Genome size drives morphological evolution in organ-specific ways

Morphogenesis is an emergent property of biochemical and cellular
interactions during development. Genome size and the correlated trait of
cell size can influence these interactions through effects on
developmental rate and tissue geometry, ultimately driving the evolution
of morphology. We tested whether variation in genome and body size is
related to morphological variation in the heart and liver using nine
species of the salamander genus Plethodon (genome sizes
29–67 gigabases). Our results show that overall organ size is a function
of body size, whereas tissue structure changes dramatically with
evolutionary increases in genome size. In the heart, increased genome size
is correlated with a reduction of myocardia in the ventricle, yielding
proportionally less force–producing mass and
greater intertrabecular space. In the liver, increased genome
size is correlated with fewer and larger vascular structures, positioning
hepatocytes farther from the circulatory vessels that transport key
metabolites. Although these structural changes should have obvious impacts
on organ function, their effects on organismal performance and fitness may
be negligible because low metabolic rates in salamanders relax selective
pressure on function of key metabolic organs. Overall, this study suggests
large genome and cell size influence the developmental systems involved in
heart and liver morphogenesis.