Armed and well dressed: The role of jaw size and ornamentation on survival probability of the Whiptail lizard, Cnemidophorus occelifer

Background/Question/Methods

Male secondary sexual traits may arise from female choice and/or from male-male competition and are related to individual reproductive success. Ornaments are used to attract mates, and weapons are used in combat with rivals for access to females. Polygyny is the most common mating system in lizards and males frequently present conspicuous coloration as ornaments and have weaponry, such as enlarged jaws. However, the allocation of energy to enhance reproduction success may reduce growth and survival. We test hypotheses concerning the influence of ornaments and weapons on survival through a mark-recapture study with a population of the Brazilian Whiptail lizard, Cnemidophorus occelifer. We captured adult males using a trapping grid, and identified them using digital photography. Using mark-recapture models, we modeled survival probability as a function of jaw size and percent of the body covered with conspicuous coloration.

Results/Conclusions

Detection probability varied over time (range 0.03 - 0.30). Three models ranked highly and included 80% of the total AICc weight. The most parsimonious model (AICc weight = 0.33) modeled survival as a function of jaw size. Individuals with larger jaws had lower survival.  However, the second (AICc weight = 0.29) and third (AICc weight = 0.18) models, suggest a more nuanced relationship between survival, jaw size and coloration as these models supported interaction effects between jaw size and conspicuous coloration. Individuals with large jaw size and much coloration, or with small jaw size and less coloration survived at high probabilities. Combats may occur when the  opponent’s quality is not obvious, which reduces survival due to injuries and/or predation, since individuals could be less vigilant. Because large-jawed, conspicuous males are generally dominant, other individuals may not enter in combat with them. Likewise, small-jawed, inconspicuous males generally choose not to enter in a combat because they do not have the necessary weapons. Hence, these two phenotypes may represent two optimal strategies in the population.