The following account is modified from Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo (©2005 by the Regents of the University of California), used with permission of University of California Press. The book is available from UC Press.

Rana rugosa Temminck and Schlegel, 1838
Wrinkled Frog

Fred Kraus¹

1. Historical versus Current Distribution. Wrinkled frogs (Rana rugosa) were probably introduced to Hawaii from Japan in 1895 or 1896 by Albert Koebele to assist in controlling introduced insects (Bryan, 1932; Oliver and Shaw, 1953). In their native range, wrinkled frogs are widely distributed in Japan, Korea, northeastern China, and parts of the Russian Far East (Maeda and Matsui, 1989; Zhao and Adler, 1993; Hasegawa et al., 1999), although the taxonomic status of populations on the mainland may need further assessment (Zhao and Adler, 1993). In Hawaii, they are presently found on Kauai, Oahu, Maui, and Hawaii Island (Cochran and Goin, 1970; McKeown, 1996), although vouchers are apparently absent from Hawaii Island. It is unclear whether wrinkled frogs are still expanding their range in Hawaii, although introduction to additional islands would provide them this opportunity. The species was apparently first released on Oahu (Oliver and Shaw, 1953), was reported from Maui by 1936 (Svihla, 1936; Fisher, 1948), and from Kauai and Hawaii Island by 1953 (Oliver and Shaw, 1953). Wrinkled frogs currently range from near sea level to at least 1,100 m elevation in Hawaii.

2. Historical versus Current Abundance. In Hawaii, abundant populations have been established for decades (Svihla, 1936; Hunsaker and Breese, 1967), and wrinkled frogs remain common (McKeown, 1996; personal observations); they also are common in their native range (Shannon, 1959).

3. Life History Features.

A. Breeding. Reproduction is aquatic.

i. Breeding migrations. In Hawaii, wrinkled frogs breed from February–August (Tinker, 1938; Oliver and Shaw, 1953), whereas in their native range, breeding is from mid May to l September (Okada, 1938, 1966; Maeda and Matsui, 1989; Hirai and Matsui, 2001). Breeding occurs only after daily average water temperatures > 18 ˚C (Chang, 1994). Females may produce multiple clutches per year (Maeda and Matsui, 1989; Chang, 1994).

ii. Breeding habitat. In Hawaii, adults breed in the pools and slow-moving waters of mountain streams and in lowland ponds (Tinker, 1938; McKeown, 1996). In their native range, wrinkled frogs breed in rice paddy fields, ponds, ditches, or pools in dry riverbeds (Okada, 1966; Maeda and Matsui, 1989) and presumably in pools of mountain streams as well. Most breeding activity occurs at night (Okada, 1938, 1966).

B. Eggs.

i. Egg deposition sites. Females deposit eggs in loose, unattached masses in pools, either among protruding sticks and vegetation or in bare areas (Svihla, 1936; Okada, 1966; McKeown, 1996). Eggs are laid in clusters of 10–200 (Okada, 1938; Chang, 1994).

ii. Clutch size. Females spawn from 400–1,350 eggs at a time, depending on their body size (Okada, 1938, 1966; Chang, 1994). Females can spawn up to three times per year (Chang, 1994).

C. Larvae/Metamorphosis.

i. Length of larval stage. Eggs hatch approximately 5 d after laying (Chang, 1994). Newly hatched tadpoles are approximately 8 mm TL (Oliver and Shaw, 1953) and grow to between 38–80 mm TL prior to metamorphosis (Okada, 1938; Gilbertson and Watermolen, 1998). Juveniles transform at lengths of 19.5–26.8 mm SVL in Hawaii (Oliver and Shaw, 1953). In their native range in Japan, tadpoles do not metamorphose in the same year they hatch, but from April–October of the following year (Okada, 1966; Maeda and Matsui, 1989; Hirai and Matsui, 2001). However, Khonsue et al. (2001) state that intra-populational variation occurs in larval overwintering, with some animals metamorphosing prior to their first winter. It seems possible that tadpoles may metamorphose in their first year in Hawaii, because Tinker (1938) notes that “frogs may be found in Hawaii in all stages of development from early spring until late in the fall.”

ii. Larval requirements.

a. Food. Tadpoles presumably feed on algae and microorganisms that use rocks and aquatic vegetation for a substrate, but to date this has not been investigated directly.

b. Cover. In Japan, tadpoles obligately overwinter in the mud of rice paddy fields or streams (Okada, 1938, 1966).

iii. Larval polymorphisms. Unknown and unlikely.

iv. Features of metamorphosis. Metamorphosis occurs during the spring and summer following hatching in their native range (Okada, 1938, 1966; Hahn, 1960), but apparently occurs during much of the year in Hawaii (Tinker, 1938).

v. Post-metamorphic migrations. Unknown and unlikely.

