Dietary carotenoids enhance SWS1 expression in female western mosquitofish (Gambusia affinis) but do not impair their likelihood of pregnancy in the presence of male guppy.

The various cone opsin genes are responsible for distinct ecological tasks, with the altered expression profiles in teleost fishes representing an excellent paradigm for studying how fishes can quickly adapt to diverse habitats within their lifecycles. The molecular mechanisms underlying transcriptional switching among cone opsin genes are still being investigated, but factors such as light conditions, developmental stages, sex hormones, and diet are known to play a role in changing cone opsin expression profiles. Based on previous research on guppies, we hypothesized that a diet rich in carotenoids could enhance expression of the opsin gene LWS in western mosquitofish (Gambusia affinis) and potentially influence female mate choice. We raised female western mosquitofish under low-level or high-level carotenoid diets and then conducted female mating preference experiments, with or without the presence of male guppy (Poecilia reticulata). qPCR revealed that high carotenoid intake upregulates SWS1 rather than LWS transcription. This positive feedback loop may promote foraging efficiency and also protect the visual system from UV damage. The carotenoid diets had no effect on pregnancy likelihood, possibly because UV light is not a critical cue in western mosquitofish female mate choice and/or the light source we used did not encompass the UV spectrum. Presence of male guppies had no effect on pregnancy likelihood, though a previous study reported that it significantly reduced brood size. Therefore, interactions between male guppies and western mosquitofish likely reduces the number of copulations and/or disrupts parenting to reduce the number of offspring.