Mate choice and visibility in the expression of a sexually dimorphic trait in a goodeid fish (Xenotoca variatus)

" Male Xenotoca variatus (Bean, 1887) have shiny scales (“speckles”) on their flanks, the number of which varies within and among populations. Using fish from two localities with turbid water and two with transparent water, we tested whether differences in the number of speckles were associated with differences either in water turbidity or with the expression of female mate choice. We also tested whether female mate choice was influenced by water turbidity. In our sample the number of speckles and water turbidity were not associated. A test including all the populations in a combined (factorial) analysis showed that in clear water females exhibit a preference for visiting the male with the largest number of speckles of a pair, though no population differences were detected. When tested in clear water, females spent more time close to a male with more speckles; in this instance, males were from a clear-water locality and possessed many speckles. Our findings suggest that female mate choice might not contribute to the geographical variation in speckle number, but may instead be constrained by the transmissibility of the signal "