DIETARY ANALYSIS: AMPHIBIANS
FROGS AND TOADS
Solé M., Beckmann O., Pelz B., Kwet A., Engels W. (2005): Stomach-flushing for diet analysis in anurans: an improved protocol evaluated in a case study in Araucaria forests, southern Brazil. Studies on Neotropical Fauna and Environment 40: 23-28.
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Abstract
Stomach-flushing is a gentle treatment in analysing the diet of vertebrates. We applied this method in the study of seasonal nutrition of anurans of 15 species at an Araucaria forest habitat on the Serra Geral of Rio Grande do Sul, Brazil. Over 500 frogs and toads of different body size were handled in order to evaluate an improved protocol without narcosis using soft infusion tubes in order to avoid negative effects of the flushing procedure. The specimens were treated soon after capture and then returned to the sampling sites. Our results are discussed with reference to the few studies on stomach flushing in amphibians. The improved technique is recommended to avoid killing of numerous animals for nutritional studies, in particular because of the worldwide threatening of amphibian populations.
Mahan R. D., Johnson J. R. (2007): Diet of the gray treefrog (Hyla versicolor) in relation to foraging site location. Journal of Herpetology 41: 16-23.
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Despite growing concern over habitat destruction, little is known regarding the activities of pond-breeding amphibians in the terrestrial environment. Yet, because most pond-breeding amphibian species spend the majority of their time in terrestrial habitats, it is important to understand what role terrestrial habitat plays in their life history. We examined the stomach contents of the gray treefrog (Hyla versicolor) in central Missouri using a stomach-flushing technique. Treefrogs were stomach-flushed; stomach contents were dried and weighed; and prey items were counted and identified for frogs caught in both artificial arboreal refugia and at breeding ponds. The majority of prey consisted of ants (41.2%) and beetles (29.6%). Both males and females caught in artificial refugia contained greater stomach content mass than those caught at breeding ponds. There was a positive correlation between mass of stomach contents and distance from breeding ponds, with the average number of beetles per stomach increasing with distance from ponds. There was also greater stomach content mass in frogs found in artificial refugia on white oaks than red oaks or sugar maples, but there was no relationship between tree diameter and stomach content mass. These results demonstrate the importance of protecting terrestrial habitat to maintain foraging areas for treefrogs.
Pafilis P., Kapsalas G., Lymberakis P., Protopappas D., Sotiropoulos K. (2019): Diet composition of the Karpathos marsh frog (Pelophylax cerigensis): what does the most endangered frog in Europe eat?. Animal Biodiversity and Conservation 42: 1-8.
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The Karpathos marsh frog (Pelophylax cerigensis) is considered the most endangered frog in Europe. Here we assess its feeding ecology and examine 76 individuals from the two known populations using the stomach flushing method. We also measured body weight, snout–vent length, mouth width and prey width and length. Pelophylax cerigensis follows the feeding pattern of green frogs of the adjacent areas, with Coleoptera, Araneae, Isopoda and Hymenoptera being the main prey groups. The two populations differed in body size but had similar values of prey abundance and frequency. It seems that P. cerigensisfollows a strict feeding strategy. Further research on prey availability in its habitats will provide valuable insight.
Pereira A., Samlali M. A., S’Khifa A., Slimani T., Harris D. J. (2021): A pilot study on the use of DNA metabarcoding for diet analysis in a montane amphibian population from North Africa. African Journal of Herpetology 70: 68-74.
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Although dietary studies are essential to design effective conservation strategies for amphibians, non-invasive studies using microscopy assessment of faecal material are known to have limitations. We assessed the use of DNA metabarcoding to determine diet in the Moroccan painted frog Discoglossus scovazzi. Nineteen families of insects were identified, and resolution of prey taxonomy to the family level identified differences between adult males and females not seen at the order level. Several prey items could be identified to the species level, providing identifications that add towards the determination of the insect diversity of the habitat. However, the 16S primers used only amplified insect prey, so a notable part of the diet could not be surveyed. Multiple markers will be needed to obtain information across the whole prey spectrum of these generalist amphibians.
SALAMANDERS AND NEWTS
Crovetto F., Romano A., Salvidio S. (2012): Comparison of two non-lethal methods for dietary studies in terrestrial salamanders. Wildlife Research 39: 266-270.
