Molecular evidence of distinct evolutionary units in the sandhopper Talorchestia capensis (Amphipoda, Talitridae) along South African coasts

Abstract

Marine geographical and ecological barriers often reflect intraspecific genetic discontinuities among populations which may experience different selective pressures and undergo evolutionary divergence. While the phylogeography of marine intertidal invertebrates across the Atlantic/Indian Ocean transition received more attention, the population genetic structures of supralittoral direct developers across such transition area have been poorly investigated. Sandhoppers are supralittoral invertebrates characterised by a direct developmental mode (low dispersal ability), and Talorchestia capensis (Amphipoda, Talitridae) represents the most abundant species of sandhoppers along the South African coasts. To define population structure of T. capensis, we used a mitochondrial marker (the cytochrome oxidase subunit I gene, COX1). T. capensis showed a clean population structure with three main haplogroups genetically well separated, although this separation is not perfectly in line with geographical boundaries described for this area. The presence of separate evolutionary significant units is also confirmed by the shape of mismatch distribution, as well as the p distance values among groups. The overall results confirm the importance of mtDNA to retrieve information on the evolutionary history of species. This study suggests the evidence of a complex-species for this sandhoppers, which have never been considered before, providing fundamental basis for further studies.

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“…The presence of cryptic lineages in southern African Ligia are also in accordance with recent studies reporting the presence of possible cryptic species among other groups of coastal invertebrates along the coastline of South Africa (Baldanzi et al 2016;Evans et al 2004;Ridgway et al 2001;Teske et al 2006;Teske et al 2007;Zardi et al 2007). To date, deeply divergent mitochondrial lineages have been reported for four other South African coastal crustacean species.…”

“…Teske et al (2006) studied the phylogeographic patterns for three coastal crustaceans (Exosphaeroma hylecoetes, Iphinoe truncata, and Upogebia africana) and reported not only the presence of multiple, deeply-divergent lineages within each of these species, but also a lack of correspondence in the geographic distributional breaks between the species. More recently, Baldanzi et al (2016) reported the presence of multiple evolutionary lineages within another coastal crustacean, the amphipod Talorchestia capensis, and found phylogeographic breaks that did not correspond with those observed by Teske et al (2006). Similar observations have been made for other coastal invertebrates (Evans et al 2004;Ridgway et al 2001;Teske et al 2007;Zardi et al 2007).…”

“…Considering that cryptic diversity has been reported for other coastal invertebrates around the world (e.g. Chan et al 2007;Hurtado et al 2013;Radulovici et al 2009;Santamaria et al 2017;Santamaria et al 2016;Santamaria et al 2014;Santamaria et al 2013;Varela & Haye 2012), the findings of Teske et al (2006) and Baldanzi et al (2016) suggest other coastal organisms in South Africa, particularly those with low vagility, may harbor previously unreported cryptic diversity. Studying such organisms may thus further our understanding of the biogeographic patterns of southern Africa and possibly uncover new taxa.…”

“…Teske et al (2006), using the same region of the mitochondrial COI gene as used in this study, uncovered three cryptic lineages each for the coastal isopod Exosphaeroma hylecoetes and for the cumacean Iphinoe truncata, and two such lineages for the decapod Upogebia africana. More recently, Baldanzi et al (2016) used a similar approach to Teske et al (2006) to study the coastal amphipod Talorchestia capensis, reporting the presence of at least three deeply-divergent lineages in this species. As with Ligia, the lineages reported for these species were largely geographically isolated and non-overlapping.…”

“…Other similar models that differ mostly by recognizing additional overlap zones, also exist (see Teske et al 2006). One positive aspect of these competing biogeographic models of the South Africa coastline has been to stimulate recent research focusing on whether the distributional patterns of genetic variance within coastal organisms match the proposed biogeographic regions (Baldanzi et al 2016;Evans et al 2004;Ridgway et al 2001;Teske et al 2006;Teske et al 2007;. Incongruent results between studies; however, underscore the need for additional research that may help further our understanding of coastal processes and their role in driving diversification along southern African shores.…”