Abstract
Laonice Malmgren, 1867 (Annelida: Spionidae) is a common polychaete genus in the deep-sea. Although most species are quite well studied morphologically, fragmentation and other damage that occurs during sampling often hampers morphological species identification of deep-sea specimens. In this study, we employ three molecular markers (16S, COI and 18S) to study the biodiversity and the distribution patterns of Laonice from the tropical North Atlantic and the Puerto Rico Trench. Based upon different molecular analyses (Automated Barcode Gap Discovery, pairwise genetic distances, phylogenetics, haplotype networks) we were able to identify and differentiate eight Laonice species. Up to four of these species co-occurred sympatrically at the same station. The majority of species were found at multiple stations and two species in the eastern as well as western Atlantic had ranges of up to 4,000 km. Genetic differentiation across these extensive geographic distances was very low. Surprisingly, one 16S haplotype was shared between individuals 2,776 km apart and individuals from the Caribbean and the abyssal plain in the eastern Atlantic (>3,389 km) differed in only a single mutation in 16S. Our results suggest that members of this genus successfully disperse across large geographic distances and are largely unaffected by topographic barriers.
Highlights
Spionidae Grube, 18501 is one of the most abundant and diverse groups of polychaetes and occur in almost all marine habitats, from shallow waters to the deep-sea[2]
The abyssal Atlantic Ocean is divided by the Mid-Atlantic Ridge (MAR) longitudinally into eastern and western basins[17]
The first morphological studies rejected a barrier effect of the MAR on the distribution of selected widespread spionid species in the abyss of the tropical North Atlantic, though other species were found to be limited to either side of the MAR24
Summary
Spionidae Grube, 18501 is one of the most abundant and diverse groups of polychaetes and occur in almost all marine habitats, from shallow waters to the deep-sea[2]. The spionid genus Laonice Malmgren, 18676 is well studied, especially species from the deep sea of the North Atlantic[7–10]. Our study area encompasses the abyssal eastern and western basins in the tropical North Atlantic along the Vema Fracture Zone as well as the Puerto Rico Trench. The first morphological studies rejected a barrier effect of the MAR on the distribution of selected widespread spionid species in the abyss of the tropical North Atlantic, though other species were found to be limited to either side of the MAR24. The aim of this study is to investigate the diversity and distribution of Laonice from the tropical North Atlantic and the Puerto Rico Trench with molecular tools and further assess the potential barrier effect of the MAR on abyssal spionid taxa
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