Molecular ecology of the freshwater shrimp Caridina natalensis and comparative analysis with other amphidromous species (Decapoda, Teleostei, and Gastropoda)

Due to their life cycle shared between rivers and oceans, amphidromous organisms serve as intriguing models for studying biogeography. To investigate the implications of their unique life history, we examined the population structure of the amphidromous shrimp Caridina natalensis across its known range in the South Western Indian Ocean. A total of 118 specimens were collected from 7 islands (Mayotte, Mohéli, Mahé, Praslin, Silhouette, Mauritius and Madagascar) and the African mainland (South Africa), and their 16S rRNA and Cox1 mitochondrial genes were sequenced. Our findings reveal significant regional structure among archipelagos, suggesting complex patterns of dispersal involving successive events of extinction-recolonization. By conducting a comparative analysis with six other amphidromous species from the South Western Indian Ocean, based on literature sources, we were able to draw conclusions regarding the amphidromous biogeography of the area. Furthermore, we propose a novel classification of amphidromous species, considering their population structure and life history traits. We defined four categories of increasing dispersal abilities and decreasing genetic population structure: 1. Land-locked species; 2. Species with reduced or facultative amphidromy; 3. Species with common amphidromy; and 4. Super-amphidromous species. Lastly, we identified the Comoros Islands (namely Mayotte and Mohéli) as a critical area for the dispersal of amphidromous species, emphasizing the need for prioritizing conservation efforts in this region.