High connectivity across the fragmented chemosynthetic ecosystems of the deepAtlanticEquatorialBelt: efficient dispersal mechanisms or questionable endemism?

Abstract

Chemosynthetic ecosystems are distributed worldwide in fragmented habitats harbouring seemingly highly specialized communities. Yet, shared taxa have been reported from highly distant chemosynthetic communities. These habitats are distributed in distinct biogeographical regions, one of these being the so-called Atlantic Equatorial Belt (AEB). Here, we combined genetic data (COI) from several taxa to assess the possible existence of cryptic or synonymous species and to detect the possible occurrence of contemporary gene flow among populations of chemosynthetic species located on both sides of the Atlantic. Several Evolutionary Significant Units (ESUs) of Alvinocarididae shrimp and Vesicomyidae bivalves were found to be shared across seeps of the AEB. Some were also common to hydrothermal vent communities of the Mid-Atlantic Ridge (MAR), encompassing taxa morphologically described as distinct species or even genera. The hypothesis of current or very recent large-scale gene flow among seeps and vents was supported by microsatellite analysis of the shrimp species Alvinocaris muricola/Alvinocaris markensis across the AEB and MAR. Two nonmutually exclusive hypotheses may explain these findings. The dispersion of larvae or adults following strong deep-sea currents, possibly combined with biochemical cues influencing the duration of larval development and timing of metamorphosis, may result in large-scale effective migration among distant spots scattered on the oceanic seafloor. Alternatively, these results may arise from the prevailing lack of knowledge on the ocean seabed, apart from emblematic ecosystems (chemosynthetic ecosystems, coral reefs or seamounts), where the widespread classification of endemism associated with many chemosynthetic taxa might hide wider distributions in overlooked parts of the deep sea.

Species are hypotheses: avoid connectivity assessments based on pillars of sand

“…Sampling is also an issue for species described as geographically restricted or ecologically specialized: sampling the targeted species and closely related taxa in other localities or habitats may help rejecting hypotheses of endemism and/or specialization. For example, recent molecular analyses revealed that chemosynthetic shrimp that were considered as distinct in cold seeps and hot vents actually corresponded to a single species with high gene flow across the Atlantic (Box 3; Teixeira et al 2013). A similar case was reported in a deep-sea mussel (genus Idas Jeffreys, 1876), where specimens sampled in a deep cold seep site and on vertebrate bones were previously falsely attributed to distinct species (Ritt et al 2012;Thubaut et al 2013).…”

Genetic population structure of four hydrothermal vent shrimp species (Alvinocarididae) in the Okinawa Trough, Northwest Pacific

“…longirostris showed no genetic differentiation among 3 vent sites in the Okinawa Trough (Hatoma Knoll, Izena Hole, and Irabu Knoll) and a seep site in Sagami Bay (the Off Hatsushima site). Similarly, no genetic differentiation was detected between local populations of alvinocaridids at seep sites in the Gulf of Mexico and West Africa, and the Logatchev vent field (Teixeira et al 2013). These results indicate that differences between vent and seep environments are not primary factors in determining the geographical distribution and genetic population structure of certain alvinocaridids.…”

“…Two species of Rimicaris shrimp, R. exoculata and R. kairei, also exhibit high haplotype diversity (0.69 to 0.89) in all local populations within their wide distributional range on the MAR and CIR, respectively (Teixeira et al 2011, Beedessee et al 2013. Moreover, a pair of synonymous species, A. muricola/markensis, which were suggested to exhibit connectivity across the Gulf of Mexico, the MAR, and West Africa, exhibit quite high haplotype diversity in each local population (0.80 to 0.91; Teixeira et al 2013). Populations of an undescribed Chorocaris shrimp, which are distributed in both the Manus and North Fiji basins in the SWP, also exhibit high haplotype diversity (0.70 to 1.00; Thaler et al 2014).…”

Exploring the Ecology of Deep-Sea Hydrothermal Vents in a Metacommunity Framework

“…For example, Young et al (2008) found a general southward pattern of migration along the northeast Pacific system, and larger effective population sizes of the siboglinid tubeworm Ridgeia piscesae in the southern populations compared to those in the north. Coalescent approaches have also been implemented to measure long-term migration rates in mollusk and polychaete species along the EPR (Plouviez et al, 2009(Plouviez et al, , 2010(Plouviez et al, , 2013, crustacean and mollusk species in the Indian Ocean ridges (Thaler et al, 2011;Beedessee et al, 2013;Chen et al, 2015), alvinocaridid shrimp from the MidCayman Spreading Center (Plouviez et al, 2015) and the Mid-Atlantic Ridge (Teixeira et al, 2012(Teixeira et al, , 2013. Despite the evident advantages of coalescent approaches over traditional Fstatistics, the migration estimates obtained through many of these approaches are considered long-term because of necessary equilibrium assumptions over the last ∼4N e generations (i.e., average time to coalescence).…”