title: Energetics reveals physiologically distinct castes in a eusocial mammal.
abstract: Eusociality, which occurs among mammals only in two species of African mole-rat, is characterized by division of labour between morphologically distinct 'castes'. In Damaraland mole-rats (Cryptomys damarensis), colony labour is divided between 'infrequent worker' and 'frequent worker' castes. Frequent workers are active year-round and together perform more than 95% of the total work of the colony, whereas infrequent workers typically perform less than 5% of the total work. Anecdotal evidence suggests that infrequent workers may act as dispersers, with dispersal being limited to comparatively rare periods when the soil is softened by moisture. Here we show that infrequent workers and queens increase their daily energy expenditure after rainfall whereas frequent workers do not. Infrequent workers are also fatter than frequent workers. We suggest that infrequent workers constitute a physiologically distinct dispersing caste, the members of which, instead of contributing to the work of the colony and helping the queen to reproduce, build up their own body reserves in preparation for dispersal and reproduction when environmental conditions are suitable.
authors.affiliation: Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa. m.scantlebury@zoology.up.ac.za
authors.forename: M
authors.initials: M
authors.lastname: Scantlebury
authors.forename: J R
authors.initials: JR
authors.lastname: Speakman
authors.forename: M K
authors.initials: MK
authors.lastname: Oosthuizen
authors.forename: T J
authors.initials: TJ
authors.lastname: Roper
authors.forename: N C
authors.initials: NC
authors.lastname: Bennett
mesh_terms: D000818:Animals; D001481:Basal Metabolism; D050218:Body Fat Distribution; D001835:Body Weight; D004734:Energy Metabolism; D005260:Female; D008297:Male; D019577:Mole Rats / Q000145:classification* / Q000378:metabolism*; D011891:Rain; D012098:Reproduction / Q000502:physiology; D012919:Social Behavior; D012930:Social Dominance; D013019:South Africa