Differentiation of skull morphology and cranial kinesis in common toads

Abstract

We examined the cranial morphology and cranial kinesis of the common toads Bufo bufo and B. spinosus with micro-computed tomography and geometric morphometrics and compared the results with published data for related species in a phylogenetic context. The species significantly diverge in skull shape. The skull of B. spinosus is shorter and higher, with a ventral arm of the squamosal bone and the jaw articulation point positioned perpendicular to the braincase, in comparison with a more lateral position in B. bufo. In either species, females have a shorter snout and a higher and wider skull at the jaw articulation point that is positioned more posteriorly, in comparison with conspecific males. High variation in the amount of bone ossification was recorded in both species, ranging from scarcely ossified and loosely connected bones to highly ossified and firmly connected bones. We also found that skull shape and inferred kinetic properties of the skull are highly variable across the Bufonini tribe. However, sample sizes are mostly small and intraspecific variation is high, which might compromise the analyses. Overall, the results suggest that developmental plasticity produces high variation in ossification and cranial kinesis, affecting individuals’ feeding performances. At the population level, this variation supports an efficient exploitation of the habitat and may promote morphological adaptation in a changing environment.

Ladies in armor: A micro‐computed tomographic study of skin calcification in European toads (genus Bufo)

“…Also, body size could associate with sexual dimorphism in skin thickness (VanBuren et al, 2019). We found that the level of head skin calcification was positively related to skull size which coincided with a marked, female biased sexual size dimorphism (Arntzen, 1999; Lüscher et al, 2001; Čađenović et al, 2013; Ivanović et al, 2022; Dursun et al, 2022). Yet, the calcification level of the head skin and the parotoids cannot be solely explained by size.…”

“…Fisher's exact test for count data was performed to test for statistical significance in character states frequency distribution. As an estimation of head size, we used skull size data obtained from the same individuals (centroid size values—CS; Supporting information, Table S1) from Ivanović et al (2022). To test if the individuals with different levels of calcification of dorsal skin and parotoids differ in skull size, we performed a nested ANOVA with calcification level, species and sex nested within species as factors and skull size as dependent variable.…”

“…We expected higher level of skin calcification in B. spinosus than in B. bufo. As there is a pronounced sexual dimorphism in the skull size of both species B. bufo and B. spinosus (Arntzen, 1999;Lüscher et al, 2001;Čađenovi c et al, 2013;Ivanovi c et al, 2022;Dursun et al, 2022), we expected that sexual dimorphism would be confirmed for the level of calcification as well.…”

“…The species may also differ in the amount of keratinization in epidermis (Arntzen et al, 2013; Čađenović et al, 2013). Both species show a significant sexual size dimorphism with females being larger than males (Arntzen, 1999; Lüscher et al, 2001; Dursun et al, 2022; Ivanović et al, 2022).…”

“…We used micro‐CT for the detailed reconstruction of dense tissues in the head region. This approach is especially useful to study well ossified bones (Waltenberger et al, 2021), including the B. bufo and B. spinosus cranial skeleton (Ivanović et al, 2022). Other dense dermal structures such as osteoderms (Broeckhoven et al, 2017; Paluh et al, 2017; Broeckhoven and du Plessis, 2018; Williams et al, 2022) and epidermal enamel structures (Woodruff et al, 2022) can also be explored with high precision while the material is kept intact.…”