Abstract
The Indian Ocean is the least known ocean in the world with the biogeography of marine species in the West Indian Ocean (WIO) understudied. The hydrography of WIO is characterized by four distinct oceanographic systems and there were few glacial refugia formations in the WIO during the Pleistocene. We used the widely distributed intertidal barnacle Tetraclita to test the hypothesis that the distribution and connectivity of intertidal animals in the WIO are determined by the major oceanographic regime but less influenced by historical events such as Pleistocene glaciations. Tetraclita were studied from 32 locations in the WIO. The diversity and distribution of Tetraclita species in the Indian Ocean were examined based on morphological examination and sequence divergence of two mitochondrial genes (12S rDNA and COI) and one nuclear gene (histone 3, H3). Divergence in DNA sequences revealed the presence of seven evolutionarily significant units (ESUs) of Tetraclita in WIO, with most of them recognized as valid species. The distribution of these ESUs is closely tied to the major oceanographic circulation systems. T. rufotincta is distributed in the Monsoonal Gyre. T. ehsani is present in the Gulf of Oman and NW India. Tetraclita sp. nov. is associated with the Hydrochemical Front at 10°S latitude. T. reni is confined to southern Madagascan and Mauritian waters, influenced by the West Wind Drift. The endemic T. achituvi is restricted to the Red Sea. Tetraclita serrata consists of two ESUs (based on mtDNA analysis) along the east to west coast of South Africa. The two ESUs could not be distinguished from morphological analysis and nuclear H3 sequences. Our results support that intertidal species in the West Indian Ocean are associated with each of the major oceanographic circulation systems which determine gene flow. Geographical distribution is, however, less influenced by the geological history of the region.
Highlights
The West Indian Ocean (WIO) consists of the Indian Ocean, the Arabian Sea and two evaporative basins, the Red Sea and the Persian Gulf, supporting high diversity of marine fauna [1,2]
During the Pleistocene glaciations, the Red Sea was isolated as the shallow connection between the Red Sea and Arabian Sea was constricted by the formation of land bridges, resulting in high endemism in the Red Sea [7]
Morphological Diversity of Tetraclita Species in the WIO We have identified six species of Tetraclita in the WIO, including one undescribed species, based on morphological approach
Summary
The West Indian Ocean (WIO) consists of the Indian Ocean, the Arabian Sea and two evaporative basins, the Red Sea and the Persian Gulf, supporting high diversity of marine fauna [1,2]. From 158–160 mya, India, Seychelles and Madagascar were part of the same continent and drifted from East Africa. From 84–96 mya, the India-Seychelles continent was separated from Madagascar and drifted northwards, along the east African coast [4]. On the East African coast, Zanzibar Island and Mafia Islands were separated from the shallow waters in the Pleistocene [4]. The Persian Gulf was completely dry during the glacial period due to its shallow depth. It was repopulated by Indo-Pacific biota after the connection with the Indian Ocean was reestablished [5]. During the Pleistocene glaciations, the Red Sea was isolated as the shallow connection between the Red Sea and Arabian Sea was constricted by the formation of land bridges, resulting in high endemism in the Red Sea [7]
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