When One Global Invasion Hides Another—Cryptic Interspecific Invasion in Freshwater Gastropods

Aim

Cryptic invasions are an understudied phenomenon among species invasions, especially in freshwater invertebrates. We study the gastropod family Physidae, including the global invaders Physella acuta and several enigmatic Stenophysa species, their phylogenetic relationships and the presence of native species among African Physidae. We infer distribution pattern, colonisation history and invasion ecology across Africa. Finally, we reconstruct the colonisation pathways and their timing into, across (and out of) Africa and model future dispersal.

Location

Global, with a focus on Africa and Indian Ocean islands.

Methods

Based on extensive sampling, multi-gene phylogenetic, phylogeographic and ecological analyses, including species distribution modelling, we here examine Physidae globally.

Results

The Physidae probably originated in the Lower Cretaceous. A robust phylogeny showed four strongly supported genus-level clades corresponding to Physella, Physa, Stenophysa and Aplexa. Physella acuta thrives in continental African countries and Indian Ocean islands. The African continent was colonised at least six times independently.

For Stenophysa, the phylogeny suggests two independent transoceanic dispersal events into Africa and the Indian Ocean islands. Physella acuta occurs not only in artificial or highly disturbed habitats but also in large natural lakes. Stenophysa marmorata is ecologically flexible. The SDM for S. marmorata based on the selected climate variables predicted high probabilities of future occurrence in equatorial Africa and regions in the Indo-Malayan Archipelago, New Guinea and eastern Australia.

Main Conclusions

Physidae contains examples of both intraspecific cryptic and interspecific cryptic invasions, with an intraspecific invasion of Physella acuta and a prime example of an interspecific cryptic invasion of Stenophysa spp. This study highlights the importance of cryptic invasions in freshwaters and also calls for their management. Stenophysa is likely to become pan-tropical in the future. Physidae are an excellent model to study differential patterns and processes of intra- versus interspecific invasions at global and regional scales.