Which came first, social dominance or big brains? Wasps may tell

There’s new evidence supporting the idea that bigger brains are better. A study of a tropical wasp suggests that the brainpower required to be dominant drives brain capacity.

University of Washington researchers have found that key processing regions in the brains of both males and females of one wasp species not only increased in size with age but were also associated with being dominant. The study also showed different patterns of brain development in males and females. Certain subregions were larger in males and others were larger in females. This matched expectations based on males’ greater use of vision and females’ greater reliance on their antennae.

UW researchers Sean O’Donnell and Yamile Molina found increased brain growth in areas of the insects’ brains called the mushroom bodies, which vaguely resemble the cerebrum in humans and other vertebrates. A mushroom body sits atop each hemisphere of the wasp brain. The mushroom bodies process input from the eyes and antennae, and are involved in learning and memory.

The social paper wasp that was studied, Mischocyttarus mastigorphorus, is unusual because males are dominant over females, a rarity among social insects, said O’Donnell, a UW associate professor of psychology. Most social insect societies – bees, ants and wasps – are predominantly female, with males short-lived and subordinate.

O’Donnell and Molina, a UW doctoral student, focused on a part of the insects’ mushroom body, called the calyx, where neural connections are made. While the overall size of the calyces did not differ between the males and females, specific subregions were larger in each sex. Males rely on vision when they leave the nest for mating opportunities, and the part of the calyx that receives visual input was larger. In contrast, most female interaction takes place on the nest, where tactile and odor senses are important and the part of the calyx that received input from the antennae was bigger among the females.

“When you are dominant among insects you get more food,” O’Donnell said, “and in this case it gives males more energy to leave the nest and mate. The fact that the males are dominant and long-lived makes this species interesting from a neurobiological standpoint. We think they have pretty sophisticated cognition compared to males of other wasp species.”

The researchers studied five wasp colonies in a tropical cloud forest near Monteverde, Costa Rica. They first marked all resident adult wasps on the nests and these individuals were excluded from further analyses. Newly emerged wasps then were captured and marked over the next several days and returned to their nest. Each colony then was observed in the morning and afternoon every three days over the course of more than a month. Behavioral data such as giving and receiving aggression were collected, as well as time spent on and off the nest. After this observation period, sections of the wasps’ brains were examined under a microscope.

Among the unanswered questions stemming from this study include how long these wasps live and how long these patterns of brain growth continued.

“We only followed them for 42 days, so we don’t know how long they live,” said O’Donnell. “We also don’t know if their brain development is similar to humans in terms of if and when they start to decline cognitively.

He said an exciting new idea – the social challenge hypothesis – suggests that large human brains evolved in response to the demands of complex social interactions. The wasp work extends this idea to individual brain variation.

“Do you get to be dominant because of a big brain or does being dominant drive brain size? That’s still an open question and we don’t know which comes first,” said O’Donnell. “This study suggests the high cognitive demands of being dominant drive brain capacity and supports the social brain hypothesis. The next step is to broaden the scope of the research by looking at more species of paper wasps. We are interested in how brains evolve in concert with social evolution. There is the intriguing possibility that there are similar patterns across wide spans of evolutionary time. My goal is to get a bigger sample of social wasp species and examine this.”

“You are looking at super-distant animals when you compare wasps and people. Yet there may be an interesting commonality between them. Increased brainpower may be part of being social, no matter who you are. What makes this exciting is we see some common patterns in how brains change as societies evolve. As we see changes in social complexity, there are changes in brain structure. If it is good for people it should be good for wolves, dolphins and paper wasps.”

The research, funded by the National Science Foundation, has been published in the online edition of the journal Developmental Neurobiology.

Source: University of Washington

Related stories:

What gets a female's attention -- at least a songbird's
Male songbirds produce a subtly different tune when they are courting a female than when they are singing on their own. Now, new research offers a window into the effect this has on females, showing they have an ear for detail. The finding provides insights not only into the intricacies of songbird attraction and devotion but also into the way in which the brain develops and responds to social cues, in birds – and humans.
Nature or nurture - why do some of us see red?
University of Manchester researchers are investigating why some people remain calm in the face of life's niggles, while others 'flip' with little provocation.

Research indicates testosterone could guard against eating disorders
Testosterone appears to protect people against eating disorders, providing further evidence that biological factors -- and not just social influences -- are linked to anorexia and bulimia, according to new research findings at Michigan State University.
Poor recognition of 'self' found in high functioning people with autism
Contrary to popular notions, people at the high end of the autism spectrum disorder continuum suffer most from an inability to model “self” rather than impaired ability to respond to others, said Baylor College of Medicine researchers in a report that appear in the journal Neuron.
When she's turned on, some of her genes turn off
When a female is attracted to a male, entire suites of genes in her brain turn on and off, show biologists from The University of Texas at Austin studying swordtail fish.
Pheromones identified that trigger aggression between male mice
A family of proteins commonly found in mouse urine is able to trigger fighting between male mice, a study in the Dec. 6, 2007, issue of Nature has found. The study, which is the first to identify protein pheromones responsible for the aggression response in mice, was funded in part by the National Institute on Deafness and Other Communication Disorders (NIDCD), one of the National Institutes of Health.
How our ancestors were like gorillas
Research published in this week’s Science journal shows that some of our closest extinct relatives had more in common with gorillas than previously thought. Dr Charles Lockwood, UCL Department of Anthropology and lead author of the study, said: “When we examined fossils from 1.5 to 2 million years ago we found that in one of our close relatives the males continued to grow well into adulthood, just as they do in gorillas. This resulted in a much bigger size difference between males and females than we see today.
Rejection sets off alarms for folks with low self-esteem
Few can tolerate such romantic or professional rebuffs as "It's not you, it's me" and "we regret to inform you that your application was not successful." But while a healthy dose of self-esteem can absorb the shock of rejection, poor self-esteem can trigger the primal fight-or-flight response, according to a new study from the University of California, Berkeley.

News discussion:

General Science news