Crawfish Frog, Southern Crawfish Frog (R. a. areolatus), Northern Crawfish Frog (R. a. circulosus)
|Taxonomic Notes: This species is placed in Lithobates by some authors, following Frost et al., 2006. This has been a controversial decision, because such well-known species as Rana catesbeiana, with an enormous literature, are made more obscure to many. What is not controversial is that Lithobates is the sister taxon of Rana, so the argument is simply one of Linnean ranks. AmphibiaWeb recommends treating Lithobates as a subgenus of Rana, with species names to be written as Rana (Lithobates) catesbeiana, as an example. This option preserves the maximal amount of phylogenetic information and preserves a long-standing taxonomy.|
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Rana areolata Baird and Girard, 1852(a)
Matthew J. Parris1
1. Historical versus Current Distribution. Crawfish frogs (Rana areolata) have a disjunct distribution, with populations localized in areas of suitable habitat. The distribution forms an arc that encircles the eastern, northern, and western boundaries of the Ozark Plateau, from western Indiana and southern Illinois, west through south-central Iowa, central and southwestern Missouri, southeastern Kansas, eastern Oklahoma, and eastern Texas, and from extreme western Kentucky south along the Mississippi Drainage to central Mississippi, and across southern Arkansas and northwestern Louisiana (Wright and Myers, 1927; Goin and Netting, 1940; Bailey, 1943; Bragg, 1953; Smith, 1961; Altig and Lohoefener, 1983; Garrett and Barker, 1987; Johnson, 1987; Dundee and Rossman, 1989; Conant and Collins, 1998; Young and Crother, 2001). They are also present in a narrow band along the Arkansas River Valley in central Arkansas (S. Trauth, Arkansas State University, personal communication). Crawfish frogs are absent from the Ozark Plateau in Missouri and Arkansas and the Mississippi River Delta in Arkansas and Mississippi (R. Altig, Mississippi State University, personal communication).
Two subspecies are recognized, based on morphological differences among larvae and adults (Goin and Netting, 1940; Bragg, 1953). Southern crawfish frogs (Rana a. areolata) occur from east-central Texas east through central and northern Louisiana and southern Arkansas, and north into southeastern Oklahoma. Northern crawfish frogs (Rana a. circulosa) occur in the northern and eastern portions of the species distribution. Sympatry between the subspecies occurs in the tallgrass prairie region between the Canadian and Arkansas rivers in Oklahoma, and in southern Arkansas (Bragg, 1953; Conant and Collins, 1998). The similarity of R. areolata to the related Florida gopher frog–dusky gopher frog (R. capito–R. sevosa) complex may contribute to inaccurate distribution records (Mount, 1975; Martof et al., 1980; Altig and Lohoefener, 1983; Dundee and Rossman, 1989; Young and Crother, 2001). Rana areolata, R. capito, and R. sevosa are distinct species (Goin and Netting, 1940; Hillis et al., 1983; Hillis, 1988; Young and Crother, 2001) and allopatrically distributed, although they are only separated by a narrow region in south-central Mississippi and central Louisiana (Dundee and Rossman, 1989; Conant and Collins, 1998), where morphologically intermediate animals were noted by Neill (1957d).
2. Historical versus Current Abundance. Listed as Endangered or of Conservation Concern in several states (Johnson, 1987; Dundee and Rossman, 1989; Christiansen and Bailey, 1991; Simon et al., 1992; Busby and Brecheisen, 1997). Probably extinct near the type locality for R. a. circulosa (Minton, 1998; M.R., unpublished data). Northern crawfish frogs have been reported from mountain valleys, oak-hickory-pine forest, and along the Gulf Coastal Plain in Texas and Louisiana, although population status is unknown in many areas (Bragg, 1953; Garrett and Barker, 1987; Dundee and Rossman, 1989). Most extant midwestern populations of northern crawfish frogs are located in remnant prairie habitats, where they may be considered a locally common species (Bragg, 1953; Busby and Brecheisen, 1997; M.R., unpublished data). Others note that populations have declined or been extirpated with the conversion of prairie to agriculture (Platt et al., 1973; Johnson, 1987; Busby and Brecheisen, 1997). Because of the secretive nature of both subspecies, population status and successful reproduction are often difficult to detect. Long-term monitoring programs of breeding adults and metamorphosing juveniles would benefit from surveys at known and potential sites (Semlitsch et al., 1995; Busby and Brecheisen, 1997; Parris and Semlitsch, 1998).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Breeding occurs in late winter to early spring: late February to early May in northern regions, January to early April in southern regions (Bragg, 1953; Smith, 1961; Garrett and Barker, 1987; Johnson, 1987; Dundee and Rossman, 1989; Busby and Brecheisen, 1997). Immigration begins after rainfall has filled temporary ponds and a saturation has occurred (Smith et al., 1947; Busby and Brecheisen, 1997). Ambient air temperatures of 10–12 ˚C (minimum 8 ˚C) are critical to initiate and maintain breeding activity (Smith et al., 1948; Bragg, 1953; Busby and Brecheisen, 1997; M.R., unpublished data). Some claim that for breeding, crawfish frogs require the most restrictive moisture and temperature conditions of any North American Rana (Smith et al., 1947), but others cite flexibility in reproductive behavior (Bragg, 1953; Busby and Brecheisen, 1997; M.R., unpublished data). Males migrate to temporary ponds 5–6 d prior to the arrival of females (Smith et al., 1948). Breeding occurs explosively, with most reproduction occurring in a short period of intense chorusing at the beginning of the breeding season, although calling and periodic reproductive activity may persist for 22–55 d (Smith et al., 1948; Busby and Brecheisen, 1997). In marginal habitats or in smaller populations, reproduction may not occur every year (Thompson, 1915; M.J.P., personal observations).
