FACIAL RECOGNITION: INTRASPECIFIC VARIATION AND DEVELOPMENT OF SPECIALIZATION IN POLISTES FUSCATUS, A MODEL SYSTEM

Abstract

Specialized face learning, the ability to learn and remember faces better than other visual stimuli, occurs across a wide range of social animal taxa. However, the ontogeny of specialized face learning, specifically whether it develops due to innate, learned, or a combination of innate and learned factors, remains debated in the literature. Empirical data on face specialization has supported all three hypotheses, yet conflicting methodologies and data interpretations complicate our understanding of the ontogeny of face specialization. In this study, we use Polistes fuscatus (paper wasp), a system with intraspecific variation in developmental environment (innate) and experience (learned), to test the ontogeny of specialized face learning. Our results support the combination hypothesis for the development of specialized face learning, with both innate and learned factors needed to fully explain intraspecific variation in face specialization. Wasps with better early nutritional environment (gynes) learned to discriminate faces more accurately than wasps with poorer nutrition during early development (workers), perhaps due to innate variation in neural structures. Furthermore, older wasps (foundresses) learned faces faster than other stimuli, while younger wasps (gynes) showed no difference in rate of learning between stimuli. We posit that older wasps have greater specialization for learning faces than younger wasps due to higher levels of facial exposure throughout life. Controlled manipulations of early development and adult experience will be useful to provide a more detailed analysis of the ontogeny of specialized face learning. Our results, which suggest that the combined effects of learned and innate factors are necessary to explain the ontogeny of specialized face learning, may be generalizable to all social animals. In many signaling systems, intraspecific variation in recognition abilities is based on developmental stage, experience, or caste. However, the occurrence of intraspecific variation in recognition has not been thoroughly examined in species with individual recognition. For example, previous work has shown that individual recognition is an important aspect of the social life of Polistes fuscatus (paper wasp) nest founding queens, as individual recognition stabilizes dominance interactions and reduces aggression. Yet, to date the potential for individual recognition among P. fuscatus workers has been largely ignored. Here, we explore whether there is intraspecific variation in individual recognition by testing P. fuscatus worker recognition abilities in a series of staged contests. The results indicate that P. fuscatus workers are capable of individual recognition: focal workers paired with previously encountered partners experienced significantly less aggression and more nonaggressive bodily contact than focal workers paired with unknown social partners. Therefore, this study finds no evidence of intraspecific variation in individual recognition across castes of P. fuscatus. We propose two potential explanations for individual recognition among workers: 1) worker individual recognition may be favored because it provides social benefits to workers, or 2) worker individual recognition may be a byproduct of selection for individual recognition in foundresses. Individual recognition is often considered a cognitively challenging form of recognition, so future studies that compare the sophistication of recognition across castes will be useful to assess whether there are more subtle differences in cognitive abilities or recognition behavior between P. fuscatus nestfounding queens and workers.