No Evidence of Long-Term Effects on Physiological Stress or Innate Immune Functioning in Northern Map Turtles Ten Years After a Freshwater Oil Spill
Description
Capture site and eco-immunology parameters for northern map turtles (Graptemys geographica) in the Kalamazoo River, Michigan, USA in 2020. Turtles were sampled either from river stretches that had been oiled in 2010 following an oil pipeline rupture, or from a control stretch upstream of the oil spill origin (SiteType). For turtles sampled from formerly oiled river stretches, we calculated the river-distance in m from each turtle’s capture location (Latitude and Longitude) to the origin of the ruptured oil pipeline (DistFromSpill). Turtles were classified (Age) as either sub-adults (5.9 – 7.0 cm for males, 5.5 – 16.0 cm for females) or adults (>7.0 cm for males, >16.0 cm for females) based on PlastronLength (cm). CarapaceLength, CarapaceWidth, and PlastronWidth were also measured in cm. A subset of turtles were known, based on presence of previously implanted PIT tags, to have been rescued and rehabilitated in the immediate aftermath of the 2010 oil spill; at their time of rescue in 2010 these turtles had been classified (OilExposureIn2010) as “heavily oiled” (>50% of the individual’s surface was oiled), “moderately oiled” (oil on 10-50% of the body surface), “lightly oiled” (<10% of body surface was oiled), or “unoiled.” From blood smear slides from each individual sampled in 2020, we counted ~100 white blood cells (TotCellsCounted) 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. 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 (BKcapacity) was adjusted to 0 for individuals where more colonies were present on plates containing plasma than on control plates (BKcapacityAdjusted). We used a natural antibody agglutination assay to quantify the final titer in which agglutination activity was observed when turtle plasma was treated with foreign red blood cells (AggTiter).