Lithobates catesbeianus (=Rana catesbeiana)
(American Bullfrog) Impacts Information
Contents
1.0 Introduction
2.0 Disease Transmission……………………………………………………......... Page 1
3.0 Reduction in Native Biodiversity…………………………………………….. Page 2
4.0 Threat to Endangered Species……………………………………………….. Page 3
5.0 Ecosystem Change……………………………………………………………. Page 4
6.0 Predation……………………………………………………………………… Page 5
7.0 Competition…………………………………………………………………… Page 5
8.0 Human Health………………………………………………………………… Page 6
9.0 Interaction With Other Invasive Species……………………………………. Page 6
10.0 References………………………………………………………………..... Page 6
Amphibian communities are very susceptible to negative impacts from introduced
species. The North American bullfrog (Lithobates catesbeianus = Rana catesbeiana) has
been introduced in amphibian declines (Kats & Ferrer 2003, Daszak et al. 2004, in
Garner et al. 2006) through generalist predation and interspecific larval competition
(Kats & Ferrer 2003, in Garner et al. 2006). However, bullfrogs coexist with many
species of amphibian while preying on or competing with them (McAlpine & Dilworth
1989, Hirai 2004, Laufer 2004, in Garner et al. 20). This suggests that predation and
competition may not be the only explanations for declines associated with bullfrog
introductions and indicates disease transmission may play an important role (Garner et al.
2006).
2.0 Disease Transmission
Chytridiomycosis, caused by the non-hyphal zoosporic fungus Batrachochytrium
dendrobatidis, is an emerging disease of amphibians first reported with population
declines of amphibians in Central America and Australia (Berger et al. 1998, Daszak et
al. 2004; Hanselmann et al. 2004). This trend has shortly after seen in amphibian
populations in North America (Muths et al. 2003. in Daszak et al. 2004), Europe (Bosch
Martinez-Solano & Garcia-Paris 2001, Daszak et al. 2004), and New Zealand (Waldman
et al. 2001, in Casper & Hendricks 2005). Experimental and field data indicate that a
range of frogs, toads and salamanders are susceptible to chytridiomycosis (Berger et al.
1998, Speare et al. 2001, in Daszak et al. 2004).
One hypothesis for the recent emergence of chytridomycosis is the human-driven global
trade in amphibians. Both the African clawed frog (Xenopus laevis) and the American
bullfrog (Lithobates catesbeianus = Rana catesbeiana) are vectors of the fungus to native
frogs. Introduced populations of Lithobates catesbeianus can habour reservoirs of the
fungal agent without showing significant clinical disease symptoms (Daszak et al. 2004;
Hanselmann et al. 2004). Consistent with this hypothesis is the fact that B. dendrobatidis
has been reported from bullfrogs that are part of an increasingly centralised and
expanding trade in live food within South America and between South and North
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America (Mazzoni et al. 2003, in Daszak et al. 2004). Also supporting the hypothesis is
the fact that the first documented occurrence of Batrachochytrium in Great Britain is at a
site having the only breeding population of L. catesbeianus in the country, as well as a
feral population of X. laevis (Cunningham et al. 2005, Fisher & Garner 2007, in Kraus
2009). Experimental evidence that bullfrogs can be infected by B. dendrobatidis, but are
relatively resistant to the disease chytridomycosis and show no pathological signs of the
disease, which is lethal to many other amphibian species, is provided by Daszak and
colleagues (2004). In addition, Garner and colleagues found the molecular signal of
chytrid infection from introduced bullfrogs collected on three separate continents (T.W.J.
Gamer <i>et al</i>. Unpub. Data, in Garner <i>et al</i>. 2005).
