Pseudacris crucifer

The spring peeper (''Pseudacris crucifer'') is a small chorus frog widespread throughout the eastern United States and Canada. They prefer permanent ponds due to their advantage in avoiding predation; however, they are very adaptable with respect to the habitat they can live in. Due to their presence in northern regions, the frog is able to endure below freezing temperatures. They are so called because of their chirping call that marks the beginning of spring. ''Crucifer'' is derived from the Latin root meaning "cross-bearing." This could be a reference to the cross-like pattern on the spring peeper's dorsal side.

These chirping calls are significant for communication in mating as females choose their mates based on the frequency and volume associated with them. Satellite males who do not make any calls also strategically place themselves near those that make louder calls in an attempt to intercept females.

Temperature plays a large role in when the spring peeper begins breeding as well as the duration of mating calls. Therefore, climate change has the ability to significantly impact this species in the near future.

Description

Spring peepers are tan or brown frog with a dark cross on their dorsa (thus the Latin name ''crucifer'', meaning cross-bearer), though sometimes the marking may be indistinct. They have a body length between less than to and a mass between .

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.

The color variations of ''P. crucifer'' are mostly tan, brown, olive green, and gray. 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. 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.

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.

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
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 18-30mm, and females have a body length ranging from 20-35mm.

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 mm and 2.5 mm in length. The spermatogonia are a cluster of masses jutting out from the tubule lumen. In the late fall, the spermatozoa, located in the seminiferous tubules 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.

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. The fiber triglyceride and glycogen contents of the female spring peeper's liver increased significantly slower than 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.

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 β-hydroxy acyl CoA dehydrogenase (a protein) 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. 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.

Thermoregulation

Due to climate playing a major role in when spring peepers begin breeding, one can determine that there is a clear association between temperature and breeding. Spring peepers begin to bread during temperatures that are warmer, showcasing a positive correlation between temperature and breeding time. Amphibians are exotherms, which shows that any change in the typical climate of their environment would leave spring peepers in a vulnerable position. Temperature increases can significantly impact reproduction-assigned behavior considerably.

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.

Geographic Range and Habitat

The southern spring peeper's habitat includes the Gulf Coast from southeastern Texas to southeastern Georgia and northern Florida, United States. Its northern conspecific occurs in the entire east of the Mississippi and spreads to eastern and central Canada.

During the breeding season, the spring peeper will be found near ponds and usually located in bodies of water that are free of fish and pollutants. During actual breeding, their choruses form near where trees hang by bushy plants or secondary forests. Their choruses can also be located within ponds, marshes, or swamps. They will usually resume call activity during warm rain, and are not commonly seen outside of their breeding choruses. During the non-breeding season, they will inhabit dead plant material from trees, shrubs, and other plants in the woods.

Spring peepers are often found in temporary ponds (which eventually dry during the summer months), intermediate ponds that have interchanging periods of being dry and wet every year, or in customarily filled ponds year-round. Although they are able to inhabit multiple types of ponds, spring peepers have been seen to be superior competitors in permanent ponds due to their higher caliber of predation resistance within the environment. Spring peepers live primarily in forests and regenerating woodlands near ephemeral or semipermanent wetlands. This amphibious species requires marshes, ponds, or swamp regions to support the aquatic environment the eggs and tadpoles need.

In the northern reaches of their range, spring peepers must endure occasional periods of subfreezing temperatures during the breeding season. The species can tolerate the freezing of some of its body fluids, and undergoes hibernation under logs or behind loose bark on trees. It is capable of surviving the freezing of its internal body fluids to temperatures as low as -8 °C (17.6 °F). This species frequently occurs in breeding aggregations of several hundred individuals, and commonly breeds in many small wetlands, including swamps and temporary pools and disturbed habitats, such as farm ponds and borrow pits.

Home Range and Territoriality

The mating displays of male spring peepers vary with different environmental factors: humidity and vegetation density. These factors play a significant role in the arboreal behavior and nature of spring peepers during mating. At sites with higher humanity and air temperature, there is increased dominance of arboreal behavior, which showcases that latitude may play a role. Spring peepers who reside in areas of warmer temperatures tend to exhibit arboreal behavior to greater extents compared to those in environments of lower temperatures. When comparing the improvement of mating calls in males, calls from above ground compared to those near the ground showcased better results. Local vegetation may also play a role in the betterment of arboreal calling compared to calling from lower levels due to the spatial aspects interrupting the call.

Diet

Juvenile

Tadpoles are suspension feeders, therefore they graze on inorganic and organic matter. They also feed on algae and other organisms in the water. Their predators include great diving beetle larvae (when in tadpole form), snakes, skunks, and larger frogs.

Adult

Spring peepers are nocturnal insectivores, emerging at night to feed primarily on small invertebrates, such as beetles, ants, flies, and spiders. They do not climb high into trees, but hunt in low vegetation. Spring peepers living in deep, damp forests are active hunters both day and night, whereas those found in woodland edges restrict most hunting and other activity to night. The spring peeper's diet involves the filtering of particles from water columns and scouring periphyton and detritus (dead, organic matter) from environmental surfaces in their habitat.

Reproduction and Life Cycle

Brood size

Spring peepers breed in southern areas from October to March, depending on the local temperature. In northern areas, they breed between March and June, when the warm rains start. ''P. crucifer'' typically lays around 900 eggs per clutch, but up to 1000 are possible. Egg clusters are hidden under vegetation or debris at the water base. In very cold weather, they hibernate under logs and loose bark. Spring peepers often call day and night as long as the temperature is above freezing, but they are mostly heard and usually not seen because they hide in dense plants. They are especially easy to hear due to their extremely loud mating call which gives them the name "peeper", but it is often hard to pinpoint the source of the sound, especially when many are peeping at once. The peepers generally breed close to dusk and throughout the evening and early morning hours. Their calls can be heard from as far as one to two and a half miles, depending on their numbers.

