Species Account. Northern Spring Peeper / Rainette Crucifère (Pseudacris crucifer crucifer)
Kathryn A. Stewart
Department of Biology, Queen’s University, Kingston, ON Canada K7L 3N6
Taxonomy: Class: Amphibia. Order: Anura. Family: Hylidae. Genus: Pseudacris. Species: Pseudacris crucifer (Wied-Neuwied 1838). Subspecies: Pseudacris crucifer crucifer.
[Note: This species was formerly placed in the Genus Hyla (Hyla crucifer; Wied-Neuwied 1838) but based on analyses of allozyme data was reclassified as a member of the genus Pseudacris (Hedges 1986). Cocroft (1994) suggested that the spring peeper could be placed within a monotypic genus based on morphological and biochemical data but also concluded that its inclusion in the genus Pseudacris was appropriate. To date, da Silva’s (1997) recommendation that the genus Pseudacris be maintained for the spring peeper has been upheld.]
Subspecific designations have been given to the southern spring peeper (Pseudacris crucifer bartramiana; Stevenson & Crowe 1992) as well as the northern spring peeper (Pseudacris crucifer crucifer; Stevenson & Crowe 1992) based primarily on colour pattern variation. Phylogenetic analyses of DNA sequences, however, do not support these subspecific designations (Austin et al. 2002).
Also known as ‘Pinkletinks’ in Martha’s Vineyard, USA, and ‘Twinkletoes’ in New Brunswick, Canada, this enigmatic harbinger of spring is a small North American chorus frog usually ranging in adult size from 1.9 to 3.2cm; record 3.7cm (Conant & Collins, 1998). A mystery to many naturalists who are familiar only with its calls in spring, spring peepers share various attributes common to frogs of both the Hyla and Pseudacris genus.
Characterised by the dark, usually imperfect cross marking on their back (hence, the Latin name crucifer, meaning cross-bearer), this species does not usually have the distinctive mottling, spotting or banding typical of Pseudacris (see Fig. 1). It does, however, have prominent bars on its hind legs. Spring peeper colours vary, usually with temperature or stress (Harding 1997), spanning shades of dark brown, grey, light tan and even orange. A dark band usually runs from the snout, continuing to the nostril, eye and ending at the tympanum. Most individuals have a dark line (or V) located between the eyes (distinct markings of most species placed within the genus Pseudacris). Peepers also have small toe disks (or pads) typical of Hylidae. This permits climbing trees and shrubs, although most individuals rarely ascend higher than one metre from the ground. Slight webbing is also evident between the back toes of these shallow-water swimmers (Conant & Collins 1998).
Sexes can easily be distinguished during the breeding season. Calling males have dark, and often inflated vocal sacs. Even deflated vocal sacs are evident due to their elasticity, and mottled brownish or greenish appearance (Harding 1997). Males have been reported to be, on average, slightly smaller in size and darker in colouration than females (Harding 1997); however evidence to attest to such dimorphisms are lacking, as well, such differences may be obscured by age as growth continues throughout life.
Tadpoles can reach up to 3 cm in total length prior to metamorphosis (MacCulloch 2002). They are distinct from other frog larva in the Great Lakes Regions, with a brown or greenish body with metallic flecks (often gold) on their dorsal surface, contrasted by an iridescent white belly (Harding 1997). Tail fins are large and clear with orange, black or purplish blotches around the edges (see Fig.2; MacCulloch 2002).
The northern subspecies of spring peeper (present at QUBS) is distinct from its southern counterpart by a plain, cream coloured venter (the southern spring peeper often contains dark spots on the ventral surface of the body; Conant & Collins 1998).
