Santos ME, Braasch I, Boileau N, Meyer BS, Sauteur L, Böhne A, Belting HG, Affolter M, Salzburger W. The evolution of cichlid fish egg-spots is linked with a cis-regulatory change.
Nat Commun 2014;
5:5149. [PMID:
25296686 PMCID:
PMC4208096 DOI:
10.1038/ncomms6149]
[Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Accepted: 09/04/2014] [Indexed: 11/09/2022] Open
Abstract
The origin of novel phenotypic characters is a key component in organismal diversification; yet, the mechanisms underlying the emergence of such evolutionary novelties are largely unknown. Here we examine the origin of egg-spots, an evolutionary innovation of the most species-rich group of cichlids, the haplochromines, where these conspicuous male fin colour markings are involved in mating. Applying a combination of RNAseq, comparative genomics and functional experiments, we identify two novel pigmentation genes, fhl2a and fhl2b, and show that especially the more rapidly evolving b-paralog is associated with egg-spot formation. We further find that egg-spot bearing haplochromines, but not other cichlids, feature a transposable element in the cis-regulatory region of fhl2b. Using transgenic zebrafish, we finally demonstrate that this region shows specific enhancer activities in iridophores, a type of pigment cells found in egg-spots, suggesting that a cis-regulatory change is causally linked to the gain of expression in egg-spot bearing haplochromines.
The mechanisms underlying the emergence of novel morphological traits are largely unknown. Here, the authors show that cis-regulatory changes controlling the expression of the fhl2b pigmentation gene are associated with the evolution of egg-spots colour markings in the male fins of a group of cichlids.
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