Étude phylogéographique et de la diversité génétique du crabe bleu Portunus segnis (Forskål, 1775)

Abstract

Portunus segnis, also known as the blue swimming crab, is an invasive species native to the Indo-Pacific region that is progressively colonizing Mediterranean coasts, notably in Tunisia, Malta, and more recently Algeria. This thesis aims to trace the origin of Mediterranean populations through phylogenetic and haplotypic analyses based on the mitochondrial COI gene. Phylogenetic results show a clear separation between Indo-Pacific populations and those from Iran and the Mediterranean Sea, and reveal a strong genetic proximity among individuals from Iran, Tunisia, and Malta, suggesting a probable origin in Iran followed by a westward expansion across the Mediterranean. Genetic diversity analyses support this structure: Indo- Pacific populations exhibit relatively high diversity and a significant deviation from neutrality, indicating either a recent demographic expansion or purifying selection. In contrast, Iranian and Mediterranean populations show more moderate diversity and signs of neutral evolution, which could reflect a recent introduction, potentially involving a substantial founding population or multiple introduction events. This study highlights the expansion dynamics of this invasive marine species and underlines the importance of continued biological and ecological monitoring, given its potential impacts on local biodiversity and coastal socio-economic activities.