Water-borne testosterone levels predict exploratory tendency in male poison frogs

Hormones play a fundamental role in mediating social behaviors of animals. However, it is less well understood to what extent behavioral variation between individuals can be attributed to variation in underlying hormonal profiles. The goal of the present study was to infer if individual androgen levels, and/or the modulation thereof, can explain among-individual variation in aggressiveness, boldness and exploration. We used as a model the dart-poison frog Allobates femoralis and took repeated non-invasive water-borne hormonal samples of individual males before (baseline) and after (experimental) a series of behavioral tests for assessing aggression, boldness, and exploratory tendency. Our results show that androgen levels in A. femoralis are quite stable across the reproductive season. Repeatability in _wbT baseline levels was high, while time of day, age of the frog, and trial order did not show any significant impact on measured _wbT levels. In general, experimental _wbT levels after behavioral tests were lower compared to the respective baseline levels. However, we identified two different patterns with regard to androgen modulation in response to behavioral testing: individuals with low baseline _wbT tended to have increased _wbT levels after the behavioral testing, while individuals with comparatively high baseline _wbT levels rather showed a decrease in hormonal levels after testing. Our results also suggest that baseline _wbT levels are linked to the personality trait exploration, and that androgen modulation is linked to boldness in A. femoralis males. These results show that differences in hormonal profiles and/or hormonal modulation in response to social challenges can indeed explain among-individual differences in behavioral traits.