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Aggression genes go way back, scientists say

Feb. 10, 2014
Courtesy of Penn State University
and World Science staff

Aggression-causing genes ap­peared early in an­i­mal ev­o­lu­tion and have kept their roles for mil­lions of years, even though an­i­mal ag­gres­sion to­day varies wide­ly, re­search­ers say.

If these genes keep their roles in dif­fer­ent an­i­mals and con­texts, then re­search an­i­mals such as bees and mice might shed light on the bi­o­log­i­cal ba­sis of ag­gres­sion in all an­i­mals, in­clud­ing peo­ple, the sci­en­tists said.

Polistes fuscatus co­lo­ny-found­ing queens fight­ing in a lab­or­a­tory dish. (Cour­tesy of Penn State U.)


Al­though ag­gres­sion varies from from ter­ri­to­rial fight­ing to set­ting up so­cial hi­er­ar­chies, many of the genes in­volved are the same or re­lat­ed, ac­cord­ing to re­search­ers from Io­wa State Uni­vers­ity, Penn State and Grand Val­ley State Uni­vers­ity in Mich­i­gan.

“This is one of the first in­ves­ti­ga­t­ions to uti­lize large da­tasets con­sist­ing of thou­sands of dif­fer­ent genes to ask wheth­er there are shared genes re­lat­ing to si­m­i­lar forms of be­hav­ior across a very wide range of an­i­mals,” said Amy Toth, a bi­ol­o­gist at Io­wa State. 

“We looked at ag­gres­sive be­hav­ior in wasps, bees, fruit flies and mice and found a few genes that are con­sist­ently as­so­ci­at­ed with ag­gres­sion. This sug­gests that even af­ter hun­dreds of mil­lions of years of ev­o­lu­tion, some genes may re­tain their an­ces­tral roles in si­m­i­lar forms of be­hav­ior.”

The team in­ves­t­i­gated the ac­tiva­t­ion of ag­gres­sion genes in the brains and ovaries of pa­per wasps, Po­lis­tes met­ri­cus. They looked at wasps be­long­ing to dif­fer­ent “castes.” The in­di­vid­u­als dis­played widely dif­fer­ent lev­els of re­pro­duc­tive dom­i­nance and, linked to that, ag­gres­sive be­hav­ior. The team then com­pared the wasp re­sults to gene acti­va­tion da­ta al­ready avail­a­ble in hon­ey­bees, fruit flies and mice.

“We found that in wasps, which are prim­i­tively so­cial in­sects, ag­gres­sion genes con­trol the es­tab­lish­ment of an in­di­vid­u­al’s dom­i­nance over a group,” said Chris­ti­na Gro­zin­ger, di­rec­tor of the Cen­ter for Pol­li­na­tor Re­search at Penn State. 

“In con­trast, in hon­ey bees, which are ad­vanced so­cial in­sects, ag­gres­sion genes con­trol al­tru­is­tic de­fen­sive be­hav­ior—for ex­am­ple, when guard bees sting a pred­a­tor or even a bee­keep­er, and die in the pro­cess. In sol­i­tary spe­cies, like fruit flies and mice, the same set of ag­gres­sion genes con­trols fight­ing be­tween males over ter­ri­to­ry. So the same genes are in­volved in ag­gres­sion across spe­cies, but are now be­ing used in dif­fer­ent ways.”

Ac­cord­ing to Grozinger, the re­sults sug­gest that mod­el or­gan­isms—such as bees and mice—can be used to study ag­gres­sion in hu­mans be­cause they share some of the same genes that reg­u­late ag­gres­sion be­hav­iors, even if those be­hav­iors are now quite dif­fer­ent.

In ad­di­tion to learn­ing that ag­gres­sion genes are shared among or­gan­isms, the team al­so found that these genes are ex­tremely sen­si­tive to the ex­ter­nal en­vi­ron­ment.

“We found that the most im­por­tant in­flu­ence on ex­pres­sion of genes in the brains of pa­per wasps was ex­ter­nal fac­tors, such as the sea­son and how large the col­o­ny was at the time,” Toth said. “This in­di­cates the im­por­tant role of ex­ter­nal cues in shap­ing the mo­lec­u­lar pro­cesses that reg­u­late be­hav­ior.”

The re­sults, which ap­pear Feb. 10 in the jour­nal BMC Ge­nom­ics, shed light on the de­bate be­tween na­ture and nur­ture, ac­cord­ing to Gro­zin­ger. “Our re­sults show that the ex­ter­nal en­vi­ron­ment plays a much great­er role in reg­u­lat­ing ex­pres­sion of genes in the brain, which ul­ti­mately reg­u­lates be­hav­ior, than phys­i­ol­o­gy. This is very sur­pris­ing.”


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Aggression-causing genes appeared early in animal evolution and have kept their roles for millions of years, even though animal aggression today varies widely, researchers say. If these genes keep their roles in different animals and contexts, then research animals such as bees and mice might shed light on the biological basis of aggression in all animals, including people, the researchers said. Although aggression varies from from territorial fighting to setting up social hierarchies many of the genes involved are the same or related, according to researchers from Iowa State University, Penn State and Grand Valley State University in Michigan. “This is one of the first investigations to utilize large datasets consisting of thousands of different genes to ask whether there are shared genes relating to similar forms of behavior across a very wide range of animals,” said Amy Toth, a biologist at Iowa State. “We looked at aggressive behavior in wasps, bees, fruit flies and mice and found a few genes that are consistently associated with aggression. This suggests that even after hundreds of millions of years of evolution, some genes may retain their ancestral roles in similar forms of behavior, like aggression.” The team investigated the activation of aggression genes in the brains and ovaries of paper wasps, Polistes metricus. They looked at wasps belonging to different “castes” including dominant colony-founding queens, subordinate colony-founding queens, established queens, dominant workers and subordinate workers. These individuals displayed widely different levels of reproductive dominance and, linked to that, aggressive behavior. The team then compared the wasp results to gene expression data already available in honeybees, fruit flies and mice. “We found that in wasps, which are primitively social insects, aggression genes control the establishment of an individual’s dominance over a group,” said Christina Grozinger, professor of entomology and director of the Center for Pollinator Research, Penn State. “In contrast, in honey bees, which are advanced social insects, aggression genes control altruistic defensive behavior—for example, when guard bees sting a predator or even a beekeeper, and die in the process. In solitary species, like fruit flies and mice, the same set of aggression genes controls fighting between males over territory. So the same genes are involved in aggression across species, but are now being used in different ways by different organisms.” According to Grozinger, the results suggest that model organisms—such as bees and mice—can be used to study aggression in humans because they share some of the same genes that regulate aggression behaviors, even if those behaviors are now quite different. In addition to learning that aggression genes are shared among organisms, the team also found that these genes are extremely sensitive to the external environment. “We found that the most important influence on expression of genes in the brains of paper wasps was external factors, such as the season and how large the colony was at the time,” Toth said. “This indicates the important role of external cues in shaping the molecular processes that regulate behavior.” The results, which appear Feb. 10 in the journal BMC Genomics, shed light on the debate between nature and nurture, according to Grozinger. “Everyone agrees that both nature—including genes and physiology—and nurture—including diet, environment and social interactions—contribute to the likelihood that an individual will behave in a certain way or develop a disease,” Grozinger said. “But our results show that the external environment plays a much greater role in regulating expression of genes in the brain, which ultimately regulates behavior, than physiology. This is very surprising.”