Unraveling the content of tail displays in an Asian agamid lizard

Understanding the information content of animal displays is crucial for studying signal function and evolution. Previous works focused largely on display variations and their adaptation to background noise, with limited attention to the information content. Here, we explored the information content of tail displays of an Asian agamid lizard Phrynocephalus vlangalii and tested two non-exclusive hypotheses, the individual condition hypothesis and the resource quality hypothesis. We recorded individual tail display videos in the field under four social contexts and measured individual condition and burrow quality. Using linear regression and model selection, we tested associations between display variables and individual condition, as well as burrow quality variables. Fast tail coiling movement and large sweep area of tail lashing are respectively associated with fast sprint speed and large body size in males, while high tail coil amplitude is correlated with large body size in females. In addition, fast tail lashing movement is associated with shallow burrow in males, while in females, fast tail coiling movement is associated with small burrow entrance, and high amplitudes during tail coiling are associated with shallow burrow. Our results show that tail displays in these lizards indeed reflect individual body condition and burrow quality, and the information may help to alleviate social conflict and to assess potential mate quality. Furthermore, both females and males use tail displays to convey important information. Taken together, these results support both hypotheses and cast important insights on the content of tail displays in lizards, which will facilitate research on function and evolution of display signals. SIGNIFICANCE STATEMENT: Many animals use visual displays to convey important information across a variety of contexts. We know much about display variations and their adaptations to background noises, but the information content of displays remains largely unclear, especially for species without colorful ornaments and sounds. This imposes significant limitations on understanding of display signal function and evolution. Here, we unraveled the content of tail displays in an Asian agamid lizard by testing two hypotheses using newly developed 3D methods. Consistent with condition and resource hypotheses, our results showed that variation of tail displays reflects individual body condition and burrow quality in the Asian agamid lizard, which suggests tail displays likely play important roles in alleviating social conflict and mate assessment in lizards. In addition, our study demonstrated a novel aspect that displays of females can also convey similar information as those of males.