Abstract # 9:

Scheduled for Saturday, September 17, 2011 09:30 AM-09:45 AM: Session 3 (Salon F (Sixth Floor)) Oral Presentation


B. Kloc1, L. G. Rapaport1, M. Warneke2, J. Ballou3 and J. Mickelberg3
1Clemson University, Department of Biological Sciences, 132 Long Hall, Clemson, South Carolina 29632, USA, 2Chicago Zoological Society, 3Smithsonian Institution
     Parent-offspring conflict theory predicts that parents will bias their offspring sex ratio in favor of the sex that will either give the highest pay-off in terms of reproductive success or in favor of the least costly sex. In cooperative breeders, offspring may mitigate parental effort by helping parents to raise subsequent offspring. Among the marmosets and tamarins (the Callitrichidae) male offspring tend to invest more effort in caring for their younger siblings. We examined international studbook data for golden lion tamarins (Leontopithecus rosalia) and Goeldi’s monkeys (Callimico goeldii) from 1988-2008 to test predictions that birth sex ratio should be male-biased. Since golden lion tamarins typically give birth to twins while callimicos almost always have singletons, we predicted that a male-biased sex ratio would be evident only in the tamarins due to the need for male helpers to help raise offspring. A logistic regression, taking into account factors such as birth year, birth order, group size and parity, revealed a significant male sex-ratio bias in the tamarins (n=1498) but not in the callimicos (n=1621), as predicted. Neither males nor females were more likely to survive to the age of 18 months (when parental care is most important; p>0.05). However, parity did play a role in survival - offspring of multiparous mothers were more likely to survive to the age of 18 months.