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.