Children of divorce: effects of adult replacements on previous offspring in Argentinean owl monkeys

According to the Evolutionary Theory of the Family, the replacement of one pair-member by an intruder may have profound consequences for the existing offspring. Step-parents are expected to provide less care towards unrelated immatures than to genetic offspring, unless caring also serves as a mating strategy. Furthermore, because an intruder will be a potential mate for opposite-sexed offspring, relationships between offspring and same-sex parents are predicted to deteriorate. To test these predictions, we studied an Azara’s owl monkey (Aotus azarai) population in Argentina exhibiting serial monogamy and biparental care. Since 1997, we have collected demographic data from ca. 25 groups and inter-individual distance data from ca. 150 marked individuals. First, we compared survival and dispersal age of immatures in groups with and without replacements to investigate whether parental care serves as a mating strategy. Second, we compared sexspecific age at dispersal for groups with replacement of opposite-sex parents, same-sex parents, or in stable groups in order to test whether relationships between offspring and same-sex parents deteriorated after the replacement of the other parent. Survival and dispersal ages were not negatively associated with replacements, suggesting that male care might serve, at least partly, as a mating strategy. The time lag between a replacement and the subsequent dispersal of female offspring was greater if the intruder was a male, while the offspring and same-sex parents were less often nearest neighbors after replacements than before. Our results suggest that family disruption through the replacement of a parent is not associated with decreased offspring survival or early dispersion of juveniles, but deteriorates parent–offspring relationships.

According to the Evolutionary Theory of the
Family, the replacement of one pair-member by an intruder
may have profound consequences for the existing offspring.
Step-parents are expected to provide less care towards unrelated
immatures than to genetic offspring, unless caring
also serves as a mating strategy. Furthermore, because an
intruder will be a potential mate for opposite-sexed offspring,
relationships between offspring and same-sex
parents are predicted to deteriorate. To test these predictions,
we studied an Azara’s owl monkey (Aotus azarai) population
in Argentina exhibiting serial monogamy and biparental
care. Since 1997, we have collected demographic
data from ca. 25 groups and inter-individual distance data
from ca. 150 marked individuals. First, we compared survival
and dispersal age of immatures in groups with and
without replacements to investigate whether parental care
serves as a mating strategy. Second, we compared sexspecific
age at dispersal for groups with replacement of
opposite-sex parents, same-sex parents, or in stable groups
in order to test whether relationships between offspring and
same-sex parents deteriorated after the replacement of the
other parent. Survival and dispersal ages were not negatively
associated with replacements, suggesting that male care
might serve, at least partly, as a mating strategy. The time
lag between a replacement and the subsequent dispersal of
female offspring was greater if the intruder was a male,
while the offspring and same-sex parents were less often
nearest neighbors after replacements than before. Our results
suggest that family disruption through the replacement of a
parent is not associated with decreased offspring survival or
early dispersion of juveniles, but deteriorates parent–offspring
relationships.

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