SPEZZANO JR., L.C.; Miami University: Safety in numbers? Aggression in juvenile painted turtles, Chrysemys picta
Painted turtles (Chrysemys picta) occur in large numbers and are a model system for studying behavior in freshwater species. However, little is known about group dynamics and intraspecific agonism, or whether it is time, density- or individual size-dependent. Here, behavior was quantified by remotely videotaping turtles (17-19 months) within an indoor aquatic habitat. An initial group of 30 were exposed to conspecific densities of 6, 12 and 24 individuals with equal numbers of small, medium or large juveniles (grouped by weight). Behavior was recorded over 8, 30-minute periods from 0800 to 1700 over a 12:12 LD photoperiod beginning at 0700. A 12 individual subsample was selected that experienced each density treatment at the same weight category (i.e. 4 small turtles experienced each density). Dependent variables were instances of positive (aggressor) and negative (recipient) avoidance (>45° change in orientation) and contact (biting or head bumping) in water and on land. Aquatic avoidances decreased linearly with time, while terrestrial avoidances increased, though only the former effect was significant. Significant density and size effects were prevalent and aggression most often involved large turtles. Relative values (correcting for density) of aquatic avoidance and both terrestrial contact and avoidance decreased linearly with increased density. In addition, percentages of total aquatic aggression received by both small and medium individuals were 95, 78 and 65% for treatments of 6, 12 and 24 individuals, respectively. Perhaps, aggressive conspecifics are presented with more complicated search images as density increases. Further discussion will address how directly agonism leads to displacement from aquatic or terrestrial media and whether temperature or nutritional state affects aggression in juvenile turtles.
