Alternative antipredator tactics in tree lizard morphs: hormonal and behavioural responses to a predator encounter

Most vertebrates respond to acute stressors with rapid plasma glucocorticoid elevations. Variation within species in this hormonal response should correlate with differences in physiological responses and behavioural tactics, yet this is rarely documented. We measured behavioural and hormonal responses of free-ranging male tree lizards (Urosaurus ornatus) during staged encounters with a collared lizard predator (Crotaphytus nebrius) or a control (stick). In our study population, males express alternate reproductive tactics that correlate with throat colour pattern: territorial males have a central blue patch on an orange background (OB males) and nonterritorial males lack the blue patch (O males). We also studied a previously uncharacterized male type with a mottled orange and blue throat (M males). A single encounter with an approaching predator initiated an elevation in plasma corticosterone that was similar among the male types (mean ± SE = 9.64 ± 3.17 (OB), 9.72 ± 2.49 (O), 10.19 ± 2.82 (M)). Despite this similarity, male types differed behaviourally. Compared to OB and M males, O males initiated flight when the predator was further away and stayed hidden longer after seeking refuge. The M males showed responses similar to OB males and may functionally be the same morph. Among individuals of all morphs, total corticosterone levels after the predator encounter correlated strongly with their flight initiation distance and hiding duration during the encounter. We conclude that male tree lizards with alternative reproductive tactics show alternative antipredator behavioural tactics, and that individual variation in escape responses is directly correlated with corticosterone levels.