Symptoms of the chytridiomycosis include (1) the presence of a substantial area of
hyperplasia and hyperkeratosis (between five and 10 cell layers thick) of the ventral skin
containing substantial numbers of the fungus; (2) clinical signs such as lack of appetite,
loss of righting reflex, and increased epidermal sloughing; and (3) rapid progression to
death (Daszak et al. 2007). For more information on chytridiomycosis and its control in
amphibian populations please visit the Amphibian Diseases Homepage. For an insight
into the life history of Batrachochytrium dendrobatidis please refer to Garner and
colleagues (2006)
Please note that a variety of other factors, including habitat modification, presence of
alien fish, commercial exploitation, disturbance regimes, diseases and toxicants may also
be involved in declines of native herpetofauna or interact synergistically to exacerbate
bullfrog effects (Kraus 2009). Negative effects of bullfrogs may be increased by habitat
modifications (Kiesecker et al. 2001, Rosen & Schwalbe 2002, in Cook & Jennings
2007).
Although infection by Mycobacterium marinum, found in the bullfrog, is not frequently
described, aquatic vertebrates such as frogs, snakes and turtles have been considered as a
source of infection for fish (Decostere et al., 2004, in Ferreira et al. 2004; also see
Human Health). A pathogens belonging to the Iridoviridae family, Ranavirus, was
suspected to be causing mortality in Uruguayan and Brazilian bullfrog farms (Galli et al.
2006). Adult and larval Falcaustra catesbeianae nematodes were collected from the
bullfrog in Japan (Hasegawa 2006).
Bullfrogs also host many parasites including helminths, platyhelminths such as
trematodes and nematodes, protozoans and mesozoans and leeches (Modzelewski &
Culley 1974, Kennedy 1980, Barta & Desser 1984, Bury & Whelan 1984, Desser et al.
1986 1990, Desser 1987, Shields 1987, Chen & Desser 1989, Siddall & Desser 1992,
Desser et al. 1995, Smith et al. 1996 2000, Crawshaw 1997, Bursey & DeWolf 1998,
McAlpine & Burt 1998, in Casper & Hendricks 2005).
3.0 Reduction in Native biodiversity
Beginning in the early 1970s, evidence began to accumulate indicating that bullfrogs are
at least partly responsible for the decline of a diversity of native herpetofauna (reptiles
and amphibians) across the western USA. Early surveys by Moyle (1973, in Doubledee
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Muller and Nisbet 2003) found an abundance of bullfrogs in habitat formerly occupied by
native frogs in California's southern central valley and suggested a causal relationship
between bullfrog presence and the absence of native anurans. Other evidence includes
anecdotal (Lardie 1963, Dumas 1966, Hammerson 1982, in Kraus 2009), statistical
(Schwalbe & Rosen 1988, Fisher & Shaffer 1996, Kupferberg 1997a, Rosen & Schwalbe
2002, in Kraus 2009) and experimental (Kieseker & Blaustein 1997 1998, Kupferberg
1997a, Lawler et al. 1999, Adams 2000, Pearl et al. 2004, Maret et al. 2006, in Kraus
2009). Because of their restricted habitat requirements, pond-breeding amphibians are
particularly affected by exotic species and habitat modifications (Cook & Jennings 2007).
It should be noted that habitat destruction and predation pressure from other introduced
predators, such as fish, red-swamp crayfish (Procambarus clarkii), and signal crayfish
(Pacifasticus leniusculus) have hampered the ability of scientists to directly assess the
threat of introduced bullfrogs on native amphibians (US Fish and Wildlife Service 2002,
in Doubledee Muller & Nisbet 2003). The impacts of these other predators are a large
decrease in survivorship of eggs and larvae, and possibly a decrease in juvenile and adult
survivorship of native frogs (Kiesecker and Blaustein 1998, Lawler et al. 1999, in
Doubledee Muller & Nisbet 2003). Hayes and Jennings (1986, in Casper & Hendricks
2005) argued that while bullfrogs are often invoked as being responsible for declines in
native ranid frogs, existing data cannot distinguish adequately among three major causal
hypotheses for this decline: bullfrogs, habitat alteration, and introduced predatory fish.
