Social interactions may well make animals smarter and more diverse, a new study of paper wasps suggests.
The study, “Evidence for a selective link between cooperation and individual recognition,” published Dec. 7 in Current Biology, offers behavioral evidence of an evolutionary link between the ability to recognize individuals and social cooperation.
Furthermore, genomic sequencing revealed that populations of wasps that recognized each other – and cooperated more – showed recent adaptations (positive selection) in areas of the genome associated with cognitive abilities such as learning, memory and vision.
The study focused on two distinct populations of paper wasps (Polistes fuscatus): A southern one from Louisiana where individuals are more uniform in appearance, and a northern one in Ithaca, where individuals have diverse color patterns on their faces. A series of experiments indicated that unlike southern counterparts, the northern population both recognized individuals and cooperated socially with some members over others.
“We can sequence their genomes and look for evidence of recent positive selection,” a sign of adaptation, said senior author Michael Sheehan, associate professor of neurobiology and behavior in the College of Agriculture and Life Sciences. James Tumulty, a former postdoctoral research in Sheehan’s lab, is the paper’s first author.
“The evidence for strong recent positive selection on cognition, learning and memory is much stronger in the northern populations compared to the southern populations,” Sheehan said.
The research team began by examining differences in cooperative behavior in populations from different latitudes, from south to north. In technical terms, the comparison is along a “cline”, which is a gradation in one or more characteristics within a species, especially between different populations. Observing nesting behaviors in the spring when females established nests, Tumulty, Sheehan and colleagues found that southern queens mostly remained solitary and established their own nests, but in the north, three or four females would inhabit a nest, with one taking over the role of queen and laying most of the eggs, and the others operating more like workers, engaged more in foraging.
While individuals from northern and southern populations are of the same species, they look very different. Southern paper wasps tend to have nearly identical red color patterns on their faces. The northern ones have distinctive black and yellow patterns.
“As you go further north, you find the individuals become more variable in their color patterning, such that roughly around the Carolinas, they start becoming substantially variable and continue to be more variable as you go further north,” Sheehan said. In the Ithaca population, every individual is pretty distinct. This result suggests that cooperation can favor diversity within populations.
Then, behavioral studies tested recognition abilities in both the Ithaca and Louisiana populations, two extremes along the cline. When paper wasps first meet, they often fight by snapping, biting and slapping. Over four days, a wasp would be introduced to a stranger, and their level of aggression was recorded. Over subsequent days, the wasp would be introduced to a second stranger, then back again with the wasp they had previously met, and finally with another stranger.
Wasps from the northern population were aggressive to strangers, but much less so to the wasp they had previously met two days earlier. “Individuals in the southern population treat everyone the same,” Sheehan said. “They don’t show any evidence of changing their behavior as a result of previously meeting a particular individual, which suggests they’re not recognizing them.”
In another experiment, they housed groups of four wasps from each population in small enclosures over a two-week period. In each treatment, wasps engaged in a common wasp behavior, called huddling, essentially a wasp cuddle pile. The southern wasps huddled indiscriminately in bigger groups, but the northern wasps tended to be more selective, preferring to huddle selectively with preferred partners over others.
Though more study is needed, Sheehan reports that there’s some indication that wasps from the northern population have more stable nesting groups, whereas the southern wasps had high turnover of members when they occasionally made nests. The data suggests that being able to recognize individuals makes northern wasps more discerning and better able to manage their social profiles, whereas the more homogenous-looking southern wasps interact more indiscriminately and have less consistent, cohesive social interactions, Sheehan said.
While a previous study in Sheehan’s lab revealed evidence of positive selection in the cognitive abilities within the northern population, this paper found genomes from southern wasps showed much weaker selection in these same areas.
Co-authors include current and former Sheehan lab members Sara Miller, Christopher Jernigan, Andrew Legan, Floria Uy, Regan Staudenraus ‘21 and Sierra Vincent ’21; Steven Van Belleghem at Ku Leuven, Belgium; Hannah Weller at Brown University; Timothy Polnaszek at Belmont Abbey College; and Alexander Walton at Iowa State University.
The study was funded by the National Science Foundation and the National Institutes of Health. Read the story in the Cornell Chronicle.