Intraspecific scarring in odontocete cetaceans: an indicator of male ‘quality’ in aggressive social interactions?

Abstract

The level of visible (i.e. white or unpigmented) scarring on cetaceans varies greatly between species, particularly for intraspecific scarring in odontocete cetaceans. In some species, unpigmented intraspecific scars may act as an indicator of male ‘quality’ during aggressive social interactions. Evidence to support this hypothesis was found in 18 species of odontocete cetacean. These were the narwhal (Monodon monoceros), the sperm whale (Physeter macrocephalus), the Risso's dolphin (Grampus griseus) and the family Ziphiidae (with the exception of Mesoplodon ginkgodens). The evolution of such signalling is related to the fact that teeth are not required for feeding on certain diets, primarily cephalopod-based diets, and as a result the number of teeth has been reduced. However, some teeth have been retained, and selected, as weapons for male-male competition. This has resulted in an increase in the level of intraspecific scarring and the greater need for a signal of ‘quality’ to avoid costly and dangerous fights. As intraspecific scarring became this signal, the repigmentation rate of scars was reduced, leading to all scars remaining permanently unpigmented in these species.