D. Juvenile Habitat. Probably similar to adult habitats, but not investigated.

E. Adult Habitat. In Hawaii adults occur in both lentic and lotic habitats, ranging from low elevation taro ponds to cool, clear, mid elevation streams (Bryan, 1932; Svihla, 1936; personal observations). In the smaller streams they typically inhabit pools; in larger streams with more current, they occur along the sides of quiet backwaters. Adults frequently bask in the sun in open grassy areas (personal observations) or on rocks protruding from streams (McKeown, 1996). In their native range, wrinkled frogs are widely distributed in plains and low mountain valleys, being found in rice paddies, ponds, ditches, and reservoirs, and along small, fast-flowing streams (Hallowell, 1860; Stejneger, 1907; Okada, 1938, 1966; Stewart, 1953; Shannon, 1959; Hahn, 1960; Webb et al., 1962; Maeda and Matsui, 1989). They frequently bask in tufts of grass or reeds along stream or pond margins (Hahn, 1960; Webb et al., 1962).

F. Home Range Size. Unknown.

G. Territories. Unknown.

H. Aestivation/Avoiding Dessication. Apparently absent inasmuch as frogs are active from March to early December and breed during the summer (Okada, 1938, 1966; Chang, 1994).

I. Seasonal Migrations. Although wrinkled frogs are typically found in or near water and hibernate under water, in wet forests in Hawaii, frogs can be found far from any permanent water body (personal observations).

J. Torpor (Hibernation). In their native range, adult wrinkled frogs will overwinter underwater (Maeda and Matsui, 1989), while tadpoles overwinter in the mud of paddy fields or streams (Okada, 1966). Hibernation season is variable and depends on latitude (Okada, 1938). In Japan and Korea, wrinkled frogs commence hibernation from late October to early December and emerge from hibernation beginning in mid March to late April (Okada, 1938; Shannon, 1959; Chang, 1994). Hibernation in Hawaii seems unlikely because of the mild climate, but this has not been investigated directly.

K. Interspecific Associations/Exclusions. Not reported.

L. Age/Size at Reproductive Maturity. Adult males range in size from 30–47 mm and females from 45–60 mm (Okada, 1938, 1966; Chang, 1994). As with most ranids, males have swollen nuptial pads during the breeding season (Okada, 1938, 1966). Age at attainment of sexual maturity is usually 1–2 yr post metamorphosis in males and 2–3 yr post metamorphosis in females, although a few females mature at 1 yr post metamorphosis (Khonsue et al., 2001).

M. Longevity. Males can live up to 4 yr post metamorphosis; females up to 5 yr (Khonsue et al., 2001).

N. Feeding Behavior. Wrinkled frogs eat primarily a variety of insects (in 98% of examined stomachs), but also are known to consume arachnids, crustaceans, chilopods, diplopods, mollusks, oligochaetes, and small frogs (Okada, 1938, 1966; Maeda and Matsui, 1989; Hirai and Matsui, 2000, 2001). They feed on ants to a larger extent than most other frogs (Hirai and Matsui, 2000), including syntopic congeners (Hirai and Matsui, 2001).

O. Predators. Chang (1994) reports goldfish (Carassius auratus) eating wrinkled frog eggs. McKeown (1996) implies American bullfrogs (Rana catesbeiana) are predators, but presents no evidence. Humans eat wrinkled frogs in Japan (Oliver and Shaw, 1953).

P. Anti-Predator Mechanisms. When alarmed, wrinkled frogs leap into the water and hide in leaf litter, bottom muck, or among rocks for ≤ 10 min before resurfacing (Shannon, 1959; Hahn, 1960; McKeown, 1996). According to Choi et al. (1999), wrinkled frogs combine a crypsis-escape predator avoidance mechanism with a crouching posture and noxious skin secretions to deter predators. These authors note that by simply crouching, wrinkled frogs increased their survival rate by 37% and delayed the time to predation by 23 min when compared to a congener that did not crouch.

Wrinkled frogs may be unpalatable to some snakes (Mori, 1989, in Chang, 1994). Nine small peptides, named gaegurins and rugosins, have been isolated from Rana rugosa skin. These compounds have antimicrobial properties against an array of bacteria, fungi, and protozoa (Park et al., 1994; Suzuki et al., 1995).

Q. Diseases. Unknown. Eggs can be infected by an unidentified fungus (Chang, 1994).

R. Parasites. The nematodes Angiostoma bufonis, Hedrurus ijimai, Oswaldocruzia insulae, Rhabdias nipponica, Spinitectus ranae, and Spiroxys japonica and the digenean helminth Opisthioglyphe japonicus have been reported from the digestive tracts or lungs of Japanese specimens (Morishita, 1926; Yamaguti, 1935; Hasegawa and Otsuru, 1977, 1978, 1979; Uchida et al., 1980). Over their native range, wrinkled frogs appear resistant to parasitism by the nematode Gnathostoma nipponicum (Kim, 1983; Oyamada et al., 1998) and by parasites in the genus Sparganum (Kim, 1983). An investigation of 39 animals from 1,100 m elevation on Kauai revealed no helminth parasites (S. Goldberg, personal communication).

4. Conservation. Wrinkled frogs have been introduced to Hawaii and have invaded native forest. They have no legal protection, and their demise in Hawaii would be a positive development.

¹Fred Kraus
Department of Natural Sciences
Bishop Museum
1525 Bernice Street
Honolulu, Hawaii 96813
fkraus@hawaii.edu

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 24 Apr 2024.

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