Infanticide and reproductive restraint in a polygynous social mammal

Alpha male chacma baboons experience uncontested access to individual estrus females. Consequently, alpha male paternity certainty is high and underpins significant levels of infanticide by immigrant males that, in turn, has selected for male defense of infants. There is also, however, a high probability that alpha males will be absent during the period when their own offspring are vulnerable, suggesting selection for additional countermeasures. We use data from a long-term study to test the prediction that alpha male chacma baboons cede reproductive opportunities to subordinate males and that this leads to the presence of other fathers that can serve as a buffer against infanticidal attack. We found that subordinate males obtained significantly more conceptive opportunities than predicted by priority of access alone, and that this occurred because alpha males did not consort all receptive periods. There was no evidence that this was due to energetic constraint, large male cohorts, alpha male inexperience, or the competitive strength of queuing subordinates. The number of males who benefited from concession and the length of time that they were resident relative to those who did not benefit in this way greatly reduced the probability that infants of alpha males would face immigrant males without a surrogate father whose own offspring were vulnerable. The absence of such males was associated with observed infanticide as well as, unexpectedly, an increased likelihood of takeover when alpha males with vulnerable infants were present.

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The Demographic and Reproductive Context of Male Replacements in Cebus Capucinus

Behaviour ◽

10.1163/1568539042245178 ◽

2004 ◽

Vol 141 (6) ◽

pp. 755-775 ◽

Cited By ~ 42

Author(s):

Katharine Jack ◽

Linda Marie Fedigan

Keyword(s):

Group Composition ◽

Study Groups ◽

Cebus Capucinus ◽

Lower Proportion ◽

Adult Males ◽

Alpha Male ◽

Term Study ◽

Annual Peak ◽

Long Term Study

AbstractMale primates may immigrate into groups by peacefully joining the residents and taking up low-ranking positions in the hierarchy, or they may enter by force, challenging the resident males and attempting to drive them from high rank or from the group. Here we address the questions of how, when, and why immigrating male white-faced capuchins (C. capucinus) at Santa Rosa replace the former resident males of our groups, rather than simply joining them. We present data on 15 male replacements in 6 study groups tracked from 1984 through March 2004. During 11 aggressive takeovers, resident males were nearly always outnumbered by coalitions of invading males; lone resident males were particularly vulnerable. Both residents and invaders were wounded and infants often perished during or soon after takeovers. Male replacements also occur when resident males abandon their groups and males from neighboring groups 'waltz in' to become resident. Three such 'waltz in' replacements occurred during the study period. If we combine takeovers with 'waltz in' cases, replacements occur about every 4 years in our study groups, almost invariably during the dry season months of January to April, about 3-6 months before the annual peak in conceptions. In the years that groups are subject to takeovers, group composition includes significantly lower proportions of adult males than in no-takeover years. We conclude that: (1) the mechanism of male replacement is usually aggressive takeover, but sometimes abandonment of the group by prior resident males occurs; and (2) aggressive takeovers are more likely to happen when the group is vulnerable because it has a lower proportion of adult males, particularly when all co-resident males have emigrated, leaving only the alpha male in residence. Our long-term study shows that adult males need coalition partners not only to gain entry to a group but also to maintain their membership within it.

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How accurately do behavioural observations predict reproductive success in free-ranging lizards?

Biology Letters ◽

10.1098/rsbl.2019.0030 ◽

2019 ◽

Vol 15 (2) ◽

pp. 20190030 ◽

Cited By ~ 1

Author(s):

Mats Olsson ◽

Tonia S. Schwartz ◽

Erik Wapstra ◽

Richard Shine

Keyword(s):

Reproductive Success ◽

Adult Males ◽

Microsatellite Data ◽

Term Study ◽

Long Term Study ◽

Lacerta Agilis ◽

Free Ranging ◽

Number Of Males ◽

Variance In Reproductive Success

Behavioural ecologists often use data on patterns of male–female association to infer reproductive success of free-ranging animals. For example, a male seen with several females during the mating season is predicted to father more offspring than a male not seen with any females. We explored the putative correlation between this behaviour and actual paternity (as revealed by microsatellite data) from a long-term study on sand lizards ( Lacerta agilis ), including behavioural observations of 574 adult males and 289 adult females, and paternity assignment of more than 2500 offspring during 1998–2007. The number of males that contributed paternity to a female's clutch was correlated with the number of males seen accompanying her in the field, but not with the number of copulation scars on her body. The number of females that a male accompanied in the field predicted the number of females with whom he fathered offspring, and his annual reproductive success (number of progeny). Although behavioural data explained less than one-third of total variance in reproductive success, our analysis supports the utility of behavioural-ecology studies for predicting paternity in free-ranging reptiles.

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