New investigations of the mechanisms involved in kin discrimination showed effects of genetic factors, as well as social environment, on mandrills vocalizations and that mandrills are able to discriminate their (unknown) kin based on their voices alone.
Few words about the kin selection theory …
The theory of kin selection has been proposed in 1964 by William Donald Hamilton to explain altruism or cooperative behavior within animal societies. Indeed, related individuals (sharing high genetic proximity) tend to be more altruist with each other compared to unrelated individuals. Kin selection theory suggests that these behaviors allow to increase inclusive fitness.
Kin selection is possible if mechanisms of kin discrimination have evolved to allow identifying related peers. These mechanisms are, however, still poorly understood. Within the framework of the Mandrillus Project, the possible implication of vocal signatures in phenotype matching processes have been investigated.
Use of vocalizations to discriminate your family's members ?
New results on two captive and a wild mandrill's populations show that the acoustic structure of contact calls is influenced by both genetic similarity between calling individuals and their social experience (familiar individuals share common acoustic features). Moreover, playback experiments showed that actor mandrills respond more intensely to vocalizations from genetically related speakers (their kin), regardless of the familial environment and origins. To conclude, kin-biased behavior observed in these animals are explained by the so-called "phenotype matching" mechanism, using vocal cues.
Levréro F, Carrete-Vega G, Herbert A, Lawabi I, Courtiol A, Willaume E, Kappeler PM, Charpentier MJE. 2015. Social shaping of voices does not impair phenotype matching of kinship in mandrills. Nature Communications 6: 7609. [PDF]
A recent study compared the tooth wear between wild mandrills from our studied population in the Lékédi Park and yellow baboons living in the savannas of the Amboseli National Park (Kenya). The paper showed that, due to environmental and ecological differences between these two species, their levels of dental wear vary.
What is dental wear ?
Tooth wear is a loss of dental tissue (enamel, dentine) caused by the mechanical and chemical properties of the food, but also by the contact between teeth when occlusion occurs (particularly during the chewing process). This paper written by Jordi Galbany et al. focuses on the macrowear (visible to the naked eye). They scored the percent of dentine exposure on the occlusal surface of the teeth and found that, for a similar age, the percentage of dentine exposure varies between mandrills and yellow baboons. As you can see on the picture on the left, mandrill molars (A) are more worn than those of yellow baboons (B).
But why is this the case?
Ecological influences on tooth wear
The study finds two different factors that are most likely to influence tooth wear: the properties of the food and the composition of the soil the food grows in. Mandrills feed on various food items, some of which are hard-shelled fruit that have strong abrasive properties. In contrast, the yellow baboons mainly consume large amounts of underground storage organs that are not particularly hard to chew. Additionally, the soil in Lékédi Park contains higher amounts of quartz than the soil in Amboseli. This mineral is known to be hard enough to affect tooth wear and the animals get in contact with it in form of dust and grit on the fruit and roots they consume.
We can wonder if the important loss of enamel on wild mandrills molars result from an adaptative process to a more abrasive diet... We keep searching...
See also: Dental ecology blog
Galbany J, Romero A, Mayo-Alesón M, Itsoma F, Gamarra B, Pérez-Pérez A, Willaume E, Kappeler PM, Charpentier MJE. 2014. Age-related tooth wear differs between forest and savanna primates. PlosOne 9: e94938. [PDF]