A comparison of immune function and physiological stress in three populations of the southwestern snake-necked turtle (Chelodina oblonga) along an urbanisation gradient

Morphological and eco-immunology parameters for southwestern snake-necked turtles (Chelodina oblonga) sampled in November 2023 from three locations differing in habitat disturbance from urbanisation in the Perth metropolitan area, Western Australia. Spectacles is the least urbanised site (surrounded by 98% native vegetation), Postans is intermediate (23% native vegetation), and Hawker is the most urbanized (0% native vegetation). Body condition was calculated using the Scaled Mass Index from Peig & Green (2009), with carapace length (in mm; CL) and Mass (in g) log-transformed (CL_lntrans and Mass_lntrans, respectively) to calculate the slope estimated by the standardized major axis regression of mass on length. Blood glucose concentration was measured in mg/dl using a portable glucometer (Glucose_mgperdL) and converted to mmol/L (Glucose_mmolperL). We used a bacteria-killing assay to quantify the mean proportion of bacterial colonies killed on two replicate plates treated with turtle plasma (Plate1 and Plate2) compared to the mean proportion killed on two control plates (Ctrl1 and Ctrl2); the final proportion of colonies killed was an individual’s bacteria-killing capacity (BKCapacity). From blood smear slides prepared from each individual, we counted ~100 white blood cells (TotalCellsCounted) and classified each cell as a Heterophil, Lymphocyte, Monocyte, Eosinophil, or Basophil; the ratio of heterophils:lymphocytes (HLRatio) was used as a proxy for physiological stress level.