Abstract
Comparative analyses of gene regulation inform about the molecular basis of phenotypic trait evolution. Here, we address a fin shape phenotype that evolved multiple times independently across teleost fish, including several species within the family Cichlidae. In a previous study, we proposed a gene regulatory network (GRN) involved in the formation and regeneration of conspicuous filamentous elongations adorning the unpaired fins of the Neolamprologus brichardi. Here, we tested the members of this network in the blockhead cichlid, Steatocranus casuarius, which displays conspicuously elongated dorsal and moderately elongated anal fins. Our study provided evidence for differences in the anatomy of fin elongation and suggested gene regulatory divergence between the two cichlid species. Only a subset of the 20 genes tested in S. casuarius showed the qPCR expression patterns predicted from the GRN identified in N. brichardi, and several of the gene-by-gene expression correlations differed between the two cichlid species. In comparison to N. brichardi, gene expression patterns in S. casuarius were in better (but not full) agreement with gene regulatory interactions inferred in zebrafish. Within S. casuarius, the dorsoventral asymmetry in ornament expression was accompanied by differences in gene expression patterns, including potential regulatory differentiation, between the anal and dorsal fin.
Highlights
Gene regulatory networks (GRNs) describe the regulatory relationships among genes involved in the development and maintenance of phenotypes
Using qPCR assays of candidate genes associated with ontogenetic and regenerative fin growth in the zebrafish[14] as well as analyses of co-expressed genes and predicted transcription factors[16], we identified potential members of a gene regulatory network involved in the formation of the ornamental fin phenotype
We predicted that the L/S expression differences and the gene expression correlations observed in N. brichardi would be detected in the distinctly elongated dorsal fin of S. casuarius, but not necessarily in its anal fin
Summary
Gene regulatory networks (GRNs) describe the regulatory relationships among genes involved in the development and maintenance of phenotypes. We tested the members of the GRN in another cichlid fish, the blockhead cichlid Steatocranus casuarius This species is interesting because the unpaired fins of males differ with www.nature.com/scientificreports respect to the presence and extent of filament elongation (Fig. 1A). We used the same experimental design as in our work with N. brichardi and compared the expression levels of 20 GRN genes between the elongated (L) and the short (S) regions of the anal and the dorsal fins, using both intact and regenerating fins All of these genes had shown significant L/S expression differences in N. brichardi, which suggested that their differential expression was associated with the growth pattern producing the fin elongations. Our findings suggest divergence in the regulation of the fin elongation phenotype between the two cichlid species
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