Blubber Testosterone: A Potential Marker of Male Reproductive Status in Short-Beaked Common Dolphins

Authors

Nicholas Kellar, Southwest Fisheries Science Center, National Marine Fisheries Service, P. O. Box 271, La Jolla, California
Marisa Trego, Southwest Fisheries Science Center, National Marine Fisheries Service, P. O. Box 271, La Jolla, California
Corina Marks, Southwest Fisheries Science Center, National Marine Fisheries Service, P. O. Box 271, La Jolla, California
Susan Chivers, Southwest Fisheries Science Center, National Marine Fisheries Service, P. O. Box 271, La Jolla, California
Kerri Danil, Southwest Fisheries Science Center, National Marine Fisheries Service, P. O. Box 271, La Jolla, California
Frederick Archer, Southwest Fisheries Science Center, National Marine Fisheries Service, P. O. Box 271, La Jolla, California

Date of this Version

2009

Comments

Published in MARINE MAMMAL SCIENCE.

Abstract

A novel molecular technique was used to measure blubber testosterone (BT) in 114 male short-beaked common dolphins, Delphinus delphis, collected from incidental fishery bycatch and strandings. When these concentrations were compared across maturity states, the mean (± SEM) BT levels of mature D. delphis (14.3 ± 3.0 ng/g) were significantly higher than those of pubertal (2.5 ± 0.5 ng/g, P = 0.006) and immature animals (2.2 ± 0.3 ng/g, P < 0.0001). BT concentrations in mature males were significantly higher in summer months (53.9 ± 2.0 ng/g) than during the rest of the year (7.9 ± 0.69 ng/g, P < 0.0001), indicating reproductive seasonality. An analysis of BT in different anatomical locations showed that hormone concentrations were not homogenous throughout the body; the levels in the dorsal fin were significantly lower than in most other areas (F = 5.39, P = 0.043). Conversely, we found no significant differences in BT concentration with respect to subepidermal depth (F = 2.09, P = 0.146). Finally, testosterone levels in biopsies from 138 free-swimming male D. delphis, of unknown maturity state, sampled off California were found to be of concentrations similar to those from the fishery bycatch and stranding samples and revealed an analogous trend with respect to ordinal date.