Genetic basis of innovative anal fin pigmentation patterns in cichlid fish

The origination of novelty is one of the most fascinating questions in evolutionary biology. The repeated evolution of innovative pigmentation patterns on the anal fin in East African cichlid fish is an ideal model to study this question. One pattern is eggspots, the circular pigmentation pattern with a transparent outer ring that emerged once in the most species rich cichlid lineage, the haplochromines, exhibiting large varieties with different numbers, sizes and colours. Eggspots have been suggested to be involved in female attraction, male-male competition and species recognition. While ancestral haplochromine species feature another fin pigment trait in form of blotch, which is reddish with ill-defined boundary. Anal fin pigmentation pattern was also independently evolved in the ectodine lineage, which possesses similar blotch pattern as the haplochromine blotch. The ectodine blotch pattern was also suggested to be involved in female attraction, although less investigated. Unlike haplochromine eggspots, the ectodine blotch shows almost no variation among species. Here, by applying next generation sequencing technology (RNAseq and Ion Torrent sequencing) followed by a series data analysis, we found that haplochromine eggspots and the ectodine blotch share at least parts of a common gene network. Further sequencing data showed that many of the anal fin pigmentation related candidate genes have eggspots specific segregating patterns. While species with the blotch showed similar sequence patterns with species without anal fin pigmentation patterns. This might suggest that eggspots, but not the ectodine blotch, might have a much more independent gene network, which might explain its higher evolvability. Besides, we also described the evolutionary history of apolipoprotein D (ApoD) gene family in teleosts, whose expansion is via gene duplication and are located in two clusters in teleost fish. One member of this gene family was found to be highly expressed in the ectodine blotch. Interestingly, although most genes showed conserved homologous expression pattern in distant related teleosts, duplicated genes with new functions evolved in a lineage specific manner, especially in cichlid fish, and were expressed in two novelties, lower pharyngeal jaw and anal fin pigmentation. By investigating the genetic basis of the innovative anal fin pigmentation patterns in cichlid fish, this doctoral work gives clues about the relationship among evo-devo, novelty and biological diversity.