L and M cone proportions in polymorphic New World monkeys

Area of Science:

• Primatology
• Neuroscience
• Genetics

Background:

• Platyrrhine monkeys possess a single X-chromosome opsin gene, with alleles encoding diverse middle- to long-wavelength photopigments.
• X-chromosome inactivation in heterozygous females generates a retinal mosaic of cones expressing either L- or M-pigments, forming the basis for trichromatic vision.

Purpose of the Study:

• To investigate the proportions of L-cones and M-cones resulting from X-chromosome inactivation in platyrrhine monkeys.
• To determine if the L:M cone ratio varies among individuals and genera.

Main Methods:

• Electroretinogram flicker photometry was employed to record spectral sensitivity functions.
• Functions were obtained from 60 heterozygous female monkeys across seven platyrrhine genera.
• Spectral sensitivity functions were fitted using linear combinations of L- and M-cone fundamentals.

Main Results:

• The average L:M cone ratio across the sample was approximately 1:1, consistent with random X-chromosome inactivation.
• Significant individual variations in L:M cone proportions were observed.
• The study identified specific cone proportions for each genus studied.

Conclusions:

• X-chromosome inactivation is the primary mechanism establishing the L:M cone mosaic for trichromatic vision in platyrrhines.
• Individual differences in cone proportions may influence visual perception.
• Further research is needed to explore the functional implications of these variations in color vision.