By attempting to recreate the pattern of opsin expression found in naturally varying populations of bluefin killifish, this study assesses the extent of flexibility in cone abundance and ascribes it to either genetic or environmental variation. Four males were bred with several random females, and the resulting clutches were divided into two tanks with water conditions that mimicked the variation in natural populations. One tank had tea-stained water that represented swamp conditions with low transmission of UV and blue light. The second tank represented spring populations which had clear water with high transmission of UV and blue light. (Male anal fin coloration, a visual cue to females, contrasts with lighting conditions: males in the swamps tend to have blue anal fins while males in the spring populations tend to have red or yellow anal fins).

Clutches in each tank were reared until adulthood, and individuals were subsequently measured for opsin expression by performing real-time PCR with primers that were unique to the 5 different types of opsin genes (which code the 5 different cone types: UV, violet, blue, yellow, and red). From ANOVA, the authors concluded that the relative frequency of the different cones is a characteristic that can be constrained by genes (heritable) but is also amendable due to environmental conditions at development (ontogenetic). The environmental influence on opsin expression was greatest for the extreme wavelength cones which makes sense since it is the frequency of UV cones and long wavelength cones that vary most among natural populations. Additionally, individuals raised in tanks with low UV/blue transmission tended to have a higher frequency of long wavelength cones while individuals raised in tanks with high UV/blue transmission tended to have a higher frequency of UV and violet cones.

We learned in lecture, that variants of the opsin proteins are responsible for creating cones and associated pigments which are selectively sensitive to different wavelengths of light . Consequently, the relative numbers of opsin genes is directly proportional to the number of different photoreceptors, which contributes to the color perception of the receiver . Due to this relationship, it is easy to see why the authors use the expression of this gene to infer the extent of visual tuning to the environment.

Also, we learned that a signal will stand out most when it contrasts with its background, and the coloration of male killifish certainly supports this idea. On the other hand, we learned that for a signal to be effective it must also be accurately received. This study shows that the receivers are most sensitive to wavelengths of light that are most abundant in their environment and therefore are NOT tuned to the colors used by signaling males. Perhaps this example demonstrates that the prominence of a contrasting signal may overcome the constraints of having a receiver that is not tuned to the signal color.