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Stellenbosch University (2021)

Camouflage as a driver of colour variation and diversity in the ‘stone’ plant genus, Lithops

Scheepers, Paul

Titre : Camouflage as a driver of colour variation and diversity in the ‘stone’ plant genus, Lithops

Auteur : Scheepers, Paul

Université de soutenance : Stellenbosch University

Grade : Master of Science (MS) 2021

Résumé partiel
Lithops is a genus of succulent plants that exhibits exceptional diversity in the colouration of its leaves. The menagerie of leaf colours and patterns of the various species often bear a remarkable resemblance to the stones which they grow amongst and this has long been assumed to represent a defensive strategy that allows the plants to avoid the attention of herbivores. Similar rocks or ‘lithologies’ are distributed patchily across the range of Lithops in a mosaic-like pattern due to spatially discrete geological processes. Because camouflage (ie the use of information to fool predator perception and avoid attack) is background-dependent, certain appearances will be optimal for camouflage in specific regions but will be sub-optimal elsewhere. When natural selection favours different genotypes spatially this can lead to a pattern of ‘local adaptation’, which is a pre-requisite for the ecological speciation model. It was the aim of this thesis to assess whether Lithops are indeed camouflaged, as this has never been quantitatively assessed and is believed to be rare among plants. In addition, I aimed to elucidate whether Lithops are locally adapted, which would point towards camouflage as a driver of diversity in the genus. Using digital photography techniques and a model of human vision, I found strong evidence that Lithops are camouflaged and that they tend to match the rocks in their environment better than the soils, although this depended somewhat on which component of colour was analysed (ie luminance versus chroma).

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