Phylogeography of a pan-Atlantic abyssal protobranch bivalve: implications for evolution in the Deep Atlantic

Abstract

The deep sea is a vast and essentially continuous environment with few obvious barriers to gene flow. How populations diverge and new species form in this remote ecosystem is poorly understood. Phylogeographical analyses have begun to provide some insight into evolutionary processes at bathyal depths (<3000 m), but much less is known about evolution in the more extensive abyssal regions (>3000 m). Here, we quantify geographical and bathymetric patterns of genetic variation (16S rRNA mitochondrial gene) in the protobranch bivalve Ledella ultima, which is one of the most abundant abyssal protobranchs in the Atlantic with a broad bathymetric and geographical distribution. We found virtually no genetic divergence within basins and only modest divergence among eight Atlantic basins. Levels of population divergence among basins were related to geographical distance and were greater in the South Atlantic than in the North Atlantic. Ocean-wide patterns of genetic variation indicate basin-wide divergence that exceeds what others have found for abyssal organisms, but considerably less than bathyal protobranchs across similar geographical scales. Populations on either side of the Mid-Atlantic Ridge in the North Atlantic differed, suggesting the Ridge might impede gene flow at abyssal depths. Our results indicate that abyssal populations might be quite large (cosmopolitan), exhibit only modest genetic structure and probably provide little potential for the formation of new species.

Diversity, distribution and spatial structure of the cold-water coral fauna of the Azores (NE Atlantic)

“…This is in line with previous surveys of deep-sea fauna at the MAR, which did not report any marked cross-ridge differences in species composition for bathypelagic (Sutton et al, 2008) and demersal fish . However, we cannot rule out the possibility that the MAR may pose an obstacle to east-west dispersal, especially in lower bathyal (Gebruk et al, 2010) and abyssal fauna (McClain et al, 2009b;Etter et al, 2011). The scarcity of records for these depths in our data set does not allow investigating this hypothesis.…”

Plasticity in shell morphology and growth among deep-sea protobranch bivalves of the genus Yoldiella (Yoldiidae) from contrasting Southern Ocean regions

“…These influences are the likely drivers of observed plasticity and ecophysiological responses (through growth and shell production), and represent how the studied species can adapt to contrasting conditions. Previous studies on small deep-sea protobranchs have discovered modest genetic structuring over large geographic distances at abyssal depths with evidence of restricted gene flow in the more heterogeneous bathyal depths or vast geographic distances in excess of 8000km (Etter et al, 2005;Zardus et al, 2006;Etter et al, 2011). The unique free-swimming lecithotrophic pericalymma larval form of protobranch bivalves is suggested to be capable of dispersing over long distances (Allen and Sanders, 1996;Zardus, 2002).…”

New genus of opecoelid trematode from Pristipomoides aquilonaris (Perciformes: Lutjanidae) and its phylogenetic affinity within the family Opecoelidae

“…if N. lanceolata does not represent a species complex, host-parasite systems in the deep-sea would seem to follow the same pattern exhibited by free-living deepsea organisms, i.e. genetic divergence is much greater between populations at different depths than with those separated geographically at the same depth (see Etter et al 2011). Manter (1966 suggested the same pattern for the cold-water adapted derogenid Derogenes varius (Müller, 1784), which is a common shallow-water parasite of fishes at higher latitudes and probably has a continuous, world-wide distribution in deeper waters.…”