Cichlid fish visual systems: mechanisms of spectral tuning

Abstract

Hundreds of species of cichlid fishes have evolved in the Great Lakes of Africa. These colorful fishes are known for their ecological diversity. Here, we discuss the diversity of their visual systems. Cichlids have seven unique cone opsin genes, which produce visual pigments sensitive from the ultraviolet to the red end of the spectrum. Different species typically express three visual pigments to produce a trichromatic visual system. Because species differ in which sets of opsin genes they express, visual sensitivities can differ widely. In addition to the large visual pigment shifts from changing gene expression, cichlids can also more finely tune visual pigments through alterations in opsin amino acid sequence. Both of these tuning mechanisms likely play an important role in cichlid ecology and could contribute to the evolution of cichlid diversity through speciation.

Genetic interactions controlling sex and color establish the potential for sexual conflict in Lake Malawi cichlid fishes

“…The rapidity of this radiation, extreme endemism (Parnell and Streelman, 2011) and continued low levels of gene flow between species (Mims et al, 2010) has led to a phenomenon wherein genetic incompatibilities between lineages are considerably outpaced by speciation (Stelkens et al, 2010). The integrity of species is maintained by pre-zygotic mechanismsassortative mating based on visual (Seehausen et al, 1997(Seehausen et al, , 2008van Oppen et al, 1998;Knight and Turner, 2004;Maan et al, 2004;Carleton, 2009), auditory (Amorim et al, 2004Simoes et al, 2008;Smith and van Staaden, 2009;Danley et al, 2011) and olfactory cues (Jordan et al, 2003;Plenderleith et al, 2005;Cole and Stacey, 2006) that sometimes breakdown. Interspecific and intergeneric hybridization has been well documented within all of the African cichlid species flocks, including LM (Ruber et al, 2001;Salzburger et al, 2002;Smith and Kornfield, 2002;Smith et al, 2003;Streelman et al, 2004;Gerlai, 2007;Mims et al, 2010).…”

Long-wavelength sensitive opsin (LWS) gene variability in Neotropical cichlids (Teleostei: Cichlidae)

“…Fragments of exon 2-5 (872 bp) were used in other research work (Terai et al 2006, Seehausen et al 2008) since they encoded the transmembrane domains of the protein. The changes in specific sites of the opsin gene sequences which provide the longest (LWS) and shortest (SWS1) wavelength appear to be more critical (Carleton 2009, especially those that occur between exon 1-3 (Terai et al 2006). Further, the opsin genes seem to accumulate the highest amount of variation (hofmann et al 2012).…”

“…Variable sites of these sequences may cause small changes in the absorbed light wavelength due to the replacement of amino acids as long as they occur in specific regions of exons (Yokoyama 2008, Carleton 2009). Since water is an environment that requires adaptations in the visual system, the heterogeneity of light would represent a strong selection pressure on these genes.…”

Seeing is believing: Dynamic evolution of gene families

“…Opsin genes expressed in photoreceptor cells are fundamental to animal vision and are a major force underlying the evolutionary adaptation to variable photic environments (12). The diversity of these genes is achieved by gene duplication followed by changes in amino acid sequence at key tuning sites.…”