Of bars and stripes: A Malawi cichlid hybrid cross provides insights into genetic modularity and evolution of modifier loci underlying colour pattern diversification

Abstract

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The repeated evolution of stripe patterns is correlated with body morphology in the adaptive radiations of East African cichlid fishes

“…Moreover, stripes are not confined to specific clades in the molecular phylogeny (Figure 1c) reflecting the high degree of evolutionary lability of stripes. Based on our phylogeny, we were not able to estimate the ancestral state of African cichlids, but based on previous work suggests that the frequent loss of stripes is explained by the “stripe inhibitor” gene agrp2 (Kratochwil et al, 2018), it seems more parsimonious that stripe presence is the ancestral state of East African cichlids (although it was likely not as exaggerated as in extant striped cichlids from the Great Lakes) and that the independent loss of stripes was caused by independent mutations affecting agrp2 expression (Kratochwil, 2019; Kratochwil et al, 2018; Urban et al, 2021) and possibly other genes (Gerwin et al, 2021).…”

“…Vertically barred snakes were shown to be more secretive and rely on crypsis or aggression as their primary mechanism of defense (Jackson et al, 1976). While vertical bars and horizontal stripes can be easily obtained by hybridization (Gerwin et al, 2021) in nature, they rarely occur in the same species, which indicates that vertical bars and horizontal stripes might have different ecological roles.…”

“…African cichlids (although it was likely not as exaggerated as in extant striped cichlids from the Great Lakes) and that the independent loss of stripes was caused by independent mutations affecting agrp2 expression (Kratochwil, 2019;Kratochwil et al, 2018;Urban et al, 2021) and possibly other genes (Gerwin et al, 2021).…”

Comparative ontogenetic and transcriptomic analyses shed light on color pattern divergence in cichlid fishes

“…To investigate agrp2 expression differences in embryos/ juveniles, we took advantage of a hybrid cross between the striped species P. cyaneorhabdos and the nonstriped species P. demasoni in which we performed qPCR for agrp2. The advantage is that we can compare individuals within the same clutch that will become striped and nonstriped based on their genotype at the agpr2 allele (Gerwin et al, 2021;Kratochwil et al, 2018). Neither at a late embryonal stage (10 days postfertilization [dpf]) nor at a later juvenile stage, shortly before stripes form (20 dpf), could we find differential expression of agrp2 between individuals homozygous for the striped P. cyanorhabdos allele and individuals homozygous for the nonstriped P. demasoni allele (Supporting Information: Figure 4).…”

“…Another family of fish in which the genetic basis and transcriptional correlates of several pigment pattern and coloration phenotypes have been thoroughly investigated are cichlid fishes. The phenotypes that have been studied from a genetic and/or transcriptomic perspective include egg spot patterns (Henning & Meyer, 2012; Salzburger et al, 2007; Santos et al, 2014), morphological color change (Henning et al, 2013; Kautt et al, 2020; Kratochwil et al, 2022), blotch patterns (Roberts et al, 2017, 2009), general differences in pigment cell distribution (Albertson et al, 2014), yellow, carotenoid‐based coloration (Ahi et al, 2020), and vertical bar patterns (Gerwin et al, 2021; Liang et al, 2020). Another common phenotype that has been investigated molecularly are horizontal stripe patterns in cichlids.…”