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1.  Social and ecological factors influencing offspring survival in wild macaques 
Behavioral Ecology  2014;25(5):1164-1172.
Lay summary
Better to live in a big group if you want your offspring to survive! Using a multivariate approach, we show how the interplay of ecological and social factors influences fetus and infant survival in wild crested macaques. Offspring are more likely to survive in bigger groups, but seasonality also influences their survival. Fetus survival is higher for higher ranking mothers, whereas the main determinant of infants’ death is an alpha-male takeover by an immigrant male.
Premature loss of offspring decreases direct fitness of parents. In gregarious mammals, both ecological and social variables impact offspring survival and may interact with each other in this regard. Although a number of studies have investigated factors influencing offspring loss in mammals, we still know very little on how different factors interact with one another. We therefore investigated fetal and infant mortality in 3 large groups of wild crested macaques (Macaca nigra) over a period of up to 5 years by including potential social causes such as maternal dominance rank, male immigration, between group encounters, and ecological conditions such as rainfall in a multivariate survival analysis using Cox proportional hazards model. Infant but not fetal survival was most impaired after a recent takeover of the alpha-male position by an immigrant male. Furthermore, infant survival probability increased when there was an increase in number of group adult females and rainfall. Fetal survival probability also increased with an increase of these 2 factors, but more in high-ranking than low-ranking females. Fetal survival, unlike that of infants, was also improved by an increase of intergroup encounter rates. Our study thus stresses the importance of survival analyses using a multivariate approach and encompassing more than a single offspring stage to investigate the determinants of female direct fitness. We further provide evidence for fitness costs and benefits of group living, possibly deriving from high pressures of both within- and between-group competition, in a wild primate population.
doi:10.1093/beheco/aru099
PMCID: PMC4160111  PMID: 25214754
between-group encounters; female reproductive success; Macaca nigra; offspring loss; proportional hazards model; socioecology.
2.  Color signal information content and the eye of the beholder: a case study in the rhesus macaque 
Behavioral Ecology  2010;21(4):739-746.
Animal coloration has provided many classical examples of both natural and sexual selection. Methods to study color signals range from human assessment to models of receiver vision, with objective measurements commonly involving spectrometry or digital photography. However, signal assessment by a receiver is not objective but linked to receiver perception. Here, we use standardized digital photographs of female rhesus macaque (Macaca mulatta) face and hindquarter regions, combined with estimates of the timing of the female fertile phase, to assess how color varies with respect to this timing. We compare objective color measures (camera sensor responses) with models of rhesus vision (retinal receptor stimulation and visual discriminability). Due to differences in spectral separation between camera sensors and rhesus receptors, camera measures overestimated color variation and underestimated luminance variation compared with rhesus macaques. Consequently, objective digital camera measurements can produce statistically significant relationships that are probably undetectable to rhesus macaques, and hence biologically irrelevant, while missing variation in the measure that may be relevant. Discrimination modeling provided results that were most meaningful (as they were directly related to receiver perception) and were easiest to relate to underlying physiology. Further, this gave new insight into the function of such signals, revealing perceptually salient signal luminance changes outside of the fertile phase that could potentially enhance paternity confusion. Our study demonstrates how, even for species with similar visual systems to humans, models of vision may provide more accurate and meaningful information on the form and function of visual signals than objective color measures do.
doi:10.1093/beheco/arq047
PMCID: PMC2892627  PMID: 22475874
color signaling; communication; receiver perception; visual discrimination threshold modeling

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