Diet variation of the South American snake-necked turtle (Hydromedusa tectifera) from two different urban neighboring streams

Dietary studies provide data about the biology of species such as food specialization, spatial and temporal feeding variation, and adaptations to different habitat characteristics. We analyzed the diet of the South American snake-necked turtle Hydromedusa tectifera using complementary techniques (stomach flushing and feces collection) from two urban watercourses in La Plata city (Buenos Aires, Argentina), one more natural and other more polluted. The Index of Relative Importance (IRI) was calculated to assess the contribution of each prey to the diet, and the Index of Electivity (E) to evaluate food selection. In general, H. tectifera displayed a generalist carnivorous habit with clear adaptations to variations in the environments in which this species lives. The diet composition showed marked differences between the two streams: in the more impacted watercourse, amphipods, aquatic coleopterans, and water bugs of the family Belostomatidae were the main items, while in the less anthropogenically disturbed one, aquatic snails dominated the turtles' diet. Our results highlight the importance of combining stomach flushing and fecal collection techniques to achieve a better trophic characterization and to avoid biased conclusions.