Ecoimmunology assesses immune function across taxa within a physiological, ecological and evolutionary framework (Martin et al., 2011; Sheldon & Verhulst, 1996). While the toolbox of vertebrate ecoimmunologists is expanding (Brown et al., 2011; Martin et al., 2006), interpretations of immune parameters are often based on endothermic species (Davis et al., 2008; Murphy, 2012). One example is the interpretation of differential white blood cell counts (Davis & Durso, 2009; Davis et al., 2008). In general, lymphocyte numbers indicate adaptive immunity and shifts in lymphocyte to neutrophil/heterophil ratios are interpreted as changes in chronic stress and the balance between specific, induced immune functions and non-specific, constitutive responses (Davis et al., 2008; Goessling et al., 2015). Immune function within ectothermic vertebrates relies heavily on B1 lymphocytes, a subclass of B cells contributing to innate, rather than adaptive, immunity (Ochsenbein & Zinkernagel, 2000; Zimmerman, Vogel, & Bowden., 2010). B1 lymphocytes often constitute a significant portion of circulating lymphocytes (Zimmerman et al., 2017), suggesting that differential white blood cell counts may overestimate adaptive immunity within taxa of ectothermic vertebrates. Further, B1 lymphocytes directly control pathogens through phagocytosis, as demonstrated in all ectothermic species studied to date (fish, an amphibian and three reptiles: