Diet composition of an invasive population of Lithobates catesbeianus (American Bullfrog) from Argentina

The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high andprobablyhasanimpactontheirprey.Freshwatercrabsarethemainitemsinthe diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region’s freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles.Fil: Quiroga, Lorena Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Moreno Avila, María Daniela. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Cataldo, Ariel Anibal. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Aragon y Traverso, Juan Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Pantano, María Victoria. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Olivares Toselli, Juan Pablo Segundo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Sanabria, Eduardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Filosofía, Humanidades y Artes. Instituto de Ciencias Básicas; Argentin

Temporal variation of thermal sensitivity to global warming: Acclimatization in the guitarist beetle, Megelenophorus americanus (Coleoptera: Tenebrionidae) from the Monte Desert

Global warming is a major threat to biodiversity, the increase in mean temperature plus the higher rate and intensity of heat waves can severely affect organisms by exposing them to temperatures beyond their tolerance limits. Desert ectotherms are particularly vulnerable due to their dependence on environmental temperatures in an extreme habitat. Thermal tolerance changes depending on environmental conditions, studying these fluctuations provides a better understanding of species susceptibility to global warming. Tenebrionids are successful desert-inhabiting ectotherm taxa because of a series of adaptations for heat tolerance and water loss. We studied the seasonal variation (acclimatization) of thermal tolerance in Megelenophorus americanus, a widely distributed species in the Monte Desert (Argentina). To do this, we measured environmental and operative temperatures: body temperature (Tb), soil temperature (Ts), air temperature (Ta), environmental temperature (Te) and maximum temperature (Tmax), and tolerance proxies volunteer thermal maximum (VTmax), Fluid release (FR) and critical thermal maximum (CTmax) in a population of M. americanus from San Juan province, Argentina from October to March (full activity season). We found that Ts and Ta are accurate predictors of Tb, suggesting thermoconformism. All tolerance proxies showed differences among months, suggesting a natural acclimatization process in situ. Insects were found operating beyond VTmax (thermal stress) but they were far from reaching CTmax under natural conditions. Organisms present different degrees of tolerance plasticity that should be considered when predicting potential impacts of climate change.Fil: Aragon Traverso, Juan Hector. Universidad Nacional de San Juan. Facultad de Filosofía, Humanidades y Artes. Instituto de Ciencias Básicas; ArgentinaFil: Piñeiro Gomez, Mauricio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Biotecnología; ArgentinaFil: Olivares, Juan Pablo Segundo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Sanabria, Eduardo Alfredo. Universidad Nacional de San Juan. Facultad de Filosofía, Humanidades y Artes. Instituto de Ciencias Básicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentin

Figure 1 in Diet composition of an invasive population of Lithobates catesbeianus (American Bullfrog) from Argentina

Figure 1. (A) Location of studied invasive population of Lithobates catesbeianus from San Juan (black dot); (B) typical environment where the bullfrogs were captured for this study, around the Castaño Viejo River.Published as part of Quiroga, Lorena Beatriz, Moreno, María Daniela, Cataldo, Ariel Aníbal, Aragón-Traverso, Juan Héctor, Pantano, María Victoria, Olivares, Juan Pablo Segundo & Sanabria, Eduardo Alfredo, 2015, Diet composition of an invasive population of Lithobates catesbeianus (American Bullfrog) from Argentina, pp. 1703-1716 in Journal of Natural History 49 (27) on page 1705, DOI: 10.1080/00222933.2015.1005711, http://zenodo.org/record/400192

Diet composition of an invasive population of Lithobates catesbeianus

The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high andprobablyhasanimpactontheirprey.Freshwatercrabsarethemainitemsinthe diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region’s freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles.Fil: Quiroga, Lorena Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Moreno Avila, María Daniela. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Cataldo, Ariel Anibal. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Aragon y Traverso, Juan Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Pantano, María Victoria. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Olivares Toselli, Juan Pablo Segundo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Sanabria, Eduardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Filosofía, Humanidades y Artes. Instituto de Ciencias Básicas; Argentin