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From the top of your head: phenotypic integration in the head and neck
Author(s) -
Villamil Catalina Isabel
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.396.1
Subject(s) - skull , cranial vault , biology , evolutionary biology , head and neck , taxon , anatomy , morphology (biology) , brain size , zoology , ecology , medicine , surgery , radiology , magnetic resonance imaging
Phenotypic integration is a powerful way of understanding morphological evolution. However, it remains unclear how integration itself evolves. I discuss here a variety of factors shaping phenotypic integration of the head and neck in a wide range of mammalian taxa. The head serves as a site for many important functions and is integrated in complex ways. Across mammals (marsupials=231, carnivores=100, primates=473) the facial skeleton is integrated with the basicranium, regardless of the factors influencing the morphology of the skull. Magnitudes of integration (MI) within the basicranium (carnivores=348, primates=1159) are strongly linked to relative brain size and to the height and breadth of the cranial vault, such that taxa with large brain sizes and relatively broad and tall cranial vaults have lower MI. When the brain can grow upwards and outwards, it may not require such tightly matched basicranial anatomy to support it. Facial size also influences MI, such that taxa with large faces tend to have higher MI. The mechanical requirements of supporting a relatively large face may serve to functionally constrain the basicranium. However, the interplay of facial and brain morphology also plays a role in these relationships. The age divergence or appearance of specific taxa may play a small role in MI as well. Although smaller taxa are better able to respond to selection generally, body size does not specifically affect MI. The head is also tightly integrated with the neck. Patterns and magnitudes of integration in the head and neck in hominoids ( Homo =120, Pan =112, Hylobates =92) largely follow those hypothesized based on Hox expression patterns in mice. Transitional vertebrae C2 and C7 differ markedly in MI from all others. Locomotor and postural behavior appears to have no influence on these relationships. Instead, aspects of facial anatomy are likely ultimately driving cervical vertebral morphology. My results support the contention that phenotypic integration patterns match underlying genetic developmental relationships. Strong natural selection favoring particular anatomical features, such as relatively large brains, may alter patterns of phenotypic integration by breaking down existing developmental patterns, especially those that are not tightly constrained. However, cervical vertebrae may be strongly buffered from environmental pressures. The extent to which external environmental influences act during ontogeny on other features, such as the face, has yet to be examined. Knowledge of such interactions will serve as an important complement to studies of phenotypic integration. Support or Funding Information This work was funded by the Wenner‐Gren Foundation and New York University.