Growth and Development in Wild Owl Monkeys (Aotus azarai) of Argentina
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Life history predicts that in sexually dimorphic species in which males are the larger sex, males should reach sexual maturity later than females (or vice versa if females are the larger sex). The corresponding prediction that in sexually monomorphic species maturational rates will differ little between the sexes has rarely been tested. We report here sex differences in growth and development to adulthood for 70 female and 69 male wild owl monkeys (Aotus azarai). In addition, using evidence from natal dispersal and first reproduction (mean: 74 mo) for 7 individuals of known age, we assigned ages to categories: infant, 0–6 mo; juvenile, 6.1–24 mo; subadult, 24.1–48 mo; adult >48 mo. We compared von Bertalanffy growth curves and growth rates derived from linear piecewise regressions for juvenile and subadult females and males. Growth rates did not differ between the sexes, although juvenile females were slightly longer than males. Females reached maximum maxillary canine height at ca. 2 yr, about a year earlier than males, and females’ maxillary canines were shorter than males’. Thus apart from canine eruption and possibly crown–rump length, the development of Azara’s owl monkeys conforms to the prediction by life history that in monomorphic species the sexes should develop at similar paces.
KeywordsFirst reproduction Growth rates Ontogeny Sexual monomorphism von Bertalanffy growth model
We thank all the students, volunteers, and assistants who helped us during the capture and examination of subjects. We also thank Mr. F. Middleton, Manager of Estancia Guaycolec, and Ing. C. Cimino (Bellamar Estancias) for the continued support of the Owl Monkey Project. The Ministerio de la Producción, Subsecretaría de Ecología and Recursos Naturales, and Dirección de Fauna from Formosa Province provided permits to conduct the research. The Owl Monkey Project has had continued approval for all research presented here by the Formosa Province Council of Veterinarian Doctors, the Directorate of Wildlife, the Subsecretary of Ecology and Natural Resources, and the Ministry of Production. At the national level, the procedures were approved by the National Wildlife Directorate in Argentina and by the IACUC committees of the Zoological Society of San Diego (2000–2005) and of the University of Pennsylvania (2006–2010). We thank Claudia Valeggia, Susan Anton, Joanna Setchell, and anonymous reviewers for useful comments on earlier drafts. We thank Uwe Liggers and Derek Ogle for help with the FSA package. E. Fernandez-Duque gratefully acknowledges the financial support during all these years from the Wenner-Gren Foundation, the L.S.B. Leakey Foundation, the National Geographic Society, the National Science Foundation (BCS- 0621020), the University of Pennsylvania Research Foundation, and the Zoological Society of San Diego. M. Huck was funded by the Deutsche Forschungsgemeinschaft (HU 1746/2-1).
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