Bigger brain linked to dominance

New evidence seems to support the idea that bigger brains are not only better, but also propel the drive for dominance.

Researchers studying the tropical wasp have found that key processing regions in the brains of both males and females not only increased in size with age but they were also associated with being dominant, Sciencedaily reported.

The study also showed different patterns of brain development in these genders. Certain sub regions 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.

Sean O'Donnell and Yamile Molina of the University of Washington 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 wasp under study, Mischocyttarus mastigorphorus, is unusual because males are dominant over females, a rarity among social insects, said O'Donnell.

Most social insect societies - bees, ants and wasps - are predominantly female, with males short-lived and subordinate.

O'Donnell and Molina focussed on a part of the insects' mushroom body, called the calyx, where neural connections are made. While their overall size did not differ between the males and females, specific sub regions 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 odour senses are important and the part of the calyx that received input from the antennae was bigger among the females.

"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.