BACULAR AND TESTICULAR GROWTH AND ALLOMETRY IN THE CAPE FUR SEAL ARCTOCEPHALUS P. PUSILLUS (OTARIIDAE)

• Published in: Marine mammal science Vol. 16; no. 1; pp. 124 - 140
• Main Authors: Oosthuizen, W. H., Miller, E. H.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.01.2000; Blackwell
• Subjects: allometry; Arctocephalus pusillus; Arctocephalus pusillus pusillus; Biological and medical sciences; Cape fur seal; Fundamental and applied biological sciences. Psychology; growth; Mammalian male genital system; Marine; Morphology. Physiology; Pagophilus groenlandicus; reproduction; sexual selection; Vertebrates: reproduction; Carnivora; Vertebrata; Reproduction; Mammalia; Sexual selection; Growth; Os penis; Corporal biometry; Allometry; Testicle; Male genital system; Pinnipedia
• ISSN: 0824-0469; 1748-7692
• DOI: 10.1111/j.1748-7692.2000.tb00908.x

The baculum in Arctocephalus p. pusillus reaches up to 14.1 cm in length, 13.5 g in mass, and 1.3 g/cm in density (= mass/length). A pubertal growth spurt occurs between 2 and 3 yr of age, when bacular length increases by 28%, mass by 124%, and density by 77%; concurrently, body length increases by 14%. A second, weaker spurt occurs at social maturity (9‐10 yr of age). Testes grow most rapidly between 1 and 2 yr of age, when testicular length increases by 29%. After 3 yr of age, growth in bacular and testicular length slows, and bacular mass continues to increase approximately linearly. Bacular and testicular lengths average 6.8% and 3.4% (respectively) of body length in adults, compared with 9.9% and 5.7% in the promiscuous harp seal (Pagophilus groenlandicus). Bacular length, mass, and density, and testicular length, are positively allometric to body length over growth; bacular length is isometric to testicular length. Among animals of the same age, bacular length and mass are positively allometric to body length in young animals, with negative allometry or isometry thereafter; testicular length is isometric to body length in young animals and negatively allometric thereafter. Patterns of early growth and allometry of the baculum and testes are interpreted as adaptations for mating opportunities, years before territoriality is possible. The baculum and testes of adult Cape fur seals and other otariids are small compared with those of most phocids, because sperm competition among male otariids is weak.