P3.100 Saturday, Jan. 5 Collared Lizards Decrease Testosterone Levels in Response to Staged Territorial Intrusions: A Test of the Challenge Hypothesis CURTIS, J.L.*; BAIRD, T.A.; HEWS, D.K; Univ. of Central Oklahoma, Edmond; Univ. of Central Oklahoma, Edmond; Indiana State Univ., Terra Haute email@example.com
The challenge hypothesis (CH) has been useful in explaining patterns of androgen responsiveness to staged territorial intrusions in birds. However, there have been fewer studies in other taxa, particularly lizards. We tested the CH in polygynous, territorial male collared lizards lacking parental care. Theoretically, breeding season levels of testosterone (T) should be at a maximum level, and thus males will not elevate androgens in response to a social challenge. Males at our site are territorial, but rarely engage in overt aggression with consexuals. Thus, we hypothesized that males may not maintain T levels at maximum throughout the breeding season therefore allowing individuals to respond hormonally to social challenges. For each trial, we recorded initial focal observations on day 1 to obtain ‘baseline’ levels of behavior as well as blood samples to determine ‘baseline’ T concentrations. To determine changes in behavior and T, on day 3 we tethered conspecific male intruders near resident males for 15 min, and then recorded a second 30 min focal observation after which we immediately obtained post intrusion blood samples. Following challenges, males increased the frequency of distant display (fullshows) and the frequency of proximal display used during male-male contests. Interestingly, challenged males decreased the number of proximal encounters with, and the frequency of proximal displays to females, suggesting that territorial advertisement was a higher priority. In direct contrast to our hormonal predictions, territorial males significantly reduced plasma T concentrations following short intruder challenges compared to baseline levels. There was no significant change in T for control males.