* Species with which the spring peeper may be confused in the Canadian portion of its range include the striped chorus frogs (P. triseriata and P. maculata). These frogs are similar in size as spring peepers but have longitudinal stripes, instead of the characteristic ‘X’, a light lip line and their call sounds like a fingernail running across a comb, instead of the typical single note ‘peep’ of the spring peeper (Harding 1997). Cricket frogs (Acris crepitans blanchardi) have rougher skin (wartier in appearance), have a dark band on the inner thigh and their call resembles a sharp, quickly repeated clicking sound (similar to hitting small stones together; Harding 1997). In Ontario, cricket frogs are known only from Pelee Island in Lake Erie and have been neither heard nor seen in many years (McCulloch 2002). The grey treefrog (Hyla versicolor) is substantially larger (3.2 to 6.2 cm) than the spring peeper and have distinctive yellow or orange on the inner portion of their thighs; grey treefrog calls are distinguishable with high pitched, short trills (Harding 1997).
The current range of the spring peeper probably represents that of recent past, reflecting historical eastern mixed and deciduous forests (Lannoo 2005). In Canada its range includes the Maritime Provinces (east to Labrador; Bergman 1999; SRank – S1S2; see footnote below), west to Manitoba (S5) and as far north as James Bay (Ontario, S5; Conant & Collins 1998). Its distributions in the United States spans much of the eastern extent of the country, including Minnesota (S5), Iowa (S5), Illinois (S5), Oklahoma (S5), eastern Texas (S5) and as far south as Florida (SNR; although only P. crucifer bartramiana is found on the southern peninsula of Florida and Georgia; Conant & Collins 1998). The spring peeper is abundant in most of Eastern North America but is considered threatened and rare in Kansas, only occupying the extreme eastern periphery of the state (S2). [Note. G, N, T and SRanks are based on a 1 (critically imperilled) to 5 (demonstrably secure) threat scale. SRanks are assigned at the local level (state or province), GRanks at the global level, NRanks at the National level and TRanks are assigned to intraspecific taxon]
Phylogenetic analysis revealed 6 major mitochondrial (mtDNA) lineages across the spring peepers’ range (see Fig.3) with various areas of overlap (hydrid/contact zones; Austin et al. 2002). Although these lineages are not officially considered ‘subspecies’ they do imply significant evolutionary divergence not captured by the simple designation of northern and southern spring peeper subspecies; Austin et al. 2004). Indeed these lineages appear to have been isolated long enough for the evolution of two congeneric sister species (Moriarty-Lemmon et al. 2007).
Spring Peepers were initially believed to have been introduced in Cuba (Schwartz & Henderson 1991), but this observation has yet to be substantiated (Powell & Henderson 1999).
Commonly located during the breeding season in or near temporary or semi-permanent ponds, peepers are more likely to be located in bodies of fish- and pollutant-free water (Hecnar & M’Closkey 1996, and Freda & Taylor 1992, respectively). When breeding they form choruses near brushy growth or secondary forests, primarily where trees over-hang, or are located within, ponds, swamps or marshes (Conant & Collins 1998). At the Queen’s University Biology Station (QUBS), spring peepers are very common in late April through late May in almost all aquatic habitats. Marshy lake edges, such as those found in Telephone Bay and Cow Island Marsh in Lake Opinicon often have spring choruses of spring peepers. Other station locations include woodland ponds near Skycroft Campground, Indian Lake Road, and Round Field Marsh, all located a short distance from Opinicon Lake Rd (pers. observation).
Although seldom observed outside of breeding choruses, Peepers often call during warm bouts of rain, allowing for sightings of small frogs hopping through damp grass and/or the forest floor. After the breeding season they usually inhabit leaf litter in woodlands, typically overwintering under such debris (MacCulloch 2002). Peepers have a unique physiology that allows for freeze and desiccation tolerance during their frigid hibernation state (Schmid 1982). A remarkable adaptation, freeze tolerance has only been noted in a few other northern frogs (Lithobates sylvaticus, Hyla versicolor, and Pseudacris triseriata; Storey & Storey 1987).
Feeding & Activity Patterns
Adults feed primarily on insects and other invertebrates while their tadpoles remain completely herbivorous, feeding on plants and algae (Fisher et al.2007). Since spring peepers often emerge from hibernation early in the year, they often rely on fat reserves (Badger & Netherton 2004). To catch prospective prey or to evade predation themselves, peepers can jump nearly 17 times their body length – a feat that would be the equivalent of a human jumping nearly 30 metres (Badger & Netherton 2004).
