Evolution of wing-propelled diving in birds
Transformations associated with a return to a
primarily aquatic ecology have been intensely studied in
organisms ranging from insects to cetaceans. However,
comparatively little attention has been paid to similar
transitions in birds. Co-option of the aerial flight stroke
for underwater propulsion has evolved multiple times in
diverse lineages within crown clade Aves and has been
associated with extremes of body size, growth rate,
skeletal modification, and integumentary specialization.
While the transition from aerial to aquatic “flight”
(wing-propelled diving) has been recognized to involve a
profound reorganization of the musculoskeletal system, bone
microstructure, and in- tegument, proposed patterns of
character acquisition have remained largely hypothetical.
The phylogenetic basis needed to explore such patterns has
been limited; relationships among and within wing-propelled
diving clades remain controversial. Basic questions such as
how many times wing-propelled diving has evolved and how
many times flight has been lost in wing-propelled div- ing
clades remain unresolved. This project, in collaboration
with
Dr. Julia Clarke (UT, Austin) and
Dr. Daniel Ksepka (North Carolina
State University), will encompass phylogenetic,
histologic, functional, and sensory evolution. Work in
the lab will address three major questions.
Character Evolution
What is the sequence of character evolution across
multiple aerial to aquatic transitions? Most hypotheses
concerning the evolution of wing-propelled diving center on
musculoskeletal changes within the pectoral skeleton to
enable propulsive force in an aqueous medium. By
identifying osteological correlates of wing-propelled
diving and quantifying their three-dimensional morphology,
we will address relative rates of evolution among forelimbs
and hind limbs using techniques that we developed.
Bone Microstructure
What is the microstructure of
osteosclerotic bone in wing-propelled diving birds?
Wing-propelled diving birds commonly exhibit extremely
thick compacta in their long bones. Osteosclerosis has
traditionally been linked to flightlessness and
hypothesized to increase the organism’s density, reducing
the depth needed to reach neutral buoyancy and thus
decrease energy expenditure. However, we hypothesize that
this unusual morphology may function more for resistance to
bending forces under the tremendous loads imparted by the
flight muscle or for rapid growth strategies retained from
early penguin evolution.
Feather Evolution
How does feather structure change with the loss of
aerial flight? In water, feathers must produce forces in a
medium that is more than 800 times denser than air. I will
study both the microstructure of feathers and their bending
properties under loads. We have evidence for the first
known fossilized penguin feathers, which will provide
valuable comparative data on the early evolution of these
unusual structures.
Visit the March of the Fossil Penguins
blog.
