Behavioral and physiological differences associated with acquisition and maintenance of a social status in male green anole lizards, Anolis carolinensis
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Social experience can modify the behavior of adult animals, and this type of behavioral plasticity associated with territorial aggression has been observed in several species including green anole lizards. Previously dominant animals were more aggressive to a novel stimulus in a new context than previously subordinate animals after 10 days of agonistic interaction. This behavioral shift could be beneficial to an animal by increasing survival and/or reproductive success to maximize its fitness. Behavioral modification through social experience can involve alteration in some physiological properties such as variations in hormone titer and hormone receptors. Steroid hormones such as testosterone (T) and corticosterone (Cort) and neurotrasmitters such as arginine vasotocin (AVT) are well known for their association with territorial aggression. Hormonal mechanisms underlying the control of this behavior are, however, context dependent, temporally dynamic, and evolutionarily very diverse. I performed experiments aimed at gaining insights into the proximate mechanisms underlying status-dependent behavioral differences in territorial aggression. First, steroid binding globulins of green anole lizards were analyzed and the presence of androgen-glucocorticoid binding globulins and sex-hormone binding globulins (SHBG) was established. Next, status differences in steroid hormone levels and the temporal pattern of hormone changes were assessed. We found that winners/dominants had elevated total T levels shortly after the onset of fighting and reduced SHBG after 10 days of agonistic interaction. These changes seemed to cause sustained increases in free T levels in winners/dominants throughout 10 days of agonistic interactions. Then, androgen receptor (AR) mRNA density levels were compared in dominant and subordinate animals. The result showed that the preoptic area (POA) and anterior hypothalamus AR mRNA density levels were higher in dominants than subordinates shortly after the agonistic interaction. Lastly, AVT immunoreactive cell counts were compared in dominant and subordinate animals. We found that subordinate animals had reduced AVT immunoreactive cell counts in the POA compared to that of dominants or control males. Findings from this dissertation suggest possible mechanisms that might be responsible for status dependent behavioral differences in territorial aggression: elevation in T and reduction in SHBG capacity, and sustained elevation of AVT immunoreactive cell counts in the POA.