Patterns of allometry and asymmetry in the craniomandibular morphological variation of the genus <i>Artibeus</i> (Phyllostomidae: Chiroptera)

Phyllostomid bats display one of the greatest diversities of any mammalian family. They are noted for their range of cranial phenotypes, ranging from slender and elongated skulls to broad and short forms. Within Phyllostomidae, however, the genus Artibeus exhibits one of the highest species richness (S = 22) yet among the lowest levels of morphological diversity in both skull and wing structures. The morphological traits proposed to distinguish Artibeus species have been regarded as inconsistent and imprecise, largely due to varying degrees of morphological differentiation across geographic scales. Cranial shape variation in bats has been associated with body size, which represents one of the main differences among Artibeus species, as well as with difference in allometric relationships among species. Nevertheless, studies exploring the relationship between biotic and abiotic factors and morphological change in bats remain relatively scarce. Investigating the presence and magnitude of asymmetry and allometry associated with morphological variation across species can yield a more comprehensive understanding of how species' morphologies diverge. This study investigates asymmetry and allometry and their influence on craniomandibular morphological variation within the genus Artibeus. Geometric morphometrics was employed to assess skull shape and size variation across 12 species of the genus. Our analyses revealed modifications in skull shape, especially in its dorsal and ventral morphology, with greater variability observed in the masticatory system. The most pronounced morphological variation was found in cranium length and width, enlargement at the supraoccipital level, reduction of the premaxilla and elongation of the zygomatic process and the maxilla. The mandibular structure showed enlargement of the mandibular condyle, the angle of the mandible and the coronoid process in Artibeus rosenbergi, Artibeus gnomus and Artibeus glauca. Levels of asymmetry among Artibeus species varied, with smaller species exhibiting higher asymmetry in dorsal and ventral structures. However, fluctuating asymmetry (FA) was not evident in cranial morphology, suggesting a reduction in FA in traits with higher functional demands. Our findings indicate a relationship between differential functional importance and asymmetry patterns across skull regions. Similarly, cranial and dental traits are correlated with diet and habitat, suggesting that skull morphology reflects or covaries with feeding habits, ecological factors, foraging strategies and roosting behaviours. As frugivores, Artibeus species have specialised in consuming fruits of varying composition, exhibiting complex and specialised feeding behaviours. Consequently, certain cranial regions associated with biting show functional specialisation, including shortened facial structures and modifications in the zygomatic process of the maxilla.