Submitted to: Integrative & Comparative Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2006
Publication Date: 10/5/2006
Citation: Harrison, J.F., Fewell, J.H., Anderson, K.E., Loper, G.M. Environmental physiology of the invasion of the Americas by Africanized honeybees. Integrative and Comparative Biology pp. 1-13. 2006. Interpretive Summary: Genetic, physiological and morphological characteristics of Africanized honey bees (AHB) in southern Arizona are reported in this paper. The data show that a feral population of honey bees in Arizona became rapidly Africanized, with over 70% of colonies tested exhibiting mitochondrial DNA within four years of the invasion, with simultaneous changes in the frequencies of allozymes of malate dehydrogenase. Within four years after the invasion, the malate dehydrogenase allozyme frequencies were identical in the colonies with European and African mitotypes, suggesting that these had formed a freely mating and reproducing population. AHB workers in Arizona had higher thorax-to-body mass ratios and thorax-specific metabolic rates than European honey bees (EHB), but the differences were smaller than reported in Honduras or in the natal homelands of the bees, suggesting that hybridization has reduced the differences in flight capacity among these races. We also reviewed the factors responsible for overwintering and colony growth rate differences between AHB and EHB, and concluded that pollen vs. nectar foraging, and longevity differences were critical to these ecological differences. Finally, we compared the current advance of the AHB in the USA to predictions based on abiotic models.
Technical Abstract: The expansion of Africanized honey bees (AHB) through the Americas has been one of the most spectacular and best-studied invasions by a biotype. African and European honey bees (EHB) hybridize, but with time, tropical and subtropical American environments have become dominated by AHB that exhibit only 20-35% genetic contribution from western European bees, and a predominance of African behavioral and physiological traits. EHB persist in temperate environments. Clines between AHB and EHB exist in ecotones of S. and Central America, and are forming in N. America. What individual-level genetic, behavioral and physiological traits determine the relative success of the AHB as an invader in the neotropics, and of the EHB in temperate areas? Preferences for pollen vs. nectar may be an important trait mediating these ecological trade-offs, as preference for pollen enhances nutrient intake and brood production for the AHB in the tropics, while a relative preference for nectar enhances honey stores and winter survival for EHB. AHB exhibit morphological (higher thorax-to-body mass ratios) and physiological (higher thorax-specific metabolic rates) traits that may improve flight capacity, dispersal, mating success and foraging intake. Enhanced winter longevity, linked with higher hemolymph vitellogenin levels, may be a key factor improving winter survival of EHB. Data from S. America and distributions of AHB in the southwestern USA suggest that AHB-EHB hydrids will extend 200 km north of regions with a January maximal temperatures of 15-16 degrees C. The formation of biotypic clines between AHB and EHB represents a unique opportunity to examine mechanisms responsible for invader range limits.