Phylogenetic study and the effect of climate change on Duckweeds (Lemnaceae) in South Africa: an ecological niche modelling approach

Abstract

Duckweeds are tiny floating plants that are anthropogenically introduced in many rivers, lakes, and wetlands in South Africa. Because of their miniature habit, they can be very difficult to identify, distinguish with naked eyes and they reproduce rapidly, forming a dense mat that diminishes the potential usage of waterbodies. Therefore, we aim to identify duckweed species using phylogenetic relationships and elucidate how climate change may affect the current and future distribution of duckweed (Lemnaceae) species in South Africa. For DNA molecular technique, we used five plastid regions (matK, rbcL, rps16, trnK (3’) and trnK (5’) to reconstruct a complete phylogeny of five duckweed genera with 38 species. 20 samples were collected from different provinces in South Africa. The phylogenetic analysis revealed two distinct clades representing the two subfamilies of Lemnaceae: Lemnoideae and Wolffioideae. Approximately, seven native and 31 invasive alien duckweed species were identified. With regards to results from the species distribution model, current climate models revealed suitable environmental niche for duckweeds species in South Africa, with the following hotspot provinces: KwaZulu-Natal, Eastern cape, Western Cape, Mpumalanga, and Limpopo. However, the future projections have shown that majority of duckweed species will experience great contraction: Spirodela polyrhiza, Lemna aequinoctialis and Lemna gibba. Therefore, this project has confirmed the placement of collected duckweed species within the two subfamilies on the phylogenetic tree and we also predicted the distribution of duckweed species in South Africa. The eastern and southern part of South Africa extending to the northern part has been identified as the most current climatically suitable areas for duckweed species. Furthermore, results differentiated between native and invasive alien duckweed species to South Africa. The study also listed some of the water bodies that may experience range expansion of duckweed species in the future where conservationist may prioritize management of dams.