Spring peepers are conspicuous in early spring (late March and early April in Ontario) when they start to breed, although males often outnumber females 9:1 or more in these breeding aggregations (Badger & Netherton 2004). During late fall when they can be located in woodlands, the sex ratio reverts closer to 1:1, suspected to be a result of road mortalities, predation and behavioural differences (i.e. prolonged chorus attendance by males; Badger & Netherton 2004). In general, spring peepers are most active from late afternoon and throughout most of the night (Fisher et al. 2007).
Breeding season home-range diameters have been observed between 1.2 to 5.5 metres, and with daily movements ranging from 6.1 to 39.6 metres (Zampella & Bunnell 2000). First year individuals travel substantially less but tend to occupy all available habitat with the exception of the breeding ponds (Delzell 1958). Adult males restrict their movements within the breeding ponds to small territories (0.5 to 6 metres depending on population density) for up to a month in length; females are not observed to hold territories and seem to attend the breeding pond for only a day or two (Delzell 1958).
After breeding, both sexes set up overlapping home-ranges ranging in diameter from 1.1 to 6 metres within woodlands (Delzell 1958). ‘Homing’ ability has also been demonstrated to be strongly expressed in peepers upon removal, although site fidelity from year to year is not observed (Delzell 1958).
Breeding Behaviour & Reproduction
In Canada, often one of the first species to emerge and begin breeding after winter, the spring peeper can be seen congregating around breeding ponds even before full spring thaw (MacCulloch 2002). Forming choruses in the beginning of March (Southern Ontario) and late March (QUBS and environs), these prolonged breeders (Wells 1977) extend their mating until the end of May or beginning of June in the northern part of their distribution. In the southern portion of their range however, this species is often referred to as a ‘winter frog’ (Badger & Netherton 2004). Breeding usually starts with the onset of cooler rains as chorusing starts in November and lasts until March in places such as Kansas, Texas and Florida (Conant 1975).
Calling males occupy small territories around pond edges, usually found perched on sticks, logs or in clumps of vegetation (MacCulloch 2002).Calling males are sometimes accompanied by satellite males (Forester & Lykens 1986). Thus, non-calling satellite males position themselves in close proximity to a calling individual (see Fig. 4), with the apparent intention of intercepting females without incurring the cost of displaying or territory defense (Land & Wells 1993). Others, however, have suggested that this tactic is merely used to steal the advertisers calling territory during his absence while engaging in copulation, at which time they start to call themselves (Badger & Netherton 2004). Whether considered a form of sexual parasitism (Perrill 1984), or a legitimate alternative mating strategy (Waltz 1982), this phenomenon has been observed across the peepers’ range, and appears to increase in frequency with chorus density; satellite males tend not to exceed 14% of total males present in any chorus (Forester & Lykens 1986).
Female spring peepers will enter a pond attracted by male calls. Once in the water, the female swims to her chosen mate, touches him, and allows him to mount her (Badger & Netherton 2004). The pair begins amplexus with the male clasping the female around the neck (axillary positioning), after which the female continues to swim and lay between 800-1000 eggs (each approx. 1mm diameter; Wright & Wright 1995).The eggs are deposited singly or in small clusters, submerged at the bottom of a pond among grasses or other aquatic plants. Eggs are laid as the female dives to the bottom of the pond and lays as the male fertilizes (Wright & Wright 1995). Eggs are half white, half black and covered with a jelly envelope.
Eggs hatch in 1-2 weeks in natural populations (Ashton & Ashton 1988), or in 5-6 days if housed at room temperature in a laboratory (Gosner & Rossman 1960). Tadpoles complete metamorphosis between 90-100 days (Minton 2001), although Gosner and Rossman (1960) observed P. crucifer bartramiana to metamorphose as early as 45 days after laying (at a minimum of 10.33 mm SVL); tadpoles of the southern subspecies, however, average 8-10% larger than those of P. crucifer crucifer (Gosner and Rossman 1960) and size may influence time to metamorphosis.