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Concerns about conservation and ethics in amphibian research have been raised recently; therefore, non-lethal methods should always be preferred to investigate food habits in wild populations. However, there are no studies that compared the data obtained by different non-lethal dietary methods in amphibians. We compared the dietary habits obtained from stomach flushing, a method validated against stomach dissection, and faecal analysis on the same 31 individuals of the European plethodontid Speleomantes strinatii, a completely terrestrial salamander. After being stomach-flushed in the field, salamanders were kept in the laboratory at constant humidity and temperature to obtain faecal samples. Analyses comprised diversity and niche overlap indexes, as well as permutation, repeated-measures tests and graphical methods. Niche overlap between the two samples was low (Ojk = 0.58) and prey diversity was significantly (P = 0.001) higher in stomach contents. There were also differences in the abundance of fly larvae, springtails and ants and the interpretation of the population trophic strategy varied according to the sampling method used. Stomach flushing and faecal analysis gave different information, because, apparently, a differential prey degradation occurred. During the digestive process, ants became dominant, whereas springtails and fly larvae became under-represented in faecal samples. Therefore, on the basis of faecal analysis, diet diversity was underestimated and many individuals improperly appeared as ant-specialist feeders. In terrestrial salamanders, results from stomach flushing and faecal analysis should not be compared among studies, populations or species. Moreover, stomach flushing should always be preferred when assessing the trophic strategy and the role in food webs of salamanders.
Romano A., Salvidio S., Palozzi R., Sbordoni V. (2012): Diet of the newt, Triturus carnifex (Laurenti, 1768), in the flooded karst sinkhole Pozzo del Merro, central Italy. Journal of Cave and Karst Studies 74: 271-277.
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Karst habitats host a high number of specialized organisms that contribute to complex and peculiar food webs. In underground aquatic habitats, vertebrates are the top predators that strongly influence and regulate prey communities. In this study, the diet of the Italian crested newt, Triturus carnifex, in the world’s deepest karst phreatic sinkhole, the Pozzo del Merro in Latium, central Italy, was analyzed. We obtained both stomach and fecal contents from twenty adult newts (ten females and ten males) sampled in summer 2010. Availability of prey in the sinkhole also was determined. Prey items were identified and classified into ten ecological groups. At Pozzo del Merro, during the summer, the aquatic stage of T. carnifex was specialized on the pre-imaginal stages of the small China-mark, Cataclysta lemnata. The recently described endemic stygobitic crustacean Niphargus cornicolanus was not found in stomach contents. Finally, our results showed that analyses of stomach and fecal contents may provide different information on the diet of newts in their aquatic phase.
Roner L., Costa A., Pedrini P., Matteucci G., Leonardi S., Romano A. (2020): A midsummer night’s diet: snapshot on trophic strategy of the Alpine salamander, Salamandra atra. Diversity 12: 202.
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Information on the trophic ecology of the Alpine salamander, Salamandra atra, is scattered and anecdotal. We studied for the first time the trophic niche and prey availability of a population from an area located in Italian Dolomites during the first half of August. Considering that S. atra is a typical nocturnal species, we collected food availability separately for diurnal and nocturnal hours. Our aims were: (i) to obtain information on the realized trophic niche; (ii) to provide a direct comparison between trophic strategy considering only nocturnal preys or considering all preys; (iii) to study trophic strategy of this species at the individual level. In two samplings nights we obtained prey from 50 individuals using stomach flushing technique. Trophic strategy was determined using the graphical Costello method and selectivity using the relativized electivity index. During the short timeframe of our sample, this salamander showed a generalized trophic strategy. The total trophic availability differed significantly from nocturnal availability. Interindividual diet variation is discussed in the light of the optimal diet theory. Finally, we highlighted that considering or not the activity time of the studied taxon and its preys may lead to a conflicting interpretation of the trophic strategies.
Marques A. J., Mata V. A., Velo-Antón G. (2022): COI metabarcoding provides insights into the highly diverse diet of a generalist salamander, Salamandra salamandra (Caudata: Salamandridae). Diversity 14: 89.
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DNA metabarcoding has proven to be an accessible, cost-effective, and non-invasive tool for dietary analysis of predators in situ. Although DNA metabarcoding provides numerous benefits in characterizing diet—such as detecting prey animals that are difficult to visually identify—this method has seen limited application in amphibian species. Here, we used DNA metabarcoding to characterize the diet of fire salamanders (Salamandra salamandra) (Linnaeus, 1758) in three distinct regions across the northwestern Iberian Peninsula. To test the efficiency of COI-based metabarcoding in determining salamanders’ diet diversity, we compared our COI-based results with results from traditional diet studies from neighboring and distant populations, as well as with recent findings obtained in a DNA metabarcoding study using 18S. Two COI primers were used in combination to investigate the potential impact of primer bias in prey detection. Our COI metabarcoding approach increased taxonomic resolution and supported a generalist diet in S. salamandra. Between primers, there were no significant differences in the diversity and richness of prey detected. We observed differences in the prevalence of prey identified between sampling regions both in our study and in other studies of S. salamandra diet. This COI metabarcoding study provides recommendations and resources for subsequent research using DNA metabarcoding to study amphibian diets.