THE CHALLENGE HYPOTHESIS AND SEASONAL-CHANGES IN AGGRESSION AND STEROIDS IN MALE NORTHERN FENCE LIZARDS (SCELOPORUS-UNDULATUS HYACINTHINUS)

The challenge hypothesis has been very successful in explaining patter ns of testosterone secretion in response to social stimuli in avian sp ecies. However, there have been few studies in nonavian vertebrates. W e tested the challenge hypothesis in male northern fence lizards (Scel oporus undulatus hyacinthinus). These males are highly territorial and nonparental. Consequently, the challenge hypothesis predicts that pla sma testosterone concentrations will be insensitive to aggressive inte ractions. Testosterone concentrations indeed were not significantly af fected by either a short (3-15 min) simulated territorial intrusion (' 'challenge'') in June or a longer (50-60 min) intrusion in July. Level s of corticosterone were elevated in challenged males in the long, but not the short, intrusion. Challenged males displayed significantly mo re intense territorial behaviors than did unchallenged control males. The intensity of territorial behavior changed significantly across the active season and was positively related to testosterone concentratio ns. Thus, while testosterone concentrations do not appear to be involv ed in rapid changes in aggressive behavior in the fence lizard, they p robably are important in larger-scale behavioral changes throughout th e season. (C) 1998 Academic Press.