Characterization of male killer whale (Orcinus orca) sexual maturation and reproductive seasonality

Longitudinal serum testosterone concentrations (n = 10 males) and semen production (n = 2 males) in killer whales were evaluated to: (1) characterize fluctuations in serum testosterone concentrations with respect to reproductive maturity and season; (2) compare morphologic changes to estimated age of sexual maturity, based on changes in serum testosterone concentrations; and (3) evaluate seasonal changes in sperm production. Classification of reproductive status and age class was based on differences (P < 0.05) in serum testosterone concentrations according to age; juvenile males ranged from 1 to 7 years (mean +/- S.D. testosterone, 0.13 +/- 0.20 ng/mL), pubertal males from 8 to 12 years (2.88 +/- 3.20 ng/mL), and sexually mature animals were 13 years and older (5.57 +/- 2.90 ng/mL). For captive-born males, serum testosterone concentrations, total body length and height to width ratio of the dorsal fin were 0.7 +/- 0.7 ng/mL, 495.6 +/- 17.5 cm and 1.14 +/- 0.13 cm, respectively, at puberty; at sexual maturity, these end points were 6.0 +/- 3.3 ng/mL, 548 +/- 20 cm and 1.36 +/- 0.1 cm. Serum testosterone concentrations were higher (P < 0.05) from March to June than from December to February in pubertal animals (4.2 +/- 3.4 ng/mL versus 1.4 +/- 2.6 ng/mL) and than from September to December in sexually mature animals (7.2 +/- 3.3 ng/mL versus 4.0 +/- 2.0 ng/mL). Ejaculates (n = 90) collected from two males had similar (P > 0.05) sperm concentrations across all months. These data represent the first comprehensive study on male testosterone concentrations during and after sexual maturation, and on reproductive seasonality in the killer whale. (c) 2005 Elsevier Inc. All rights reserved.