Warren G. Holmes - US grants

The overall goal of the proposed research is to explain the behavioral development of kin recognition abilities that result from social interactions during early ontogeny. Kin recognition, inferred when differential treatment of individuals correlates with genetic relatedness to the actor, will be investigated in a comparative study of Belding's ground squirrels, a relatively social rodent, and golden-mantled ground squirrels, a relatively nonsocial rodent. For Belding's ground squirrels, questions to be answered are: (1) when do weaned juveniles first recognize siblings? (2) how do social interactions with littermates and nonlittermates affect sibling recognition? and (3) how do juveniles retain the ability to recognize siblings after litters dissolve? For golden-mantled ground squirrels, effects of kinship (related vs. unrelated) and rearing association (reared together vs. reared apart) on the development of dam-offspring and sibling recognition will be investigated. Predictions about inter-specific differences in kin recognition will be tested by recording behavioral interactions between animals that inhabit large, outdoor enclosures for up to 14 days. Recognition abilities will be inferred by examining differences in rates of behavioral interactions (e.g., play) between animal groups that vary in kinship and early social experience. Kin recognition is central to inclusive fitness theory, which predicts that preferental treatment of kin (nepotism) will often enhance an individual's evolutionary (reproductive) success. Here, ground squirrels will be studied in a comparative framework to learn how social experience during early development produces generalized "rules of thumb" that allow kin to be recognized in many species. The proposed research will enhance our understanding of the developmental and evolutionary basis of social discrimination and nepotism, phenomena that are crucial to human social relations.

9311508 Holmes Alarm calls are vocalizations elicited by predators that can alert other members of the species to impending danger. Alarm calls have functional value only if they are responded to appropriately for the type of predator. Ms. Jill M. Mateo's doctoral-dissertation research seeks to determine when and how responses to alarm calls develop in young Belding's ground squirrels, as her pilot data show that alarm-call responses are not fully developed when young ground squirrels first emerge from the burrow where they were born. Ms. Mateo will test three predictions about the relative importance of auditory experience and social context for the development of alarm-call responses: (1) experience with the mother's vocalizations before weaning helps the young to discriminate alarm calls after weaning; (2) development of alarm-call responses after weaning is socially facilitated by observing adult alarm-call responses, and (3) the quality of juvenile alarm-call responses improves rapidly if they repeatedly hear alarm calls in the presence of other responding individuals. These predictions will be tested by playing back tape-recordings of alarm calls and recording the cardiac responses of unweaned pups and the behavioral responses of juveniles housed in a semi-natural environment or living in the field. Results will help explain how social influences contribute to the development of a critical survival skill, and will advance our understanding of how behavior develops through tightly-woven interactions between the organism and the series of environments it encounters throughout its life.

Kin Favoritism and Communal Nesting
Dr. Warren Holmes
Stephanie Jesseau

This combined laboratory- and field-research project will investigate kin recognition and nepotism in a communally-nesting, South American rodent, the degu (Octodon degus). Field evidence suggests that female degus nest communally, which means that two or more females share a burrow in which both females rear their litters. Due to communal nesting and birth synchrony, degu mothers encounter and become familiar with pups that are not their own offspring. Similarly, pups interact with both their siblings and non-siblings from the time they are born. In general, if a mother and her offspring share an early rearing environment with others, thus contaminating the correlation between rearing association and kinship, simple "familiarity" is unlikely to explain discriminative maternal care or sibling nepotism. In prior work, captive degu mothers discriminated between the odors of their own young and those produced by their co-nesting partner despite having lived with both kinds of pups. Three follow-up laboratories studies are proposed to investigate how kinship and being reared together affect maternal care and sibling relationships. First, it will be determined whether co-nesting mothers preferentially nurse their own young. Observations will be made of mothers' behavior toward their own vs other offspring. Differential milk transfer will also be determined by injecting mothers with small amounts of radiation (thus labeling their milk) and measuring the amount of radiation in the pups' feces. Second, food quality will be manipulated to evaluate how nutrition affects nursing preferences. The same behavioral observations and milk-labeling techniques as the previous experiment will be used. Third, I will examine juveniles' social preferences, specifically play-partner preferences, to determine how growing up together and kinship affect social development. Several field studies will also be conducted at Quebrada de la Plata, the field station of Universidad de Chile. It is not known whether degu mothers in the wild share the same natal chamber even though they occupy the same burrow system. Therefore, the first portion of the proposed field work will consist of monitoring co-nesting mothers using radio telemetry to determine if they share underground burrows before and/or after they give birth. The genetic relationship of co-nesting females in the wild is also not known. Therefore, small tissue samples will be taken from free-living degus to perform genetic analyses of DNA to determine the kinship of females sharing the same burrow. Behavioral observations will also be made to examine how agonistic and amicable behaviors vary with relatedness in degus. This study will reveal how kin recognition and nepotism are mediated in a group-living species in which "simple" familiarity is an inadequate proxy for kinship.