Wasps: aggression evolved into tests of strength – 08/15/2023 – Science

Studying the natural history of wasps is a risky undertaking. Known for their aggressiveness, the insects can either fill the researcher with painful bites or leave the nest to start a new one elsewhere, making observation and data collection unfeasible.

These survival strategies, however, were factors that allowed this tribe of wasps, known as Epiponini, to evolve in different branches over the last 55 million years, giving rise to societies that are quite complex in terms of nest building, foraging strategies and, above all, social interactions.

Studies from the 1970s already showed that, in wasps, the old dominance hierarchy strategy, in which a queen is responsible for reproduction — aggressively preventing other females from laying eggs — was replaced by the coexistence of queens that do not compete for reproduction, but which are eliminated by workers when they do not exhibit typical behaviors.

Through lunges, exhibitions and even bites, the workers submit the queens to their control. As a consequence, only the most capable breeders generate new individuals for the colony, ensuring the survival of these species.

The result of many hours of observation and a few bites, a study signed by Brazilian researchers was able to demonstrate that this reproductive strategy occurs in the entire Epiponini tribe. Previously, few species had been studied.

In addition, the study shows that the behaviors are not the same for all species, and those displayed by workers to test the queens evolved from more aggressive behaviors to less violent and more stereotyped ones.

The conclusions were published in the journal Cladistics by researchers from Unesp (Universidade Estadual Paulista) and USP (Universidade de São Paulo).

“We observe that in the most recent branches of the phylogeny [história evolutiva do grupo], workers and queens began to develop more complex and stereotyped behaviors, replacing those of biting and attacking. In addition, the queens developed a greater repertoire of behaviors to signal their potential, thus avoiding being eliminated from the colony”, explains Fernando Noll, professor at the Institute of Biosciences, Letters and Exact Sciences (Ibilce) at Unesp, in São José do Rio Preto , and study coordinator.

The work is part of two projects supported by FAPESP, “Taxonomic clearance of aculeate wasps: micro and macro-regional views of the neotropical fauna” and “Molecular phylogeny of Epiponini and the relationship between the basal genera (Hymenoptera, Vespidae)”. The first is conducted under the Biota-Fapesp Program.

In a previously published work, the group carried out the most complete phylogeny of the Epiponini tribe so far, which allowed advancing to results such as the current ones. Unlike other wasps and bees, wasps have more than one queen and workers control the production of eggs by these fertile females (read more at: agencia.fapesp.br/35495/).

Brazil and Costa Rica

Observing how wasps behave in their nests was the task of Laura Chavarría-Pizarro, at the time a doctoral student at the Faculty of Philosophy, Sciences and Letters of Ribeirão Preto (FFCLRP) at USP and with a scholarship from FAPESP.

It was necessary to make an opening in the protective envelope of the nest to observe the interior. Sometimes, this removed top was replaced by a red plastic, which the wasps cannot see and still allows them to be observed.

“Taking into account all the tests I did, in addition to opening the nests and marking the individuals with paint [para diferenciar rainhas de operárias], until they didn’t sting me too much. In addition, I wore a protective suit,” recalls Chavarría-Pizarro, currently a professor at the School of Biology at the Technological Institute of Costa Rica in Cartago.

Part of the field work was carried out in Costa Rica, the researcher’s home country, where it was possible to observe nests of six of the nine species studied (all Epiponini genera, except three).

In total, 15 colonies were analyzed, six in Brazil and nine in Costa Rica. 51 behaviors were documented, adding action and response and who performed (queen or worker) and responded, when it happened. The behaviors were monitored live or filmed for later analysis.

workers dance

One of the most important behaviors demonstrating the potentiality of queens as breeders is the bending display, in which the queen bends her abdomen towards the worker. Usually, it is a response to worker dance behavior (“dance of the worker”, in a free translation), where the worker vibrates her body continuously. In case the queen does not respond, she is removed from the colony.

The study showed that the bending display appeared 55 million years ago. Around 30 million years ago, however, a variation of this behavior appeared, called bending display 2. In species that appeared more recently, both types of bending display need to be performed to ensure the survival of the queen.

“Interestingly, 30 million years ago, the worker dance also appeared, which suggests that this behavior and the bending display 2 are related”, says Noll.

In older wasps, in which there is no worker dance, the workers’ test behaviors are more aggressive, such as dart (“invest with the head”) and bite (bite). These arose in the common ancestor of the Epiponini and were later replaced by the worker bee dance, suggesting that more aggressive behaviors gave way to stereotyped ones.

In the same period, queens began to exhibit a wider range of behaviors, suggesting greater complexity in their relationships. “These are more refined behaviors that probably have advantages over all that violence,” says Noll.

“Hornets are very important, as they are predators of other insects and help control species that we consider pests. Understanding their behavior and evolutionary strategies can allow for better coexistence with them and guarantee their survival”, concludes Chavarría-Pizarro.

The article “Behavioural Evolution of Neotropical Social Wasps (Vespidae: Polistinae): the Queen Selection Process” (“Behavioral evolution of neotropical social wasps (Vespidae: Polistinae): the process of selecting the queen”) can be read here.