A soft selective sweep during rapid evolution of gentle behaviour in an Africanized honeybee

Abstract

Highly aggressive Africanized honeybees (AHB) invaded Puerto Rico (PR) in 1994, displacing gentle European honeybees (EHB) in many locations. Gentle AHB (gAHB), unknown anywhere else in the world, subsequently evolved on the island within a few generations. Here we sequence whole genomes from gAHB and EHB populations, as well as a North American AHB population, a likely source of the founder AHB on PR. We show that gAHB retains high levels of genetic diversity after evolution of gentle behaviour, despite selection on standing variation. We observe multiple genomic loci with significant signatures of selection. Rapid evolution during colonization of novel habitats can generate major changes to characteristics such as morphological or colouration traits, usually controlled by one or more major genetic loci. Here we describe a soft selective sweep, acting at multiple loci across the genome, that occurred during, and may have mediated, the rapid evolution of a behavioural trait.

Colonization history and population differentiation of the Honey Bees (Apis mellifera L.) in Puerto Rico

“…Our results suggest a hypothesis that the higher genetic diversity in the present population of gAHB may have allowed them to respond and adjust more efficiently to environmental changes than the EHB that preceded them in Puerto Rico (Delgado et al, 2012;Rivera-Marchand, Oskay and Giray, 2012). gAHB is a distinct population derived from the broader AHB hybridization spectrum, further evolved on the island (Avalos et al, (2017) and Figure 3b). It appears that the colonization event c.a.…”

“…The single colonization hypothesis Rico (Delgado et al, 2012;Rivera-Marchand, Oskay and Giray, 2012). 1994 (Cox, 1994) initiated a process of hybridization that after 20 years leads to the establishment of an admixed island population (Avalos et al, 2017). It appears that the colonization event c.a.…”

“…It appears that the colonization event c.a. 1994 (Cox, 1994) initiated a process of hybridization that after 20 years leads to the establishment of an admixed island population (Avalos et al, 2017). Currently, the island population is an important reservoir of genetic diversity with traits of high interest for apiculture and agriculture as discussed in relation to Varroa resistance, reduced aggressiveness, and low viral load.…”

“…These characteristics foster the rapid development of novel combinations of genetic variation. In Puerto Rico, gAHB has undergone a soft selective sweep favoring retention of genetic variation in the frequency profile of many alleles across the genome (Avalos et al, 2017) and leading to a genetic mosaic.…”

“…Though much is known about the events surrounding introduction and spread of AHB in the island and the selective pressures it experienced to become the gAHB (Avalos et al, 2017), the genetic origin and patterns of admixture of this population remain poorly understood. Past studies identified that gAHB is a contiguous population spanning Puerto Rico and two adjacent islands (Vieques, Culebra) with no detectable population substructure (Galindo-Cardona et al, 2013).…”