Sublethal predators and their injured prey: linking aquatic predators and severe limb abnormalities in amphibians.
ABSTRACT While many predators completely consume their prey, others feed only on blood or tissue without killing the prey, sometimes causing ecologically significant levels of injury. We investigated the importance of sublethal predator attacks in driving an emerging issue of conservation importance: missing-limb deformities in amphibians. We combined long-term field data and manipulative experiments to evaluate the role of sublethal predation in causing abnormalities in two regions of central Oregon, U.S.A. Since 1988, western toads (Bufo boreas) in Lake Aspen have exhibited abnormalities dominated by partially missing limbs and digits at annual frequencies from <1% to 35%. On Broken Top volcano, we found comparable types and frequencies of abnormalities in Cascades frogs (Rana cascadae). Field sampling and observational data implicated two aquatic predators in these abnormality phenomena: introduced sticklebacks (Gasterosteus aculeatus) at Lake Aspen and corduliid dragonfly larvae (Somatochlora albicincta) at Broken Top. In experiments, these predators produced limb abnormalities identical to those observed in the respective regions. At Lake Aspen, in situ predator exclosures effectively eliminated abnormalities in toads, while comparisons among years with low and high stickleback abundance and between wetlands with and without sticklebacks reinforced the link between fish and amphibian abnormalities. Neither trematode parasite infection nor pesticide contamination could explain observed abnormalities. Our results suggest that predators are an important explanation for missing-limb abnormalities and highlight the ecological significance of sublethal predation in nature.
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ABSTRACT: Rhinella jimi (Anura, Bufonidae) is an introduced species in the archipelago of Fernando de Noronha, north-eastern Brazil. It is known as one of the greatest amphibian anomaly hotspots in the world, with almost half of the adult individuals in the population having external anomalies, but tadpoles from this population have not previously been examined. Therefore, we evaluated the presence of anomalies in tadpoles of this population, described their types and identified possible handicaps of anomalous tadpoles in foraging behaviour and food intake. We found anomalies in 52.5% of all tadpoles inspected, mostly involving labial teeth. Anomalous tadpoles, when compared to normal individuals, spend less time foraging and have a lower foraging efficiency. We also observed that anomalous toadlets originate both from normal and anomalous tadpoles. We suggest that the reduced feeding fitness may result in a reduced growing rate, longer time spent until metamorphosis, higher predation risk, different body mass, size and morphology in metamorphs and adults. However, this apparent handicap may not affect the post-metamorphic population, as anomalous adults may rise from normal tadpoles.Herpetological Journal 10/2014; 24(4). · 1.34 Impact Factor
Herpetozoa 01/2015; 27(3/4):115-121. · 0.54 Impact Factor
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ABSTRACT: Multiple factors are thought to cause limb abnormalities in amphibian populations by altering processes of limb development and regeneration. We examined adult and juvenile axolotls (Ambystoma mexicanum) in the Ambystoma Genetic Stock Center (AGSC) for limb and digit abnormalities to investigate the probability of normal regeneration after bite injury. We observed that 80% of larval salamanders show evidence of bite injury at the time of transition from group housing to solitary housing. Among 717 adult axolotls that were surveyed, which included solitary-housed males and group-housed females, approximately half presented abnormalities, including examples of extra or missing digits and limbs, fused digits, and digits growing from atypical anatomical positions. Bite injury likely explains these limb defects, and not abnormal development, because limbs with normal anatomy regenerated after performing rostral amputations. We infer that only 43% of AGSC larvae will present four anatomically normal looking adult limbs after incurring a bite injury. Our results show regeneration of normal limb anatomy to be less than perfect after bite injury.This article is protected by copyright. All rights reserved.06/2014; 1(3). DOI:10.1002/reg2.17