Memory of conspecifics in male salamanders Plethodon cinereus: Implications for territorial defense

Abstract

Abstract We investigated how exposure duration (time that two individuals initially interact) and separation interval (time between the initial interaction and a subsequent interaction) affect recognition memory of conspecifics in male red-backed salamanders Plethodon cinereus. Previous studies have demonstrated that this species aggressively defends territories. We recorded aggressive behavior to assess recognition memory, because aggression is more intense toward previously unencountered individuals compared to previously encountered individuals in this species. We found that with 15-min exposures and 5-day separation intervals, focal males did not spend significantly more time threatening ‘unfamiliar’ intruders than ‘familiar’ intruders. After either 8-hour exposures and 5-day separation intervals and 5-day exposures and 5-day separation intervals, focal males spent significantly more time threatening unfamiliar intruders than familiar intruders. These results suggest that male red-backed salamanders can remember familiar conspecifics (e.g., territorial neighbors) after at least an 8-hour exposure duration and that memory persists at least as long as 5 days. After 5-day exposure and 15-day separation intervals, we found no significant difference in aggressive behavior toward familiar and unfamiliar intruders. Long separation intervals (15 days) may lead either to loss of memory of previously familiar individuals or, alternatively, aggressive reassessment of individuals as only a change in behavior indicates positively that memory has occurred. Thus, variance in territorial defense within an individual may depend on its ability to recognize conspecific males.