Morphological anomalies in amphibians of the Sierra Madre Occidental and a review of cases reported in Mexico.

The data on the incidence and diversity of anomalies in amphibian populations in Mexico are primarily derived from opportunistic observations, which pose challenges for conducting comparisons and monitoring long-term trends. In this study, we document new cases of morphological anomalies in amphibians from the Sierra Madre Occidental and provide a systematic bibliographic review of reported cases across Mexico. During the 2023 rainy season, we conducted surveys in Surutato, Sinaloa, documenting nine cases of morphological anomalies, including the first documented case of dyscoria in the country. The bibliographic review covered 34 sources and identified 31 types of anomalies, with the family Ambystomatidae being the most affected. We observed significant ambiguity in the terminology used across reports, which hinders data comparability. To address this issue, we propose promoting a standardized approach to the description and classification of anomalies. Based on the available data, we estimate a national mean anomaly frequency of 18.43% in amphibians, which can serve as a preliminary benchmark for future studies. The most commonly identified causes of anomalies include agrochemical pollution and parasitism; however, in 37% of the cases, no specific cause could be determined. These findings underscore the importance of standardizing anomaly reports, as they can serve as valuable early indicators of environmental degradation.