Short-term stress response of the common toad Bufo bufo to poison secretion from parotoid macroglands

Toads produce potent poison in their parotoid macroglands, a rich source of toxic molecules against predators, parasites and pathogens. Production of such complex and toxic secretions is energetically costly and competes for energy resources with other physiological processes. We hypothesized that poison secretion from toad parotoids by electrical stimulation induces a short, transient stress response manifested by an increase in the neutrophil to lymphocyte (N:L) ratio, a marker of acute stress. We studied the effects of poison excretion on N:L ratio using 27 male common toads (Bufo bufo Linnaeus, 1758), which were randomly divided into three groups: control (no treatment), milked by electrical stimulation (poison release) and sham-stimulated (no poison release). Blood was sampled from clipped toes of toads. Bleeding and smears were done at four time points (0, 12, 24, and 48 h after treatment). At 12 h after treatment we found elevated N:L ratio in milked toads, but this effect disappeared before 24 h. Our results indicate that poison secretion may cause transient disruption of homeostasis, leading to temporary stress. However, the short duration of stress response suggests that the technique of electrical stimulation is less harmful than previously assumed and can be applied to obtain poison samples.