DOI: 10.5061/dryad.43hd6
title: Data from: Hybridization between two cryptic filamentous brown seaweeds along the shore: analysing pre- and post-zygotic barriers in populations of individuals with varying ploidy levels

description: We aimed to study the importance of hybridization between two cryptic
 species of the genus Ectocarpus, a group of filamentous algae with
 haploid-diploid life cycles that include the principal genetic model
 organism for the brown algae. In haploid-diploid species, the genetic
 structure of the two phases of the life cycle can be analysed separately
 in natural populations. Such life cycles provide a unique opportunity to
 estimate the frequency of hybrid genotypes in diploid sporophytes and
 meiotic recombinant genotypes in haploid gametophytes allowing the effects
 of reproductive barriers preventing fertilization or preventing meiosis to
 be untangle. The level of hybridization between E. siliculosus and E.
 crouaniorum was quantified along the European coast. Clonal cultures (568
 diploid, 336 haploid) isolated from field samples were genotyped using
 cytoplasmic and nuclear markers to estimate the frequency of hybrid
 genotypes in diploids and recombinant haploids. We identified admixed
 individuals using microsatellite loci, classical assignment methods and a
 newly developed Bayesian method (XPloidAssignment), which allows the
 analysis of populations that exhibit variations in ploidy level. Over all
 populations, the level of hybridization was estimated at 8.7%. Hybrids
 were exclusively observed in sympatric populations. More than 98% of
 hybrids were diploids (40% of which showed signs of aneuploidy) with a
 high frequency of rare alleles. The near absence of haploid recombinant
 hybrids demonstrates that the reproductive barriers are mostly
 post-zygotic and suggests that abnormal chromosome segregation during
 meiosis following hybridisation of species with different genome sizes
 could be a major cause of interspecific incompatibility in this system.
description: Genotypes
 sporophytesGenotypes of sporophytes
 individuals identified (based on diagnostic microsatellite, ITS1 and
 species-specific cytoplasmic marker) as E. siliculosus (Esil, n = 338) and
 E. crouaniorum (Ecro, n = 151). This identification was used previous to
 the admixture analyses. The number of samples in each population, name of
 the strain, ITS1 length (850 = Esil, &gt;1000 = Ecro) and positive
 amplification in the cytoplasmic marker (Esil = positive amplification
 Esil, Ecro = positive amplification Ecro) are shown. In diagnostic loci,
 the non-amplification in one of the parental species corresponds to a
 phylogenetic signal but should be distinguished from a null allele. To
 solve this problem, these missing data points were replaced by an
 artificial allele of an arbitrary size of (800bp). In contrast, missing
 data or null alleles were noted as 0.Genotype
 Sporophyte.xlsxGenotype
 gametophyteGenotypes of
 gametophytes individuals identified (based on diagnostic microsatellite,
 ITS1 and species-specific cytoplasmic marker) as E. siliculosus (Esil, n =
 158) and E. crouaniorum (Ecro, n = 176). This identification was used
 previous to the admixture analyses. The number of samples in each
 population, name of the strain, ITS1 length (850 = Esil, &gt;1000 = Ecro)
 and positive amplification in the cytoplasmic marker (Esil = positive
 amplification Esil, Ecro = positive amplification Ecro) are shown. In
 diagnostic loci, the non-amplification in one of the parental species
 corresponds to a phylogenetic signal but should be distinguished from a
 null allele. To solve this problem, these missing data points were
 replaced by an artificial allele of an arbitrary size of (800bp). In
 contrast, missing data or null alleles were noted as 0.Genotype
 Gametophyte.xlsx