Analysis of caste diversification and the origin of thelytoky in North American honey bees, Apis mellifera (Hymenoptera: Apidae): a morphological perspective
Morris-Olson, Laura Shay
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Thelytoky is a subset of parthenogenetic processes in which a female produces unfertilized eggs that develop into an all-female lineage. Thelytoky frequently occurs in the African Cape honey bee. Apis mellifera capensis, but is rarely seen in European honey bees: e.g., A. m. iberica, A. m. camica and A. m. mellifera. Localized colonies of queenless honey bees fi-om Arizona, of unknown lineage, were determined to be serially thelytokous. The question arose as to whether this represented a trait expressed de novo in European honey bees or a reversion to a trait retained from A. m. capensis. Examination of the thelytokous colonies also revealed the presence of a caste member that is intermediate between the recognized castes (e.g., queens, workers, and drones), termed an intercaste. The relatedness of the intercaste to the other more defined caste members was posed as a second question of topic in this research. This research focused on the multivariate discrimination of this unknown honey bee lineage as morphologically compared with those of known African, European, and Africanized origin in an attempt to determine the source of this thelytokous behavior. The samples of African honey bees, against which the unknown thelytoky sample was tested, included A. m. capensis and A. m. scutellata. The European honey bee contrasts were represented by A. m. iberica, A. m. camica and A. m. mellifera. While many African and European bees are taxonomically identified to subspecies, Africanized bees are not distinguishable by taxonomic characters and therefore retain their European subspecies label of A. m. mellifera. Sample specimens of queens, drones, workers, and intercastes were also obtained and examined using multivariate discrimination. The right forewings from the honey bees were removed and measurements were recorded using established landmarks and venation patterns on the wing. Multivariate statistical techniques were applied (i.e., discriminate function analysis, size -free discriminate function analysis, Mahalanobis distances, and phenograms) to patterns in wing variation in order to discriminate among known categorical groups and align the thelytokous bees with a determined group.