Three Cases Revealing Remarkable Genetic Similarity Between Vent-Endemic Rimicaris Shrimps Across Distant Geographic Regions

Deep-sea hydrothermal vent fauna is often regarded as highly endemic, although exceptions have been reported. We examined genetic connectivity across broad spatial scales within the alvinocaridid genus <i>Rimicaris</i>, which has undergone substantial adaptive radiation worldwide. We analyzed six <i>Rimicaris</i> species using three genetic markers, cytochrome c oxidase subunit I (<i>COI</i>), 16S ribosomal rRNA gene (<i>16S</i>), and histone h3 (<i>H3</i>), and complete mitogenomes, employing newly generated sequences combined with publicly available sequence data. A genetic tree and haplotype networks were constructed, and divergence analyses were performed. Three clades of paired <i>Rimicaris</i> species were identified, each made up of taxa from different oceanic regions but showing relatively low <i>COI</i> divergence (0.35-1.90%). In Clade I, <i>Rimicaris chacei</i> and <i>Rimicaris hybisae</i> are morphologically similar and exhibit bidirectional gene flow, implying a dispersal route between the Mid-Atlantic Ridge (MAR) and the Mid-Cayman Spreading Center (MCSC). In Clade II, <i>Rimicaris exoculata</i> and <i>Rimicaris kairei</i> are morphologically, genetically, and ecologically distinct, reflecting restricted connectivity between the MAR and the Carlsberg Ridge (CR)-Central Indian Ridge (CIR). In Clade III, <i>Rimicaris variabilis</i> and <i>Rimicaris</i> cf. <i>variabilis</i> differ in nutritional strategies, showing a unidirectional dispersal route from the CIR to the southwestern Pacific (SWP), but morphological data to distinguish them are currently lacking. Some <i>Rimicaris</i> lineages maintain connectivity across distinct oceanic regions while others still form unique regional populations. This finding highlights the need for conservation strategies that incorporate both global-scale connectivity and regional endemism, rather than treating individual vent ecosystems as a single homogeneous management unit.