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

## TL;DR

This study reveals that Rimicaris shrimp, found in deep-sea hydrothermal vents, show surprising genetic similarity across distant regions, suggesting complex patterns of connectivity and conservation needs.

## Contribution

The study identifies three genetically similar Rimicaris species across different oceans, revealing new insights into their global connectivity and conservation implications.

## Key findings

- Three clades of Rimicaris species show low COI divergence despite being from different oceanic regions.
- Some Rimicaris populations exhibit strong genetic connectivity, while others remain distinct and localized.
- The findings suggest conservation strategies should consider both global connectivity and regional endemism.

## Abstract

Deep-sea hydrothermal vents are unique seafloor habitats that support highly endemic organisms with high species abundance and biomass. Among vent-endemic fauna, Rimicaris shrimp are common and play key ecological roles in vent communities of the Atlantic, Indian, and Pacific Oceans. Using multiple genetic markers, we identified three groups of closely related Rimicaris species with cytochrome c oxidase subunit I (COI) divergence of only 0.35–1.90%, reflecting very low genetic differences. We also examined how Rimicaris shrimp populations may be connected across vast oceanic distances and discussed the gene-flow patterns, biological traits, and biogeographic relationships within this monophyletic genus. We found that some deep-sea vent shrimp populations exhibit strong genetic connectivity across distant regions, whereas others remain genetically distinct and localized. These results underscore the need for conservation strategies that incorporate both global-scale connectivity and regional endemism.

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 Rimicaris, which has undergone substantial adaptive radiation worldwide. We analyzed six Rimicaris species using three genetic markers, cytochrome c oxidase subunit I (COI), 16S ribosomal rRNA gene (16S), and histone h3 (H3), 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 Rimicaris species were identified, each made up of taxa from different oceanic regions but showing relatively low COI divergence (0.35–1.90%). In Clade I, Rimicaris chacei and Rimicaris hybisae 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, Rimicaris exoculata and Rimicaris kairei are morphologically, genetically, and ecologically distinct, reflecting restricted connectivity between the MAR and the Carlsberg Ridge (CR)–Central Indian Ridge (CIR). In Clade III, Rimicaris variabilis and Rimicaris cf. variabilis 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 Rimicaris 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.