Life-Span

After they hatch, they remain tadpoles for two to three months before transforming into frogs and are ready to leave the water. Following breeding in the spring, the spring peepers' larval stage lasts two to three months. The spring peeper can live an estimated three years in the wild.

By looking at the different shading/coloring of concentric rings in the skeletons of spring peepers, age can be determined regarding the way of bone growth. Darker lines coincide with periods of higher survival rates during winter months. Lighter lines and areas represent periods of bone deposition and rapid growth. These lines allow it to be determined that spring peepers begin to breed, going into their third spring when they are two years old. Male spring peepers have reached sexual maturity at this time yet are smaller in size than females. Between spring peepers' second and third years, their body size increases significantly, then subsequentially plateaus. During the first season of breeding, the two-year-old males produce higher frequency calls than males in their third and fourth seasons do

Mating

Mate Searching Behavior

As their common name implies, the spring peeper has a high-pitched call similar to that of a young chicken, only much louder and rising slightly in tone. They are among the first frogs in the regions to call in the spring. The mating calls of the spring peeper consist of a sound very similar to a "peep" and are repeated by males up to 13,500 times per night. As a chorus, they resemble the sounds of sleigh bells. They are heard early in spring not long after the ice melts on the wetlands. The males usually call from the edges of the bodies of water in which they breed, hidden near the bases of shrubs or grasses. Even when calling, they may be difficult to locate and are most easily seen when in amplexus in the shallows. As in other frogs, an aggressive call is made when densities are high. This call is a rising trill closely resembling the breeding call of the southern chorus frog (''Pseudacris nigrita nigrita'').

Female/Male interactions

Courting

Females choose mates based on the speed and volume of these male calls. Interestingly, females also discriminate between distinct genetic lineages, with females preferring males of their own lineage, possibly due to the detrimental effects of hybridization. Older, larger males tend to have faster and louder calls that are preferred by the females. A segment of the male population, known as 'satellite males' do not make these calls, but instead position themselves near loud males and attempt to intercept females drawn in by these calls. Males normally call between 15-25 times per minute to attract mates. This can continue from the evening unto 3am. Male spring peepers have also been found to increase the duration and frequency of aggressive calls in response to increased calling intensity from others. These satellite males are also known to circumvent female choice and increase rates of hybridization between spring peeper lineages.

Mate Choice

It has been established that the mating call of male spring peepers acts as an etiological isolating mechanism. As a potential agent of sexual selection, the mating call has many variations that may come into play as a major factor in mate choice by females. During mating, females monitor body size in correlation to the frequency of calls in an inverse matter. The basilar papilla of the inner ear is responsible for decoding and detecting mating calls. The basilar papilla units within the female ear are tuned between 2100 and 3700 Hz and are dependent on intensity. Females tend to select low-frequency calls over high-frequency ones because the calls at the lower end of the spectrum are easier to detect. The calls of spring peepers are often repeated, which has been deemed essential concerning the evolution of the mate choice of females reacting to particular mating and courtship behavior.

Enemies

Spring peepers encounter enemies in their natural environments early in their development. Compared to intermediate or temporary ponds, permanent ponds host a large abundance of tadpoles and larger predators. Drying periods of ponds typically align before or during the metamorphic larval stage of spring peepers due to their slower growth rates. This suggests that higher mortality rates may be an effect. Salamanders and particular kinds of fish are seen to have profound impacts on the survivorship of spring peeper tadpoles. Each type of pond typically hosts different predators: temporary bonds host beetle larvae and dragonflies, intermediate ponds host salamanders and beetle larvae, and permanent ponds host fishes and dragonfly larvae. Each predator plays a role as a potential predator to the spring peeper, depending on which type of pond they inhabit.

Spring peeper larvae are thought to be poor competitors in environments where other anurans are present. This is typically due to the larval spring peepers' small size and lower levels of activity. The small size of the larval allows them to be able to deal with their depressed resource density. Larval spring peepers harvest smaller amounts of resources, resulting in them having lower metabolic costs and a maintained growth rate. Spring peepers are said to occupy locations where predators have previously gotten ridden of bigger competitors.

Conservation Status

The spring peeper has no special status in most areas. They are common and widespread in the eastern regions. However, their habitats change quickly due to loss of wetlands. In some areas, their populations have decreased significantly.

The species is listed as threatened in both Iowa and Kansas.

Taxonomy

There are currently two subspecies recognized, although detailed genetic and behavioral analysis demonstrates they likely are not taxonomically accurate:
* The northern, ''P. c. crucifer'', found all over the eastern United States and eastern Canada.
* The southern, ''P. c. bartramiana''. The southern is distinguished by a strong dark marking on its belly. ''P. c. bartramiana'' is found along the southern Gulf Coast from southeastern Texas to northern Florida and southern Georgia.

References

External links

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Spring peeper
audio recording
Spring Peeper on Reptiles and Amphibians of Iowa

{{Taxonbar, from=Q135015

Chorus frogs
Cryozoa
Amphibians of the United States
Amphibians of Canada
Fauna of the Great Lakes region (North America)
Fauna of the Northeastern United States
Fauna of the Southeastern United States
Ecology of the Appalachian Mountains
Amphibians described in 1838