BackgroundImperfect detection of hard‐to‐sample organisms has motivated the development of novel monitoring techniques. Environmental DNA (eDNA) can provide a sensitive, relatively low‐cost sampling method in aquatic systems, but biotic and abiotic factors can affect its reliability.AimsWe used a reintroduced population of radio‐tracked alligator snapping turtles (Macrochelys temminckii) to test the efficacy and ecology of eDNA in a lotic system.Materials & MethodsWe collected samples at turtle locations as well as random up‐ and downstream sites. Using a novel eDNA assay, we modeled occupancy and detection of eDNA using turtle biomass and remotely sensed UV exposure and also tested the relationship between these parameters and eDNA concentration.ResultsWe found eDNA occupancy was best explained by upstream biomass and detection probability decreased with greater upstream UV exposure. The concentration of eDNA in a sample was not significantly affected by biomass measures, but decreased with higher upstream UV exposure, and the effect was significant.DiscussionOur results show that UV exposure can affect aquatic eDNA sampling in situ with free‐ranging animals. The use of radiotelemetry allowed for higher control when modeling eDNA persistence and transport in a natural setting relative to laboratory, enclosure, or mesocosm studies.ConclusionWe propose using wildlife tracking techniques to provide added realism to studies of eDNA dynamics.

Reptiles are declining worldwide yet our understanding of their immune function lags far behind other taxa. The innate immune system is the primary mode of defense in reptiles, and the serum complement cascade is its major component. We assessed serum complement activity of plasma in two closely related aquatic turtle species, the common snapping turtle (CST; Chelydra serpentina ) and alligator snapping turtle (AST; Macrochelys temminckii ). We used a sheep red blood cell (SRBC) hemolysis assay to assess serum complement activity. Although the antibacterial activities of the plasma of these turtle species are similar, the hemolytic activity was much stronger in CST than AST. Treatment with inhibitors of the serum complement cascade indicated differences in the mechanisms of complement activation between the turtle species. We subjected plasma from both turtle species to mannan affinity chromatography and analyzed the eluate with SDS-PAGE, which revealed that plasma from the CSTs contained only small amounts of one C-type lectin protein while the AST plasma contained high concentrations of two C-type lectins (31.0 and 35.9 kDa). Edman degradation analyses confirmed that the two AST proteins contained identical N-terminal sequences. Thus, the CST appears to rely more heavily on the alternative mechanism of serum complement activation, while the AST appears to rely more on the lectin-mediated pathway, which is a pattern recognition response to prokaryotes not activated by the SRBCs. These results are unique in that the use of serum complement pathways are generally assumed to be conserved within clades.

Innate immunity provides a fast‐acting and nonspecific defense against microbial infection, and appears to have particular importance in the immune response of ectothermic vertebrates. Chelonians are a globally distributed and diverse group, yet little is known about their basic immune function. The chelonian family Chelydridae is made up of two genera (Chelydra and Macrochelys), represented in our study by the widespread common snapping turtle ( Chelydra serpentina; CST) and the southeast USA endemic alligator snapping turtle ( Macrochelys temminckii; AST). Our goal was to quantify the innate immune response of the family Chelydridae, using the antibacterial activity of plasma as a measure of immune function. Our results show that the plasma of both species has strong antibacterial properties, but CST plasma kills a higher percentage of bacteria than AST plasma. In addition, while both species showed the highest antibacterial activity at 25 to 30°C, CST plasma retained its antibacterial properties at lower and higher temperatures than AST plasma. Our results indicate that, like many ectotherms, Chelydridae have a relatively strong innate immune response. The stronger, more robust immune response of CSTs compared with ASTs is likely correlated to the differences in geographic ranges but may also have implications for each species’ tolerance to anthropogenic habitat degradation and global climate change.