Depth-dependent gene flow in Gulf of Mexico cold seep Lamellibrachia tubeworms (Annelida, Siboglinidae)

Lamellibrachia vestimentiferan tubeworms form aggregations at hydrocarbon cold seeps in the deep Gulf of Mexico (GoM), creating structures that provide living space for other fauna. In the GoM, three Lamellibrachia taxa vary in morphology and depth ranges: Lamellibrachia luymesi (300-950 m), Lamellibrachia sp. 1 (950-2,604 m), and Lamellibrachia sp. 2 (1,175-3,304 m). While Lamellibrachia sp. 2 is consistently identified as a separate species, L. luymesi and sp. 1 cannot be discriminated using barcoding markers cytochrome oxidase subunit 1 (COI) and large ribosomal subunit rDNA (16S). To determine if limited gene flow was a factor in the formation of these taxa, we employed more quickly evolving markers, including mitochondrial cytochrome B (CYTB), hemoglobin subunit B2 intron (HbB2i), and six polymorphic microsatellites; microsatellites were amplified across 45 L. luymesi and sp. 1 individuals. Additionally, we used microsatellites to ask whether populations of Lamellibrachia sp. 1 and sp. 2 show evidence of significant structure. Despite a lack of resolution seen with CYTB and HbB2i, L. luymesi and sp. 1 form genetically differentiated clusters at the cross-amplified microsatellites. Furthermore, we find no evidence for population structure for either Lamellibrachia sp. 1 or sp. 2 across the GoM.