Revisiting the Iberian honey bee (Apis mellifera iberiensis) contact zone: maternal and genome-wide nuclear variations provide support for secondary contact from historical refugia

Dissecting diversity patterns of organisms endemic to Iberia has been truly challenging
for a variety of taxa, and the Iberian honey bee is no exception. Surveys of genetic
variation in the Iberian honey bee are among the most extensive for any honey bee
subspecies. From these, differential and complex patterns of diversity have emerged,
which have yet to be fully resolved. Here, we used a genome-wide data set of 309 neutrally
tested single nucleotide polymorphisms (SNPs), scattered across the 16 honey
bee chromosomes, which were genotyped in 711 haploid males. These SNPs were analysed
along with an intergenic locus of the mtDNA, to reveal historical patterns of population
structure across the entire range of the Iberian honey bee. Overall, patterns of
population structure inferred from nuclear loci by multiple clustering approaches and
geographic cline analysis were consistent with two major clusters forming a welldefined
cline that bisects Iberia along a northeastern–southwestern axis, a pattern that
remarkably parallels that of the mtDNA. While a mechanism of primary intergradation
or isolation by distance could explain the observed clinal variation, our results are
more consistent with an alternative model of secondary contact between divergent
populations previously isolated in glacial refugia, as proposed for a growing list of
other Iberian taxa. Despite current intense honey bee management, human-mediated
processes have seemingly played a minor role in shaping Iberian honey bee genetic
structure. This study highlights the complexity of the Iberian honey bee patterns and
reinforces the importance of Iberia as a reservoir of Apis mellifera diversity.


Chávez-Galarza, J.; Henriques, D.; Johnston, J.C.; Patton, J.C.; Rufino J.; Carneiro M.; Pinto, M.A. Revisiting the Iberian honey bee contact zone: maternal and genome-wide nuclear variation provide support for secondary contact from historical refugia in Iberian honey bees (Apis mellifera iberiensis). Molecular Ecology (2015) 24, 2973–2992. DOI: 10.1111/mec.13223