Fig. 5

The advantage of UV vision for visualizing leaf achromatic and color contrasts. Boxplots show the median, interquartile range (IQR), and lowest and highest data, within 1.5 IQR, below and above the IQR (outliers not shown). a Michelson¹⁰ leaf achromatic contrasts seen by the different cone channels in different habitats. In each habitat, UV-cones saw higher leaf-contrast than all other cone channels at P < 0.0001. b Color contrasts in units of just noticeable differences (JNDs)¹¹ seen by a LMSU tetrachromat and all possible trichromatic and dichromatic combinations of avian photoreceptors, again separated by habitat. To make our results as general as possible across the animal kingdom, all photoreceptor compositions were assumed to have the same number of each photoreceptor class in an integrative unit. In each habitat, transforming a trichromat in the visible range (LMS) into a tetrachromat with a UV-cone (LMSU) enhanced color contrast at P < 0.0001. All cone compositions containing both a U- and M-cone (highlighted in orange) saw higher leaf color contrast than any other composition having the same number of cones at P < 0.0001. All P values were derived from paired two-sided sign tests, i.e., “signtest” in MATLAB. Details of statistical tests can be found in Table 1