What pigments do dogs have? - briefly
Dogs primarily possess two types of color pigments: eumelanin and pheomelanin. These pigments are responsible for the diverse coat colors seen in different dog breeds.
What pigments do dogs have? - in detail
Dogs, like many mammals, possess two primary types of photoreceptor cells in their retinas: rods and cones. These photoreceptors contain light-absorbing pigments that are essential for vision. The two main pigments found in dogs' eyes are rhodopsin and iodopsin.
Rhodopsin, also known as visual purple, is the primary pigment in rod cells. Rods are responsible for low-light vision and detecting motion, which is crucial for dogs' nocturnal activity and hunting instincts. Rhodopsin is composed of a protein called opsin and a light-absorbing molecule called 11-cis retinal. When light hits the rhodopsin, it triggers a cascade of reactions that ultimately leads to the transmission of visual information to the brain.
Iodopsins are the pigments found in cone cells, which are responsible for color vision and high acuity vision. Dogs have two types of cone cells: those containing short-wavelength sensitive (SWS) iodopsin and medium-wavelength sensitive (MWS) iodopsin. SWS cones are more sensitive to blue light, while MWS cones detect green light. The absence of long-wavelength sensitive (LWS) cones, which are responsible for red color perception in humans, is the reason why dogs are considered dichromatic and have limited color vision compared to humans.
In addition to these photoreceptor pigments, dogs also possess melanopsin, a light-sensitive protein found in a small subset of retinal ganglion cells. Melanopsin plays a role in non-image forming visual functions such as circadian rhythm regulation and pupil constriction in response to bright light.
Overall, the pigments in dogs' eyes are specialized for their unique visual needs, emphasizing motion detection and low-light vision over color discrimination. This adaptation has evolved to support their ancestral role as predators and scavengers, where detecting movement in dim conditions was more critical than distinguishing a wide range of colors.