Abstract
BackgroundMalaria mosquitoes have had a remarkable stability in the number of chromosomes in their karyotype (2n = 6) during 100 million years of evolution. Moreover, autosomal arms were assumed to maintain their integrity even if their associations with each other changed via whole-arm translocations. Here we use high-coverage comparative physical genome mapping of three Anopheles species to test the extent of evolutionary conservation of chromosomal arms in malaria mosquitoes.ResultsIn this study, we developed a physical genome map for Anopheles atroparvus, one of the dominant malaria vectors in Europe. Using fluorescence in situ hybridization (FISH) of DNA probes with the ovarian nurse cell polytene chromosomes and synteny comparison, we anchored 56 genomic scaffolds to the An. atroparvus chromosomes. The obtained physical map represents 89.6% of the An. atroparvus genome. This genome has the second highest mapping coverage among Anophelinae assemblies after An. albimanus, which has 98.2% of the genome assigned to its chromosomes. A comparison of the An. atroparvus, An. albimanus, and An. gambiae genomes identified partial-arm translocations between the autosomal arms that break down the integrity of chromosome elements in evolution affecting the structure of the genetic material in the pericentromeric regions. Unlike An. atroparvus and An. albimanus, all chromosome elements of An. gambiae are fully syntenic with chromosome elements of the putative ancestral Anopheles karyotype. We also detected nonrandom distribution of large conserved synteny blocks and confirmed a higher rate of inversion fixation in the X chromosome compared with autosomes.ConclusionsOur study demonstrates the power of physical mapping for understanding the genome evolution in malaria mosquitoes. The results indicate that syntenic relationships among chromosome elements of Anopheles species have not been fully preserved because of multiple partial-arm translocations.
Highlights
Malaria mosquitoes have had a remarkable stability in the number of chromosomes in their karyotype (2n = 6) during 100 million years of evolution
The physical genome map developed for the European malaria vector An. atroparvus in this study demonstrates the power of chromosome-based assemblies for understanding genome evolution
The chromosome rearrangements identified here would be impossible to observe with routine cytogenetic techniques or with unmapped genome assemblies
Summary
Malaria mosquitoes have had a remarkable stability in the number of chromosomes in their karyotype (2n = 6) during 100 million years of evolution. We use high-coverage comparative physical genome mapping of three Anopheles species to test the extent of evolutionary conservation of chromosomal arms in malaria mosquitoes. Chromosome rearrangements play a role in species’ adaptation and evolution by generating structural genomic variations [1], affecting recombination [2], and changing the pattern of gene expression [3, 4]. Chromosome rearrangements affect all groups of living organisms, genomes of different lineages have been preferentially shaped by particular types of rearrangements. Karyotypes of Anopheles species have no variations in the number of chromosomes that is always 2n = 6 [9]. The mechanisms of the observed lineage-specificity in the patterns of genome rearrangements are not well understood
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