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.