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SEXUAL DIMORPHISM AND BODY SCARRING IN THE BOTO (AMAZON RIVER DOLPHIN) INIA GEOFFRENSIS
Author(s) -
Martin A. R.,
Da Silva V. M. F.
Publication year - 2006
Publication title -
marine mammal science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.723
H-Index - 78
eISSN - 1748-7692
pISSN - 0824-0469
DOI - 10.1111/j.1748-7692.2006.00003.x
Subject(s) - sexual dimorphism , intraspecific competition , polygyny , biology , mating system , amazon rainforest , mating , zoology , ecology , demography , population , sociology
Measurements and quantitative descriptions of a large sample of live adult botos ( Inia geoffrensis ) were obtained from the Mamirauá Reserve in the central Amazon. Males were on average 16% longer and weighed 55% more than females, demonstrating that this species is one of the most sexually dimorphic of all cetaceans for size. Males were also pinker than females, more heavily scarred by intraspecific tooth rakes, and had more life‐threatening injuries. Some larger males had areas of modified skin that may simply be scar tissue, but may also be a heritable characteristic used as a shield or weapon. As in sperm whales, sexual size dimorphism and male‐male aggression appear to be linked in botos, suggesting fierce competition for a resource—probably mating opportunities. The boto is unique among river dolphins in that males are larger than females. This distinction implies long evolutionary separation and fundamental differences in social behavior.