Thiago S. Marques

Isotopic Discrimination Factors (Δ13C and Δ15N) between Tissues and Diet of the Broad-Snouted Caiman (Caiman latirostris)

Abstract Natural variation in stable isotope ratios is a useful tool in diet studies. However, the correct interpretation of isotopic data is reliant on proper estimates of discrimination factors. This study aimed to describe the magnitude of the discrimination factors of carbon and nitrogen isotopes between diet and tissues (Δ13Ctissue-diet and Δ15Ntissue-diet) of the Broad-snouted Caiman (Caiman latirostris) and to verify potential differences between age classes. The isotopic ratios of carbon and nitrogen (δ13C and δ15N) were determined in samples of two tissue types (claw and scute) collected from 18 captive animals and in 15 samples of their diet. The Δ13Ctissue-diet was 1.2 ± 0.1 ‰ for claw and 0.9 ± 0.2‰ for scutes; the Δ15Ntissue-diet was 1.1 ± 0.1‰ for claw and 0.8 ± 0.2‰ for scutes. These values were much lower than the values assumed commonly in ecological studies (3–5‰), and similar to a previous study with crocodilians. Our results emphasize the need to determine discrimination factors specific to taxa instead of assuming average values derived from the literature.

Primeiro registro de larvas de Chironomus inquinatus Correia, Trivinho-Strixino & Michailova (Diptera, Chironomidae) vivendo no casco do cágado Phrynops geoffroanus Schweigger (Testudines, Chelidae) na região Neotropical

In this study we report for the first time the occurrence of Chironomus inquinatus larvae Correia, Trivinho-Strixino & Michailova living on the shell of the side-necked turtle, Phrynops geoffroanus Schweigger, possibly by the intense accumulation of sediment, in a polluted river of the Neotropics.

Characterization of innate immune activity in Phrynops geoffroanus (Testudines: Chelidae)

3 Corresponding author. ABSTRACT. The innate immune activity of the freshwater turtle Phrynops geoffroanus (Schweigger, 1812) was investi- gated, using a sheep-red-blood cell hemolysis assay. The time- and concentration-dependent hemolytic activity of the turtle plasma was low compared to that reported for other reptiles. However the plasma of P. geoffroanus exhibited higher activity at elevated temperatures, resulting in temperature-dependent hemolysis. The sensitivity of turtle plasma to temperature could be interpreted as a mechanism by which freshwater turtles use basking behavior to elevate body temperature, thus enhancing the innate immune response. However, we cannot discard the possibility that environ- mental contaminants could be affecting the turtles immune response, since the animals in this investigation were captured in a polluted watercourse.

Intraspecific isotopic niche variation in broad-snouted caiman (Caiman latirostris)

Strategies to minimise intraspecific competition are common in wild animals. For example, individuals may exploit food resources at different levels of the food chain. Analyses of stable isotopes are particularly useful for confirming variations in an intraspecific niche because the chemical composition of animals tends to reflect both the food consumed and the habitats occupied by the species. However, studies using this methodology to investigate neotropical crocodilians are scarce. This study aimed to verify the existence of ontogenetic and sexual niche variation in broad-snouted caiman in a silvicultural landscape in Brazil through the use of carbon and nitrogen stable isotopes. The isotopic ratios of carbon and nitrogen were determined in claw samples collected from 24 juveniles, 8 adults, and 16 hatchlings of C. latirostris. We identified a discrete ontogenetic variation in the isotopic niche and sexual difference only for juveniles. These results may indicate differences in the exploitation resources and a consequent reduction in competition between age classes.

Isotopic signatures (δ 13C and δ15N) of muscle, carapace and claw in Phrynops geoffroanus (Testudines: Chelidae)

The isotopic composition ( δ13C and δ 15N) of muscle, carapace and claw was determined from six wild individuals of Phrynops geoffroanus (Schweigger, 1812) in order to verify the variation between those tissues. The mean values of δ13C e δ 15N were, respectively, -19.48 ± 0.81‰ (-20.8 - -18.64‰) and 7.23 ± 0.67‰ (6.49 - 8.3‰) for muscle, -16.52 ± 0.98‰ (-17.88 - -15.43‰) and 7.29 ± 0.54‰ (6.74 - 7.97‰) for carapace and -18.57 ± 0.97‰ (-19.97 - -17.26‰) and 4.36 ± 0.33‰ (3.93 - 4.79‰) for claw. We found a significant difference for the tissues evaluated for both δ13C and δ15N. Muscle and claw were statistically similar and more depleted in 13C than the carapace. Nonetheless, claw was more depleted in 15N than muscle and carapace tissues. These results are likely related to differences in metabolic processes involved on each tissue formation. The description of the isotopic signatures variation in P. geoffroanus tissues provides a baseline for future investigations on the diet reconstruction of this species when more than one tissue is involved.

The Use of Stable Isotopes Analysis in Wildlife Studies

The application of stable isotopes analysis in wildlife studies has increased in recent decades due to the wide range of information that can be obtained with this methodology. This chapter aims to present the basic principles of the stable isotopes analysis and their potential applications in wildlife studies. The main topics presented are diet reconstruction, trophic level, animal movements, tissue turnover rates, and ecotoxicology.