Admixture in Africanized honey bees (Apis mellifera) from Panamá to San Diego, California (U.S.A.)

Abstract

The Africanized honey bee (AHB) is a New World amalgamation of several subspecies of the western honey bee (Apis mellifera), a diverse taxon grouped into four major biogeographic lineages: A (African), M (western European), C (eastern European), and O (Middle Eastern). In 1956, accidental release of experimentally bred “Africanized” hybrids from a research apiary in Sao Paulo, Brazil initiated a hybrid species expansion that now extends from northern Argentina to northern California (U.S.A.). Here, we assess nuclear admixture and mitochondrial ancestry in 15 bees from each of four regions across this expansive range: the Isthmus of Panamá; Guanacaste, Costa Rica, Tapachula, Mexico; and San Diego, U.S.A to assess ancestry of AHB several decades following initial introduction and test the prediction that African ancestry decreases with increasing latitude. We find that AHB nuclear genomes from Central America and Mexico have majority African ancestry (Mexico, 79%; Costa Rica 90%; and Panamá 94%) with varying contributions from western and eastern European lineages. AHB from San Diego (CA) show markedly lower African ancestry (40%) with substantial genomic contributions from all four major honey bee lineages. The mitochondria of all bees sampled in Costa Rica and Panamá originated in Africa. The majority (11) of bees sampled in Mexico carried African mitochondria with the remainder carrying eastern European mitochondria. In the San Diego population, mitochondria from all four lineages are present. Genetic diversity measures from all New World populations are similar and exceed those of ancestral forms. The unique genetic makeup of the San Diego honey bee population makes it a rich source of genetic material for honey bee breeding.

Dominance of African racial ancestry in honey bee colonies of Mexico 30 years after the migration of hybrids from South America

“…The nuclear analysis revealed that Mexican honey bee colonies had principally African ancestry and a minor proportion of European racial ancestry, with admixture patterns varying across the country, according to management, beekeeping regions, and latitude. that found a latitudinal effect on African ancestry (Agra et al, 2018;Porrini et al, 2022;Sheppard et al, 1991;Whitfield et al, 2006;Zárate et al, 2022), suggesting that A lineage may be disadvantaged at higher latitudes and altitudes due to lower temperatures and longer winters (Calfee et al, 2020;Harrison et al, 2006). In managed colonies of the Northern beekeeping region, there was a higher decline in the proportion of African nuclear ancestry compared to feral colonies.…”

“…These SNPs distinguish between the three lineages most abundant in the Americas: C, M, and A (Chapman et al, 2015). Lineages O and Y have not been detected in the Americas, except for a few reports of O (Magnus & Szalanski, 2010;Zárate et al, 2022). The amplicons containing the SNPs were amplified in four PCR multiplex sets following the authors' recommendations and then sequenced using the MiniSeq platform (Illumina, San Diego, CA, USA) (Chapman et al, 2015).…”

Population origin, body mass, and viral infections influence drone honey bee (Apis mellifera) heat tolerance

“…Perhaps most interestingly, in the second common garden experiment (which did test managed and unmanaged colonies), we found that drones from different origins within California did have different patterns of survival, with unmanaged-origin drones being more likely to survive the heat challenge than commercial-origin drones. This is exciting because the experiment was conducted in Southern California, where feral colonies tend to have a greater proportion of African ancestry than the drones from commercial colonies, which originate from Northern California (outside the Africanized zone) [24]. We speculate that colonies surviving without management in Southern California are under continuous natural selection for heat tolerance.…”

“…For example, a major heat-wave from September 5-7, 2020, in Riverside County caused daytime highs to reach 47 °C [22], and inland counties such as Riverside and San Bernardino are expected to experience higher temperatures during future heat-waves compared to coastal counties, such as Los Angeles [23]. Interestingly, unmanaged (feral) honey bees in Southern California have been genetically characterized and found to contain approximately 25% African ancestry [24]. Since African honey bees survive in hot climates, and unmanaged honey bees in Southern California have been historically exposed to intense heat, we expect bees from this population to possess adaptations to heat and drought stress.…”

“…In a common garden experiment, we compared heat tolerance (survival) of drones originating from Ukraine, Australia, and California with variable body sizes. In a second common garden experiment, we conducted a similar analysis of drones from feral (hybridized, with some African ancestry) [24] and commercial (managed, with no African ancestry) lineages in California. Finally, we investigated interactions between body mass, viral infection, and fertility of both naturally infected and experimentally infected drones whose sperm cells were subjected to heat challenges.…”