The genome sequence of the leaf-cutter ant Atta cephalotes reveals insights into its obligate symbiotic lifestyle.

Leaf-cutter ants are one of the most important herbivorous insects in the Neotropics, harvesting vast quantities of fresh leaf material. The ants use leaves to cultivate a fungus that serves as the colony's primary food source. This obligate ant-fungus mutualism is one of the few occurrences of farming by non-humans and likely facilitated the formation of their massive colonies. Mature leaf-cutter ant colonies contain millions of workers ranging in size from small garden tenders to large soldiers, resulting in one of the most complex polymorphic caste systems within ants. To begin uncovering the genomic underpinnings of this system, we sequenced the genome of Atta cephalotes using 454 pyrosequencing. One prediction from this ant's lifestyle is that it has undergone genetic modifications that reflect its obligate dependence on the fungus for nutrients. Analysis of this genome sequence is consistent with this hypothesis, as we find evidence for reductions in genes related to nutrient acquisition. These include extensive reductions in serine proteases (which are likely unnecessary because proteolysis is not a primary mechanism used to process nutrients obtained from the fungus), a loss of genes involved in arginine biosynthesis (suggesting that this amino acid is obtained from the fungus), and the absence of a hexamerin (which sequesters amino acids during larval development in other insects). Following recent reports of genome sequences from other insects that engage in symbioses with beneficial microbes, the A. cephalotes genome provides new insights into the symbiotic lifestyle of this ant and advances our understanding of host-microbe symbioses.

The effect of unhealthy food and liking on stress reactivity.

In many individuals, stress appears to stimulate an increase in energy intake as well as a shift in food choice toward unhealthy food items or "comfort foods". Eating during stress is widely assumed to have anxiolytic properties, but there is little empirical support for this. The current two studies examined if either an unhealthy food item or a healthy food item could reduce stress reactivity and extended previous findings by examining whether participant liking contributes to any potential stress reduction. In the first experiment, participants rated baseline anxiety, were assigned to eat no food, carrots, or a candy bar, rated their anxiety a second time, and reported their liking of the assigned condition. The second experiment followed a similar procedure, except participants underwent a stressor before being asked to eat a food item. In addition, physiological measures of stress (salivary cortisol and α-amylase, and cardiovascular measures) were recorded. In both experiments, there was no effect of food on any measure of emotional or physiological stress. In contrast, participants who highly liked their condition exhibited a suppression of anxiety in both experiments and showed enhanced post-stress recovery of α-amylase. The anxiolytic effects of liking were not dependent on whether participants engaged in the healthy, unhealthy, or no food condition, which indicates that the self-perceived liking of a post-stress activity affects stress recovery more than the nutritional value. This has potential implications in how the population thinks about which activities to engage in to stimulate stress recovery.