Additional Cases of Defensive Visual Batesian Mimicry Among Plants

Abstract

Leaf shape is known to partly explain herbivorous insect richness on various plant taxa (Jones and Lawton 1991), and this is probably related to more than one mechanism. The little known, and even less tested visual Batesian leaf mimicry will be briefly discussed in this short chapter. Shimshi (1979/1980) proposed that the hill ecotype of Iris atrofusca from the heavily grazed desert/steppe transition zone in Israel with its erect (ensiform) leaves that differ from the regular curved (falcate) leaves of the common type in other ecosystems is a mimic of the poisonous common geophyte Asphodelus ramosus (= A. microcarpus) of the Liliaceae that grows in the same habitat, which is not grazed in the winter and spring because of toxicity (Seligman et al. 1959). Brown and Lawton (1991) postulated that the two non-spiny species Celmisia lyalli and C. petriei (Asteraceae) growing in New Zealand look rather like spiny members of the genus Aciphylla (Apiaceae). Brown and Lawton (1991) also described the close resemblance of general plant morphology and leaf shape of the European white dead-nettle (Lamium album) to the well-defended stinging nettle (Urtica dioica) as a case of Batesian mimicry. This nettle mimic and other species that visually mimic nettle (Lamium purpureum, Lamiastrum galeobdolon, Ballota nigra, Galeopsis tetrahit and other Galeopsis species) are named dead nettles because they lack the stings of stinging nettle (Wheeler 2004). Interestingly, in November 2015, a group of my first-year biology students wrongly identified a Ballota saxatilis plant growing on Mount Carmel, Israel as nettle during a field class when they had to collect and identify several plant species. Recently, morphological Batesian mimicry was proposed to exist between the chemically defended leaves of the model Pseudowintera colorata by the leaves of the non-defended Alseuosmia pusilla, two species from New Zealand (Yager et al. 2016). Yager et al. (2016) showed that these two species had leaves that were morphologically distinct from all neighboring species, and that A. pusilla individuals were more similar to neighboring than to distant P. colorata plants. Moreover, 90 % of the leaf shape variation in these two species varied similarly across an altitudinal gradient. These authors used a quantitative geometric morphometric approach that allows for comparisons based on actual values and not only on general visual similarity. This is expected to allow better quantitative critera for mimicry and for comparative studies on the strength of evolution in cases of visual mimicry. These few examples probably reflect a much broader phenomenon, partly discussed above, for instance when mimicry of host leaf shape by mistletoes was described. These few examples probably reflect a much broader phenomenon, partly discussed above, for instance when mimicry of host leaf shape by mistletoes was described.