Abstract
Abstract: Global biodiversity loss and disease emergence are interrelated and have become a challenging environmental issue. Infection by the digenetic trematode, Riberioa ondatrae induces malformations in amphibians and is considered an emerging infection. The effect of infection on amphibians is not only parasite and host species specific, but also depends on the timing of infection. Recent evidence suggests that infection by cercariae of a monostome trematode species induces severe malformations in the common hourglass tree frog, Polypedates cruciger Blyth (1852) when exposed at the limb-bud stage of development. The aim of this study was to examine whether infection by this treamtode species at the pre-limb-bud stage also induces malformations in P. cruciger . Infection at the pre-limb-bud stage resulted in malformations (64.5%) and significantly reduced survival (77.5%). It also affected the growth and lengthened the larval period. Infections acquired at the pre-limb-bud stage caused a higher mortality and induced fewer malformations than infections at the limb-bud stage, as reported in a previous study. Hence, the effect of infection of monostome cercariae seems to depend on the developmental stage at which the tadpoles are exposed. Understanding the stage specific dynamics of malformations and associated mortality might be important to amphibian conservation. Keywords : Amphibians, Polypedates cruciger , frog malformations, trematode infection. Doi: 10.4038/jnsfsr.v38i4.2651 J.Natn.Sci.Foundation Sri Lanka 2010 38 (4):241-248
Highlights
During the past decade, reports on malformed frogs in the wild have increased worldwide1,3
The results show that exposure of pre-limb-bud stage tadpoles (Gosner stages 25 and 26) of P. cruciger to monostome cercariae significantly affected its survival and induced malformations
A previous study has shown that tadpoles of the same frog species exposed to the same type of cercariae at limb-bud stage (Gosner stages 27 and 28) produce a much higher percentage of malformations (92%) but do not cause a significant reduction in survival[8]. This shows that the infection by the same monostome cercariae may have two distinct detrimental effects on P. cruciger when exposed at different stages of its development
Summary
Reports on malformed frogs in the wild have increased worldwide1,,3. Both laboratory and field experiments have confirmed that infection by the digenetic trematode, Riberioa ondatrae, induces malformations in amphibians that are consistent with malformations observed in wild amphibian populations[4,5,6,7]. Infection by R. ondatrae is considered an emerging disease of amphibians and is closely associated with anthropogenic alterations of the ecological and evolutionary relationships between hosts and pathogens[8,9,10,11]. A previous study[20] showed that amphibian responses to trematode infections depended on host stage. Infections acquired at the paddle stage had no effect on limb development or tadpole survival[20]
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