BOLD OR BOXED?: TESTING FOR MORPHOLOGICAL AND PHYSIOLOGICAL DIFFERENCES BETWEEN EASTERN BOX TURTLES (TERRAPENE CAROLINA) WITH INDIVIDUAL VARIATION IN BOLDNESS

Abstract

Consistent individual variation in behavior has become a well-known and recognized phenomenon across animal taxa and is commonly referred to as animal personality. As the number of animal species and populations exhibiting personality continues to grow, many researchers have turned their attention towards studying the proximate causes and fitness implications of personality traits. In behavioral ecology and evolution consistent differences in individual state (intrinsic and/or extrinsic) are often theorized to co-vary with animal personality traits. Relatedly, some research has suggested that animal personality may involve individual differences in coping styles (e.g., proactive vs reactive), pace-of-life, and behavioral plasticity. The eastern box turtle, Terrapene carolina, is a long-lived reptile that is relatively easy to track and recapture and may therefore present an interesting and accessible vertebrate model for studies of animal personality traits in the wild. Past studies on this species have suggested it exhibits boldness personality and that this trait may interact with temperature and shell damage but not sex, age, or morphology. This study sought to further explore boldness as a personality trait in wild T. carolina and these previously studied interactions in addition to body condition, pinch force, innate immunity, plasma triglycerides, steroid hormone concentrations, and gastrointestinal nematode loads. The results indicate that eastern box turtles display consistent bold personalities across individuals and suggests that less bold individuals tend to display higher levels of plasticity in their bold responses (emergence from the shell) than bolder turtles. Moreover, box turtles appear to have the ability to habituate to repeated handlings which may increase their likelihood to behave boldly in subsequent tests. Turtles that are consistently proactive in their use of active defenses during a potentially threatening encounter may be more vulnerable to predation as they appear less likely to tightly close the shell (had lower pinch force values). However, turtles with the inability to fully close the shell (regardless of boldness) may also suffer similar consequences. Interestingly, boldness appears to be largely independent of the short-term physiological variables considered in this study, although there was a negative trend between average eye emergence and body condition, suggesting turtles that emerge quicker (bolder) may have higher body conditions. Additionally, boldness appeared to be dependent on some short-term environmental conditions, such as cloud coverage and immediate shell temperature, but appears to be largely uncoupled from the daily temperatures experienced across several days. Lastly, daytime temperatures differed between sexes and negatively correlated with age, suggesting that turtles of these distinctions may thermoregulate differently. Daytime temperatures also exhibited nearly significant positive trends with shell injury scores and body condition meaning there could be differential consequences for thermoregulators and thermoconformers. Further studies are needed to better understand the implications of these interactions and their possible correlation with other potential personality traits like aggression and exploration.