Editing Spring peeper (section)

== Anatomy and physiology ==
The species has large toe pads for climbing, although it is more at home amid the loose debris of the forest floor.<ref name="NG" /> Because of its toepads, the spring peeper was once thought to be more closely related to treefrogs than chorus frogs and was placed in the genus ''Hyla'', but it is now in the genus ''Pseudacris''.<ref name=":0" />

The color variations of ''P. crucifer'' are mostly tan, brown, yellow, pink, olive green, and gray.<ref>Tipton, Bob L., and Bob L. Tipton. Texas Amphibians a Field Guide. 1st ed., University of Texas Press, 2012, https://doi.org/10.7560/737358.</ref> All have a slightly pale yellow coloration on the inside of the thighs. Females are lighter-colored, while males are slightly smaller and usually have dark throats. Females have a bulkier abdomen.<ref name=Rugh1941>{{Cite journal |last=Rugh |first=Roberts |date=1941 |title=Experimental Studies on the Reproductive Physiology of the Male Spring Peeper, Hyla Crucifer |journal=Proceedings of the American Philosophical Society |volume=84 |issue=5 |pages=617–632 |jstor=984843 }}</ref> Skin color of Spring Peepers is also affected by temperature and light. Coloration is dynamic and adaptable in this species. It can be altered quickly, in 15 to 45 minutes, in order to better camouflage from predators.<ref>{{Cite journal |last1=Kats |first1=Lee B. |last2=van Dragt |first2=Randall G. |date=1986 |title=Background Color-Matching in the Spring Peeper, Hyla crucifer |journal=Copeia |volume=1986 |issue=1 |pages=109–115 |doi=10.2307/1444895 |jstor=1444895 }}</ref>

This frog has a vocal sac that expands and deflates like a balloon to create a short and distinct peeping sound. Only males can make this loud high-pitched noise, and they use it to attract mates.
<gallery>
File:Spring peeper-Florida.jpg|Spring peeper, adult, Florida
File:Spring peeper.jpg|Spring peepers are distinguished by a dark X-shaped marking on their back.
File:Pseudacris crucifer.jpg|Spring peeper, adult
File:Pseudacris crucifer01.jpg|Spring peeper, adult
</gallery>In the female spring peeper, protruding beyond the lower jaw of the frog sits its snout. Through the use of [[adhesive]] pads located on the tips of their non-webbed fingers, spring peepers can stick to particular materials. Males and females are differentiated from one another through the darkening of the skin beneath the jaw in males. Males have a body length ranging from {{convert|18|-|30|mm|in}}, and females have a body length ranging from {{convert|20|-|35|mm|in}}.<ref name=Rugh1941/>

=== Glands and toxins ===
In ''Hyla crucifer'' males, the blackened pigmentation of the testis affects the [[seminiferous tubules]], the underside of the [[peritoneum]], and the organ itself. The tubules of the testis are surrounded by a pigment layer and a layer of flattened epithelial cells which are located within the surrounding connective tissue. The thickness of an average testis is about 1.10&nbsp;mm and 2.5&nbsp;mm in length. The [[spermatogonia]] are a cluster of masses jutting out from the [[Proximal tubule|tubule lumen]]. In the late fall, the spermatozoa, located in the [[seminiferous tubule]]s of the spring peeper, mature and remain there until the spring for breeding. After the seminiferous tubules are emptied, during mating season, the pigmentation of the testis changes from black to a dull grey.<ref name=Rugh1941/>

