Literature synthesis
Phylogeography was conceived as a science in 1987, since then the number
of publications has grown exponentially. In Brazil, the first two marine
phylogeographic studies were both published in 1991 using allozymes
(Aron & Solé-Cava, 1991; Russo & Solé-Cava, 1991). New publications
have increased ever since. The years 2016 and 2018 presented the highest
number of Brazilian marine phylogeographic publications to date (15
articles). Considering the 16 taxonomic groups assessed in this study,
fishes have been the most studied taxon, accounting for 33% of all
publications. This is more than the second and third most studied taxa
combined (crustaceans 21%, mollusks 9%). A conspicuous publication
bias towards fish phylogeographic studies is observed in the literature
globally. Beheregaray (2008) reviewed all phylogeographic articles
published between 1987 and 2006 and fishes were ranked second, after
mammals, as the taxonomic group with the largest number of publications
without much difference whether they were freshwater (45%) or marine
species (55%). Turchetto-Zolet et al. (2013) reviewed all
phylogeographic articles published on South America terrestrial and
freshwater biota between 1987-2011 and reported fishes as the second
ranked taxonomic group (13%) together with overall invertebrates and
second only to plants (17%). This bias towards fishes is probably due
to their economic importance as human food and ecotourism, relative
easier taxonomic identification, simple life-cycle and ploidy, the
availability of well-suited genetic markers, and probably, the existence
of a large number of hired expertise in research institutions.
Differently, otaries, Kinorhynchs and flatworms presented very localized
sampling due to low number of publications (one each).
The numbers of marine vertebrate and invertebrate studies in Brazil were
quite even, 47% and 49%, respectively. This is opposite to what was
recorded by Beheregaray (2008) and Turchetto-Zolet et al. (2013) who
observed a bias towards vertebrate studies, 57% and 70% respectively.
The number of marine plants and algae studies in Brazil were quite
underrepresented (4%) as they are in terrestrial and freshwater
autotrophic species in South America (1% algae in Turchetto-Zolet et
al., 2013), terrestrial and marine plants in eastern North America (11%
in Soltis et al., 2006) and world widely in general (2% reported in
Beheregaray 2008). In the past, the disparity between the number of
phylogeographic studies between heterotrophic x autotrophic species was
attributed in part to the faster mutation rates observed in animal
markers (mitochondrial genome) compared to markers available for plant
studies (Soltis et al., 2006). An increase in the number of studies
addressing macroalgal phylogeography would improve our understating of
population genetic histories and marine phylogeography considering they
are poorly-dispersers (Kinlan & Gaines, 2003), potentially being able
to identify a larger number of local and regional BGF and concordant
phylogeographic patterns.
The first study using genotypic data addressing the phylogeography of a
Brazilian marine species was published in 1998 (Secchi et al., 1998), 11
years after the Avise’s seminal 1987 publication. Before 1998, the only
six phylogeographic studies (= four articles) addressing Brazilian
marine biota used phenotypic (isozyme) data. In Brazil mitochondrial
genotypic data started being utilized first in the form of
fragment-based methods (e.g. Secchi et al., 1998). Between 2007-2010,
RAPD, AFLP, RFLP and similar fragment-based techniques played an
important role increasing the number of publications. Microsatellites
remain a poorly used technique with only 29 studies (12%) published
since 2001 (Beheregaray & Sunnucks, 2001). A similar pattern was
observed for genome-wide techniques, such as SNPs, where only one marine
study was published to date (Siccha-Ramirez et al., 2018). In the world,
genome wide SNP and high-throughput DNA sequencing techniques are
becoming the powerhouse in phylogeographic studies (e.g. ddRadseq, B.
Peterson, Weber, Kay, Fisher, & Hoekstra, 2012).
The two most well sampled and phylogeographically well studied
geopolitical states were Rio de Janeiro and São Paulo, which happens to
be the two richest states and the ones that hold the largest number of
research universities in the country, followed by Bahia (the state with
the longest coastline). The relationship between number of
phylogeographic studies and economic affluence is a well-known worldwide
pattern in the phylogeographic literature (reported in Beheregaray,
2008; Turchetto-Zolet et al., 2013). The weaker studied regions of
Brazil are those located in the extreme northern and southern reaches of
the country, where physical accessibility is challenging. Particularly
the northernmost reaches, along the Amazonian Rainforest coastline
towards Amapá, west of Belém (48° 29’ 25” W) where nearly nothing is
known about the phylogeographic structure of any coastal marine species.
The mouth of the Amazon river is considered a strong BGF in coastal
South America but studies that attributed it to explain genetic
discontinuities used populations samples thousands of kilometers apart
across the western Atlantic Ocean (e.g. Caribbean versus Brazilian
population (see de Souza et al., 2015; Nauer et al., 2019; Santos,
Hrbek, Farias, Schneider, & Sampaio, 2006).