Tadpoles do form aggregations in the wild (Brattstrom 1962) but no sibling recognition has been observed in laboratory tests (Fishwald et al. 1990). Once metamorphosed froglets move from wetlands to forest floors, or low brush (Lannoo 2005). Reproductive maturity is not attained until 23 mm SVL for females and 18mm SVL for males with mature spermatozoa (Oplinger 1966). Bartlett & Bartlett (1999), however, suggest a range of 10 to 31mm SVL, probably achieved in the second or possibly third year. Indeed, Delzell (1958) observed individuals to remain terrestrial in their first year of life, declining the opportunity to enter the breeding pond. Average lifespans for wild spring peepers are unknown; however captive raised individuals live up to 3-4 years (Blaustein et al. 2001).
Only uttered by the males of the species, the call is produced using a single vocal sac. Peepers have one of the largest vocal-sac-to-body ratios of any temperate frog. The advertisement call is a single, clear whistling note (at about 3KHz; see Fig. 5), repeated at intervals of less than a second. Although seemingly simple, this call probably helps to maintain species boundaries and may even vary diagnostically among mtDNA lineages (K.A. Stewart, J.Austin & S.C. Lougheed, unpubl. data).
To improve reception and maximize the signal-to-noise ratio, male spring peepers often give longer ‘peeps’ when females are close (Rosen & Lemon 1974) and may even climb to a more elevated calling position (Parris 2002; see Fig. 6). Some individuals also use an ‘aggressive call’, an ascending, trilling peep usually when a rival infiltrates a calling male’s territory. Spring peepers with higher call rates or lower frequency calls are more likely to be larger, heavier and/or older individuals (Zimmitti 1999; Lance & Wells 1993, respectively). Individual males call at an amplitude of between 80.2-92.4dB (at 50cm distance from source) while their chorus ambient noise registers at an astonishing 64.7dB (Brenowitz et al. 1984). So loud are peeper choruses that they have been likened to deafening sleigh bells (Conant & Collins 1998). Because large choruses can be heard up to a kilometre away, they are a common backdrop to most warm spring evenings.
Natural Heritage Status
Global Status: G5 T5 – secure
Global Status Last Reviewed: 11 Nov. 1997
Global Status Last Changed: 01 Nov. 1996
Reasons: Abundant over most of range.
National Status: N5 (01 Nov. 1996)
Nation: United States
National Status: N5 (04 Oct. 1998)
*For SRANK see ‘Distribution’.
IUCN Red List: Least concern (LC) due to its wide distribution, presumed large population and because the spring peeper is unlikely to decline in abundance fast enough to require listing in a more threatened category (Hammerson 2004).
No CITES Listing.
COSEWIC: Not at risk.
OMNR: Not at risk.
Although this species is not under any major threats on a global scale, urbanization and intense agriculture obviously negatively affects population persistence. Wetland drainage, habitat fragmentation due to development, pathogens (such as chytrid fungus) and pollutants do threaten many amphibians and may drastically diminish long-term sustainability of even “wide ranging” species like the spring peeper (Hammerson 2004).
Although myriad studies have been conducted on spring peepers, their broad-range, local abundance and striking phylogeographic structure make them ideal candidates for many other interesting studies.
Although smaller males may be more likely to be satellites (but see Lance & Wells 1993) and demonstrate greater agility during competitive trials to amplex a female (Forester & Lykens 1986), no research, to my knowledge has explored whether these satellites intercept females or are successful at fertilizing eggs. Since satellites are also present within hybrid zones between mtDNA lineages, it would be interesting to study whether hybrids assume this satellite tactic. If hybrids deploy calls that are unattractive to potential pure lineage suitors, perhaps they would increase their fitness through interceptions rather than advertisement (a study that I am currently undertaking). Testing whether satellite behaviour is a viable heritable alternative strategy or simply a manifestation of age and/or inexperience would also be worthwhile. Satellite behaviour could mask the effective expression of true female preference and may allow for stable hybrid zones between the various mtDNA lineages of Northern spring peepers.