They believed that fish predation was the most compelling hypothesis in relation to the
USA (Casper & Hendricks 2005)
In the USA the bullfrog has been implicated in the decline of (Casper & Hendricks 2005;
Kraus 2009):
 the entire suite of central Californian amphibians (Fisher and Shaffer 1996, in
Kraus 2009); and
 native amphibians in Iowa (Lannoo et al. 1994, in Casper & Hendricks 2005).
 the Pacific chorus frog (Pseudacris regilla); (Jameson, 1956, in Kraus 2009);
 the plains leopard frog (Lithobates blairi); (Colorado; Hammerson 1982a 1982b,
in Casper & Hendricks 2005);
 the northern leopard frog (Lithobates pipiens); (Hammerson 1982, in Kraus
2009);
o Hecnar & M’Closkey (1996, in Hirai 2004) observed the increase of
the northern leopard frog and green frogs (Rana clamitans) after the
extinction of the introduced bullfrog in Canada.
 the lowland leopard frog (Lithobates yavapaiensis); (Schwalbe & Rosen 1988,
Rosen & Schwalbe 1995 2002, in Kraus 2009); and
 Blanchard's cricket frog (Acris crepitans); (Ontario, Oldham 1992; in Casper &
Hendricks 2005),
 the Pacific treefrog (Pseudacris regilla); (Oregon; Jameson 1956b, in Casper &
Hendricks 2005; California; Kupferberg 1997, in Casper & Hendricks 2005);
o Kupferberg (1997) also found a 16% reduction in the size of newly
metamorphosed Pacific treefrogs (Hyla regilla</i>), but no significant
effect on survivorship;
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the northern red-legged frog (Rana aurora); (Oregon; Kiesecker & Blaustein
1997, Kiesecker et al. 2001, in Cook and Jennings 2007);
o Large overwintering bullfrog tadpoles had significant competitive
impacts on young R. aurora tadpoles. They decreased survival and
delayed time to metamorphosis of R. aurora, presumably by reducing
food resources (Lawler et al. 1999, in Boone 2004);
o However, in aquatic habitats which dry up seasonally and where
overwintering of bullfrog tadpoles is prevented, competitive effects
may not be significant.
In addition to amphibians, the bullfrog may also threaten the Mexican garter snake
(Thamnophis eques). Schwalbe and Rosen (1988 1999, in Casper & Hendricks 2005)
found evidence that bullfrogs are responsible for declines in Mexican garter snakes from
the San Bernardino National Wildlife Refuge (Arizona, USA).
Similar declines in native species concurrent with the introduction of bullfrogs have been
noted in Europe, in Germany (C.R. Boettger 1941, Thiesmeier et al. 1994, in Kraus
2009), Florence (Italy) (native Rana</i>; Touratier 1992b, in Kraus 2009) and in the
Aquitaine of southwestern France (native fish; Touratier 1992a, in Kraus 2009). Concern
has been expressed about their potential effects elsewhere in Europe (Albertini & Lanza
1987, Stumpel 1992, in Kraus 2009).
In Japan Hirai (2006b) identified, via stomach analysis, the following prey items taken by
bullfrogs:
 the long-jawed water spider (Tetragnatha maxillosa);
 the paddy field grasshopper (Oxya velox);
 the giant water bug (Appasus japonicus); and
 the Japanese Fire-bellied Newt (Cynops pyrrhogaster)
o It is said that in the skin of Cynops pyrrhogaster there is a
tetrodotoxin which the bullfrog may be immune to.
4.0 Threat to Endangered Species
Introduced exotic predators, including the bullfrog, threaten the following amphibian
species:
 the possibly Extinct (according to the IUCN Red List) Vegas Valley leopard frog
(Lithobates fisheri); (Nevada; Moyle 1973, Cohen 1975, in Casper & Hendricks
2005);
 the Federally Endangered Sonoran tiger salamander Ambystoma tigrinum
stebbinsi (subspecies of the tiger salamander (Ambystoma tigrinum)); (Maret et al.
