Lack of Kin Recognition: Why Do Père David's Deer Respond Indiscriminately to Calf Distress Calls?

Abstract

Altruistic maternal behavior is widespread among mammals, yet its underlying evolutionary mechanisms and driving factors remain to be thoroughly investigated. Building upon previous observations of altruistic care behavior in Père David's deer (Elaphurus davidianus) in response to distress calls from non-related offspring, we designed a series of playback experiments to test several hypotheses explaining altruistic maternal behavior: the lack of kin recognition hypothesis, the "move-on" defense hypothesis, kin selection theory, reciprocal altruism, and the "learning to mother" hypothesis. Our results revealed that maternal responsiveness to calf distress calls was significantly influenced by whether the calf accompanied its mother: when it did, response intensity was significantly lower, whereas when separated, females responded indiscriminately to calls from both own and alien calves. These findings indicate that the allomaternal care behavior observed in Père David’s deer is consistent with the "lack of kin recognition" hypothesis, and neither the other observational data nor playback results supported the alternative hypotheses. These findings enhance our understanding of ungulate altruism and suggest future research should systematically explore evolutionary mechanisms driving diverse motivations for altruistic maternal behavior across species, considering varied environmental pressures and social structures.