Animals embedded between trophic levels must simultaneously balance pressures to deter predators and acquire resources. Venomous animals may use venom toxins to mediate both pressures, and thus changes in this balance may alter the composition of venoms. Basic theory suggests that greater exposure to a predator should induce a larger proportion of defensive venom components relative to offensive venom components, while increases in arms races with prey will elicit the reverse. Alternatively, reducing the need for venom expenditure for food acquisition, for example because of an increase in scavenging, may reduce the production of offensive venom components. Here, we investigated changes in scorpion venom composition using a mesocosm experiment where we manipulated scorpions' exposure to a surrogate vertebrate predator and live and dead prey. After six weeks, scorpions exposed to surrogate predators exhibited significantly different venom chemistry compared with naive scorpions. This change included a relative increase in some compounds toxic to vertebrate cells and a relative decrease in some compounds effective against their invertebrate prey. Our findings provide, to our knowledge, the first evidence for adaptive plasticity in venom composition. These changes in venom composition may increase the stability of food webs involving venomous animals.
First milking data
FPLC absorbance time-series output for the initial (before treatments, t=0) venom extraction. Each of the four treatments are presented on separate sheets. Each column is a different scorpion, values are absorbance at 280nm. The leftmost column specifies the volume eluted in mL (beginning at 5mL due to an initial 5 mL to prime the equipment).
Second milking data
FPLC absorbance time-series output for the second (after completion of treatments, t=1) venom extraction. Each of the four treatments are presented on separate sheets. Each column is a different scorpion, values are absorbance at 280nm. The leftmost column specifies the volume eluted in mL (beginning at 5mL due to an initial 5 mL to prime the equipment).
Third milking data
FPLC absorbance time-series output for the third (3 weeks after the second venom extraction, t=2) venom extraction. Each of the four treatments are presented on separate sheets. Each column is a different scorpion, values are absorbance at 280nm. The leftmost column specifies the volume eluted in mL (beginning at 5mL due to an initial 5 mL to prime the equipment).
xCELLigence output for vertebrate cell assays
Raw xCELLigence output measuring changes to cell index in response to each venom fraction and the whole venom mixture (20 µL). Cell response is a combination measure of changes in media conductivity or cell contact/toxicity, which varies as the cells deform in response to exposure to a chemical sample. The maximum drop value in 2 hours after venom addition was deemed the predator cell response. Each fraction was replicated with 3 cell wells.
Cricket bioassay results
Caption: Results of invertebrate toxicity assays, evaluating toxin activity using the righting response of immature crickets to each venom fraction. 3 µL of one of the 14 chemical fractions was injected ventrally into the pronotum of an immature cricket, which was then rolled onto its back every 10 seconds 18 times for a total of 3 minutes. A compromised righting response was recorded when a cricket was unable to right itself within 60 seconds of being rolled onto its dorsal side. Each fraction was replicated with 10 crickets.
