Understanding diversity patterns, speciation, and biogeography of shallow-water marine organisms in the Atlantic realm

Since Charles Darwin's work in the 19th century, the formation of species (speciation) in the ocean has been a subject of ongoing debate. Marine species' ability to disperse, whether through swimming (as seen in fish) or via the drifting of larvae by oceanic currents, coupled with the seeming absence of physical barriers, poses a challenge to traditional ideas of speciation. With such extensive connectivity between distant places, it would seem difficult for isolation to occur, leading to the assumption that marine speciation would be rare. However, this is far from the case. Groups such as snails, crustaceans, and worms demonstrate remarkable species diversity, with thousands of species existing within these taxa. Interestingly, most species found in the Atlantic Ocean are unique and not observed in the Pacific or Indian Oceans. This distinctiveness is likely the result of tectonic, oceanographic, and climatic events that have shaped the region since the Miocene epoch, approximately 18 million years ago. However, the precise mechanisms and timing of species origin and extinction remain poorly understood. The MarDivA project aims to unravel the processes behind the origin and current diversity of species in the Atlantic, as well as the timing of these events. To achieve these objectives, researchers are using snails of the genus Haminoea as model organisms, examining their shells, morphology, DNA, and fossil records, combined with evolutionary theory. Key questions include: How many species exist, and why are some regions more diverse than others? Does speciation occur within the same area, or only when populations are isolated? Were certain time periods more conducive to speciation? And how might speciation be linked to climate change? These are some of the questions MarDivA aims to address. During the project's first year (September 2022–September 2023), over 150 specimens of Haminoea snails were DNA barcoded from across the genus’s geographic range, leading to the identification of about 19 species. To trace the evolutionary history of these species, the mitochondrial genome and selected nuclear genes of every species have been sequenced. An evolutionary tree is now being constructed to determine the relationships between species. Preliminary findings reveal that only one species of Caribbean affinities is also found on the Eastern Atlantic, specifically in the Cabo Verde Islands. In September 2024, the team conducted a field trip to this African archipelago to collect more samples, aiming to understand the factors behind this unique distribution and to explore the possibility of overlooked endemic species. Cabo Verde is known for its high rate of endemism, making it a prime location for such research. Simultaneously, the technical and pedagogical staff of the University Museum of Bergen and the Kystmuseet i Øygarden are collaborating on educational projects at both museums. These projects aim to reach out the general public in particularly school pupils and raise awareness about biodiversity's importance and conservation in our changing world.

Tectonic, oceanographic, and climatic events that occurred particularly between the Miocene and Pleistocene epochs (e.g., closure of the Tethys Sea, uplift of the Isthmus of Panama, Benguela current, intermittent opening of the Bering Strait, glacial cycles, sea-level oscillations), have contributed to shape the identity of the Atlantic biome. The impact of these events created opportunities for speciation and modified the barriers for species dispersal and consequently the distribution of species, leading to changes in biodiversity composition. Nevertheless, the effectiveness of these barriers and the timing of impacts on the rearrangement of biotic communities are still questioned and not fully understood particularly in soft-bottom shallow water faunas. The main objective of MarDivA is to understand the time and processes underlying the origin and diversification of Atlantic shallow-water species, using Haminoea gastropods as a case-study. A multidisciplinary approach using original morpho-anatomical data, micro-CT scan, phylogenetic inference based on mitogenomes, will be combined with biogeographic models, and oceanographic and historical climatic data, and used as a proxy to answer questions about the diversity and distribution of species, time, mode, and geography of speciation. This project builds, develop, and strengths capacities on areas of major relevance in biodiversity research, natural history museology, and societal concern, such as, the inventorying of global marine biological diversity, the origin and extinction of life in the Ocean and its relation with historical and current climatic events. Collaborative actions between museums (research and non-research institutions) are promoted and research data is used to establish educational programmes aiming to raise understanding and awareness among society.