Do gray wolves (Canis lupus) support pack mates during aggressive inter-pack interactions?
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For group-living mammals, social coordination increases success in everything from hunting and foraging (Crofoot and Wrangham in Mind the Gap, Springer, Berlin, 2010; Bailey et al. in Behav Ecol Sociobiol 67:1–17, 2013) to agonism (Mosser and Packer in Anim Behav 78:359–370, 2009; Wilson et al. in Anim Behav 83:277–291, 2012; Cassidy et al. in Behav Ecol 26:1352–1360, 2015). Cooperation is found in many species and, due to its low costs, likely is a determining factor in the evolution of living in social groups (Smith in Anim Behav 92:291–304, 2014). Beyond cooperation, many mammals perform costly behaviors for the benefit of group mates (e.g., parental care, food sharing, grooming). Altruism is considered the most extreme case of cooperation where the altruist increases the fitness of the recipient while decreasing its own fitness (Bell in Selection: the mechanism of evolution. Oxford University Press, Oxford 2008). Gray wolf life history requires intra-pack familiarity, communication, and cooperation in order to succeed in hunting (MacNulty et al. in Behav Ecol doi: 10.1093/beheco/arr159 2011) and protecting group resources (Stahler et al. in J Anim Ecol 82: 222–234, 2013; Cassidy et al. in Behav Ecol 26:1352–1360, 2015). Here, we report 121 territorial aggressive inter-pack interactions in Yellowstone National Park between 1 April 1995 and 1 April 2011 (>5300 days of observation) and examine each interaction where one wolf interferes when its pack mate is being attacked by a rival group. This behavior was recorded six times (17.6 % of interactions involving an attack) and often occurred between dyads of closely related individuals. We discuss this behavior as it relates to the evolution of cooperation, sociality, and altruism.
KeywordsAltruism Aggression Cooperation Canis lupus Empathy Fighting Kin selection Reciprocal altruism Support
We would like to thank Douglas Smith, Daniel Stahler, Erin Stahler, Matt Metz, Emily Almberg, Nathan Varley, Laurie Lyman, and numerous technicians for their assistance in field data collection and recording of details in the events described here. We also thank donors to the Yellowstone Wolf Project: Valerie Gates, Annie and Bob Graham, and Frank and Kay Yeager, as well as the U. S. National Park Service, and National Science Foundation (DEB-0,613,730 and DEB-1245373). Any use of trade, firm, or product names does not imply endorsement by the U.S. government.
Compliance with ethical standards
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the American Society of Mammalogists at Yellowstone National Park, WY (IUCUC Protocol Approval Number: IMR_YELL_Smith_Wolf_2012; National Park Service Scientific Research and Collecting Permit Number: YELL-2014-SCI-1818).
Conflict of interest
The authors declare they have no conflict of interest.
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