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Morphological and Cranial Variation and Reproductive Data of Invasive Rodents in Southeastern Mexico
Gloria Tapia-Ramírez1, Consuelo Lorenzo1
1El Colegio de La Frontera Sur,, San Cristóbal de Las Casas, Chiapas, Mexico.
Journal of Morphology
|July 13, 2026
Summary
This study analyzed body and cranial variations in Norway rats (Rattus norvegicus) and black rats (Rattus rattus) in Chiapas, Mexico. Findings aid species identification and reveal significant morphological differences between the two rat species.
Area of Science:
- Zoology and Wildlife Biology
- Mammalogy
- Comparative Morphology
Background:
- Rattus norvegicus and Rattus rattus are invasive species with significant ecological and economic impacts globally.
- Understanding their population dynamics and morphological variations is crucial for effective management and control strategies.
- Limited data exists on the specific morphometrics of these species in southeastern Mexico.
Purpose of the Study:
- To conduct the first comprehensive analysis of body variation and cranial morphology for Rattus norvegicus and Rattus rattus in San Cristobal de Las Casas (SCLC), Chiapas, Mexico.
- To provide a valuable tool for accurate species identification in the region.
- To elucidate the variability and sexual dimorphism within these rat populations.
Main Methods:
- Collected and analyzed 125 specimens: 78 Rattus norvegicus and 47 Rattus rattus.
- Utilized traditional morphometrics to assess body mass, body length, and cranial characteristics.
- Examined reproductive status and sex ratios to understand population structure.
Main Results:
- Significant cranial morphological differences were observed: Rattus norvegicus exhibited a robust skull, while Rattus rattus showed reduced rostral depth and a shorter mandibular ramus.
- Sexual dimorphism was noted in Rattus norvegicus, with males possessing significantly larger ears.
- Rattus norvegicus specimens from SCLC were considerably smaller than those from Baltimore, USA, whereas Rattus rattus from SCLC were larger than Yucatan populations.
Conclusions:
- The study establishes distinct morphological criteria for differentiating Rattus norvegicus and Rattus rattus in southeastern Mexico.
- Morphological variations suggest potential environmental influences or distinct evolutionary trajectories for these populations.
- The findings contribute essential data for ecological studies and pest management programs targeting invasive rodents in the Neotropics.
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