Revista Chilena de Historia Natural 78 (2): 229-238, 2005
RESEARCH ARTICLE
Free and total testosterone levels in field males of Octodon degus (Rodentia,
Octodontidae): accuracy of the hormonal regulation of behavior
Animals exhibit continuous seasonal changes in physiological, morphological and
behavioral traits associated to their natural annual cycles. One of the most important changes in the organism occurs at the initiation of
breeding season. In males these changes include activation of spermatogenesis, enhance of sexual secondary characters and an
increase of aggressiveness. All of theses changes are basically regulated by testosterone, but the physiological basis of this
testosterone regulation and the effective hormone proportion that acts in target tissues are unknown. In this work I evaluated the
relationship between total testosterone, free testosterone associated to aggressive behavior in wild males of Octodon
degus. I compared hormonal levels and aggressive behavior during pre, middle and post breeding periods. Results showed that
behavioral aggressiveness was correlated with both total and free testosterone in June, during the beginning of breeding season, but
not at other times. Results also indicated a lack of relationship between free and total testosterone in most of breeding period. I discuss
the importance of this behavior-hormonal regulation (determined by free testosterone) and the physiological importance of this
mechanism to the organism.
Key words:
free testosterone, total
testosterone, globulin, binding-proteins, aggressive behavior, challenge hypothesis, Octodon degus
