DOI: 10.5061/dryad.bvq83bk8w
title: Barriers in a sea of elasmobranchs

description: Background The interplay of animal dispersal and environmental
 heterogeneity is fundamental for the distribution of biodiversity on
 earth. In the ocean, the interaction of physical barriers and dispersal
 has primarily been examined for organisms with planktonic larvae. Animals
 that lack a planktonic life stage and depend on active dispersal are
 however likely to produce distinctive patterns. Methods We used available
 literature on population genetics and phylogeography of elasmobranchs
 (sharks, rays and skates), to examine how marine barriers and dispersal
 ecology shape genetic connectivity in animals with active dispersal. We
 provide a global geographic overview of barriers extracted from the
 literature and synthesize the geographic and hydrologic factors, spatial
 and temporal scales to characterize different types of barriers. The three
 most studied barriers were used to analyse the effect of elasmobranch
 dispersal potential and barrier type on genetic connectivity. Results We
 characterized nine broad types of marine barriers, with the three most
 common barriers being related to ocean bathymetry. The maximum depth of
 occurrence, maximum body size and habitat of each species were used as
 proxies for dispersal potential, and were important predictors of genetic
 connectivity with varying effect depending on barrier type. Environmental
 tolerance and reproductive behaviour may also play a crucial role in
 population connectivity in animals with active dispersal. However, we find
 that studies commonly lack appropriate study designs based on a priori
 hypotheses to test the effect of physical barriers while accounting for
 animal behaviour. Main conclusions Our synthesis highlights the relative
 contribution of different barrier types in shaping elasmobranch
 populations. We provide a new perspective on how barriers and dispersal
 ecology interact to rearrange genetic variation of marine animals with
 active dispersal. We illustrate methodological sources that can bias the
 detection of barriers and provide potential solutions for future research
 in the field.
description: Peer-reviewed
 publications that reported intra-specific genetic or genomic
 differentiation in one or more elasmobranch species were obtained via the
 online search engines Google Scholar and Web of Science by entering
 combinations of the key words, ‘shark’, ‘ray’, ‘genetic*’, ‘genomic*’,
 ‘phylogeograph*’, ‘population structure’, ‘connectivity’ (until 16 January
 2020) and were screened to discover additional publications. Obligate
 fresh-water species were excluded. Additional information was compiled on
 the taxonomy and biology (<i>maximum depth of occurrence</i>,
 <i>maximum body size</i>, and <i>habitat</i>) for
 each elasmobranch species from secondary literature and fishbase.org
 (Ebert <i>et al.</i> 2013; Last <i>et al.</i>
 2016; Weigmann 2016; Froese & Pauly. 2018). Elasmobranch habitat
 was described as one of three broad categories: 1. Benthopelagic habitat
 on the continental shelves and upper slopes, 2. neritic habitat of the
 water column above the continental shelves and upper slopes, 3. oceanic
 habitat including the pelagic and deep sea. Finally, we extracted
 information on the type and number of genetic markers used to study
 elasmobranch population genetic structure from the primary
 literature. Genetic
 comparisons across barriers were then extracted from the publications. A
 genetic comparison was recorded as a single data point if sampling design
 was adequate to formally test for intra-specific genetic differentiation
 across a single barrier. Sampling was considered adequate if there was at
 least one sampling location with a minimum of five samples on either side
 of a barrier and there were no other barriers that could simultaneously
 act on the genetic differentiation between the same locations. Genetic
 differentiation between the locations must have been statistically
 assessed using pairwise fixation or differentiation indices between
 individual locations or analysis of molecular variance (AMOVA) between
 groups of sampling locations (Weir & Cockerham 1984; Excoffier,
 Smouse & Quattro 1992; Meirmans & Hedrick 2011). Pairs of
 locations that lack any physical barriers between them and are separated
 by the same or smaller geographic distances than locations on either side
 of a barrier of interest can be used as controls because genetic
 differences are likely caused by geographic distance alone, not a barrier.
 Therefore, data points of significant genetic differences across barriers
 were not included if authors also reported significant differences between
 control locations, because differences could be caused by geographic
 distance, the barrier, or both. Data points were also excluded if
 behaviour, specifically reproductive philopatry, was identified as the
 main driver of genetic differentiation between locations on either side of
 a physical barrier in question. They were excluded to avoid bias in our
 synthesis because it is not possible to distinguish between the effect of
 a physical barrier or behaviour on genetic differentiation if not
 explicitly tested for separately. We then synthesized information on the
 barriers extracted from the literature to characterized different barrier
 types based on similarity of the geographic and hydrologic factors that
 form each barrier, their geographic scale, time scale and temporal
 variability. Detailed information on each barrier and source references
 are reported in the Appendix 1 Table A3 of the main manuscript (Global
 Ecology and Biogeography: Barriers in a sea of elasmobranchs: From
 <i>fishing</i> for populations to testing hypotheses in
 population genetics).
description: This data set forms part of the manuscript <b>Barriers in a
 sea of elasmobranchs: From <i>fishing</i> for populations to
 testing hypotheses in population genetics</b> submitted to
 <i>Global Ecology and Biogeography.</i> The
 data set was used to create the figures, tables and models reported in the
 main text and the Appendix 1 of the main manuscript. Please also refer to
 the main manuscript and the <i>Dryad Data Description</i>
 section for additional information. <b>The data
 set contains three documents:</b> 
 <strong>Readme file</strong> (this document):
 ReadMe_Hirschfeld_et_al2021_Barriers_in_a_sea_of_Elasmobranchs.docx) <strong>A data base</strong> in .csv format: (Hirschfeld_et_al2021_Barriers_in_a_sea_of_Elasmobranchs_data.csv) curated for and used to construct the figures, tables and data analyses reported in the main manuscript of the article and the supplementary information. See a description of each column in the data set below. <strong>R Markdown document:</strong> <i>Hirschfeld_et_al2021_Barriers_in_a_sea_of_Elasmobranchs_SuppInfo.pdf</i>. This document contains background information, a description of the data set and information on any missing data points as well as an annotated R code of the analyses used to produce the models and graphical output that were included in the main manuscript.