Visual adaptation in Lake Victoria cichlid fishes: depth-related variation of color and scotopic opsins in species from sand/mud bottoms

Abstract

BackgroundFor Lake Victoria cichlid species inhabiting rocky substrates with differing light regimes, it has been proposed that adaptation of the long-wavelength-sensitive (LWS) opsin gene triggered speciation by sensory drive through color signal divergence. The extensive and continuous sand/mud substrates are also species-rich, and a correlation between male nuptial coloration and the absorption of LWS pigments has been reported. However, the factors driving genetic and functional diversity of LWS pigments in sand/mud habitats are still unresolved.ResultsTo address this issue, nucleotide sequences of eight opsin genes were compared in ten Lake Victoria cichlid species collected from sand/mud bottoms. Among eight opsins, the LWS and rod-opsin (RH1) alleles were diversified and one particular allele was dominant or fixed in each species. Natural selection has acted on and fixed LWS alleles in each species. The functions of LWS and RH1 alleles were measured by absorption of reconstituted A1- and A2-derived visual pigments. The absorption of pigments from RH1 alleles most common in deep water were largely shifted toward red, whereas those of LWS alleles were largely shifted toward blue in both A1 and A2 pigments. In both RH1 and LWS pigments, A2-derived pigments were closer to the dominant light in deep water, suggesting the possibility of the adaptation of A2-derived pigments to depth-dependent light regimes.ConclusionsThe RH1 and LWS sequences may be diversified for adaptation of A2-derived pigments to different light environments in sand/mud substrates. Diversification of the LWS alleles may have originally taken place in riverine environments, with a new mutation occurring subsequently in Lake Victoria.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-1040-x) contains supplementary material, which is available to authorized users.

Cardinalfishes (Apogonidae) show visual system adaptations typical of nocturnally and diurnally active fish

“…Fish visual systems are generally adapted to the overall light available in their environment (Crescitelli, McFall‐Ngai, & Horwitz, ; Lythgoe, ). Therefore, small differences in habitat depth (Stieb et al, ; Terai et al, ) and substrate (Sabbah et al, ) can influence opsin expression according to gradients in available light and environmental reflectance, respectively, leading to diverse photoreceptor spectral sensitivities (Cronin et al, ; Lythgoe et al, ). Within the boundaries of the available light, colour sensitivity may also be shaped by specific behavioural tasks, such as mate choice, conspecific recognition, or foraging (Marshall, Vorobyev, & Siebeck, ; Marshall, ; Marshall & Vorobyev, ; Miyagi et al, ; Sandkam et al, ).…”

Visual pigment evolution in Characiformes: the dynamic interplay of teleost whole-genome duplication, surviving opsins and spectral tuning

“…Since variation in spectral sensitivities is due, to a large extent, to differences in vitamin A 2 content, it is not surprising that, with the notable exception of G. atracaudatus , there was little variation in blue cone sensitivity across species, as the effects of the chromophore are minimal at short wavelengths (Whitmore and Bowmaker 1989). Chromophore-based spectral tuning is characteristic of fish inhabiting long-wavelength-shifted habitats (Whitmore and Bowmaker 1989; Carleton et al 2006; Toyama et al 2008; Hofmann et al 2009; Miyagi et al 2012; Saarinen et al 2012; Weadick et al 2012; Liu et al 2016; Terai et al 2017; Torres-Dowdall et al 2017; Escobar-Camacho et al 2019), and is well suited to the variable light environments of Neotropical freshwater ecosystems, famously among the most diverse in spectra on the planet, from clear fast-running mountain creeks, to muddy ‘white waters’ (from ‘ agua blanca’ , indicating turbid highly scattering brown-tainted waters), and tannin-rich black waters (Wallace 1865; Costa et al 2013; Escobar-Camacho et al 2019). Finally, non-significant variation in rod chromophore proportions was observed between individuals, with some species exhibiting a similar proportion across individuals, while other species exhibit a larger range (Table S7).…”

Diversity in rest-activity patterns among Lake Malawi cichlid fishes suggests novel axis of habitat partitioning

“…In Lake Malawi alone, there are over 500 species of cichlids, inhabiting a diversity of environmental and feeding niches. Cichlid species exhibit a high degree of habitat fidelity and partition their environment along discrete ecological axes, including distinct biotic (food availability, predation, and parasites) and abiotic (light, water chemistry) environments that play a critical role in the origins and maintenance of cichlid biodiversity [12][13][14][15][16][17]. Predation on Malawi cichlids is considered to be relatively low, which is thought to have contributed to their evolutionary and ecological success [18].…”