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Trophic niche parameters and forage preferences of capybara Hydrochaeris hydro- chaeris Linnaeus, 1766 were studied at three areas of east-central Argentina: Lower Delta Islands (LDI), only capybara present; Puerto Constanza (PC), capybara and cattle, and Villaguay (VI), capybara, cattle and sheep. Significant correlation was found in the annual botanical composition of capybara faeces at LDI and PC, but no cor­relation was found between faecal composition at these two areas and those at VI. The narrowest trophic niche corresponded to LDI, while the widest corresponded to VI, with significant differences in the values among the three areas. Capybara consumed Carex riparia, Cynodon dactylon and Panicum grumosum in LDI, and P. milioides in VI in proportion greater than availability. Three and eight food items were consumed less than availability in VI and PC, respectively. The greater the species number and density of livestock animals, the more generalist the behavior of capybara, possibly due to direct interaction in the use of grazing resources. Changes in availability of foraging species may influence the capybara's preference patterns and the consumption of suboptimal feeding items may indicate a greater pressure on foraging resources in the areas where capybaras share their habitat with livestock.
Fossil capybaras are morphologically extremely varied, but previous studies have disagreed on whether this diversity reflects intraspecific variation or the existence of multiple species. Here, we review the capybaras from the classic Argentinian Late Miocene localities of Paraná River cliffs (“conglomerado osífero” of the Ituzaingó Formation, Entre Ríos), and Chillhué and Guatraché shallow lakes (Cerro Azul Formation, La Pampa), and perform a morphometric analysis of their upper cheek teeth and the posterior portion of the rostrum. Our results confirm that all of the specimens from the “conglomerado osífero” belong to the single species Cardiatherium paranense. In addition, we refer a specimen from Tupungato (Río de los Pozos Formation, Mendoza) to C. paranense, thus expanding its geographical range. The material from La Pampa represents a different taxon, and is here preliminary referred to Cardiatherium aff. orientalis. Our systematic interpretation of Late Miocene capybaras suggests that the early radiation of this group was not as explosive as previously thought, and was likely constrained by the early acquisition of large size, increasing complexity of the cheek teeth, and probably semi-aquatic habits.
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Capybaras, size, shape, and time: A model kit

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The capybaras (Hydrochoeridae) are outstanding rodents for their large size and euhypsodont and multilaminated cheek teeth. Although today they are represented by a single species, it was generally thought that their past diversity was much higher, especially during the late Miocene–early Pliocene. Such diversity is here analyzed taking into account the ontogenetic variation of the p4–m3 in different populations. Numerous isolated teeth of different size found in the upper levels of the Puerto Madryn Formation (late Miocene, Peninsula Valdés, Argentina) were interpreted as members of an ontogenetic series of a new species here described, Cardiatherium patagonicum. They provided clues to evaluate ontogenetic variation and a new framework to analyze the family diversity. In this context, it is proposed that multiple species described from the Ituzaingó Formation (late Miocene, Entre Ríos, Argentina) based on lower teeth, may actually represent specimens of different stages of the ontogenetic trajectory of a single species. Likewise, we found that several nominal taxa from other localities were based on juvenile specimens. According to these results, the diversity of the Hydrochoeridae during the late Miocene and early Pliocene was drastically reduced. The validity of the subfamily Cardiatheriinae is debated. Finally, it is suggested that the whole family should be revised taking into account the ontogenetic variation.
A survey of Babesia, Theileria and Hepatozoon was conducted in wild mammals, including the capybara (Hydrochaeris hydrochaeris; n = 14) from Brazil, the jaguar (Panthera onca; n = 2) and crab-eating raccoon (Procyon cancrivorus; n = 4) from Venezuela, and the red deer (Cervus elaphus; n = 70), red squirrel (Sciurus vulgaris; n = 5) and Eurasian pine marten (Martes martes; n = 3) from Spain. Diagnostic procedures included both microscopy and molecular methods (PCR and sequencing of the 18S rRNA gene). Microscopic examination of blood smears revealed no hematozoan infections — unlike the molecular analyses. Nine Brazilian capybaras were found to be infected with Hepatozoon canis (prevalence 64%), two of which were coinfected with a previously unknown babesid (prevalence 14%) loosely related to Theileria equi (90% 18S rRNA gene similarity according to BLAS® analysis). One jaguar and one crab-eating raccoon from Venezuela were infected by H. canis. Four of the red deer were infected with theilerids (5.7% prevalence), two with Theileria sp. and two with T. annulata. One red squirrel and three pine martens were infected with Hepatozoon sp. The isolate form the red squirrel was phylogenetically related to Hepatozoon sp. reported in Spanish bank voles, whereas those infecting the pine martens were related to Hepatozoon felis reported in Spanish cats. In conclusion, the molecular findings show that some non-canid mammals are carriers of H. canis in South America, while red deer may carry T. annulata in Europe. Small mammals in Europe appear to be unlikely hosts of H. canis and H. felis.
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