Editing Spring peeper (section)

=== Respiratory and circulatory system ===
The bigger, older, and more fit male spring peepers are typically superior callers. These types of males utilize [[citrate synthase]] and [[3-hydroxyacyl-CoA dehydrogenase|β-hydroxyacyl CoA dehydrogenase]] in their muscles at greater levels. Males with higher calling rates also tend to inhibit larger ventricles and greater concentrations of blood [[hemoglobin]]; both the large ventricle size and blood hemoglobin concentrations play a significant role in the speed of oxygen consumption, which is intensely linked to the calling rate.<ref name="Zimmitti-1999">{{Cite journal |last=Zimmitti |first=Salvatore J. |date=November 1999 |title=Individual Variation in Morphological, Physiological, and Biochemical Features Associated with Calling in Spring Peepers (''Pseudacris crucifer'') |journal=Physiological and Biochemical Zoology |volume=72 |issue=6 |pages=666–676 |doi=10.1086/316706 |pmid=10603330 |s2cid=34950753 }}</ref> When a male spring peeper calls, the sound is made by the contraction of external and internal oblique muscles which subsequently force air out of the lungs, then move through the larynx to the vocal sac. Of the total body weight of male spring peepers, 15% is made up of the trunk muscles – which contain 2% of lipids in the body by volume – and showcase enzymes with mitochondrial markers. Calls that occur at rapid rates result in prominent energetic costs, which is why stored lipids are the source of 90% of energy applied to calling.<ref name="Zimmitti-1999" />