A Microsatellite-Based Genetic Linkage Map of the Cichlid Fish, Astatotilapia burtoni (teleostei): A Comparison of Genomic Architectures Among Rapidly Speciationg Cichlids

Cichlid fishes compose an astonishingly large number of species and fonned species flocks in recordbreaking time. To facilitate efficient genome scans and comparisons of cichlid genomes, we constructed a medium-density genetic linkage map of microsatellite markers of Astaloliklpia burloni. The mapping cross was derived from two inbred laboratory lines to obtain F2 progeny by intercrossing. The map revealed 25 linkage groups spanning 1249.3 cM of the genome (size ~950 Mb) with an average marker spacing of6.12 cM. The seven Hox clusters, ParaHox Cl, and two paralogs of Pdgfrf!> were mapped to different linkage groups, thus supporting the hypothesis of a teleost-specific genome duplication. The A. burloni linkage map was compared to the other two available maps for cichlids using shared markers that showed conservation and synteny among East African cichlid genomes. Interesting candidate genes for cichlid speciation were mapped using SNP markers. THE adaptive radiations of cichlid fishes of East Mrica are well-known examples for rapid diversification and explosive speciation. More than 2000 species are phylogenetically very closely related since they originated within extremely short evolutionary time spans (MEYER et al. 1990; MEYER 1993; KORNFIELD and SMITH 2000; VERHEYEN et al. 2003; KOCHER 2004; SALZBURGER and MEYER 2004; SALZRURGER et aL 2005). Astonishingly, large numbers of species make up the three species flocks, each composed of hundreds of species, in lakes Victoria, Malawi, and Tanganyika (FRYER and ILES 1972). Despite the huge phenotypic diversity displayed by each of the species flocks, molecular phylogenetic studies on this problem revealed that many of the species evolved similar morphologies convergently in each of these three adaptive radiations (MEYER et al. 1990; KOCH ER et al. 1993; MEYER 1993; STIASSNY and MEYER 1999). These striking phenotypic similarities among cichlid fishes from different species flocks that have evolved in parallel make the study of the underlying genetic architecture of cichlids particularly interesting. Supporting information is available online at hllp:!www.genetics.org/ cgi/ content/full! genetics.108.089367 /OCI. Sequence data from this article have been deposited with the EMBL/ GenBank Data Libraries under accession nos. EU564211-EU564333. J Comsponding auJlwr: Lehrstuhl fUr Zoologie und Evolutionsbiologie, Fachbereich Biologic, Universitiit Konstanz, Fach M617. Univcrsitiitssu"assc 10, 78457 Konstanz, Germany. E-mail: [email protected] The obseIVed redundant patterns in the evolutionary diversification of cichlid fishes support the view that the three large East African lakes are a natural experiment of evolution, in which this parallel evolution might ultimately help to better understand the processes that led to the repeatedly evolved patterns of diversification. Particularly in the species of cichlids in lakes Victoria and Malawi, adaptive radiations are very young and genetically extremely similar. Comparative studies on the genomic organization of these closely related yet morphologically diverse fishes will help to unravel the genetics of speciation (Kocm:R 2004; ALBERTSON and KOCHER 2006; HOEGG et al. 2007). Investigation of the molecular basis of those different phenotypes, i.e., the genetic and transcriptional changes that underlie differences among organisms, can be achieved through detailed comparisons of genome and transcriptome scans also including candidate gene approaches (STREELMAN and KOCH ER 2000; BRAASCH et al. 2006; SALZRURGER et al. 2007, 2008; GERRARD and MEYER 2007). For example, the gene for longwaveltmgth-sensitive opsin (Lws) has been reported to be involved in sympatric speciation through ecological adaptation and mate choice of cichlids (CARLETON et al. 2005; MAAN et al. 2006; TERAI et al. 2006; SEEHAUSEN et al. 2008), while the microfibril-as.mciated glycoprotein (Mfap4) is a good candidate for examining species differences with regard tojawdevelopment (KOBAYASHI et al. 2006). Species-specific linkage maps have recently become established as important genetic tools in an effort to gain more detailed knowledge of genotype-phenotype