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 (Rundel et al., 1976). Examples of fog deserts include the Atacama Desert of coastal Chile as well as the Namib Desert of Southern Africa. Previous studies have demonstrated that animals and plants living in fog deserts have evolved quite extraordinary morphological and physiological adaptations specific to these bioms (Vogel et al., 2011; Hou et al., 2014). Such adaptations allow organisms to efficiently harvest moisture from the fog via condensation, and then absorption. Several types of adaptations based on different mechanisms may occur. Condensation may, for example, be allowed by nano-scale surface structures on the back of beetle (Stenocara gracilipes) of the Namibia desert that help droplets of water to stick to the surface of the beetle and accumulate there until they roll down the beetle’s back to its mouth, where the water is absorbed (Hou et al.,2014). 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 (Pan et al., 2016). Finally, 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 (Eller et al.,2013). 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 (Burges et al., 2004), absorbent trichomes (Helliker et al., 2014), and properties of the cuticle and leaf (e.g. Pan et al., 2016). Same organisms 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 (Vogel et al., 2011), but this hypothesis has yet to be rigorously tested.