A RAD-tag genetic map for the platyfish (Xiphophorus maculatus) reveals mechanisms of karyotype evolution among teleost fish.
Mammalian genomes can vary substantially in haploid chromosome number even within a small taxon (e.g., 3-40 among deer alone); in contrast, teleost fish genomes are stable (24-25 in 58% of teleosts), but we do not yet understand the mechanisms that account for differences in karyotype stability. Among perciform teleosts, platyfish (Xiphophorus maculatus) and medaka (Oryzias latipes) both have 24 chromosome pairs, but threespine stickleback (Gasterosteus aculeatus) and green pufferfish (Tetraodon nigroviridis) have just 21 pairs. To understand the evolution of teleost genomes, we made a platyfish meiotic map containing 16,114 mapped markers scored on 267 backcross fish. We tiled genomic contigs along the map to create chromosome-length genome assemblies. Genome-wide comparisons of conserved synteny showed that platyfish and medaka karyotypes remained remarkably similar with few interchromosomal translocations but with numerous intrachromosomal rearrangements (transpositions and inversions) since their lineages diverged ∼120 million years ago. Comparative genomics with platyfish shows how reduced chromosome numbers in stickleback and green pufferfish arose by fusion of pairs of ancestral chromosomes after their lineages diverged from platyfish ∼195 million years ago. Zebrafish and human genomes provide outgroups to root observed changes. These studies identify likely genome assembly errors, characterize chromosome fusion events, distinguish lineage-independent chromosome fusions, show that the teleost genome duplication does not appear to have accelerated the rate of translocations, and reveal the stability of syntenies and gene orders in teleost chromosomes over hundreds of millions of years.
Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403.
Angel
A
Amores
Institute of Ecology and Evolution, University of Oregon, Eugene, Oregon 97403.
Julian
J
Catchen
Institute of Human Genetics, University of Würzburg, D-97074 Würzburg, Germany.
Indrajit
I
Nanda
The Genome Institute, Washington University School of Medicine, St. Louis, Missouri 63108.
Wesley
W
Warren
Department of Chemistry and Biochemistry, Texas State University, San Marcos, Texas 78666.
Ron
R
Walter
Physiological Chemistry, University of Würzburg, Biozentrum, Am Hubland, and Comprehensive Cancer Center, University Clinic Würzburg, 97074 Würzburg, Germany.
Manfred
M
Schartl
Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403 jpostle@uoneuro.uoregon.edu.
John H
JH
Postlethwait
D000818:Animals; D005075:Biological Evolution; D020451:Contig Mapping; D003532:Cyprinodontiformes / Q000235:genetics*; D005260:Female; D008040:Genetic Linkage; D059785:Karyotype; D008126:Lod Score; D008297:Male; D018895:Microsatellite Repeats; D026801:Synteny
conserved synteny; genome evolution; medaka; stickleback; swordtail; zebrafish