Population genetic structure of the abyssal grenadier (Coryphaenoides armatus) around the mid-Atlantic ridge H. Ritchie a,n , N.J. Cousins b , S.J. Cregeen a,1 , S.B. Piertney a a Institute of Biological and Environmental Sciences, University of Aberdeen, Zoology Building, Aberdeen AB24 2TZ, UK b Oceanlab, University of Aberdeen, Newburgh, Aberdeenshire AB41 6AA, UK article info Keywords: Coryphaenoides armatus Population differentiation Microsatellite Gene flow Mid-Atlantic Ridge Abyssal grenadier abstract Understanding the factors that affect the levels and distribution of genetic diversity in oceanic and deep sea environments is a central focus in marine population genetics. Whilst it has been considered that the oceans represent a homogenous environment that would facilitate dispersal and minimise population structure, it is now clear that topographical features and current patterns can influence the extent of spatial gene flow and promote significant population genetic divergence even at local scales. Here we examine patterns of population genetic structure among N. Atlantic populations of the cosmopolitan abyssal grenadier Coryphaenoides armatus in relation to two hypothesised barriers to gene flow—the mid-Atlantic Ridge and the Charlie-Gibbs Fracture Zone/Sub-Polar Front. A suite of microsatellite markers were developed to examine the spatial pattern of allelic variation among 210 individuals from ten sampling locations encompassing sites east and west of the MAR and north and south of the CGFZ, plus a geographically distinct sample of individuals from the Crozet Islands in the Indian Ocean. Considerable genetic diversity was detected among individuals (n a ¼5 À13 and H O ¼0.46 À0.69 across populations) but with an overall lack of genetic divergence between populations. Pairwise estimates of divergence among NE Atlantic samples were small and non-significant (max F ST ¼0.04) and Structure-based Bayesian analysis of genetic clusters returned no distinct population structure. The only indication of genetic structure was between the Atlantic and Indian Oceans, with F ST estimates of ca. 0.05. Patterns of genetic diversity and divergence are discussed in relation to what has been resolved in Coryphaenoides congeners, and what is known about the life history and ecology of C. armatus. Crown Copyright & 2013 Published by Elsevier Ltd. All rights reserved. 1. Introduction A long-held perception in marine population genetics was that intra-specific genetic differentiation should be minimal given the homogeneous nature of the marine environment (Pampoulie et al., 2004) and a concomitant high potential for gene flow (McMillen- Jackson et al., 1994). However, the burgeoning number of popula- tion genetics studies focused on marine species have overturned this view, resolving a variety of patterns of genetic structure underpinned by the interplay of life history, oceanography, seabed topology and variation in selection pressure over macro- and micro-geographic scales (Bowen and Avise, 1990; Banks et al., 2007; Papetti et al., 2012; Andrade and Solferini, 2007). Studies on species from bathyal, abyssal and hadal zones are scarce relative to intertidal, coastal and near-coastal species, but the highly speciose nature of the deep sea environment implies that there are barriers to gene flow which partition genetic variation. What data are available provide a mixed picture. For example, blue hake (Antimora rostrata), orange roughy (Hoplostethus atlanticus) and the hydrothermal vent shrimp species (Rimicaris exoculata) show no genetic structure over large spatial scales (White et al., 2011b; White et al., 2009; Teixeria et al., 2012, res- pectively). Conversely, the deep-water demersal fish tusk (Brosme brosme) shows genetic heterogeneity indicative of spatial differen- tiation where bathymetric barriers may be limiting adult migration (Knutsen et al., 2009). Genetic structure has also been shown among populations of the bluemouth (Helicolenus dactlopterus) (Abiom et al., 2005) and the hydrothermal vent tubeworm, Ridgeia piscescie (Young et al., 2008). In many cases where genetic structure has been detected, the often limited nature of most deep-sea sampling compared with shallow water studies precludes an ability to tease apart the different stochastic and deterministic processes that may drive the observed patterns. There is, however, a growing understanding of how major oceanographic processes and topographic factors could influence the patterns of dispersal and gene flow in abyssal species. The distribution and dispersal of faunal communities are significantly Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsr2 Deep-Sea Research II 0967-0645/$ - see front matter Crown Copyright & 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dsr2.2013.06.014 n Corresponding author. Tel.: +44 01224 273270. E-mail address: r01hr12@abdn.ac.uk (H. Ritchie). 1 Present address: Ocean and Earth Science, National Oceanography Centre, University of Southampton, Waterfront Campus, Southampton SO14 3ZH, UK. Please cite this article as: Ritchie, H., et al., Population genetic structure of the abyssal grenadier (Coryphaenoides armatus) around the mid-Atlantic ridge. Deep-Sea Res. II (2013), http://dx.doi.org/10.1016/j.dsr2.2013.06.014i Deep-Sea Research II ∎ (∎∎∎∎) ∎∎∎–∎∎∎