similarly, in experiments to investigate loser effects, a pre-decided losing experience was given to a random focal individual by pairing it with an extremely strong individual (termed habitual winner) of the population. This, in turn, ensured that the pool of focal individuals used for testing loser effects did not have only weak individuals, but included individuals with a wide range of intrinsic strengths. The focal individuals with such pre-decided contests were then paired with a random naive individual in the second contest.


R. marginata females engaged in a dominance-subordinate interaction. The behaviour displayed here is called ‘sit over’, where the dominant individual sits over the subordinate individual and renders her immobile. Fights such as these are quite common in R. marginata. This helps to establish a dominance hierarchy between individuals, and has important implication on survival and reproduction of individuals, and work regulation in the colony. Photo credit: Alok Bang.

Each experiment thus consisted of a first contest between a focal individual and a habitual loser/winner, giving it a pre-decided contest that occurred for one hour, followed by a 45-minute gap, which then was followed by a second contest of one-hour between the focal individual with a random naïve opponent. In such an experimental set-up, a second successive win (or loss), in significantly more than half the cases, would indicate that the individuals’ self-perception was impacted due to their prior experience. During all these contests, dominance-subordinate interactions between individuals were observed, and winners and losers of the contests were declared. All experiments were carried out  blind.

We indeed found that there was a significantly high number of pairs in which a win was followed by a second win, and a significantly high number of pairs in which a loss was followed by a second loss, indicating that both winner and loser effects are present in the Indian paper wasp, R. marginata.

Winner effects may evolve due to advantages associated with winning, but why would a species evolve loser effects? Moreover, how do two such apparently opposing phenomena concurrently exist in a species? Winner and loser effects are most likely independent or even interdependent effects. If self-assessment of winners and losers are independently advantageous, these effects would exert independent feedback loops on individuals and co-exist. For example, winning a contest may allow winners a higher access to resources and mates, thus developing and reinforcing winner effects. Losing a contest on the other hand, though seemingly disadvantageous, may allow individuals to forego costs associated with fighting such as injuries, exhaustion and death. If the benefits of avoiding these costs are much higher than the benefits acquired from winning, loser effects will simultaneously develop in the population.

Here we show that wasp behaviour is not only governed by their own internal constitution, but to a considerable extent by their surroundings. The role of external and social determinants of behaviour balances the hitherto unduly skewed importance given to individual characteristics.

Finally, is the Indian paper wasp R. marginata a unique and only eusocial species that displays winner-loser effects? It is definitely the first eusocial species, but we believe it will not be the last. The uniqueness of R. marginata in this regard may have less to do with ecology of the species, and more due to lack of such investigations in other social insects. This study should steer efforts towards finding the presence, extent and longevity of winner-loser effects in other social species. A comparative approach to studying proximate and ultimate factors governing winner and loser effects in social species will be key to understanding sociobiology of group living animals.

Facultative slave-making ants tolerate alien slaves but not their masters

A blog post highlighting the article written by Włodarczyk in Insectes Sociaux

Written by Tomasz Włodarczyk

Many ant species in nature are closely associated with other ant species. The closest form of such an association is called a mixed colony where ants of both species inhabit common nest, share food and raise their brood side by side. Mixed colonies arise as a result of social parasitism when one species exploits the labor of the other, such as in slave-making ant species. Slave-maker ants raid the nests of the host species, steal the pupae and bring them back to their home nests. Newly-emerged individuals integrate into the parasite’s society and perform all domestic duties.

In the lab, we can also create mixed colonies using species that would never form such an association in nature. The species don’t even have to co-exist geographically. This is because ants learn (imprint) colony odor after eclosion from pupae and use it as a template for subsequent nestmate recognition. Thus, by putting together callow ants of different species we can create a mixed colony of individuals that have imprinted on the odor of each other.

