Markers
Ten different molecular techniques were reported in the literarure: allozymes, DNA sequencing, ddRAD, RAPD, ISSR, AFLP and RFLP, cariology, SNP and microsatellites (Fig. 3A). DNA sequences obtained via automated Sanger sequencing were the most commonly used type of molecular data (71% studies). Among DNA sequence markers, a total of 38 different genes were used; 16, 19 and 3 encoded in the mitochondrial, nuclear and chloroplast genomes, respectively. DNA sequencing of mitochondrial genes was by far the most used technique among all markers and across all studies (80%), followed by the DNA sequencing of nuclear (18%) and chloroplast-encoded markers (2%). Within the mitochondrial genome, the D-loop region and the COI DNA barcode marker were the most used marker (34% each), followed by the cytochrome B gene (15%). The number of articles using microsatellites or allozymes were similar (12% and 10%, respectively). The first allozyme study was published in 1991 (Aron & Solé-Cava, 1991; Russo & Solé-Cava, 1991) and the last in 2018 (Pazoto, Ventura, Duarte, & Silva, 2018). Only four articles (6%) targeted autotrophic organisms, two terrestrial vascular plants (mangroves) and two red macroalgae, and two of them used chloroplast-encoded markers (Ayres-Ostrock et al., 2019; Mori, Zucchi, Sampaio, & Souza, 2015). Only one more recent article used the SNP technique (Siccha-Ramirez et al., 2018).