Phenotypic Adaptation and/or Plasticity:
Size, mass and colour does vary geographically in this species (K. A. Stewart, J. Austin & S.C. Lougheed, unpublished data). Lacking are studies that assess the heritability and potential adaptive significance of such variation.
Phylogeographic studies have revealed a dynamic history of geographic isolation followed by post-glacial recolonization in the spring peeper (Austin et al. 2002; Austin et al. 2004). This striking geographic restriction across the spring peepers’ range provides a unique scenario to test for the importance of geographical isolation and secondary contact among distinct evolutionary lineages in the generation of new, reproductively isolated species (work currently being undertaken by myself, J.D. Austin and S.C. Lougheed).
Genetic Sex Determination:
Although not unique to P. crucifer, there is a deficit in our knowledge about sex determination in amphibians, with only a few species described. To elucidate sex ratios, hybrid viability, and pollution effects, detailed work is required for the spring peeper as well as many other species.
Literature & Further Reading:
- Ashton, R. E., Jr., & P. S. Ashton. 1988. Handbook of Reptiles and Amphibians of Florida. Part Three. The Amphibians. Windward Publishing, Inc., Miami.
- Austin, J. D., Lougheed, S. C., Neidrauer, L., Check,A.A., & P.T. Boag.2002. Cryptic lineages in a small frog: post-glacial history of the spring peeper, Pseudacris crucifer (Anura: Hylidae). Mol. Phylogenet. Evol. 25: 316-325.
- Austin, J. D., Lougheed, S. C., & P. T. Boag. 2004. Discordant temporal and geographic patterns in maternal lineages of eastern North American frogs, Rana catesbeiana and Pseudacris crucifer. Mol. Phylogenet. Evol. 32: 799–816.
- Badger, D. P. & J. Netherton. 2004. Frogs. Voyageur Press. MN. Pp74-76.
- Bartlett, R. D. & Bartlett, P. P. 1999. A Field Guide to Florida Reptiles and Amphibians. Gulf Publishing Company, Houston, Texas.
- Bergman, C. M. 1999. Range extension of spring peepers, Pseudacris crucifer, in Labrador. Can. F. Nat. 113:309-310.
- Blaustein, A., L. Belden, D. Olson, D. Green, T. Root, & J. Kiesecker. 2001. Amphibian breeding and climate change. Cons. Biol. 15(6): 1804-1809.
- Brattstrom, B. H. 1962. Thermal control of aggregation behavior in tadpoles. Herpetologica 18:38-46.
- Brenowitz, E. A., Wilczynski,W. & H. H. Zakon. 1984. Acoustic communication in spring peepers. Environmental and behavioural aspects. J. Comp. Phys. A 155:585-592.
- Cocroft, R. B. 1994. A cladistic analysis of chorus frog phylogeny (Hylidae: Pseudacris). Herpetologica 50:420-437.
- Conant, R., & J. T. Collins. 1998. A field guide to reptiles and amphibians: Eastern / Central North America. Third Ed. Houghton Mifflin Company, NY.
- Delzell, D. E. (1958) Spatial movements and growth of Hyla cruficer. Ph.D. Dissertation, Univ. Michigan, Ann Arbor, MI.
- Fisher, C., Joynt, A., & R. J. Brooks. 2007. Reptiles and amphibians of Canada. Lone Pine Pub. Edmonton, AB.
- Fishwald, T. G., R. A. Schemidt, K. M. Jankens, K. A. Berven, A. J. Gamboa, & C. M. Richards. 1990. Sibling recognition by larval frogs (Rana pipiens, R. sylvatica, and Pseudacris crucifer). J. Herp. 24:40-44.
- Forester, D. C., & D. V. Lykens. 1986. Significance of satellite males in a population of spring peepers (Hyla crucifer). Copeia 3:719-724.
