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Female sociality and sexual conflict shape offspring survival in a Neotropical primate - PubMed

  • ️Sun Jan 01 2017

Female sociality and sexual conflict shape offspring survival in a Neotropical primate

Urs Kalbitzer et al. Proc Natl Acad Sci U S A. 2017.

Abstract

Most mammals live in social groups in which members form differentiated social relationships. Individuals may vary in their degree of sociality, and this variation can be associated with differential fitness. In some species, for example, female sociality has a positive effect on infant survival. However, investigations of such cases are still rare, and no previous study has considered how male infanticide might constrain effects of female sociality on infant survival. Infanticide is part of the male reproductive strategy in many mammals, and it has the potential to override, or even reverse, effects of female reproductive strategies, including sociality. Therefore, we investigated the relationships between female sociality, offspring survival, and infanticide risk in wild white-faced capuchin monkeys using long-term data from Santa Rosa, Costa Rica. Female capuchins formed differentiated bonds, and bond strength was predicted by kin relationship, rank difference, and the presence of female infants. Most females formed stable bonds with their top social partners, although bond stability varied considerably. Offspring of highly social females, who were often high-ranking females, exhibited higher survivorship during stable periods compared with offspring of less social females. However, offspring of highly social females were more likely to die or disappear during periods of alpha male replacements, probably because new alpha males are central to the group, and therefore more likely to target the infants of highly social, central females. This study shows that female sociality in mammals can have negative fitness consequences that are imposed by male behavior.

Keywords: capuchin; infanticide; mammal; reproductive success; social bond.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.

Differences in bond strength among different kin categories. Each point represents the log-transformed DSI (+0.1) value for each dyad during each year in which both females were coresident (n = 499 data points from 134 dyads and 32 females; dyads with insufficient information about kin relationships and grandmother–granddaughter dyads, of which only two existed within our dataset, were sorted out). The boxes represent the estimate of the LMM with upper and lower 95% confidence limits for each of the kin categories (assuming mean values for all other variables in the model). The lines and asterisks at the top of the figure denote the significant differences between kin categories. *P < 0.05; ***P < 0.001 (P values were adjusted using the Tukey method).

Fig. S1.
Fig. S1.

Averaged bond strengths for different partner ranks (i.e., first top partner, secondary top partner, etc.). Box plots depict log-transformed DSI (+0.1) values (n = 285), for which all dyads were included during each year both females were coresident. The vertical dashed line indicates the average bond strength [which is, per definition, DSI = 1 (SI Materials and Methods, Method S1: Calculation of DSI), and therefore log (1.1) in this plot]. Asterisks above boxplots indicate significant differences between bond strength for each partner rank and average bond strength: **P < 0.01 and ***P < 0.001 (results from t tests using log-transformed DSI + 0.1 values).

Fig. S2.
Fig. S2.

Stability of bonds with top three partners. The plot shows the histograms for observed and simulated PSI values.

Fig. S3.
Fig. S3.

Relationship between annual centrality values and sociality (ASI) of females. The dashed line depicts the prediction of the LMM, and dotted lines depict the bootstrapped 95% confidence intervals (n = 84 data points from 31 different females and 3 different years).

Fig. 2.
Fig. 2.

Effect of female sociality on infant survival for infants at low risk of infanticide (A; n = 50 infants) and infants at high risk of infanticide (B; n = 25 infants). The circles (●) show the observed survival probability, summarized for five equally large intervals of ASI, and the area of the circles is proportional to the (square rooted) number of infants included in each of these intervals. The dashed lines show the survival probability predicted by the GLMM, and the dotted lines depict the bootstrapped 95% confidence intervals (number of bootstraps = 1,000). The GLMM was calculated with ASI scaled to a mean of 0 and SD of 1 but shown here on the original scale from 0 to 1.

Fig. S4.
Fig. S4.

Effect of female rank on infant survival for infants at low risk of infanticide (A; n = 50 infants), and infants at high risk of infanticide (B; n = 25 infants). The circles (●) show the observed survival probability, summarized for five equally large intervals of rank, and the area of the circles is proportional to the (square rooted) number of infants included in each of these intervals. The dashed line shows the survival probability predicted by the GLMM, and the dotted lines depict the bootstrapped 95% confidence intervals (number of bootstraps = 1,000).

Fig. S5.
Fig. S5.

Changes in ASI and dominance ranks over time. (Top) Three plots show changes over time in ASI values for each group and female separately. (Bottom) Three plots show the same for dominance ranks.

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