Alpha male geladas who allowed subordinate competitors into their group had a longer tenure as leader, resulting in an average of three more offspring each during their lifetimes.
Two male gelada monkeys threaten an intruder while grooming with an infant. Credit: Clay Wilton
The findings, collected from data during a five-year period ending in January 2011 through the University of Michigan Gelada Research Project, were published in the Proceedings of The Royal Society.
The research was conducted by Noah Snyder-Mackler, then a graduate student in the Department of Psychology in Penn's School of Arts and Sciences. He collaborated with Thore Bergman, assistant professor of psychology at Michigan, and Susan Alberts, professor of biology at Duke.
Cooperation is surprisingly common among wild animals, the researchers said. While it makes evolutionary sense for animals to help their kin, it is harder to explain cases where competitors — especially unrelated adult males — join forces. This conundrum is particularly hard to explain because mating is generally a zero-sum game in which males can only reproduce by stealing mating opportunities from each other.
Why would an alpha male allow other males to be a part of his unit, if they will inevitably decrease the probability that he will pass on his own genes? The researchers felt there must be a reason since this kind of behavior is observed in many species."For example, in some species unrelated males will sometimes tolerate the presence of one another and, in rare cases, form bonds and even appear to cooperate," Snyder-Mackler said.
Even more tantalizing is evidence that the subordinate males that are allowed to mate stay around in the group for much longer.
"This suggests," Bergman said, "that the alpha males may allow the subordinate to reproduce as a 'staying incentive' for defending the group, a payment for their services."
While it is not yet clear that a willing exchange is occurring — subordinate males may simply "steal" some chances at reproduction — the evidence is strong that subordinates confer some benefit to the leader.
"These findings demonstrate a benefit of forming multi-male groups in a predominantly single-male system, an important step in the evolution of sociality among unrelated competitors," Bergman said.In studying wild geladas in the Simien Mountains National Park in Ethiopia, researchers identified the leader and follower males, noted the numbers of females in all units; tracked individuals involved in unit takeovers; and noted all new births. They used non-invasively collected genetic samples to conduct paternity analysis to determine the identities of the fathers.
Even though geladas primarily form single-male groups, researchers showed a benefit to forming multi-male groups. Multi-male units had fewer takeovers (a rate of 0.27) per year from other competitors and longer tenure (3.7 years as leader) compared with single-male units (0.35 takeovers per year and 2.86 years as leader.)
"Overall, this means that, just because animals appear to be in direct competition for a limited resource, they may still benefit from the relationship overall," Snyder-Mackler said.
Thus, cooperation can evolve among competitors through a variety of mechanisms. In the study, researchers chronicled how it can evolve in the context of reproductive sharing.
"More comparative research on other species will give us a better understanding of how and under what circumstances cooperation among unrelated individuals may have evolved," Snyder-Mackler said.
The research was funded by the National Science Foundation, Leakey Foundation and National Geographic Society.
Synder-Mackler is now a postdoctoral fellow at Duke.
Evan Lerner | EurekAlert!
Multi-year study finds 'hotspots' of ammonia over world's major agricultural areas
17.03.2017 | University of Maryland
Diabetes Drug May Improve Bone Fat-induced Defects of Fracture Healing
17.03.2017 | Deutsches Institut für Ernährungsforschung Potsdam-Rehbrücke
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
23.03.2017 | Life Sciences
23.03.2017 | Power and Electrical Engineering
23.03.2017 | Earth Sciences