Courtship displays in anurans and lizards: Theoretical and empirical contributions to our understanding of costs and selection on males due to female choice

1. Male frogs and toads expend considerable energy and experience potential predation risk while calling in breeding aggregations; similarly, male lizards display behaviourally and exhibit striking colour patterns during courtship interactions. These apparently costly displays of male anuran amphibians and squamate reptiles have been argued to play an important role in mate selection by females. Although female preferences for male display traits under controlled conditions have been documented for both taxonomic groups, directional selection on male displays has rarely been adequately assessed under natural conditions. 2. We discuss theoretical and empirical considerations of display costs in the context of sexual selection due to female preferences in anurans and lizards. We review experimental evidence of female preferences for apparently costly displays by males and estimation of selection on male traits due to female choice in the field in these taxonomic groups. 3. Evidence of female preferences for apparently costly display traits is not uncommon for thoroughly studied populations, and there is some field evidence of significant selection on these traits in at least one well studied group: prolonged breeding toads. Studies have been hampered by confusion over the definitions of costs, difficulty in adequately describing variation in male displays, and overly simplistic approaches to documentation of female preferences. 4. Future work should include recognition of variation in definitions of cost in relation to male display behaviour, acknowledgement that female choice may be based on multiple male characteristics, and that considerable effort, including documentation of consistency in male behaviour, is required before inferences regarding the importance of female choice in sexual selection can be drawn.