| Â | Juvenile | Adult |
|---|
| Â | Surface | 1.25 m | Surface | 1.25 m |
|---|
G
| 3.74 | 2.70 | 4.68 | 4.45 |
G
0
| 1.85 | 1.50 | 1.76 | 1.66 |
b
| 2.01 | 1.80 | 2.64 | 2.67 |
d
| 1.54 | 1.37 | 2.05 | 1.98 |
r
| 1.30 | 1.31 | 1.29 | 1.34 |
- *(yellow ellipsoidal/paraboloidal pigments and red oil droplets)
- G and G0denote the shape factor (essentially volume) of the object colour solid with and without spectral filters in the cone photoreceptors, respectively; b is the gross benefit due to the change in shape of the colour solid and is defined as G/G0; d is the factor describing the cost of the spectral filters due to increased signal noise. The overall (net) benefit is given as r = b/d. Discrimination thresholds are assumed to be limited by noise in receptor channels arising from fluctuations in the number of absorbed photons, i.e. shot noise under dim-light conditions. The benefit of spectral filters should be greater in brighter conditions; for details see Methods and [25]. Because at a depth of 1.25 m UV light is not present in significant amounts (Fig. 4A), the UV receptor was not used in calculations for the juvenile lungfish at this depth. The overall benefit to colour discrimination of the spectral filters in dim light is a factor of about 1.3 and is similar between juvenile and adults and between different habitat depths.