In the spring peeper, most of its energy is used during courtship. Higher energetic costs in female spring peepers are associated with [[gametogenesis]], which occurs before breeding. Stored reserves of fat and [[glycogen]] contents can be measured early in the reproductive process to determine the amount used in spring peepers and their correlation to body size. Nonpolar lipid and glycogen content in male spring peepers increased with body mass, whereas in females, it decreased or had minimal variation.<ref name="Duffitt-2011">{{Cite journal |last1=Duffitt |first1=Ashley D. |last2=Finkler |first2=Michael S. |date=2011 |title=Sex-Related Differences in Somatic Stored Energy Reserves of ''Pseudacris crucifer'' and Pseudacris triseriata during the Early Breeding Season |journal=Journal of Herpetology |volume=45 |issue=2 |pages=224–229 |doi=10.1670/09-263.1 |jstor=41415272 |s2cid=83807187 }}</ref> The fiber [[triglyceride]] and glycogen contents of the female spring peeper's liver increased significantly slower than in males as body mass increased. At the beginning of the breeding season, male spring peepers have more significant amounts of bodily lipid content. Therefore, those that are larger are experiencing lower efficiencies in calling. More reserves of glycogen and lipids are required to maintain calling during the season and require additional rationing of reserves to prepare themselves for courtship. In females, there is a positive correlation between their snout length and wet ovary mass, which also correlates to an increase in body size.<ref name="Duffitt-2011" />

=== 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" />

=== Thermoregulation ===
Climate plays a major role in the timing of spring peeper breeding: studies have shown a correlation between temperature and the date of first call (when spring peepers start to breed).<ref>{{cite journal |last1=Blaustein |first1=Andrew R. |last2=Belden |first2=Lisa K. |last3=Olson |first3=Deanna H. |last4=Green |first4=David M. |last5=Root |first5=Terry L. |last6=Kiesecker |first6=Joseph M. |date=14 December 2001 |title=Amphibian Breeding and Climate Change |journal=Conservation Biology |volume=15 |issue=6 |pages=1804–1809 |doi=10.1046/j.1523-1739.2001.00307.x |doi-access=free |bibcode=2001ConBi..15.1804B |s2cid=26685121|hdl=2027.42/75127 |hdl-access=free }}</ref><ref name="Gibbs-2001">{{Cite journal |last1=Gibbs |first1=James P. |last2=Breisch |first2=Alvin R. |date=2001 |title=Climate Warming and Calling Phenology of Frogs near Ithaca, New York, 1900–1999 |journal=Conservation Biology |volume=15 |issue=4 |pages=1175–1178 |doi=10.1046/j.1523-1739.2001.0150041175.x |jstor=3061337 |bibcode=2001ConBi..15.1175G |s2cid=86182135 }}</ref> Though the precise factors affecting breeding timing are complex, there has been a trend towards earlier breeding as average temperatures have increased since the early 20th century.<ref name="Gibbs-2001" /><ref name="Lovett2013" />

Another impact of temperature is the duration of mating calls. There is a negative relationship between the length of mating calls and throat temperature. However, male spring peepers with superior calling frequencies are positively related to throat temperature. The temperature of the surrounding environment of spring peepers also plays a role in the rate of calls, which is positively associated with the success of males during the mating and breeding period, showing that increasing site and throat temperatures result in increasing dominant frequency.<ref name="ReferenceA">{{Cite journal |last1=Sullivan |first1=Brian K. |last2=Hinshaw |first2=Steven H. |date=1990-12-31 |title=Variation in Advertisement Calls and Male Calling Behavior in the Spring Peeper (''Pseudacris crucifer'') |journal=Copeia |volume=1990 |issue=4 |page=1146 |doi=10.2307/1446500 |jstor=1446500 }}</ref>

Spring peepers are known to tolerate freezing temperatures by producing a glucose-based cryoprotectant to limit cell shrinkage and prevent cell freezing.<ref name=":1">{{Cite journal |last1=Ethier |first1=Jeffrey P. |last2=Fayard |first2=Aurore |last3=Soroye |first3=Peter |last4=Choi |first4=Daeun |last5=Mazerolle |first5=Marc J. |last6=Trudeau |first6=Vance L. |date=2021-08-27 |title=Life history traits and reproductive ecology of North American chorus frogs of the genus Pseudacris (Hylidae) |journal=Frontiers in Zoology |volume=18 |issue=1 |page=40 |doi=10.1186/s12983-021-00425-w |issn=1742-9994 |pmc=8394169 |pmid=34452622 |doi-access=free }}</ref>