Avian gut passage reduces the germination light-response of Pokeweed (Phytolaca americana)

It has been shown that passage through a bird's gut has the potential to alter seed germinability (overall percent germination) and the timing of germination. However, little is known about the potential of avian gut passage to alter the germination response of seeds to abiotic gradients, such as light availability. Specifically, it is unclear if gut-passage makes seeds more or less sensitive to variability in light. We addressed this issue using a growth chamber experiment where the germination rate of both gut-passed and control (de-pulped) seeds of the understory herb Phytolaca americana (Pokeweed) were compared across three light levels. Both avian gut-passage and light increased germination rate. Additionally, it was found that gut-passage and light interacted to influence the germination rate, such that gut-passed seeds showed no response to light and control seeds had a strong, positive light response. Results from this experiment suggest that avian gut-passage has the potential to reduce seed’s sensitivity to light, which could play a role in the recruitment of avian-dispersed plant populations across variable light environments.