The delimitation of cryptic species represents one of the main challenges, particularly in groups with low external morphological differentiation. In this context, scanning electron microscopy (SEM) enables the detection of diagnostic characters at the microscale. This study evaluates the potential of ocular morphology for interspecific discrimination within a group of species of the genus Temnothorax. A total of 246 workers from 52 nests, 13 populations, and 8 species from the Iberian Peninsula and North Africa were analyzed. Morphometric variables related to compound eyes were quantified from SEM images (ommatidia number, interommatidial setae, eye diameter). Data were analyzed using ANOVA, effect size estimation (η2), Linear Discriminant Analysis (LDA), and Random Forest models. All variables showed significant differences among species (p < 0.001), with varying discriminative power. Variables related to ommatidial organization exhibited the highest classification performance, achieving high rates of correct species assignment in multivariate analyses. The use of nest-level means values substantially improved classification accuracy. These results demonstrate that ocular morphology analyzed through SEM represents a promising complementary tool for species discrimination in Temnothorax, complementing traditional and molecular approaches.
Joaquín L. Reyes-López (Mon,) studied this question.