2006, in Kraus 2009);
o This genetically distinct race is restricted to about 30 small ponds in
the San Rafael Valley 111 southern Arizona, USA;
 the IUCN Red List Endangered Amargosa Toad (Anaxyrus nelsoni); (Nevada;
Jones et al. 2003, in Kraus 2009); (restricted range)
 the Federally Endangered and IUCN Vulnerable California tiger salamander
(Ambystoma californiense); (California; Balfour and Stitt 2003, in Kraus 2009);
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the IUCN Vulnerable Chiricahua leopard frog (Lithobates chiricahuensis);
(Arizona Schwalbe & Rosen 1988, in Casper & Hendricks 2005);
the Federally Threatened and IUCN Vulnerable California red-legged frog (Rana
draytonii); (Miller et al. 1996, in Cook & Jennings 2007);
o An approximately 70% decline in the range of this frog, primarily due
to habitat loss and the introduction of exotic species, including the
bullfrog has resulted in the listing of this species as threatened under
the federal Endangered Species Act;
the IUCN Vulnerable Oregon spotted frog (Rana pretiosa); (Montana; Dumas
1966, Black 1969a, in Cook & Jennings 2007);
the IUCN Near Threatened boreal toad (Anaxyrus boreas); and
the IUCN Near Threatened foothill yellow-legged frog (Rana boylii); (California.
Kupferberg 1997, in Casper & Hendricks 2005);
o Presence of bullfrogs was correlated with decreased growth rates and
survival of tadpoles of the foothill yellow-legged frog (Rana boylii),
probably due to bullfrogs being better adapted at exploiting algal
resources (Laufer & Sandte 2004, Kupferberg 1997a, in Kraus 2009);
o The presence of bullfrog tadpoles resulted in a 48% reduction of
survivorship of foothill yellow-legged frog (Rana boylii</i>) tadpoles,
and a 24% decline in mass at metamorphosis (Kupferberg 1997).
In addition to amphibians in the USA the bullfrog may also threaten these native fauna:
 the endangered Gallinula chloropus sandvicensis in Hawaii, subspecies of the
common moorhen (Gallinula chloropus); (Viernes 1995, in Kraus 2009).
 the endangered Poeciliopsis occidentalis sonoriensis, subspecies of the charalito
(fish) (Poeciliopsis occidentalis) (Schwalbe & Rosen 1988);
 the endangered yaqui chub (fish) (Gila purpurea) (Schwalbe & Rosen 1988, in
Kraus 2009);
 the IUCN Red List Vulnerable Pacific pond turtle (Actinemys marmorata); Hays
et al. 1999, in Kraus 2009);
 the IUCN Red List Endangered Razorback Sucker (Xyrauchen texanus);
o Tadpoles of L. catesbeianus prey on the eggs and larvae of the
razorback sucker in laboratory conditions and their densities in
artificial habitats can decrease fish larvae recruitment (Mueller et al.
2006, in Kraus 2009);
 the IUCN Vulnerable giant garter snake (Thamnophis gigas) in California (Wylie
et al., 2003, in Kraus 2009); and
 the regionally rare white-cheeked pintail (Anas bahamensis) in Puerto Rico
(López-Flores et al. 2003, in Kraus 2009).
In Japan the bullfrog also preys upon:
 the IUCN Near Threatened black-spotted pond frog (Pelophylax
nigromaculatus); and
 an endangered (according to Ota et al. 2004a, in Kraus 2009) freshwater crab
(Candidiopotamon kumejimense) on Kumejima Island.
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5.0 Ecosystem change
Several field studies portray tadpoles as ‘‘ecosystem engineers’’ that alter the biomass,
structure and composition of algal communities (Dickman 1968, Seale 1980, Osborne &
McLachlan 1985, Kupferberg 1997a, Flecker et al. 1999, Peterson & Boulton 1999, in
Pryor 2003). Tadpoles play an influential role in transferring nutrients between
ecosystems (Pryor 2003). Upon metamorphosis, anuran larvae transfer nutrients from
aquatic to terrestrial ecosystems. High food intake (Wassersug 1984, in Pryor 2003) and
high population densities (up to thousands of individuals per m²; Alford, 1986, in Pryor
2003) suggest that tadpoles have considerable impact on nutrient cycling and primary
production in freshwater ecosystems.
