Runners and fighters: clutch effects and body size drive innate antipredator behaviour in hatchling lizards

Abstract

Innate antipredator responses are integral for survival in many species, particularly those which lack parental care. Antipredator responses include both active (fight or flight) and passive behaviours (immobility). As the success of antipredator responses directly relates to survival and fitness, investigating the drivers that explain variance in these traits is key to understanding how predation shapes the instinctive behaviour of animals. We quantified innate antipredator behaviour of hatchling Australian water dragons (Intellagama lesueurii) immediately after hatching using a model snake to simulate a series of attacks, and scored their behaviour using a fight or flight index. Then we explored which factors were related to dragon antipredator behaviour, such as habitat disturbance, origin population, morphology, and parental genetic effects and phenotype (clutch effects). We developed multiple hypotheses and used model selection to determine which factors drive variation in hatchling antipredator behaviour. Clutch effects explained a significant proportion of variation in innate antipredator responses, suggesting a heritable component. We also found an effect of body size on innate antipredator behaviour: larger hatchlings were more prone to flight behaviour (e.g. short-distance runs and long-distance sprinting), while smaller individuals were more prone to standing their ground and being aggressive (e.g. throat puffing, mouth gaping, biting). Clutch effects also explained a significant proportion of the variance in dragon body size. Our study provides evidence that the innate antipredator responses of water dragons are heritable in origin (directly through clutch effects, and indirectly through body size) and not associated with particular populations or habitat types. We suggest future research examine the survival implications of these responses. The action an animal takes in response to a predator is a life or death decision, and can be required immediately after birth. These innate antipredator behaviours may be genetically linked, and enable individuals to emerge into their environment with the necessary behaviour to promote survival. We examined what factors drive hatchling lizards to exhibit different innate antipredator behaviour. Our study found that body size affected their innate behaviour: larger hatchlings were more prone to flee and smaller hatchlings were more likely to fight. Interestingly, parental genetics and phenotype (clutch effects) also significantly explained the variation in innate antipredator behaviour, which supports the hypothesis that these behaviours are heritable. Understanding what drives variation is a cornerstone of evolutionary biology, and our findings raise questions about how selection acts on antipredator behaviour and the degree to which they are plastic.