Long-Range Dispersal and High-Latitude Environments Influence the Population Structure of a “Stress-Tolerant” Dinoflagellate Endosymbiont

<div><p>The migration and dispersal of stress-tolerant symbiotic dinoflagellates (genus <i>Symbiodinium</i>) may influence the response of symbiotic reef-building corals to a warming climate. We analyzed the genetic structure of the stress-tolerant endosymbiont, <i>Symbiodinium glynni</i><i>nomen nudum</i> (ITS2 - <i>D1</i>), obtained from <i>Pocillopora</i> colonies that dominate eastern Pacific coral communities. Eleven microsatellite loci identified genotypically diverse populations with minimal genetic subdivision throughout the Eastern Tropical Pacific, encompassing 1000’s of square kilometers from mainland Mexico to the Galapagos Islands. The lack of population differentiation over these distances corresponds with extensive regional host connectivity and indicates that <i>Pocillopora</i> larvae, which maternally inherit their symbionts, aid in the dispersal of this symbiont. In contrast to its host, however, subtropical populations of <i>S. glynni</i> in the Gulf of California (Sea of Cortez) were strongly differentiated from populations in tropical eastern Pacific. Selection pressures related to large seasonal fluctuations in temperature and irradiance likely explain this abrupt genetic discontinuity. We infer that <i>S. glynni</i> genotypes harbored by host larvae arriving from more southern locations are rapidly replaced by genotypes adapted to more temperate environments. The strong population structure of <i>S. glynni</i> corresponds with fluctuating environmental conditions and suggests that these genetically diverse populations have the potential to evolve rapidly to changing environments and reveals the importance of environmental extremes in driving microbial eukaryote (e.g., plankton) speciation in marine ecosystems.</p> </div

Biogeographic map of the eastern Pacific showing differentiated populations of <i>S. glynni</i>.

<p>Differentiated populations of <i>S. glynni</i> as determined by statistical analyses of microsatellite data. Open circles represent sampling locations with name abbreviations and arrows depict prevailing ocean currents: Gulf of California (GoC), Banderas Bay (BB), Gulf of Tehuantepec (OAX), Clipperton Atoll (CLP), Gulf of Panama (PAN) and Galapagos Islands (GAL). Populations in the subtropical Gulf of California (shaded in purple) were genetically distinct from tropical populations (orange). The left most Structure plot shows genetic homogeneity across <i>Pocillopora</i> type 1 populations throughout the eastern Pacific (data obtained from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0079208#B16" target="_blank">16</a>]). The inset panel in the upper right quantifies the instances where a cloned <i>S. glynni</i> genotype was found between geographically distant locations (proportions = individuals shared/total # unique MLGs between two locations). </p

Ten year averages of monthly means of SSTs and PAR for the six sampling locations.

<p>Ten year averages of monthly means (2000 - 2009) of sea surface temperatures (SSTs) and photosynthetically available irradiance (PAR) for the six sampling locations. (a) and (c) depict monthly averages and standard deviations at all locations, while (b) and (d) are box plots showing annual mean, first and third quartiles, and maximum and minimum seasonal ranges by location. Monthly averages were acquired from NASA’s Giovanni website.</p

Structure plot of <i>S. glynni</i> populations from the tropical and subtropical eastern Pacific.

<p>Structure plot of <i>S. glynni</i> populations based on allelic frequencies at 11 microsatellite loci. Each bar in the graph represents the probability that a sample belongs to a particular color-coded population. Each graph represents analyses for a particular number of populations (K) run under an admixture with a correlated allele frequency model. (a) Major differentiation occurred between the Gulf of California population and populations in the ETP (<i>k</i> = 2). (b) Additional clustering occurred in the ETP, yet did not correspond to location, depth or host morphospecies (<i>k</i> = 3).</p

BaumsEtAl_14_DRYAD_Sfitti_NetworkInputFile

Input file of Symbiodinium fitti unique multilocus genotypes for Network 4.6 (Fluxus Technoloy Ltd.). Default settings were used to construct median joining network

Symbiodinium fitti Structure input file

This files contains all unique, haploid Symbiodinium fitti multilocus genotypes as generated with 13 microsatellite loci by Baums et al. 2014 Mol Ecol. The file is in the format of a Structure input file

Symbiodinium fitti multilocus genotypes Structure parameters

This files contains the parameters for Structure analysis of Symbiodinium fitti multilocus genotypes by Baums et al. 201

Symbiodinium fitti multilocus genotypes

This file contains multilocus genotype data from 13 haploid microsatellite loci for Symbiodinium ITS-2 type A3, provisionally named Symbiodinium fitti. Please see ReadMe file for important information

Transects & Plots

Microsatellite data for 2006 transects and 2009 polar plots in the Gulf of California

Within Colony

Micrsatellite data for Pocillopora colonies sampled multiple times in 2006, 2007, 2008 & 2009