6.0 Predation
American bullfrogs are voracious predators and are considered detrimental to native
amphibians and other fauna (Moyle 1973, Bury & Luckenbach 1976, Rosen & Schwalbe
1995, in Adams Pearl & Bury 2003). Experiments have confirmed bullfrogs mediate their
negative effects in part via direct predation (Kiesecker & Blaustein 1997; also see
relevant information provided in Reduction in Native Species and Threat to Endangered
Species). As the bullfrog is known to feed frequently on aquatic prey such as crayfish,
dragonfly nymphs, aquatic hemipterans and water beetles (Tyler & Hoestenbach 1979,
Werner et al. 1995, in Hirai 2004), and therefore benthos and aquatic insect communities
can receive a certain impact from the bullfrog’s predation.
7.0 Competition
Bullfrogs compete with native species (Kupferberg 1997, Kiesecker & Blaustein 1997, in
Hanselmann et al. 2004) and unlike many other frogs can coexist with predatory fish
(Hecnar 1997, in Casper & Hendricks 2005). Overwintered bullfrog tadpoles can affect
development and survival of other anuran species (e.g., Kupferberg 1997, Lawler et al.
1999, Kiesecker et al. 2001, in Boone 2004) and can be competitively superior to anurans
with larval periods of less than one year (Werner & Anholt 1996, in Boone 2004).
The presence of overwintered bullfrog tadpoles reduced the mass at metamorphosis of the
southern leopard frog (Rana sphenocephala) and shortened the larval period and reduced
mass at metamorphosis for the spotted salamander (Ambystoma maculatum) (Boone
2004). In experimental environments, Werner and Anholt (1996, in Cook & Jennings
2007) and Kiesecker and colleagues (2001, in Cook & Jennings 2007) demonstrated
competition between bullfrog tadpoles and green frog (Rana clamatans) tadpoles at
densities of 22 tadpoles/m² and between bullfrog tadpoles and red-legged frogs at 9
tadpoles/m², respectively. However competitive densities as obtained in experimental
studies above may not occur at field sites (Cook & Jennings 2007).
For amphibian species that have evolved with bullfrogs, the presence of bullfrogs may be
less serious. The effects of overwintered bullfrog tadpoles in the study by Boone (2004)
were neutral or negative, affecting time to metamorphosis and/or weight at
metamorphosis. Studies with bullfrogs outside their range have shown similar results and
additionally found that bullfrog tadpoles have negative effects on survival. Kiesecker and
Blaustein (1997, in Boone 2004) found tadpoles of red-legged frogs (Rana aurora)
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syntopic with Bullfrogs increased their survival by altering their behavior in the presence
of bullfrogs. Populations of red-legged frogs allopatric (ie. evolutionarily naive) to
bullfrogs, however, suffered increased mortality because tadpoles did not alter their
behavior in the presence of bullfrogs.
8.0 Human Health
The occurrence of mycobacteriosis caused by Mycobacterium marinum in a commercial
breeding farm of bullfrogs (Lithobates catesbeianus ) in Rio de Janeiro, Brazil is
described by Ferreira and colleagues 2004. Human cases of M. marinum infection have
been reported from different parts of the world (Ghittino & Bozzetta 1994, Lewis et al.
2003, in Ferreira et al. 2004). It is characterised by skin lesions commonly called
‘‘swimming pool granuloma ’’ or ‘‘fish tank granuloma’’ (Ferreira et al. 2004).
9.0 Interaction With Other Invasive Species
Positive interactions among non-native species could greatly exacerbate the problem of
invasions (Adams Pearl & Bury 2003). Bullfrog invasion in Oregon, USA, is facilitated
by the presence of non-native fish, which increase tadpole survival by reducing predatory
macroinvertebrate densities. Native dragonfly nymphs in caused no survival of bullfrog
tadpoles in a field experiment unless a non-native sunfish was present to reduce
dragonfly density. This evidence supports the “invasional meltdown” hypothesis (see
Simberloff & Von Holle 1999) (Adams Pearl & Bury 2003).
10.0 References
For references please see the GISD Species Profile for Lithobates catesbeianus
(References Section).
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