2019-2020 Dr Loubab Zedane - Fog-harvesting adaptations in genus Eriospermum
The evolution of fog-harvesting adaptations in the genus Eriospermum
A fog desert is a type of desert where non-precipitating fog moisture supplies most of the water needed by the organisms that live there – that is, fog supplies the water, instead of rain. Well-known fog deserts include the Atacama Desert of coastal Chile, and the Namib Desert of southern Africa.
Animals and plants living in fog deserts have evolved extraordinary adaptations to enable them to survive in these extreme environments. These physiological and morphological adaptations allow organisms to efficiently harvest moisture from the fog via condensation, and then absorption.
For example, nano-scale surface structures on the back of the Stenocara gracilipes beetle allow droplets of water to stick to its surface and accumulate there. The droplets accumulate until they roll down the beetle’s back to its mouth for it to drink.
Other adaptations such as mist-net leaves, spiraled leaves, and hairy leaves in plants (e.g. in the desert moss Syntrichia caninervis), allow for water condensation and fog-drip by increasing the edge-to-surface area of the organism. Foliar Water Uptake (FWU) is a common water acquisition mechanism for plants in ecosystems affected by fog, having as a consequence a net increase in leaf water mass. Recent studies have shown that the diffusion of fog water intercepted by the leaves in a number of species could be mediated by fungal hyphae, absorbent trichomes (leaf hairs), and the properties of the cuticle and leaf. Individual plant species may potentially use several pathways for water acquisition.
However, little is known about the water use proportions from various sources and potential water uptake pathways in Eriospermum (Asparagaceae), a plant genus native to sub-Saharan Africa with more than two thirds of the estimated 125 species occurring uniquely in semi-arid deserts in Southern Africa. This plant genus demonstrates a remarkable range of unusual leaf morphologies, including reduction of the leaf lamina and the production of unusual leaf enations on the adaxial surface of the leaf (Perry, 1994). These enations have been suggested to be associated with the harvesting of non-precipitating moisture in the form of fog, mist, and dew, but this hypothesis has yet to be rigorously tested.