Ecological dispersal barrier across the equatorial Atlantic in a migratory planktonic copepod

Resolving the large-scale genetic structure of plankton populations is important to understanding their responses to climate change. However, few studies have reported on the presence and geographic extent of genetically distinct populations of marine zooplankton at ocean-basin scales. Using mitochondrial sequence data (mtCOI, 718 animals) from 18 sites across a basin-scale Atlantic transect (39 N–40 S), we show that populations of the dominant migratory copepod, Pleuromamma xiphias, are genetically subdivided across subtropical and tropical waters (global FST = 0.15, global Phi-ST = 0.21, both P < 0.00001), with a major genetic break observed in the equatorial Atlantic (between gyre FCT and Phi-CT = 0.23, P < 0.005). This equatorial region of strong genetic transition coincides with an area of low abundance for the species. Transitional regions between the subtropical gyres and the equatorial province also harbor a distinct mitochondrial clade (clade 2), have higher haplotype and...