Individual differences and reproductive success in yellow-bellied marmots

Abstract

Mirror-image stimulation (MIS) was used to determine the individual behavioral phenotypes of 90 adult, 132 yearling, and 135 young yellow-bellied marmots (Marmota flaviventris). Linear typal analysis (LTA) was used to group individuals based on similarities in their MIS scores. Principal component analysis (PCA) was used to evaluate the patterns of variation in behaviors and discriminant function analysis (DFA) was used to determine if there were consistent differences in marmot behavior. LTA produced two interpretable groups that were significantly and negatively correlated. Marmots in each group formed a shy-bold continuum. Bold animals were those that approached the mirror early and made nose contact with the image whereas shy animals approached the mirror late in the run, spent time in the back half of the arena, and frequently chirped at the image. Behaviors shifted with age; young were predominantly bold and adults were predominantly shy. This shift appears to be developmental and not genetically determined. Reliability and predictability analyses indicated that there is a 75% probability that a MIS run correctly identifies an individual's behavioral phenotype. The probability increases to 90% for those individuals with high loading scores. Play, agonistic, and amicable behaviors of female yearlings recorded in the field were significantly correlated with their MIS behavioral phenotypes whereas only play of male yearlings was so correlated. Correlations among eight life-history traits of adult females were independent of behavioral phenotypes. Shy females were more likely to be associated with female non-kin, produced more daughters, and were more likely to be immigrants. Among female yearlings, shy phenotypes were likely to become recruits and bold phenotypes were more likely to disperse. Bold adult females recruited yearlings regardless of their behavioral phenotype whereas shy adult females recruited primarily shy yearlings and the majority of bold yearlings dispersed. Among adult males, shy phenotypes were more likely to be territorial-colonial and to produce more young. Lifetime reproductive success (LRS) of females was strongly related to the number of years of residency, which was strongly correlated with the frequency of reproduction and the production and recruitment of offspring. The demographic patterns were independent of behavioral phenotype. Behavioral phenotype impacts demographic trends mainly by increasing the recruitment of daughters by bold females. LRS of males depends on the length of residency. Shy males have a higher LRS because they are territorial-colonial for a longer time and produce more young. Bold individuals appear to be those that are sub- ordinate and attempt to affiliate with other marmots whereas shy individuals appear to be dominant and less likely to be affiliative. By being more aggressive, the shy marmot is more likely to achieve residency as a yearling or adult whereas the more affiliative adult is more likely to recruit offspring, but affiliative yearlings are less likely to become recruits, especially when the adults are the dominant, “shy” individuals.