ii. Breeding habitat. Northern crawfish frogs utilize a variety of breeding habitats, including shallow ditches, temporary ponds, flooded overflows from small streams, pasture ponds, and prairie wetlands (Bragg, 1953; Dundee and Rossman, 1989). Southern crawfish frogs are largely limited to tallgrass or outlier prairie, degraded grasslands, wooded regions along streams associated with grasslands, and pastures, although smaller breeding choruses may be found in areas where prairie has been converted for agriculture (Bragg, 1953; Smith, 1961; Johnson, 1987; Busby and Brecheisen, 1997).
i. Egg deposition sites. Oviposition occurs in shallow water. Emergent aquatic vegetation often supports eggs masses, although not invariably so (Smith, 1934; Bragg, 1953; Smith, 1961; Dundee and Rossman, 1989; Busby and Brecheisen, 1997). Egg masses are often clustered within a pond (Bragg, 1953; Busby and Brecheisen, 1997).
ii. Clutch size. Eggs are deposited at or slightly beneath the water surface in plinth, cylindrical, or disc-shaped masses of 2,000–7,000 eggs (Wright and Myers, 1927; Smith et al., 1948; Bragg, 1953; Smith, 1961; Johnson, 1987; Dundee and Rossman, 1989; Trauth et al., 1990; Redmer, 2000). Eggs are large, with a vitellus of 2–3 mm (Bragg, 1953; Smith, 1961; Redmer, 2000).
C. Larvae/Metamorphosis. Larvae hatch within 7–15 d after oviposition and metamorphose in 63–75 d in the field (Bragg, 1953; Johnson, 1987; Busby and Brecheisen, 1997). Hatching occurs in 7–10 d and metamorphosis in 80–95 d in the laboratory (M. Redmer, personal observations). Parris and Semlitsch (1998) demonstrated that crawfish frogs have an average larval period of 65 d when reared in artificial ponds, and that this increases to an upper limit of 90 d when reared with larvae of other Rana species. Larvae feed primarily on phytoplankton and algae (Bragg, 1953; Parris and Semlitsch, 1998). Larvae reach up to 63 mm in length before metamorphosing and are distinguishable from other Rana larvae by having a relatively narrow interruption between the two halves of the inner row of upper labial teeth (Smith et al., 1948; Bragg, 1953) and by a series of dermal pits along the lateral line (Bragg, 1953; Dundee and Rossman, 1989). Newly metamorphosed individuals are 30 mm in SVL and weigh 2–3 g (Wright and Myers, 1927; Smith, 1961; Parris and Semlitsch, 1998).
D. Juvenile Habitat. Unknown, presumably similar to that of adults. Newly metamorphosed crawfish frogs use existing holes, cracks, and other substrate irregularities as sites to initiate burrowing under experimental xeric conditions (Parris, 1998).
E. Adult Habitat. Northern crawfish frogs occupy several different habitats, including open wet woodlands, wooded valleys, prairies, river floodplains, pine forests, and meadows (Bragg, 1953; Garrett and Barker, 1987; Dundee and Rossman, 1989). Southern crawfish frogs are largely limited to prairie, wet pastures, or grassland habitats, although populations may also persist in low-lying hay fields, and occasionally in woodland stream watersheds and river floodplains (Bragg, 1953; Johnson, 1987; Busby and Brecheisen, 1997). Crawfish frogs are also common in the hardpan, clay soil region of southern Illinois (Smith, 1961). Adults of both subspecies are extremely fossorial, seldom emerging from the abandoned crayfish or other small animal burrows they use as shelter. Adults can be found under logs, in road-side banks, and in sewers (Goin and Netting, 1940; Dundee and Rossman, 1989). Burrows may exceed 1–1.5 m in depth, often have flattened platforms at the entrance, and may be located several meters away from breeding ponds (Thompson, 1915; Smith, 1934; Johnson, 1987). Agricultural practices (i.e., cultivation and mowing) may reduce or limit crawfish frog abundance by eliminating suitable burrowing habitat (Thompson, 1915).
