Skip to main content

Interrelations Between the Cranium, the Mandible and Muscle Architecture in Modern Domestic Dogs

Abstract

Many studies have attested to the consequences of the recent and intense artificial selection on the morphological variability of the cranium and mandible in domestic animals. However, the functional relations of the cranium with other constituents of the masticatory apparatus (the mandibles and the adductor muscles) have rarely been explored. Previous work has demonstrated strong relationships between the overall shape of the mandible and muscle data, however, drastic artificial selection in dogs has led to frequent malocclusions, suggesting a possible decoupling between the cranium and the mandible. Moreover, the more complex role of the cranium suggests that it is likely less impacted by, and correlated with, the architecture of the jaw muscles than the mandible. We explored the covariations between cranial and mandibular shape and between cranial shape and the masticatory muscle architecture. Shape analyses were conducted on 58 dogs from various breeds and we used muscle data previously obtained from the dissection of 48 of these dogs. The shape of the cranium was quantified using 3D geometric morphometric approaches. Principal component analyses (PCA) and two-block partial least square analyses (2B-PLS) were used to quantify the variations in cranial shape and the covariations with mandible shape and muscle architecture, respectively. Interestingly, our results reveal strong covariations between cranial shape and mandibular shape and between cranial shape and masticatory muscles mass or physiological cross-sectional area, irrespective of whether size is taken into account or not. We conclude that the drastic artificial selection in domestic dogs has not tainted the integrity of the jaw system, which reinforces previous assumptions hypothesising that phenotypic variability in dogs may be limited by developmental factors.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5

References

Download references

Acknowledgements

We thank the Veterinary school ONIRIS-Nantes (France) and Anses (Nancy, France) for providing dog heads for dissection. We are grateful to Manuel Comte, Mickaël Godet and Frederic Lebatard for their help in managing specimens and their helpful discussions about the preparation of the skulls. We also thank Arnaud Delapré for his help with photogrammetry. We are very grateful to two anonymous reviewers for their comments and advice on an earlier version of the manuscript.

Funding

This research was funded by the Ministère de l’Enseignement supérieur, de la Recherche et de l’Innovation.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Colline Brassard.

Ethics declarations

Conflict of interest

The authors declare that they have no conflicts of interest.

Additional information

Colline Brassard and Marilaine Merlin are co-first authors.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Supplementary Fig. S1

Distribution of the specimens along the allometric slope with a visualisation of the differences between large and small specimens relative to consensus shape. Ages are indicated by different shapes and morphotypes are indicated by different colors. Beagles are located in the green area. Ams: American Staffordshire terrier; Box: Boxer; Buld: Bulldog; Bult: Bull terrier; Chi: Chihuahua; Can: Cane Corso; Kin: Cavalier King Charles Spaniel; Pap: Papillon; Pit: Pitbull; Rot: Rottweiler; Mas: Mastiff; Fox: Fox terrier; Bel: Belgian Shepherd; Bor: Border collie; Col: Collie; Dac: Dachshund; Ger: German Shepherd; Gol: Golden retriever; Hus: Husky; Leo: Leonberg; She: Shetland sheepdog. (TIFF 7423 kb)

Supplementary Fig. S2

2-Block Partial Least Square Analyses between cranial shape and the masses of the jaw muscles, with vectors and shapes at the minimum and maximum of the PLS axis. Illustrations represent the deformations from the consensus to the extreme of the axis in lateral and dorsal views. Ages are indicated by different shapes and morphotypes are indicated by different colors. Beagles are located in the green area. Ams: American Staffordshire terrier; Box: Boxer; Buld: Bulldog; Bult: Bull terrier; Chi: Chihuahua; Can: Cane Corso; Kin: Cavalier King Charles Spaniel; Pap: Papillon; Pit: Pitbull; Rot: Rottweiler; Mas: Mastiff; Fox: Fox terrier; Bel: Belgian Shepherd; Bor: Border collie; Col: Collie; Dac: Dachshund; Ger: German Shepherd; Gol: Golden retriever; Hus: Husky; Leo: Leonberg; She: Shetland sheepdog. Dig: M. digastricus; MS: M. masseter pars superficialis; MP: M. masseter pars profunda; ZMA: M. zygomaticomandibularis pars anterior; ZMP: M. zygomaticomandibularis pars posterior; SZ: M. temporalis pars suprazygomatica; TS: M. temporalis pars superficialis; TP: M. temporalis pars profunda; PM+PL: M. pterygoideus pars medialis and lateralis. (TIFF 6503 kb)

Supplementary Fig. S3

2-Block Partial Least Square Analyses between the allometry-free cranial shape and the residual masses of the jaw muscles, with vectors and shapes at the minimum and maximum of the PLS axis. Illustrations represent the deformations from the consensus to the extreme of the axis in lateral and dorsal views. Ages are indicated by different shapes and morphotypes are indicated by different colors. Beagles are located in the green area. Ams: American Staffordshire terrier; Box: Boxer; Buld: Bulldog; Bult: Bull terrier; Chi: Chihuahua; Can: Cane Corso; Kin: Cavalier King Charles Spaniel; Pap: Papillon; Pit: Pitbull; Rot: Rottweiler; Mas: Mastiff; Fox: Fox terrier; Bel: Belgian Shepherd; Bor: Border collie; Col: Collie; Dac: Dachshund; Ger: German Shepherd; Gol: Golden retriever; Hus: Husky; Leo: Leonberg; She: Shetland sheepdog. Dig: M. digastricus; MS: M. masseter pars superficialis; MP: M. masseter pars profunda; ZMA: M. zygomaticomandibularis pars anterior; ZMP: M. zygomaticomandibularis pars posterior; SZ: M. temporalis pars suprazygomatica; TS: M. temporalis pars superficialis; TP: M. temporalis pars profunda; PM+PL: M. pterygoideus pars medialis and lateralis. (TIFF 6098 kb)

11692_2020_9515_MOESM4_ESM.xlsx

Table S1. Details of the specimen used in this study including raw jaw muscles masses, pennation angles, fiber lengths and PCSAs. (XLSX 109 kb)

Supplementary file 5 (DOCX 14 kb)

Supplementary file 6 (DOCX 81 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Brassard, C., Merlin, M., Guintard, C. et al. Interrelations Between the Cranium, the Mandible and Muscle Architecture in Modern Domestic Dogs. Evol Biol 47, 308–324 (2020). https://doi.org/10.1007/s11692-020-09515-9

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s11692-020-09515-9

Keywords

  • Dog
  • Skull
  • Masticatory system
  • Jaw muscle architecture
  • Domestication
  • Geometric morphometrics