Background:

The recent origin of the genera Chirostoma and Poblana, and the scarce morphological differentiation between them, have made it difficult to define their taxonomic validity, in addition to the fact that both genera share a common ancestor, Menidia. Many taxonomic studies have recognized Chirostoma and Poblana as well-defined genera. Genetic analyses, however, indicate that Poblana is nested within Chirostoma, while other authors synonymize all silversides of the Central Plateau of Mexico within Menidia. Nevertheless, the differentiation between these genera has not currently been explored through a morphometric analysis.

Goals:

Under this scenario, in which the taxonomic validity of the genus Menidia is not in doubt, but the existence of Poblana is uncertain given that for some authors it pertains to the genus Chirostoma, the morphometric variations among the three genera and their species were analyzed in this study through Geometric Morphometrics.

Methods:

Seventeen landmarks were used on a sample of 393 Mexican specimens from various biological collections (216 of Chirostoma, 150 of Poblana and 27 of Menidia) obtained from several localities. The differences among the genera and species were tested using a Generalized Procrustes Analysis (GPA) and Discriminant Analysis (DA) computing the regression of shape on size-the vector of allometry, then remove this aspect of variation by looking at residual variation.

Results:

The cross-validated analysis showed 98.5% and 84.2% of classification among genera and species respectively, where the misclassifications were among species of Chirostoma.

Conclusions:

Morphometric differences were found among Poblana, Chirostoma and Menidia, therefore considered as discrete units.