Spectral sensitivity of mollies: comparing surface‐ and cave‐dwelling Atlantic mollies,Poecilia mexicana

The visual pigments of cones and rods in three species of mollies,Poecilia mexicana,Poecilia latipinnaand their asexual hybridPoecilia formosa, were examined using microspectrophotometry. InP. mexicana, populations from extreme photic habitats were used: one population originated from a clear water habitat, one from a milky water habitat and another from a completely dark cave. Ultraviolet‐sensitive cones were found in all species. Differences in the λmaxvalues of the visual pigments were small between species and among the threeP. mexicanapopulations, but dark‐reared cave fishes showed appreciably higher variance. The hybrid speciesP. formosashowed a highly variable long wavelength cone absorbance, ranging from 528·9 to 598·5 nm, suggesting multiple opsin expression or chromophore mixing.