Paternal kin discrimination by sons in male chimpanzees transitioning to adulthood

Although paternal investment explains the evolution of fatherhood from a functional perspective, its evolutionary origins are unclear. Here we investigate whether a building block for paternal investment, father-offspring discrimination, is present in our closest living relatives, chimpanzees. Adolescent and young adult males (12 - 21 years old) maintained proximity and groomed with their fathers more frequently than with other males given how often they associated. This discrimination did not likely increase the short-term inclusive fitness of fathers or sons because the absolute time they spent in proximity or grooming did not exceed the time spent in these activities by other dyads. Almost all grooming was done by sons rather than fathers, suggesting that sons are responsible for observed biases in father-son behavior. Father-offspring discrimination could partly be explained by young males socializing with males who were more likely to be their father based on their age at the time of the young male’s conception. Two other cues of paternity, the other male’s rank at the time of the young male’s infancy and the other male’s association frequency with the young male’s mother during the young male’s infancy/juvenility, failed to predict association-controlled proximity or grooming. Father-son biases persisted even after controlling for characteristics of males that predicted paternity probability, implicating other cues that we did not examine. These results suggest that an important factor for the evolution of highly investing fathers in humans, father-offspring discrimination, may have been present in simpler form in the last common ancestor they shared with chimpanzees.

Offspring Discrimination Without Recognition: California Towhee Responses to Chick Distress Calls

AbstractAccurate offspring discrimination improves parental fitness by ensuring appropriate parental investment. In colonial avian species, offspring discrimination is often mediated by recognition of individual offspring vocalizations, but spatially segregated species do not necessarily need sophisticated recognition abilities if parents can use alternative information to distinguish offspring from nonoffspring. I experimentally tested the hypothesis that territorial California Towhee (Pipilo crissalis) parents use a location-based decision rule, instead of true vocal recognition of offspring, when deciding whether to respond to chick distress calls. Accurate responses to offspring distress calls should be favored by natural selection because they can have large fitness benefits if parents succeed in chasing away potential nest predators. Responses to nonoffspring, in contrast, may be costly and should not be favored by natural selection. Towhee parents were presented with a series of three playback experiments in which I manipulated the identity of the vocalizing chick, the age of resident chicks, and the location of the distress call broadcast. Parents showed no evidence of individual vocal recognition and no pattern of differential response to distress calls when offspring age differed from that of the calling chick. Parents did, however, exhibit a significant tendency to approach distress calls originating near their offspring more often than distress calls originating elsewhere on their territory. These results provide support for the evolution of an offspring discrimination strategy based on a simple location-based decision rule instead of true vocal recognition.

Parent-offspring discrimination in the prairie vole and the effects of odors and diet

The objectives of this study on the prairie vole (Microtus ochrogaster) were to determine whether (i) parents are able to distinguish their own young from alien young, (ii) conspecific odors influence parent-offspring discrimination, and (iii) diet affects the cues used in parent-offspring discrimination. Parent-offspring discrimination was inferred from differential behaviors directed by adults towards their own offspring and alien offspring. In experiment 1, parent-offspring dyads showed high frequencies of cohesive behaviors and low frequencies of agonistic behaviors, while dyads of adults and alien offspring showed significantly more agonistic and fewer cohesive behaviors. In experiment 2, dyads of parents with their own offspring were tested in an arena containing their own soiled shavings, soiled shavings from another family, or clean shavings. Dyads engaged in significantly fewer investigatory behaviors and more cohesive behaviors when tested with their own familiar odors than when tested with unfamiliar odors or odors from clean shavings. In experiment 3, we tested dyads of unrelated adults and young that had been fed either the same or different dietary supplements. There were no significant differences in the frequencies of investigatory, cohesive, or agonistic behaviors in dyads fed the same diet and those fed a different diet.