Predictors of contest outcome in males of two subspecies of Gallotia galloti (Squamata: Lacertidae)

In many species, male coloration signals aggressiveness and/or fighting ability. Males of the Tenerife lizard (Gallotia galloti) have conspicuous ultraviolet (UV)-blue cheek and lateral color patches that are brighter in the breeding season and larger than those of females. We analyzed experimentally the effect of morphological and behavioral traits, including spectral variables from UV-reflecting color patches, on the outcome of staged dyadic contests between males of two subspecies of G. galloti. We performed two experiments: (1) using pairs of unmanipulated males and (2) reducing the UV reflectance of the UV-blue patches of one of the contestants with sunscreen lotion. Results from experiment 1 showed no significant difference between subspecies in the effect of any variable on contest outcome. Overall, winners had larger body mass, head width, and fore-limb length and showed a higher rate of aggressive behavior patterns than losers, whereas losers showed a higher rate of “tail shake,” which is considered a submissive behavior. Winners also had lateral UV-blue patches with higher (more blue-biased) hue than losers, but no other spectral trait had a significant effect on contest outcome. Results from experiment 2 showed that reducing patch reflectance in the UV range had no effect in one subspecies but significantly increased fighting success in the other. The probability of winning was positively associated with the frequency of bites (irrespective of whether individuals had manipulated patches or not). Results from both experiments suggest that while multiple traits (morphometric, coloration, and behavioral) may influence the outcome of male contests in G. galloti, behavioral traits take prevalence over morphological, including coloration, traits. The effect of several traits on the outcome of contests has been previously analyzed in males of several lizard species. These analyses have commonly considered the effect of a single trait on contest outcome. However, as even males of the same age and experience often vary across multiple morphological (including coloration), performance, and behavioral traits, it has been suggested that contest outcome could be influenced by several interacting traits. We tested this hypothesis by staging dyadic contests between males of two subspecies of the Tenerife lizard. Results from a first experiment showed that larger body mass, head width, fore-limb lengths, higher frequency of bites, throat extension, and higher peak reflectance (hue) of UV-blue patches significantly affected the probability of winning, while a large frequency of tail shakes was associated with losing. Results from a second experiment, in which we experimentally manipulated patch UV reflectance in one of the contestant lizards, showed that bite frequency and reduction of UV reflectance affected the probability of winning; we discuss the complex effect of this latter trait on contest outcome.