# Phenotypic Variation Patterns in Oecomys catherinae (Rodentia: Sigmodontinae): Craniodental Morphometric Analysis and Its Relationship with Latitudinal Variation in the Atlantic Forest and Cerrado Biomes

## TL;DR

This study explores how the skull shape of a rodent species varies across different Brazilian biomes and latitudes, suggesting environmental influences on physical traits.

## Contribution

The study identifies biome-specific cranial adaptations in Oecomys catherinae and links them to ecological and latitudinal factors.

## Key findings

- Cranial morphology differs significantly between the Atlantic Forest and Cerrado biomes.
- Southern populations have slightly larger cranial dimensions, aligning with Bergmann’s rule.
- Bony palate length is the most discriminating trait between biomes, possibly linked to diet.

## Abstract

Understanding how animals adapt to natural environments reveals essential physical and behavioral traits for survival. We examined skull shape variation in the arboreal rodent Oecomys catherinae across two Brazilian biomes, the Atlantic Forest and Cerrado, and its relationship with latitude. Through cranial and dental measurements of 45 specimens from scientific collections, no significant differences were observed between males and females. However, cranial morphology differed between biomes, likely due to dietary adaptations and ecological pressures. Southern populations exhibited slightly larger cranial dimensions than northern counterparts, consistent with Bergmann’s rule (which posits that larger body sizes occur in colder climates). These results demonstrate how environmental pressures shape physical traits in small mammals. Further research is required to determine whether these differences reflect genetic adaptations or plastic responses (non-heritable changes induced by local environments).

The arboreal rodent Oecomys catherinae, which has a wide geographic distribution across Brazilian biomes, provides a model for investigating environmental influences on morphological variation. We assessed craniodental differences between the Atlantic Forest and Cerrado biomes, as well as along latitudinal gradients, using 45 specimens from 18 localities. Linear morphometric analyses (21 measurements) revealed no significant sexual dimorphism, allowing for pooled analyses. Principal Component Discriminant Analysis (DAPC) confirmed significant morphological divergence between biomes (72% accuracy, p < 0.01). We identified bony palate length (BPL) as the most discriminating variable, with higher values in the Atlantic Forest, suggesting a possible dietary adaptation in response to ecological pressures. Latitudinal effects were modest (adjusted R2 = 0.05) although significant (F1,43 = 3.63; p = 0.03), with southern populations exhibiting larger cranial dimensions than northern ones. We conclude that biome type and latitude played important roles in shaping cranial morphology in O. catherinae populations.