The role of soil features in shaping the bite force and related skull and mandible morphology in the subterranean rodents of genusCtenomys(Hystricognathi: Ctenomyidae)

Abstract

For rodents that live underground, digging in highly compacted soils requires a higher energy expenditure than digging in poorly compacted soils. We tested how soil hardness affects the bite force as well as the shape and size of the skulls and mandibles of tuco-tucos. Our hypothesis is that species that inhabit harder soils would show a stronger bite force, which should be reflected in the shape of the skull and mandible, while species living in softer soils should have a weaker bite force. We used 24 species of the genus Ctenomys to estimate bite force (through the incisor strength formula) and quantify the shape and size of the skull and mandible. Information on soil bulk density in the regions occupied by each species was obtained from the literature. We used a combination of geometric morphometric and comparative methods to test our hypothesis. A phylogenetic linear regression (PGLS) between bite force (N) and centroid size was used to account for the dependence of bite force on size. We employed a series of two-block partial leastsquares analyses to uncover the covariation between bite force and the shape of the skull and mandible. Finally, we ran five independent PGLS analyses to assess the influence of bulk density on bite force, skull shape and mandible shape, taking into account phylogenetic non-independence. Species with higher bite forces tend to inhabit more-compact soils. However, for most species, the relationship between bite force and soil bulk density was unclear, resulting in a low overall correlation. Nonetheless, differences in skull and mandible shapes were generally associated with bite force (r = 0.60). In denser soils, species with high and low bite forces occur, whereas in lower density soils, we found only species with weak bite forces. Differences in the excavation strategies among species may be responsible for this pattern.

Skull shape and size variation within and between mendocinus and torquatus groups in the genus Ctenomys (Rodentia: Ctenomyidae) in chromosomal polymorphism context

“…A more confined amount of morphological variation was observed in the mandible of C. minutus ( Fornel et al , 2010 ). This is probably the result of stabilizing selection, since the functions of the mandible are more restricted than in the rest of the skull ( Borges et al , 2017 ).…”

Interspecific skull variation at a small scale: The genus Eospalax exhibits functional morphological variations related to the exploitation of ecological niche

“…Fornel et al (2010) found significant differences in the skull shape of Ctenomys minutus between habitats (dune and field) in the dorsal, ventral, and lateral views. Based on a comprehensive analysis of 164 individuals from 24 species of the genus Ctenomys , Borges et al (2016) revealed the relationship between skull shape and bite force, as well as the influence of habitat soil compaction on the bite force. A comparison of morphological variations in the skull of animals affected by different environments will help to understand not only the phenotypic variations in the skull but also the life‐history strategies and evolutionary changes in animals (Lu, 2003).…”

“…Various studies have investigated interspecific morphological changes in rodents using advanced geometric morphometric techniques (e.g., Alhajeri, 2017; Borges et al, 2016; Maestri et al, 2018; Martínez & Di Cola, 2011). Geometric morphometrics is a powerful tool for the quantitative analysis of biological and organ morphology (Adams et al, 2004).…”

Correlation of skull morphology and bite force in a bird-eating bat (Ia io; Vespertilionidae)

“…The relationships between skull morphology, bite force, and diet have been investigated in a variety of animal groups, including fish [29,30], lizards [24,31], crocodilians [32], turtles [33], rodents [12,34], birds [23]. Many studies have also focused on bats [19][20][21][35][36][37][38][39][40], but studies involving skull morphology, in vivo bite force, and diets in a single study are limited.…”