Abstract
BackgroundThe bumblebee Bombus terrestris is an ecologically and economically important pollinator and has become an important biological model system. To study fundamental evolutionary questions at the genomic level, a high resolution genetic linkage map is an essential tool for analyses ranging from quantitative trait loci (QTL) mapping to genome assembly and comparative genomics. We here present a saturated linkage map and match it with the Apis mellifera genome using homologous markers. This genome-wide comparison allows insights into structural conservations and rearrangements and thus the evolution on a chromosomal level.ResultsThe high density linkage map covers ~ 93% of the B. terrestris genome on 18 linkage groups (LGs) and has a length of 2'047 cM with an average marker distance of 4.02 cM. Based on a genome size of ~ 430 Mb, the recombination rate estimate is 4.76 cM/Mb. Sequence homologies of 242 homologous markers allowed to match 15 B. terrestris with A. mellifera LGs, five of them as composites. Comparing marker orders between both genomes we detect over 14% of the genome to be organized in synteny and 21% in rearranged blocks on the same homologous LG.ConclusionsThis study demonstrates that, despite the very high recombination rates of both A. mellifera and B. terrestris and a long divergence time of about 100 million years, the genomes' genetic architecture is highly conserved. This reflects a slow genome evolution in these bees. We show that data on genome organization and conserved molecular markers can be used as a powerful tool for comparative genomics and evolutionary studies, opening up new avenues of research in the Apidae.
Highlights
The bumblebee Bombus terrestris is an ecologically and economically important pollinator and has become an important biological model system
For the remaining 2’020 loci, a total of 960 primer pairs were tested for amplification products. 910 of those (95%) yielded PCR products and were screened for polymorphisms in B. terrestris. 586 primer pairs (64.4%) showed two or more alleles of which 564 were tested for polymorphism in the mapping population “BBM1” [17], a subset of 300 loci by using fluorescent labels, 264 loci by using unlabeled primers
A screen of 2’304 A. mellifera SSR markers [23,40,41,42] yielded 15 loci that were polymorphic in BBM1. (Additional file 1)
Summary
The bumblebee Bombus terrestris is an ecologically and economically important pollinator and has become an important biological model system. The buff-tailed bumblebee Bombus terrestris is a key pollinator for crops and wild flowering plants as well as a model system in various disciplines of biological research This includes studies on population genetics, mating biology, sexual selection, caste determination, social behavior, host-parasite interactions, immunology and plant-pollinator interactions [1,2,3,4,5,6,7,8,9,10,11]. The genome of A. mellifera revealed several exceptional traits including an extremely high recombination rate, a very high AT-content, the lack of retrotransposons, and a high density of simple-sequence-repeats (SSR/microsatellites) [20] The evolution of these extraordinary genome characteristics is unclear. A comparison with the bumblebee genome might reveal common patterns resulting from the phylogenetically close relationship, and differences due to different social colony structures and ecologies of honeybees and bumblebees
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