The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Why does time spent gestating and lactating scale differently with body size across primates?


1Department of Biological studies, Simon Fraser University, 2Department of Archaeology, Simon Fraser University

Friday 4:15-4:30, Galleria North Add to calendar

Pregnancy (gestation) and nursing (lactation) are the two most costly phases of a female primate’s reproductive cycle. In the first part of this study, we show that the time spent on these processes scales differently with body size across primates. Time spent in both phases increases with body size, but small mother monkeys (e.g. pygmy marmosets) spend more than twice as long gestating thanlactating, while large mother apes (e.g. chimpanzees) do the reverse. This leads the allometric slope of gestation on body size to be much shallower than the allometric slope for lactation (n=83 species, phylogenetically-informed linear models, p<0.0001). In the second part of the study, we investigate why the allometric slope of gestation duration on body mass is so much lower than the allometric slope for lactation duration. We find intriguing comparative evidence that gestation duration across primates may be influenced by a general biomechanical (and therefore selective) constraint associated with locomotion: for a given body size, monkeys and apes that are more orthrograde (upright) in their posture are pregnant for longer than monkeys and apes that are more pronograde (move about on all fours). If skeletal biomechanics constrain gestation length and hence neonate size and developmental state, longer compensatory lactation durations might be expected. If corroborated, this would be a general, non-human-specific explanation for the relatively short gestation and long lactation durations of many large primates.

Supported by NSERC Canada and Simon Fraser University

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