The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


The effect of sibling birth on parent-offspring relationships in lemurs

AMY L. SCHREIER1, NANCY L. BARRICKMAN2 and KEMP KNOTT3.

1Biology Department, Regis University, 2Anthropology Department, University of Waterloo, 3Evolutionary Anthropology Department, Duke University

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Parent-offspring conflict theory proposes that parents will redirect investment to subsequent offspring when the benefit of investing in the current offspring is less than that of investing in new offspring. The current offspring, however, seeks continued investment from the parent, and the theory thus predicts conflict between the parent and offspring when new siblings are born. To date, empirical support for parent-offspring conflict theory is limited.

We examined parent-offspring conflict in a group of ring-tailed lemurs (Lemur catta) at the Duke Lemur Center from October 2010-February 2012. In October 2010 the group consisted of three recently weaned juveniles and three adults (including both the mother and father of each juvenile). In March 2011 three infants were born, such that each juvenile had at least one new sibling. We predicted that mother-juvenile affiliative behavior would decrease after sibling birth while aggressive behavior would increase. We conducted scan sampling at 2-minute intervals, recording the activity and nearest neighbor of each juvenile and adult, for 108 total hours of observation.

Juveniles were nearest neighbor with their mother significantly more before sibling birth than after their birth. Similarly, juveniles huddled with their mother significantly more before sibling birth than after. While overall aggression was rare, all instances of parent-juvenile aggression occured after the birth of new siblings. Before sibling birth juveniles spent significantly more time with their mother than father, while after they spent equal amounts of time with each parent. These results suggest a shift in maternal investment coinciding with sibling birth.

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