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Unknown.
I. Seasonal Migrations. Individuals migrate from overwintering sites to breeding ponds in early spring (Smith et al., 1948; Johnson, 1987; Dundee and Rossman, 1989; Busby and Brecheisen, 1997). Females leave ponds shortly after oviposition, and males occasionally call from burrows after breeding (Smith et al., 1948). They are seldom encountered above ground outside of their breeding season.
J. Torpor (Hibernation). Assumed to use burrows as hibernacula (Thompson, 1915; Smith et al., 1948).
K. Interspecific Associations/Exclusions. Crawfish frogs may be excluded from larval communities containing plains leopard frogs (Rana blairi) or southern leopard frogs (R. sphenocephala) because of weak interspecific competitive ability (Parris and Semlitsch, 1998). They may breed syntopically with northern cricket frogs (Acris crepitans), American toads (Bufo americanus), Cope’s gray treefrogs (Hyla chrysoscelis), eastern gray treefrogs (H. versicolor), spring peepers (Pseudacris crucifer), western chorus frogs (P. triseriata), plains leopard frogs, green frogs (R. clamitans), and southern leopard frogs (Wright and Myers, 1927; Busby and Brecheisen, 1997; M.J.P., personal observation).
L. Age/Size at Reproductive Maturity. Females are larger than males at maturity. Estimated age (using skeletochronology) of mature adults was 2–5 yr (mean = 3.5 yr) for males, and 3–5 yr (mean = 3.8 yr) for females in a southern Illinois population (Redmer, 2000). SVLs for those specimens were 71–90 mm (mean = 82.8 mm) for males, and 79–102 mm (mean = 89.6 mm) for females. Other reported sizes include modal SVLs of 100 mm (males) and 95 mm (females), and maximum SVLs of 117 mm (males) and 118 mm (females; Smith et al., 1948). Bragg (1953) reported mean SVLs of adults from three Oklahoma populations of 80.6 mm (range 67–89 mm), 81.8 mm (61–95 mm), and 92.3 mm (72–108 mm). Reported size maxima are 99 mm in Missouri (Powell et al., 1982); 104 mm for males and 108 mm for females in Indiana (Minton, 1972); and 110 mm in Kansas (Collins, 1993). The presence of small (61–71 mm) but sexually mature adults at breeding choruses has been noted (Smith et al., 1948; Bragg, 1953; Trauth et al., 1990; Redmer, 2000). No male < 77 mm SVL has been found in amplexus in a southern Illinois population (Redmer, 2000).
M. Longevity. Five years for both males and females (Redmer, 2000).
N. Feeding Behavior. Larvae forage nocturnally in benthic regions of shallow water when young, in deeper water when older (Bragg, 1953). Adults feed from the platforms of their burrows at dawn and dusk (Thompson, 1915). Stomach contents of adults include ants, beetles (Carabidae, Scarabidae), centipedes, crayfish, crickets, millipedes, and spiders (Thompson, 1915; Goin and Netting, 1940; Smith et al., 1948). Captive adults accept crickets, earthworms, small crayfish, and small mice (M.R., unpublished data).
O. Predators. Natural predators are unknown. Other vertebrates may be important predators on adults (e.g., snakes, birds, raccoons). Larval experiments identified backswimmers (Notonecta sp.) and dragonfly naiads (Anax sp.) as effective predators (Travis et al., 1984; Cronin and Travis, 1986). Adults frequently are killed by automobiles during breeding migrations (M.R., unpublished data).
P. Anti-Predator Mechanisms. Larvae are nocturnally active and swim away from any disturbance (Bragg, 1953). Adults are extremely wary. Breeding activity may cease following slight disturbances (Bragg, 1953; Busby and Brecheisen, 1997; M.R., unpublished data). When alarmed, adults quickly retreat to their burrows and remain there for long periods of time (Thompson, 1915; Busby and Brecheisen, 1997). Juveniles and adults may deter predators with defensive postures and by occasionally snapping their jaws when cornered (Thompson, 1915; Altig, 1974; Marchisin and Anderson, 1978). Adults may produce a foul-smelling skin secretion (Dundee and Rossman, 1989).
Q. Diseases. Unknown.
R. Parasites. Trematodes, nematodes, and mites (Kuntz, 1941; Walton, 1949).
4. Conservation. Crawfish frogs are of considerable conservation concern and are listed as Endangered or In Decline in several states including Iowa, Indiana, and Kansas (Levell, 1997). Crawfish frogs may be susceptible to regional extinction because they are often associated with tallgrass prairies, outlier prairies, or other native grasslands—habitats that increasingly are being fragmented or converted to cropland. Crawfish frogs may be strongly influenced by larval interactions with other ranid species, potentially leading to reduced recruitment or competitive exclusion in sympatric areas. Furthermore, because of their fossorial nature, accurate accounts of population viability and recruitment are difficult to develop.
1Matthew J. Parris
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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