Visual acuity in the cathemeral strepsirrhine Eulemur macaco flavifrons

Area of Science:

• Primate vision
• Comparative visual acuity
• Sensory ecology

Background:

• Diurnal haplorhine primates exhibit high visual acuity.
• Limited data exists for non-haplorhine primate visual acuity, especially strepsirrhines.
• Previous estimates cover only four strepsirrhine genera.

Purpose of the Study:

• To measure visual acuity in the cathemeral blue-eyed black lemur (Eulemur macaco flavifrons) for the first time.
• To investigate ecological factors influencing primate visual acuity variation.
• To compare acuity across different primate groups and activity patterns.

Main Methods:

• Behavioral assessment using a two-alternative forced choice discrimination task.
• Stimuli comprised high contrast square wave gratings at seven spatial frequencies.
• Acuity threshold determined by a 70% correct response criterion.

Main Results:

• Maximum visual acuity: 5.1 c/deg for the female and 3.8 c/deg for the male E. macaco.
• Acuity in E. macaco is lower than diurnal Lemur catta but comparable to nocturnal Microcebus murinus and Otolemur crassicaudatus.
• Theoretical acuity calculations for Cheirogaleus medius and Tarsius syrichta were performed.

Conclusions:

• Primate visual acuity is influenced by activity patterns, diet, and phylogenetic history.
• High visual acuity in species like Tarsius syrichta and Galago senegalensis suggests visual predation as a selective pressure.
• This study provides crucial data on strepsirrhine visual capabilities.