Comparison of morphometric patterns and blood biochemistry in capybaras (Hydrochoerus hydrochaeris) of human-modified landscapes and natural landscapes

BENATTI, H. R. Comparison of morphometric patterns and blood biochemistry in capybaras (Hydrochoerus hydrochaeris) of human-modified landscapes and natural landscapes. 2020. 90 f. Thesis (Doctorate in Sciences) – School of Veterinary Medicine and Animal Science, University of São Paulo, São Paulo, 2020. The capybara (Hydrochoerus hydrochaeris) is the largest rodent in the world, reaching up to 100 kg, with an average adult weight of 50 kg. In southeastern Brazil, capybara occupy a fundamental role in maintaining Brazilian spotted fever (BSF), since it functions as an amplifying host for the bacterium Rickettsia rickettsii, the agent of the disease. Among the characteristics necessary for amplification of the agent, high prolificacy and generation of new individuals susceptible to rickettsemia are essential in the epidemiological scenario of BSF. Many human-modified landscapes (HMLs) in southeastern Brazil have experienced horizontal and vertical expansion of capybaras populations in recent decades due to the large supply of food, thanks to the expansion of crops, as for example, sugarcane. It was conjectured, then, that capybaras in HMLs are increasing their body reserves, leading them to a picture of obesity, when compared to capybaras in Natural Landscapes (NLs) of the Brazilian Pantanal biome. It was also observed that the population density of capybaras in a given occupation area is much higher in HMLs than in NLs, possibly due to greater reproductive success due to the abundant supply of food. It was conjectured, therefore, that the obesity of animals in HMLs may be generating biochemical disorders of nutritional and metabolic nature. These disorders, added to greater reproductive capacities, can therefore increase the replacement rates of individuals, maintaining the BSF in southeastern Brazil. To answer these hypotheses, during the years 2015–2019, capybaras were captured in seven HMLs in southeastern Brazil, and in two NLs of the Pantanal biome, all with established populations of capybaras. Blood collection, measurement of total length, height and circumferences of neck, thorax and abdomen were performed to compare the results between populations, with NLs capybaras being the control group and HMLs being the experimental group. The results showed that animals in HMLs were heavier than animals in NLs, and, despite being heavier, they did not present larger linear measurements, excluding any type of size interference in the individuals' body mass values. Interestingly, HMLs capybaras showed larger neck and chest circumferences than those recorded for NLs capybaras. In addition, the present work registered a new superior weight limit for the species (105.2 kg). The results found in blood tests showed that, of the eleven biochemical factors analyzed, five (albumin, creatine kinase, cholesterol, fructosamine and total protein) were significantly different between populations and two (calcium and aspartate aminotransferase) were borderline. The analysis of biochemical factors directly or indirectly related to obesity proves that the capybara populations of HMLs are developing, due to excess fat, a series of biochemical disorders of metabolic and nutritional order, which can lead to increased mortality rates in these populations. In addition, rodents exposed to high-energy diets exhibit greater reproductive success.