At http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.3077.html:
2014 Nature America, Inc. All rights reserved.
A worldwide survey of genome sequence variation provides insight into the
evolutionary history of the honeybee Apis mellifera
Andreas Wallberg, Fan Han, Gustaf Wellhagen, Bjørn Dahle, Masakado Kawata,
Nizar Haddad, Zilá Luz Paulino Simões, Mike H Allsopp, Irfan Kandemir, Pilar
De la Rúa, Christian W Pirk & Matthew T Webster
The honeybee Apis mellifera has major ecological and economic importance. We
analyze patterns of genetic variation at 8.3 million SNPs, identified by
sequencing 40 honeybee genomes from a worldwide sample of 4 populations at a
combined total depth of 634×. These data provide insight into the
evolutionary history and genetic basis of local adaptation in this species.
We find evidence that population sizes have fluctuated greatly, mirroring
historical fluctuations in climate, although contemporary populations have
high genetic diversity, indicating the absence of domestication bottlenecks.
Levels of genetic variation are strongly shaped by natural selection and are
highly correlated with patterns of gene expression and DNA methylation. We
identify genomic signatures of local adaptation, which are enriched in genes
expressed in workers and in immune system– and sperm motility–related genes
that might underlie geographic variation in reproduction, dispersal and
disease resistance. This study provides a framework for future
investigations into responses to pathogens and climate change in honeybees.
Insect pollination is necessary for one-third of our food and is a vital
part of the ecosystem. The honeybee A. mellifera is a key pollinator, with
its services to agriculture valued at >$200 billion per year worldwide1. It
is therefore a major cause of concern that honeybees have faced huge and
largely unexplained colony losses in recent decades2. However, little is
known about global patterns of genomic variation in this species, which hold
the key to an understanding of its evolutionary history, the biological
basis of adaptation to different climates and mechanisms governing
resistance to disease.
The native distribution of A. mellifera encompasses Africa, Europe and
western Asia3–8, and molecular dating suggests that the population expanded
into this range around 1 million years ago3,4. Conflicting hypotheses have
been proposed for the origin of this expansion8, with analyses of limited
numbers of genetic and morphometric markers supporting an origin in the
Middle East3–5 and a study of nuclear SNPs arguing for an African origin7,9.
Honeybees show substantial phenotypic variation across their extensive
geographic range. European bees exhibit morphological and behavioral
adaptations to survive colder winters, whereas African colonies are more
aggressive and show a greater tendency to swarm. African bees are also
reported to have greater resistance to the pathogenic mite Varroa
destructor10–12, a major honeybee pathogen13,14. The genetic basis of this
phenotypic variation is largely unknown.
Humans began harvesting wax and honey from honeybee colonies at least 7,000
years before the present15. Human activity has led to the transportation of
honeybee colonies all over the world, artificial selection for desirable
traits and gene flow between native subspecies16, including the expansion of
hybrid strains of Africanized bees, known for their highly aggressive
stinging behavior, across the Americas17 after their introduction to Brazil.
The effects of these processes on the levels of genetic variation in
honeybees have not been comprehensively evaluated. Here we investigate the
evolution and genetic basis of adaptation in honeybees by performing
whole-genome sequencing of 140 A. mellifera worker bees from 14 separate
populations from a worldwide sample.
Received 17 January; accepted 1 August; published online 24 August 2014;
doi:10.138/ng.3077.
Kind regards,
Ghislain De Roeck
Belgium.
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