Sexually dimorphic transitions revealed in the relationships of yearling rhesus monkeys following the birth of siblings |
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Authors: | S D Holman R W Goy |
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Institution: | (1) Wisconsin Regional Primate Research Center, 1220 Capitol Court, 53706 Madison, Wisconsin;(2) MRC Neuroendocrine Development and Behaviour Group, AFRC Institute of Animal Physiology, CB2 4AT Babraham, Cambridge, UK |
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Abstract: | We report here that in a large captive group of monkeys, Macaca mulatta,sudden sex-related changes occur in social interactions in one short phase of an infant’s development. Social interactions
of 1-year-old animals (males, N =12; females, N =8) 6 weeks before the birth of siblings were compared with interactions occurring 6 weeks after the birth. On the day of the
siblings’ birth, depression-like postures were seen in two yearling males (YMs); 10 YMs showed hyperactivity. In the postbirth
period, YMs refocused their attentions away from their mother and toward other, often unrelated members of the group. Although
YMs initiated disengagement of interactions with their mothers, there was evidence that mothers attempted to lessen this disengagement.
The YMs had close relationships with specific (“preferred”) male individuals. These relationships (particularly those with
adult males) became more pronounced following the birth of the sibling. The adult-male group also took an active role in maintaining
interactions with YMs. The preferred partners in the YM-other male relationship before the birth of the sibling were, however,
not always the same as those in the period after the birth. Dominance relationships and probably genetic factors determined
patterns of interaction between YMs and their preferred male partners. Among yearling females (YFs), no dramatic changes in
interactions with their mothers or with other group members were detected after their mothers gave birth. Relationships in
YF-mother and YF-other-individual pairs (especially when the other individual was kin) seemed to be consolidated during the
postbirth interval. There was little evidence of jealousy between the YFs and their younger siblings. Thus, sibling birth
acted as a stimulus for the occurrence of sexually dimorphic interactions in yearlings. We suggest that in natural environments,
social interactions in YFs promote relationships that will serve to integrate them into the matrilineal social structure,
whereas comparable behavior in YMs encourages relationships with males that they may emigrate with into, or meet again in,
nonnatal troops. |
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Keywords: | captiveMacaca mulatta juvenile relationships sibling birth sex differences social development |
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