Sex steroid hormones are important for reproduction in all vertebrates, but few studies examine inter-individual, temporal, and population-level variations, as well as environmental influences on circulating steroid levels within the same species. In this study we analyzed plasma 11-ketotoestosterone (11-KT) and 17β-estradiol (E2) levels in the oyster toadfish to test for 1) individual and temporal variations by serially sampling the same individuals during the reproductive and post-reproductive period, 2) variations in steroid levels among toadfish obtained from different sources or maintained under different holding conditions, and 3) correlations with environmental parameters. Results from serial sampling showed marked inter-individual variations in male 11-KT levels in two separate groups of toadfish, but no temporal differences from June to September. Females also showed inter-individual variations in E2 concentrations, but most had elevated levels late in the reproductive season coincident with oocyte growth prior to winter quiescence. E2 concentration, but not 11-KT, was positively correlated with water temperature, and negatively correlated with daylength and lunar phase. Maricultured toadfish held under constant conditions had elevated levels of E2 and 11-KT that should be considered when using these fish for experimentation. This study provides important comparative information on the relationship between individual variations in steroid levels, and how they relate to physiological and environmental correlates in a model marine teleost.
|Number of pages
|Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology
|Published - Apr 2009
Bibliographical noteFunding Information:
We thank Jack Lyons for help with data collection, Beth Giuffrida and the Marine Resources Center at MBL for toadfish care, Woods Hole Oceanographic Institute (WHOI) for tank space, NIH-BioCurrents facility at MBL for use of the plate reader, and two anonymous reviewers for insightful comments that helped to improve the manuscript. This study was funded by Grass Foundation Fellowships to KPM (2007) and WJK (2006), and we gratefully acknowledge their support. We also thank the Marine Biological Laboratory Neuroscience Institute (KPM) and National Science Foundation (Award #0316130 to AFM) for additional funding.
- Individual variation
- Steroid cycling