Some organisms produce their own chemical defenses against predators, making themselves distasteful or poisonous. Others avoid expending energy on such chemicals, and instead mimic the appearance of noxious prey in order to repel predators. This defense mechanism, known as Batesian mimicry, has been well described in the animal world. Among plants, however, Batesian mimicry has not been clearly demonstrated.
Recently, ecophysiologists Karl Yager and Kevin Gould at the Victoria University of Wellington, New Zealand, along with evolutionary biologist H. Martin Schaefer at the University of Freiburg, Germany, used an approach called geometric morphometrics to assess similarity between leaves of different plants. This technique involves more detailed computer measurements of leaf shape than the traditional, basic metrics of leaf length, width, and area. The researchers focused on the palatable evergreen shrub Alseuosmia pusilla and the noxious shrub Pseudowintera colorata, two plants that grow near each other and have similar-looking leaves, making them a potential example of Batesian mimicry.
After collecting plants from roughly 2.8 miles of track through Tararua Forest Park, New Zealand, the team quantified leaf characteristics of A. pusilla, P. colorata, and seven other species with similar leaves. They found that P. colorata and A. pusilla had similar leaf shapes that were distinct from those of surrounding species. When the two species were compared according to leaf size and shape, about a third of the leaves were indistinguishable as one species or the other. The researchers also examined reflectance spectra and found negligible differences in leaf color between the species.
The two species were also found to vary similarly in size and shape as the altitude changed, indicating that they respond similarly to changes in environmental variables. Additionally, the closer the two species were found to one another, the more alike they appeared.
The strong resemblance between these two shrubs, along with their distinctiveness from other surrounding plants, suggest that A. pusilla may be a Batesian mimic of P. colorata. Conclusive proof of mimicry will require identifying an animal that consumes both of these plants and cannot distinguish between them, and demonstrating that A. pusilla benefits from its association with P. colorata. (Botany)