Reduced opsin gene expression in a cave-dwelling fish

Abstract

Regressive evolution of structures associated with vision in cave-dwelling organisms is the focus of intense research. Most work has focused on differences between extreme visual phenotypes: sighted, surface animals and their completely blind, cave-dwelling counterparts. We suggest that troglodytic systems, comprising multiple populations that vary along a gradient of visual function, may prove critical in understanding the mechanisms underlying initial regression in visual pathways. Gene expression assays of natural and laboratory-reared populations of the Atlantic molly ( Poecilia mexicana ) revealed reduced opsin expression in cave-dwelling populations compared with surface-dwelling conspecifics. Our results suggest that the reduction in opsin expression in cave-dwelling populations is not phenotypically plastic but reflects a hardwired system not rescued by exposure to light during retinal ontogeny. Changes in opsin gene expression may consequently represent a first evolutionary step in the regression of eyes in cave organisms.

Adult plasticity in African cichlids: Rapid changes in opsin expression in response to environmental light differences

“…When reared under different light regimens, developmental plasticity in opsin expression was observed in guppies (Ehlman et al 2015) and black bream (Shand et al 2008). Contrary to these results, rearing conditions had no effect on opsin expression in cave-dwelling mollies (Tobler et al 2010) and South American cichlid Aequidens pulcher (Wagner & Kroger 2000). Although not tested during development, adult sticklebacks showed minor plasticity in opsin expression (Flamarique et al 2013).…”

Pronounced heritable variation and limited phenotypic plasticity in visual pigments and opsin expression of threespine stickleback photoreceptors

“…Similar changes in cone numbers following metamorphosis of amphibians are considered inconsequential (Chen et al, 2008). Our results are in line with those from cave-dwelling mollies, where differences in LWS opsin mRNA expression between populations living in different light environments show little to no phenotypic plasticity (Tobler et al, 2010). It remains to be determined whether the changes in opsin mRNA expression due to phenotypic plasticity reported for other fishes (Fuller et al, 2005;Shand et al, 2008;Hofmann et al, 2010;Fuller and Claricoates, 2011) are ecologically meaningful.…”

An indigenous religious ritual selects for resistance to a toxicant in a livebearing fish

“…Overall, this study indicates that trait differentiation in this system may not only be affected by the major differences in abiotic environmental conditions, but also by more fine-scale differences within habitat types. Further evidence for this comes from morphological and heritable gene expression gradients within the sulphidic cave [18,19] as well as population genetic structure within habitat types (figure 1b) [11,12,20]. In summary, human cultural practices might not only affect population dynamics, but also drive adaptive divergence on small spatial scales.…”