Molecular approaches to phylogeny and species boundaries in Lethrinus (Teleostei, Lethrinidae): insights from a taxonomic complex along Mozambique coast

Abstract Accurate species delimitation is essential for understanding the evolutionary processes that generate and maintain biodiversity, particularly in marine systems characterized by high connectivity and widespread distributions. Reef-associated fishes of the Indo–West Pacific provide an ideal framework to investigate these dynamics, yet many taxa remain poorly resolved due to morphological conservatism and cryptic diversity. Here, we present a comprehensive molecular assessment of the genus Lethrinus (Teleostei: Lethrinidae), integrating morphological data with mitochondrial markers (COI and Control Region) across 430 specimens spanning the Indo–Pacific, with a focus on the Western Indian Ocean. Using an integrative framework combining species delimitation analyses, genetic distances, and phylogenetic reconstruction, we investigate patterns of lineage diversification and species boundaries within this widespread reef fish lineage. Our results reveal substantial hidden diversity and deep genetic structuring within several nominal species, indicating that species richness in Lethrinus is currently underestimated. In particular, the L. nebulosus complex comprises two highly divergent lineages with distinct geographic distributions, whilst additional cases highlight previously unrecognised evolutionary lineages and range expansions within the south-western Indian Ocean. These patterns suggest that regional environmental factors and oceanographic barriers may play a key role in shaping population structure and diversification across the Indo–West Pacific. Overall, our findings demonstrate that morphology alone is insufficient to resolve species boundaries in this group and that integrative taxonomy approaches are essential for accurate biodiversity assessment. These results have important implications for marine biodiversity monitoring and fisheries management, highlighting the need to incorporate molecular tools into environmental and conservation frameworks in data-deficient regions.