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Author: Samantha Berkey
Primates live in complex social structures and have developed extensive and highly varied communication systems. A distinctive type of communication found across primate species is loud, attention drawing calls. These are alarm calls , which are adaptive as anti-predation measures. The specific alarm calls’ structure and function vary from species to species, as each type of primate faces different ecological challenges and lives in different kinds of groups.
Alarm calls can function to alert group members which specific predator is approaching (Seyfarth et al, 1980). Primates such as the vervet monkey or white-faced capuchin have evolved very distinct calls that they only use in response to certain predators (Digweed et al, 2005; Seyfarth et al, 1980). This system allows the primate to recognize the difference in calls and to pick the anti-predator response that is most adaptive. For example, a predator that hunts from the air should elicit a different alarm call than one that hunts from the ground, and the primates should respond appropriately by moving lower or higher in the trees (Seyfarth et al, 1980).
The primates used to illustrate the functions of alarm calls have varying degrees of relatedness. They can be classified as Old World (residing in Africa and Asia) or New World (residing in the Americas) monkeys, and exhibit a few distinct differences. The Old World monkeys, or Platyrrhines, have flatter, outward-pointing noses, larger canines, and are generally larger in body size. The New World monkeys, or Catarrhines, are hook-nosed and tend to be more terrestrial. We can evaluate species’ relatedness by examining a phylogenetic tree (see [link] ).
The capuchins and tamarins are both New World monkeys related by two past divergence events. Their common ancestor split once, and then each of these two species diverged again to give four new species, two of which were the capuchins and tamarins.
The vervet monkeys and Diana monkeys (guenons) and baboons are Old World monkeys that also share a common ancestor. After diverging at this ancestor, the vervet monkey and Diana monkey ancestral line underwent three more speciation events, while the baboons stayed a distinct lineage.
By this phylogenetic tree, it appears the vervet monkeys and Diana monkeys are the closest relatives, and are about equally related to baboons as capuchins and tamarins are to each other. The types of alarm calls observed in each species match this tree. The Diana monkeys and vervet monkeys both use three referential alarm calls (see [link] ). The tamarins and capuchins each have an aerial alarm call and a terrestrial alarm call. In addition, both species use their terrestrial alarm call as a general warning (see [link] ).
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