Interview with the authors: High indirect fitness benefits for helpers across the nesting cycle in the tropical paper wasp Polistes canadensis

Understanding how complex social systems evolve is a long-standing and challenging goal of evolutionary biology. Many animal taxa are eusocial, where individuals forego reproduction in order to help raise young produced by another member their group. This behavior only makes sense if there are potential benefits – either direct or indirect – to the helpers. The genus of paper wasps Polistes is commonly used as a model system for studying sociality, however most of the research on this group has been conducted in temperate ecosystems, whereas relatively little is known about their behavior in tropical ecosystems where the genus likely originated. Does our understanding of how direct and indirect benefits contribute to the evolution of complex social systems depend on the environment where we conduct the research? Below, we go behind the scenes with Emily Bell and Robin Southon on their latest paper in Molecular Ecology to find out.

Link to the study: https://onlinelibrary.wiley.com/doi/10.1111/mec.15137

Polistes canadensis nest. Photo by RJ Southon.

What led to your interest in this topic / what was the motivation for this study? 
Wasps provide a fascinating insight into the evolution of sociality; among them you can find various levels of social complexity ranging from solitary to highly eusocial. Many studies have focused on the emerging model organism Polistes dominula. An interesting aspect of this wasp’s behaviour is that female ‘foundresses’ often form new nests in the spring with unrelated individuals – they help even though reproductive skew is monopolised by a single female. However, this is unlikely to be true in tropical species. Tropical Polistes do not experience an overwinter break in the colony cycle, and highly related foundresses may form new nests together directly from their previous natal nest. We wanted to highlight that although Polistes species share many traits, such as high reproductive skew, fitness payoffs for nonreproductive foundresses in temperate and tropical species are unlikely to be equivalent. This is an important consideration in making conclusions about the evolution of group living within the genus – Robin Southon

https://onlinelibrary.wiley.com/doi/10.1111/mec.15137

What difficulties did you run into along the way? 
With most field work it comes down to logistical issues. Along the Panama Canal are many ‘wasp havens’ – abandoned buildings containing a high density of nests. Which is great, unless you happen to live on the other side of the canal to your field site. There is one bridge that crosses the canal near our site, which is only accessible when boats are not passing through the nearby lock. This takes many hours for giant container ships! We’d spot ships approaching from afar and try to beat them to the lock in time to cross. Although if we missed our chance, at least all our datasheets were processed and backed up in the downtime – Robin Southon

Beating a container ship to the lock. Photo by EF Bell.

What is the biggest or most surprising finding from this study? 
In large established nests a reproductive monopoly is held by one queen. Our SNP and microsatellite pedigree analyses of post-emergence nests revealed in nearly all nests brood belonged to a single queen. Control over reproduction in Polistes is maintained primarily through physical aggression, and in the case of small temperate nests there is relatively few nestmates to dominate. However, nests of the tropical Polistes canadensis can reach 200+ in membership. It seems unlikely the queen could physically aggress that many wasps in a network! It would be interesting to see what other mechanisms may be at play, such as vibrational or odour signalling – Robin Southon

Moving forward, what are the next steps for this research?
We have established that there are differences in founding group structure between Polistes from different environments, but it’s rather simplistic to look at such differences as tropical vs temperate. There will be exceptions in both environments, for example montane ecosystems. The next step should look at what exactly is it about these environments that influence founding behaviour. Studying wasps in subtropical climates is likely to be key, especially in looking at species that have distributions which transition through tropical, subtropical, and temperate regions – Robin Southon

What would your message be for students about to start their first research projects in this topic?
Do your background research before you start a new project – literature reviews are an invaluable learning experience. They act as a chance for you to explore your new field and come up with lots of ideas for where you may want to take your project over your studies. Wasps are an amazing organism to work with, fascinating life history and captivating to watch in the field. I would wholehearted recommend taking a chance to observe your species in their natural habitat, if that is possible. It will enable you to learn what techniques might work for your project and novel ways that you could implement techniques in the field – Emily Bell

What have you learned about science over the course of this project? 
Molecular work is never straight forwards, it takes time (lots of time) to perfect methodologies – problem solving is a key skill that will always help with this. Sharing troubleshooting ideas with your lab group and other experts in departments is a brilliant way to learn new ways to analyse data. Once you have got a technique that works it really is such a satisfying experience and so exciting to be able to explore your species in a totally new way
– Emily Bell

Describe the significance of this research for the general scientific community in one sentence.
Environment influences the membership composition of new groups, resulting in varied group genetic structure and fitness payoffs for nonreproductive helpers in Polistes paper wasps – Robin Southon

Citation
Robin J. Southon, Emily F. Bell, Peter Graystock, Christopher D. R. Wyatt, Andrew N. Radford, & Seirian Sumner (2019). High indirect fitness benefits for helpers across the nesting cycle in the tropical paper wasp Polistes canadensis. Molecular Ecology, 28(13), 3271-3284. https://onlinelibrary.wiley.com/doi/10.1111/mec.15137

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