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ABSTRACT
Upon discovery that the Boquila trifoliolata is capable of flexible leaf mimicry, the question of the mechanism behind this ability has been unanswered. Here, we demonstrate that plant vision possibly via plant-specific ocelli is a plausible hypothesis. A simple experiment by placing an artificial vine model above the living plants has shown that these will attempt to mimic the artificial leaves. The experiment has been carried out with multiple plants, and each plant has shown attempts at mimicry. It was observed that mimic leaves showed altered leaf areas, perimeters, lengths, and widths compared to non-mimic leaves. We have calculated four morphometrical features and observed that mimic leaves showed higher aspect ratio and lower rectangularity and form factor compared to non-mimic leaves. In addition, we have observed differences in the leaf venation patterns, with the mimic leaves having less dense vascular networks, thinner vascular strands, and lower numbers of free-ending veinlets.
KEYWORDS:
Boquila trifoliolata chameleon-like leaves leaf mimicry plant ocelli plant vision vascular network
Introduction
Seven years ago, Gianoli and Carrasco-Urra reported on their discovery of Boquila trifoliolata (Lardizabalaceae), a woody vine from temperate rainforests of southern Chile, capable of complex leaf mimicry, when leaves of up to three different host plants were mimicked by leaves of one B. trifoliolata plant. 1 However, according to a side-by-side published commentary, the absence of any plausible hypothesis for such a phenomenon makes this report unexplainable and mysterious. 2
Gianoli and Carrasco-Urra preferred some chemical volatile signals released from the host plants, which would allow the B. trifoliolata to mimic leaves of host plants. 1 , 3 As an alternative proposal, they also speculated that horizontal gene transfer between host plant and Boquila vine, mediated perhaps via airborne microbes, might allow this leaf mimicry. They proposed this scenario because B. trifoliolata leaves mimic the nearest foliage, irrespective if these leaves are from the host plants or some other neighboring plants. 1 , 3 The complexity of this mimicry, when B. trifoliolata leaves were shown to mimic shapes, colors, leaf orientations, petiole lengths, and vein conspicuousness and patterns may have a third hypothesis, totally different from the volatile signals from host plants or gene transfer via airborne microbes. This third hypothesis would support the possibility that plant vision based on plant ocelli 4 , 5 is behind this unique form of plant behavior. 6 , 7
The plant ocelli concept was elaborated by Gottlieb Haberlandt in 1905 and two years later supported by Francis Darwin 8 which consists of the upper epidermis cells have a planoconvex or convex shape acting as lenses, allowing the convergence of light radiation into light-sensitive subepidermal cells. 5 With the discovery that the B. trifoliolata is able to mimic the leaves of the nearest plant, 1 , 3 we have been given a rare opportunity to test plant vision in more detail. The simplest way to test the vision hypothesis with the B. trifoliolata would be to see if it would mimic a non-living leaf shape from an artificial plant. In this study, B. trifoliolata was exposed to the artificial plastic plant with a characteristic leaf shapes. The results of this study show that this is indeed the case as leaves of B. trifoliolata mimicked leaves of the artificial plant. Hopefully, this report will stimulate more experiments in future to improve our understanding of the plant sensory abilities.
Results and discussion
Boquila trifoliolata grows in very wet conditions in the Valdivian temperate rainforest. The standard leaves of the B. trifoliolata plants show a variation of leaf shapes and the number of lobes. The majority of leaves have three lobes with blunted tips ( Figure 1a ). Variation of the number of lobes can be seen with some leaves having multiple lobes and others having less than three. Some leaves showed similar pattern to the fake leaves with respect to lobe variation ( Figure 1b ). In this research, lower leaves were used as control (non-mimic) leaves due to being below the line of the opaque shelf 1, therefore without direct visual contact with the false leaves ( Figure 2 ).
Boquila trifoliolata mimics leaves of an artificial plastic host plant
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