Biogeographical studies on the invasive alien Hygrophila polysperma
Hygrophila polysperma (Acanthaceae: EPPO List of Invasive Alien Plants) is an aquatic species native to Asia and an invasive alien species in Australia, the USA (Alabama, Florida, Kentucky, South Carolina, Texas and Virginia), Mexico and Germany. H. polysperma can out-shade other submersed plants by occupying the entire water column, restricting light to other species and displacing native flora and fauna. Additionally, when large stands of H. polysperma die, their decomposition can create anoxic conditions resulting in fish death. Mats formed by the plant may also provide suitable breeding grounds for mosquitoes. H. polysperma clogs irrigation and flood-control canals, and interferes with water control pumping stations. It is also detrimental to navigation and recreational activities such as fishing and swimming. As part of an ongoing biological control programme against the species in the USA, a molecular biogeographical study using microsatellites and chloroplast DNA sequencing was conducted to evalute genetic variation in native and introduced populations and to understand its invasive history. Samples were collected from all regions where the species is known to have invaded, and its native range in India and Bangladesh. The results showed that in the invasive range, the samples of H. polysperma were nearly identical which suggests the invasive populations are most likely to have originated from one single individual or a clonal lineage. When historical information and the results of this study are considered together, it is likely that H. polysperma was first introduced into the USA and it is these populations that are source of introductions into Mexico and Australia. The German population may potentially be the result of an independent introduction from the same source population.
Sources
Mukherjee A, Williams D, Gitzendanner MA, Overholt WA, Cuda JP (2016) Microsatellite and chloroplast DNA diversity of the invasive aquatic weed Hygrophila polysperma in native and invasive ranges. Aquatic Botany 129, 55-61.