- Freda, J., & D. H. Taylor. 1992. Behavioural response of amphibian larvae to acidic water. J. Herp. 26 (4): 429-433.
- Gosner, K. L., & D. A. Rossman. 1960. Eggs and larval development of the treefrogs Hyla crucifer and Hyla ocularis. Herpetologica. 16:225-232.
- Hammerson , G. 2004. Pseudacris crucifer. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1. http://www.iucnredlist.org. Downloaded on 28 July 2009.
- Harding, J. H. 1997. Amphibians and reptiles of the great lakes region. University of Michigan Press. Michigan, USA.
- Hecnar, S. J. & R. T. M’Closkey. 1996. The effect of predatory fish on amphibian species richness and distribution. Biol. Cons. 79: 123-131
- Hedges, S. B. 1986. An electrophoretic analysis of holarctic hylid frog evolution. Syst. Zool. 35:1-21.
- Lance, S. L, & K. D. Wells. 1993. Are spring peeper satellite males physiologically inferior to calling males? Copeia. 1993:1162-1166.
- Lannoo, M. 2005. Amphibian declines: The conservation status of United States Species. University of California Press.
- MacCulloch, R. D. 2002. The ROM field guide to amphibians and reptiles of Ontario. Royal Ontario Museum and McClelland & Stewart Ltd.
- Minton, S. A., Jr. 2001. Amphibians & Reptiles of Indiana. Revised 2nd Edition. Indiana Academy of Science, Indianapolis.
- Moriarty-Lemmon, E., Lemmon, A. R. & D. C. Cannatella. 2007. Geological and climatic forces driving speciation in the continentally distributed trilling chorus frogs (Pseudacris). Evolution 61:2086-2103.
- Oplinger,C . S. 1966. Sex ratio, reproductive cycles, and time of ovulation in Hyla crucifer crucifer. Herpetologica 22:276-283.
- Parris, K. M. 2002. More bang for your buck: the effect of caller position, habitat and chorus noise on the efficiency of calling in the spring peeper. Ecol. Mod. 156: 213-224.
- Perrill, S. A. 1984. Male mating behavior in Hyla regilla. Copeia. 1984:727-732.
- Powell, R., & R. W. Henderson. 1999. Addenda to the checklist of West Indian amphibians and reptiles. Herp. Rev. 30:137-139.
- Rosen M. & R. E.Lemon.1974. The vocal behavior of spring peepers, Hyla crucifer. Copeia 1974:940–950.
- Schmid, W. D. 1982. Survival of frogs in low temperature. Science 215:697-698.
- Schwartz, A., & R. W. Henderson. 1991. Amphibians and Reptiles of the West Indies: Descriptions, Distributions, and Natural History. University of Florida Press, Gainesville, Florida. xvi + 720 pp.
- Stevenson D. & D. Crowe. 1992. Geographic Distribution Note. Pseudacris crucifer. Herp. Rev. 23: 86.
- Storey, K. B., & J. M. Storey. 1987. Persistance of freeze tolerance in terrestrial hybernating frogs after spring emergence. Copeia 1987: 720-726.
- Waltz, E. C. 1982. Alternative mating tactics and the law of diminishing returns: the satellite thresh-old model. Behav. Eco. Sociobio. 10:75-83.
- Wells, K. D., 1977. The social behaviour of anuran amphibians. Anim. Behav. 25: 666-693.
- Wright, A. H. & A. A. Wright. 1995. Handbook of frogs and toads of the United States and Canada. Comstock publishing Co. Inc., Cornell University, Ithaca, NY.
- Zampella, R., & J. Bunnell. 2000. The distribution of anurans in two river systems of a coastal plain watershed. J. Herp. 34: 210-221.
- Zimmitti, S. J. 1999. Individual variation in morphological, physiological and biochemical features associated with calling in spring peepers (Pseudacris crucifer). Physiol. Biochem. Zool. 72: 666-676.
Reviewers: James Austin (Univ. Forida) and Gregory Bulte (Univ. Ottawa).