As a part of my PhD project I investigated the recognition behavior of ants using a colony of the facultative slave-making ant species, Formica sanguinea. By supplying them with pupae of Formica polyctena or F. rufa -which soon emerged- I formed mixed colonies (Włodarczyk 2012, Włodarczyk and Szczepaniak 2014). These experiments were inspired by the studies conducted by Wojciech Czechowski (1994) whose results suggested that F. sanguinea ants acquire their recognition signature form their slaves, as in the obligate slave-making species Polyergus samurai (Yamaoka 1990).


Formica sanguinea is a facultative slave-making species enslaving ants from the subgenus Serviformica. Here, a colony with black F. fusca slaves has been excavated.

Later I became curious about how things look in the case of F. sanguinea colonies containing the most frequently used slave species, F. fusca. Results of chemical studies revealed that odor of F. sanguinea ants is quite different from that of its host species (Martin et al. 2008, Włodarczyk and Szczepaniak in prep.). Moreover, we found that enslaved F. fusca ants develop a chemical recognition signature which is intermediate between that of their parasite and ants from free-living colonies (Włodarczyk and Szczepaniak in prep.). This raised the question about how recognition cue diversity in F. sanguinea colonies affect the recognition abilities of ants. Even more interesting was whether there are differences in the recognition abilities between F. sanguinea and F. fusca ants given that the parasite is the only party to be under selective pressure to live in such a condition.

I collected eight queenright F. sanguinea colonies containing F. fusca slaves and maintained in the the laboratory. The slave-making F. sanguinea ants and their slaves were exposed on a Petri dish to anesthetized ants from alien colonies. I measured the number of aggressive behaviors in various encounter combinations. I showed that F. sanguinea ants are able to discriminate other individuals from the same species from alien colonies towards which they exhibit aggressive behavior. However, slaves from alien colonies were generally tolerated. This result supports the hypothesis that F. sanguinea ants are intrinsically tolerant to individuals whose odor indicates that they are slaves. Otherwise slave-making ants might accidentally attack their own slaves, which possess a recognition signature that deviates from that of the other slaves. This situation would arise when slaves from new source colony appear in the slave-maker’s society.

The other result was that slaves (F. fusca) are poor at discriminating slave-making ants and slaves from alien colonies and do not exhibit an overt aggression toward them. This could be explained by the high within-colony recognition cue diversity that hampers formation of an accurate template during colony’s odor learning phase. This is intuitive explanation since it might be hard to recognize an object of a given class when this class is relatively heterogeneous. Thus, there is no recognition barrier for F. sanguinea ants to take over slaves from alien colonies. However, such a phenomenon has not been recorded for F. sanguinea ants. Therefore we can hypothesize that intraspecific raids play at best very limited role as a way of slave gaining.


Formica fusca slaves showing aggressive behavior towards an anesthetized conspecific ant.

Moreover, I conducted an experiment in which slaves and slave-makers were reared separately. After about 2-month period, ex-slaves elicited aggression in ants from stock colonies (both in slave-makers and in slaves). Conversely, slave-makers separated from slaves were still treated as nestmates. This result suggests that F. sanguinea exert a strong impact on the odor of F. fusca ants, possibly by the transfer of recognition cues during food exchange.

The results of my study highlight that selective pressures associated with different life histories can lead to differences in recognition systems between social insect species.



Czechowski W (1994) Impact of atypical slaves on intraspecific relations in Formica sanguinea Latr. (Hymenoptera, Formicidae). Bull Pol Acad Sci 42(4):345–350

Martin SJ, Helantera H, Drijfhout FP (2008) Evolution of species-specific cuticular hydrocarbon patterns in Formica ants. Biol J Linn Soc 95:131–140

Włodarczyk, T (2012) Recognition of individuals from mixed colony by Formica sanguinea and Formica polyctena ants. J Insect Behav 25: 105–113

Włodarczyk T, Szczepaniak L (2014) Incomplete homogenization of chemical recognition labels between Formica sanguinea and Formica rufa ants living in a mixed colony. J Insect Sci 14:214

Yamaoka R (1990) Chemical approach to understanding interactions among organisms. Physiol Ecol Japan 27:31–52