A variation on leaf variegation

Most cases of plant mimicry involve the mimicry of a single host species, with detailed leaf morphology such as variegation eventuating over many generations. The climbing plant Boquila trifoliolata is different, it is capable of mimicking multiple hosts, even within the same plant. The twining vine is endemic to the temperate rainforest of southern South America, with its leaves variable in size and shape and composed of three pulvinated leaflets that can change their orientation. B trifoliolata mimics the leaves of its supporting trees, capable of copying shape, colour and vein conspicuousness among multiple other features, and is able to change its leaf morphology accordingly when transversing multiple hosts (Gianoli and Carrasco-Urra, 2014).

Variables unsupporting of the mimicking hypothesis of B trifoliolata have been disregarded. Different light patterns can be excluded because the light environment across the vines are generally homogenous, and in all measured cases leaf type did not differ when the light environments were different. Also the leaves of B trifoliolata that were not supported by a host and located on the ground largely differed from the leaves of the plant when it was supported by a host tree, and were similar to the leaves present when growing on a bare tree trunks. It can therefore be established that when there is no leaf to mimic, the supported vines very similar to the unsupported vines, which shows the ‘standard’ leaf phenotype of the species (Gianoli and Carrasco-Urra, 2014).

The mimicry of B. trifoliolata,the vine denoted by a V and the host tree by a T.

 Herbivory avoidance is a hypothesis that can be used to explain why B trifoliolata mimics its hosts. Evidence of this can be seen when comparing rates of herbivory of the host plant, to the mimicking vine; the rates are very similar, especially when compared to the high rates of herbivory observed in the vines when they are not displaying mimicry; unsupported by a host tree. Leaf herbivory was also higher on vines that were climbing unleafed hosts of which they could not mimic, and were displaying their ‘standard’ leaf types. This suggests that the vines are not only avoiding herbivory from climbing a host and by avoiding ground herbivores, but also from mimicking a tree that the herbivores don’t eat. It has even been observed that B trifoliolata can display leaf mimicry without any contact with its host (Gianoli and Carrasco-Urra, 2014).

Herbivory index of B. trifoliolata when on a host tree (a), when unsupported (b), and when on a leafless host tree (c).

 B trifoliolata displays advanced phenotypic plasticity with its ability to resemble several hosts simultaneously, and while there is not currently a mechanism to explain this phenomenon, there are two hypotheses. One hypotheses describes the host plant volatiles in triggering specific phenotypic changes in the nearby B trifoliolata vine leaves, which has been shown as a mechanism in other plant mimicry systems. Volatile compounds have the ability to initiate numerous changes in the plant transcriptome to elicit specific responses in neighboring plants, however this plant to plant signaling has not yet been reported to cause specific morphological changes in leaf morphology and the reprogramming of genes in a mimicking species. An alternative, but less plausible hypothesis involves horizontal gene transfer between plants. B trifoliolata leaf plasticity could involve horizontal gene transfer that may be mediated by airborne microorganisms, which is supported by the fact that mimicry is observed with respect to the vegetation to which the vine is nearest. Further research into B trifoliolata leaf mimicry may lead to the identification of host tree volatiles or even vector mediated gene transfers that can trigger different leaf morphologies (Gianoli and Carrasco-Urra, 2014).