Quantifying the genetic influence
on mammalian vascular tree structure
Robb Glenny *, Susan Bernard *, Blazej Neradilek ,
and Nayak Polissar
*Division of Pulmonary and Critical Care Medicine,
School of Medicine, Box 356522, and Department of Physiology and
Biophysics, University of Washington, Seattle, WA 98195; and Mountain-Whisper-Light
Statistical Consulting, 1827 23rd Avenue East, Seattle, WA 98112
Edited by James H. Brown, University of New Mexico,
Albuquerque, NM, and approved March 1, 2007 (received for review
December 11, 2006)
The ubiquity of fractal vascular trees throughout
the plant and animal kingdoms is postulated to be due to evolutionary
advantages conferred through efficient distribution of nutrients
to multicellular organisms. The implicit, and untested, assertion
in this theory is that the geometry of vascular trees is heritable.
Because vascular trees are constructed through the iterative use
of signaling pathways modified by local factors at each step of
the branching process, we sought to investigate how genetic and
nongenetic influences are balanced to create vascular trees and
the regional distribution of nutrients through them.
We studied the spatial distribution of organ blood
flow in armadillos because they have genetically identical littermates,
allowing us to quantify the genetic influence. We determined that
the regional distribution of blood flow is strongly correlated between
littermates (r2 = 0.56) and less correlated between unrelated animals
(r2 = 0.36). Using an ANOVA model, we estimate that 67% of the regional
variability in organ blood flow is genetically controlled.
We also used fractal analysis to characterize the
distribution of organ blood flow and found shared patterns within
the lungs and hearts of related animals, suggesting common control
over the vascular development of these two organs.
We conclude that the geometries of fractal vascular
trees are heritable and could be selected through evolutionary pressures.
Furthermore, considerable postgenetic modifications may allow vascular
trees to adapt to local factors and provide a flexibility that would
not be possible in a rigid system.
Author contributions: R.G. designed research; R.G.,
S.B., B.N., and N.P. performed research; R.G., B.N., and N.P. analyzed
data; and R.G. wrote the paper.
The authors declare no conflict of interest.
To whom correspondence should be addressed.
Robb Glenny, E-mail: email@example.com