Testosterone, endurance, and darwinian fitness: Natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards

The mechanistic bases of natural and sexual selection on physiological and behavioral traits were examined in male morphs of three colors of the side- blotched lizard, Uta stansburiana. Orange-throated males are aggressive and defend large territories with many females. Blue-throated males defend sma ller territories with fewer females; however, blue-throated males assiduous ly mate guard females on their territory. Yellow-throated males do not defe nd a territory, but patrol a large home range. They obtain secretive copula tions from females on the territories of dominant males. Males with bright orange throats had higher levels of plasma testosterone (T), endurance, act ivity, and home range size and concomitantly gained greater control over fe male home ranges than blue- or yellow-throated males. Experimentally elevat ing plasma T in yellow- and blue-throated males increased their endurance, activity, home range size, and control over female territories to levels th at were seen in unmanipulated orange-throated males that had naturally high plasma T. However, the enhanced performance of orange-throated males is no t without costs. Orange-throated males had low survival compared to the oth er morphs. Finally, some yellow-throated males transformed to a partial blu e morphology late in the season and the endurance of these transforming yel low-throated males increased from early to late in the season. In addition, yellow-throated males that transformed to blue also had significantly high er plasma T late in the season compared to the plasma T earlier in the seas on. T appears to play an important role in the physiological changes that a ll three color morphs undergo during the process of maturation. In some yel low males, T plays an additional role in plastic changes in behavior and ph ysiology late in the reproductive season. We discuss natural and sexual sel ection on physiological and behavioral traits that leads to the evolution o f steroid regulation in the context of alternative male strategies. (C) 200 0 Academic Press.