title: Kinship, parental manipulation and evolutionary origins of eusociality.
abstract: One of the hallmarks of eusociality is that workers forego their own reproduction to assist their mother in raising siblings. This seemingly altruistic behaviour may benefit workers if gains in indirect fitness from rearing siblings outweigh the loss of direct fitness. If worker presence is advantageous to mothers, however, eusociality may evolve without net benefits to workers. Indirect fitness benefits are often cited as evidence for the importance of inclusive fitness in eusociality, but have rarely been measured in natural populations. We compared inclusive fitness of alternative social strategies in the tropical sweat bee, Megalopta genalis, for which eusociality is optional. Our results show that workers have significantly lower inclusive fitness than females that found their own nests. In mathematical simulations based on M. genalis field data, eusociality cannot evolve with reduced intra-nest relatedness. The simulated distribution of alternative social strategies matched observed distributions of M. genalis social strategies when helping behaviour was simulated as the result of maternal manipulation, but not as worker altruism. Thus, eusociality in M. genalis is best explained through kin selection, but the underlying mechanism is likely maternal manipulation.
authors.affiliation: Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322-5305, USA karen.kapheim@usu.edu.
authors.forename: Karen M
authors.initials: KM
authors.lastname: Kapheim
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 621 Charles E. Young Drive South, Los Angeles, CA 90095, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Nonacs
authors.affiliation: Department of Biological Sciences, George Washington University, Washington, DC 20052, USA.
authors.forename: Adam R
authors.initials: AR
authors.lastname: Smith
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 621 Charles E. Young Drive South, Los Angeles, CA 90095, USA.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Wayne
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843, Balboa, Republic of Panama.
authors.forename: William T
authors.initials: WT
authors.lastname: Wcislo
mesh_terms: D000533:Altruism; D000818:Animals; D001516:Bees / Q000235:genetics / Q000502:physiology*; D001522:Behavior, Animal; D019143:Evolution, Molecular; D005260:Female; D056084:Genetic Fitness; D008954:Models, Biological; D009425:Nesting Behavior; D012098:Reproduction; D012919:Social Behavior
keywords: eusociality; inclusive fitness; kin selection; parental manipulation