The shapes of bird beaks are highly controlled by nondietary factors

TY - JOUR

T1 - The shapes of bird beaks are highly controlled by nondietary factors

AU - Bright, Jen

AU - Marugán-Lobón, Jesús

AU - Cobb, Samuel Nicholas Frederick

AU - Rayfield, Emily

PY - 2016/5/10

Y1 - 2016/5/10

N2 - Bird beaks are textbook examples of ecological adaptation to diet, but their shapes are also controlled by genetic and developmental histories. To test the effects of these factors on the avian craniofacial skeleton, we conducted morphometric analyses on raptors, a polyphyletic group at the base of the landbird radiation. Despite common perception, we find that the beak is not an independently targeted module for selection. Instead, the beak and skull are highly integrated structures strongly regulated by size, with axes of shape change linked to the actions of recently identified regulatory genes. Together, size and integration account for almost 80% of the shape variation seen between different species to the exclusion of morphological dietary adaptation. Instead, birds of prey use size as a mechanism to modify their feeding ecology. The extent to which shape variation is confined to a few major axes may provide an advantage in that it facilitates rapid morphological evolution via changes in body size, but may also make raptors especially vulnerable when selection pressures act against these axes. The phylogenetic position of raptors suggests that this constraint is prevalent in all landbirds and that breaking the developmental correspondence between beak and braincase may be the key novelty in classic passerine adaptive radiations.

AB - Bird beaks are textbook examples of ecological adaptation to diet, but their shapes are also controlled by genetic and developmental histories. To test the effects of these factors on the avian craniofacial skeleton, we conducted morphometric analyses on raptors, a polyphyletic group at the base of the landbird radiation. Despite common perception, we find that the beak is not an independently targeted module for selection. Instead, the beak and skull are highly integrated structures strongly regulated by size, with axes of shape change linked to the actions of recently identified regulatory genes. Together, size and integration account for almost 80% of the shape variation seen between different species to the exclusion of morphological dietary adaptation. Instead, birds of prey use size as a mechanism to modify their feeding ecology. The extent to which shape variation is confined to a few major axes may provide an advantage in that it facilitates rapid morphological evolution via changes in body size, but may also make raptors especially vulnerable when selection pressures act against these axes. The phylogenetic position of raptors suggests that this constraint is prevalent in all landbirds and that breaking the developmental correspondence between beak and braincase may be the key novelty in classic passerine adaptive radiations.

KW - Allometry

KW - Birds

KW - Geometric morphometrics

KW - Integration

KW - Modularity

KW - Species Specificity

KW - Organ Size/genetics

KW - Beak/anatomy & histology

KW - Morphogenesis/genetics

KW - Biological Evolution

KW - Raptors/anatomy & histology

KW - Animals

KW - Diet

KW - Body Size/genetics

KW - Feeding Behavior/physiology

UR - http://www.scopus.com/inward/record.url?scp=84966318946&partnerID=8YFLogxK

U2 - 10.1073/pnas.1602683113

DO - 10.1073/pnas.1602683113

M3 - Article

C2 - 27125856

SN - 0027-8424

VL - 113

SP - 5352

EP - 5357

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 19

ER -