Comparative Parasitology 67(1) 2000 - Peru State College

COMPARATIVE PARASITOLOGY, 67(1), JANUARY 2000
(Leon-Regagnon et al., 1999). Species of Haematoloechus
apparently have experienced a diversification
in frogs and salamanders in central
Mexico, representing the group with the highest
species richness (6) in our samples. Glypthelmins,
parasitic mainly in frogs of the new world,
also shows high species richness. However, the
presence at least of 4 species is mainly the result
of independent host capture events, either from
the neotropical or nearctic zones.
The distribution of the nonendemic frogs from
the lowlands ranges from Ecuador and Colombia
to Veracruz, Mexico (R. vaillanti), to Sonora,
northwestern Mexico (L. melanonotus), and Texas
(S. baudinii). Their digenean fauna in Veracruz
is composed of a combination of neotropical
and nearctic species. Only 2 digenean species,
Glypthelmins sp. and M. monas, were recovered
from L. melanonotus and S. baudinii,
respectively. The former probably represents an
undescribed species, and M. monas has been reported
in numerous host genera in South America
and Africa (Prudhoe and Bray, 1982). Seven
digenean species were collected from R. vaillanti,
and 3 of them show a neotropical distribution:
C. rodriguezi in Panama (Caballero, 1955) and
G. parva in Brazil (Prudhoe and Bray, 1982),
both described from Leptodactylus ocellatus,
and G. facioi in Costa Rica (Brenes et al., 1959)
and Veracruz, Mexico (Razo-Mendivil et al.,
1999), from Rana palmipes Spix, 1824, and R.
vaillanti, respectively. The presence of these
neotropical digeneans in Los Tuxtlas reflects the
geographic distribution of the host genus Leptodactylus
and the "Rana palmipes complex"
(Frost, 1985; Hillis and De Sa, 1988). One species
is endemic, L. (L.) macrocirra, and the 3
remaining species parasitizing R. vaillanti have
a nearctic distribution; 2 of these species (G. attenuata
and C. americanus) are also present in
the endemic frogs of the Transverse Volcanic
Axis, and the third species (H. medioplexus) has
been recorded in several species of frogs from
the United States and Canada, most commonly
in members of the "Rana pipiens complex."
The 3 species have a low host specificity and
have been able to colonize several host groups,
thus expanding their distribution range.
Apparently, a mixture of neotropical and
nearctic species of parasites is taking effect in
the lowlands of the Gulf of Mexico, with a series
of very interesting phenomena of colonization of
new hosts and habitats. Little is known about the
amphibian parasite fauna of the tropical lowlands
of the Pacific slope of Mexico or the
southeastern part of the country. Those areas
will undoubtedly be a source of extensive phylogenetic
and biogeographic information on parasites
and hosts in the future.
Contemporary ecological conditions are also
important determinants of the parasitic fauna of
a host species. Several authors have demonstrated
a marked correlation between the relative
amount of time spent in association with aquatic
habitats and the number of species of platyhelminths
hosted by frogs (Brandt, 1936; Prokopic
and Krivanec, 1975; Brooks, 1976, 1984; Guillen,
1992). Our data clearly demonstrate that
frogs and salamanders harbor the richer digenean
fauna compared with the less water-dependent
hylids or toads, where digeneans were almost
or absolutely absent (the small sample size
in leptodactylids precludes any discussion about
their helminth fauna). Within frogs and salamanders,
diet is the factor that most determines the
richness of the digenean communities. Frogs become
infected when they prey upon insects or
copepods (which is the case in species of Haematoloechus
and Halipegus, respectively), when
they swallow their own skin bearing encysted
metacercariae during ecdysis, or when they feed
upon infected tadpoles (species of Catadiscus,
Cephalogonimus, Glypthelmins, Gorgoderina,
and Megalodiscus) (Yamaguti, 1975; Prudhoe
and Bray, 1982). Salamanders of the genus Ambystoma
Tschudi, 1838, hosted fewer digenean
species than frogs. Garcia-Altamirano et al.
(1993) reported that A. dumerilii in Lake Patzcuaro
feeds mainly on crayfish and fish. As evidenced
by the presence of C. americanus, G.
attenuata, and Haematoloechus spp. in salamanders
of our samples, it is possible that they oc-
Figures 16-20. Ventral views. 16. Loxogenes (I^angeronia) macrocirra (Caballero y Bravo, 1949) Yamaguti,
1971. 17. Mesocoelium monas (Rudolphi, 1819) Teixeira de Freitas, 1958. 18. Halipegus occidualis
Stafford, 1905. 19. Fibricola sp. (inetacercaria). 20. Ochetosoma sp. (metacercaria). Scales in millimeters.
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