Department of Zoology and Museum of Natural and Cultural History, Oklahoma State University, Stillwater, Oklahoma 74078.
SEXUAL DIMORPHISM IN SPOTTED DOLPHINS (STENELLA ATTENUATA) IN THE EASTERN TROPICAL PACIFIC OCEAN
Article first published online: 26 AUG 2006
Marine Mammal Science
Volume 1, Issue 1, pages 1–14, January 1985
How to Cite
Schnell, G. D., Douglas, M. E. and Hough, D. J. (1985), SEXUAL DIMORPHISM IN SPOTTED DOLPHINS (STENELLA ATTENUATA) IN THE EASTERN TROPICAL PACIFIC OCEAN. Marine Mammal Science, 1: 1–14. doi: 10.1111/j.1748-7692.1985.tb00529.x
- Issue published online: 26 AUG 2006
- Article first published online: 26 AUG 2006
- Received: February 1, 1984 Accepted: July 24, 1984
We analyzed 4 meristic and 32 morphometric cranial traits of 612 adult specimens of spotted dolphins (Stenella attenuata) from the eastern tropical Pacific Ocean for sexual dimorphism. Eleven 5″ latitude/longitude blocks with five or more of each sex were assessed with a two-way ANOVA for sex and geographic differences. Interaction between these two factors was found for six measurements, suggesting that the degree of sexual dimorphism varies geographically for a few characters (although in no discernible geographic pattern). Sexual dimorphism was demonstrated for 23 of the 36 characters, with differences ranging from 0.00 to 5.88 percent. Females characteristically had a longer rostrum, while males generally had larger skulls overall. In terms of number of characters, the extent of sexual dimorphism demonstrated for skulls of spotted dolphins goes considerably beyond that shown for any other small delphine. A discriminant function involving a combination of 10 characters enabled us to identify correctly the sex of more than 75 percent of the specimens. A procedure for correcting specimen measurements is outlined that would enable an investigator to combine male and female specimens in geographic variation studies. A term (zwitter) is proposed for use when referring to specimens where measurements have been corrected to take into account differences between the sexes.