1 INTRODUCTION
In marine species, the phylogeography and genetic differentiation were
influenced by historical events, including ocean current systems,
vicariance, Pleistocene climatic cycles, and life-history
characteristics of organisms (Liu et al., 2007; Ding et al., 2018). It
is worth noting that some marine fishes have fragile genetic structure
due to their extensive larval and adult dispersal (Ashrafzadeh et al.,
2021; Caccavo et al., 2018). Climate oscillations during the Pleistocene
greatly altered the environment of marginal seas of the western Pacific,
including the South China Sea (SCS). During glacial periods, the SCS
formed a semi-enclosed sac-shaped gulf and exposed approximately 0.7
million km2 of continental shelf (Wang & Sun, 1994).
Previous molecular studies have shown that many marine fishes with high
mobility exhibit low genetic structure in the SCS, such asCirrhimuraena chinensis (Li et al., 2014) and Nuchequula
mannusella (Gao et al., 2019). The phylogeographic study of marine
fishes alive in the SCS has particular significance for interpreting the
consequences of past events, geological configurations, and modern
oceanographic aspects in this environment (He et al., 2010).
Lagocephalus spadiceus is a non-toxic Lagocephalus species
(Tuney, 2016), belonging to Tetraodontiformes, Tetraodontidae, andLagocephalus . It is a nearshore warm-water demersal fish that
inhabits depth between 3 to 200 meters (Tuncer et al., 2008),
distributed along the southern coast of Africa in the Indian Ocean,
eastward to the Indonesia and the Philippines of the Pacific Ocean, and
northward to the coast of China (Liu et al., 2016). In China, it occurs
along the coastal areas of the SCS. Almost L. spadiceus is
imported from China in Japan (Yamaguchi et al., 2013), but this also
makes it an easy target for widespread exploitations. Recently, since
the continuous increase in fishing intensity and deteriorating
environmental conditions, the wild resources of L. spadiceus have
been drastically reduced (Hardy et al., 2014). There are fewer reports
on germplasm resource and genetic diversity evaluation of L.
spadiceus . To better protect and rationally develop the wild germplasm
resources of L. spadiceus , it is imperative to conduct a genetic
diversity assessment to establish a theoretical basis for the scientific
conservation and sustainable utilization of its genetic resources.
Genetic diversity is a vital component of biodiversity and prerequisite
for the continuous adaptation of species or populations to environment
change and survival evolution. Species with a higher genetic diversity
possess a greater ability to environmental changes (Roldan et al.,
2000). Mitochondrial DNA (mtDNA) constitutes a tiny fraction of
organismal genome size but has been widely used as a marker of molecular
diversity in animals for the past four decades (Galtier et al., 2009).
This tool has been widely embraced by population geneticists, following
the works of Avise et al (1987) and Moritz et al (1987), among others.
Experimentally, mtDNA is present in most cells in high copynumber and is
relatively easy, rapid, and inexpensive to sequence (Zink &
Barrowclough, 2008). Due to the relationship between the rate and time
of evolution, effective information sites are different, and their
resolving power is different. Therefore, concatenating COI and
Cyt b markers can increase the number of effective genetic sites,
resulting in more accurate and effective information compared to single
gene analysis (Halasan et al., 2021; Barrientos-Villalobos &
Schmitter-Soto, 2019).
Our study examines the phylogeography, population genetic diversity, and
demographic history of L. spadiceus using COI and Cytb gene datasets. As of current knowledge, there has not been a
documented report on the population genetic of L. spadiceus . This
study aims to address the lack of information on L. spadiceus in
the region by providing a comprehensive background report. Meanwhile,
our study has contributed to a better understanding of the evolutionary
process that have influenced the phylogeography of coastal marine fishes
in China.