Social modulation of testosterone levels in male black howlers (Alouatta pigra) |
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Authors: | Rangel-Negrín Ariadna Dias Pedro A D Chavira Roberto Canales-Espinosa Domingo |
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Institution: | a Departamento de Biología Animal, Universidad de Barcelona, Gran Via de les Corts Catalanes 585, Cp 08007 Barcelona, Spainb Instituto de Neuroetología, Universidad Veracruzana, Av. Dr. Castelazo Ayala S/N, col. Industrial Animas, Ap 566, Cp 91190 Xalapa, Mexicoc Departamento de Biología de la Reproducción, Instituto de Ciencias Médicas y Nutrición Salvador Zubirán, Vasco de Quiroga 15, Colonia Seccion XVI, Tlalpan Cp 14000, México D.F., Mexico |
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Abstract: | The influence of social factors on the modulation of male testosterone levels has been demonstrated among several vertebrate species. In addition to sexual activity, parental care and reproductive competition affect testosterone secretion. We examined variations in testosterone levels among male black howlers (Alouatta pigra) in various social contexts. Fecal samples were collected from nine males living in five different groups in the Mexican state of Campeche. The potential for intragroup and extragroup competition varied among the groups. The number of resident males living in the groups was the only variable that significantly explained variations in testosterone levels. Males living in unimale groups had higher testosterone levels; the highest testosterone levels were recorded for males that had experienced a shift from multimale to unimale group compositions. In this species, the probability of being challenged by extragroup males and evicted from the group during immigration events increases when males live in unimale groups. Therefore, our results suggest that male black howlers respond to competition for group membership by increasing their testosterone levels. In this context, testosterone secretion represents an anticipatory response to reproductive conflicts. Therefore, although males living in unimale groups have exclusive access to females, they face higher physiological costs associated with sustaining high testosterone levels for extended time periods. |
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Keywords: | Testosterone Alouatta pigra Reproductive challenges Group membership Number of males Campeche Reproductive competition |
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