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).