Biological invasions are increasingly recognized as a significant threat to marine biodiversity worldwide (Lallias et al., 2015). Invasions occur when species colonize areas beyond their natural range due to human behavior. The origin of this phenomenon dates back to interoceanic travel during colonization, when people began traveling great distances by boat for various reasons, including to move to new areas, trade, and make war. Over the past few centuries, population growth and globalization has increased travel and trade exponentially, resulting in greater maritime transport to meet rising global demands. However, despite this threat, understanding the ecological and evolutionary circumstances and implications of successful invasions is not well established.
One of the most important questions in invasion biology is why some species are successful at invasions and others are not (Schulz et al., 2019). Species typically remain restricted to their natural habitats due to their limited capacity for long-distance dispersal -often a consequence of short larval phases and/or a sessile or sedentary adult stage, which tends to restrict them to their native regions. Paradoxically, many documented cases of successful marine invasions involve species with limited dispersal (e.g., mollusks, crustaceans, ctenophores, cnidarians, tunicates). One explanation of this is that those with great dispersal capacities have dispersed as far as they can based on their fundamental niche. And, those invasions we do see are forced by the maritime activities over the past centuries in altering the distribution of taxa across large geographical scales (Goulletquer et al., 2002; Ruiz et al., 2000).
Transport of marine organisms occurs mainly through the attachment or embedding of organisms in the hulls of ships (biofilm), ballast water, or introduction for cultivation/aquarium purposes. While attachment events are centuries old, introducing the ballast water system at the end of the 19th century to improve the stability and buoyancy of ships is more recent and created an unprecedented problem related to biological invasions (Molnar et al. 2008). Although ballast water is a very efficient means for the long-distance transport of many organisms, surviving the conditions of these systems during long voyages can indicate a certain adaptive capacity, contributing to the success of introduction and subsequent establishment. Therefore, diapause eggs in many marine species, especially crustaceans, can be favorable (Ricciardi, 2011).
In contrast to the previously discussed vectors, potential invasions stemming from aquaculture introductions have received comparatively less attention. This is often attributed to the perception that aquaculture introductions result in lower propagule pressure or necessitate multiple introductions for successful establishment (Facon et al., 2003). However, it is important to note that a substantial proportion of invasive species originate, either directly or indirectly, from aquaculture (e.g., species from the genera Perna, Ostrea, Mytilus, Ruditapes, Crassostrea, Penaeus). Despite this, the literature addressing aquaculture-mediated invasions remains relatively limited (Aguirre-Pabón et al., 2015; Lallias et al., 2015; Voisin et al., 2005), as research has primarily focused on broader topics, including biology, ecology, and evolution (Roman and Darling, 2007; Lejeusne et al., 2014), transport mechanisms and geographic pathways (Hulme, 2009; Wilson et al., 2009), factors influencing invasion success (Williamson, 2006; Blackburn et al., 2015), spatial distribution prediction (Muirhead and MacIsaac, 2005; Floerl et al., 2009; Larson et al., 2014), and local ecological impacts (Dick et al., 2013; Alexander et al., 2014; Jeschke et al., 2014).
Regardless of the specific invasion scenario, a reduction in genetic diversity is generally anticipated due to the bottleneck effect, where only a limited subset of the source population's genetic variation is introduced (Dlugosch and Parker, 2008; Prentis et al., 2008). While some studies have shown that invasive species can establish and proliferate despite this reduced diversity (Genetic Paradox of Invasions; Frankham, 2004; Pérez et al., 2006; Roman and Darling, 2007; Hufbauer, 2008; Chandler et al., 2008), a substantial body of research highlights the significant role of propagule pressure and genetic mixing in driving invasion success (Oliveira et al., 2017; Darling et al., 2012; Ghabooli et al., 2011; Gillis et al., 2009; Dlugosch and Parker, 2008; Roman and Darling, 2007; Kolbe et al., 2004; Facon et al., 2003). These factors can effectively counteract the bottleneck effect, as evidenced by numerous studies that report comparable levels of genetic diversity between wild and introduced populations (Kelly et al., 2006; Rius et al., 2012, 2015b), even in controlled experiments with varying propagule pressure (Clark and Johnston, 2009; Hedge et al., 2012; Arnott, 2016).
Here we explore the genetics of the biological invasion of one of the most important commercial and aquaculture species worldwide, the tiger shrimp (Penaeus monodon). Penaeid shrimp are a group of decapods of significant commercial importance, distributed across tropical and subtropical regions worldwide, with the highest diversity found in the Indo-Pacific Ocean (Chan et al., 2008; Rajacumaran et al., 2014). This group includes the majority of shrimp species with high economic value, accounting for more than one-third of the annual wild crustacean catch. Additionally, over 20 species are critical to aquaculture. Despite their economic relevance, there is no consensus on the phylogeny of the Penaeidae family, and the taxonomic identification of some species remains uncertain (Samadi et al., 2016; Tavares and Gusmão, 2016; Ma et al., 2011).
At least 10 species within this family have been reported as invasive or exotic (Aguirre-Pabón et al., 2015; Wakida-Kusunoki et al., 2011; Quigley et al., 2013; Özcan et al., 2006). Some of these species, such as Penaeus monodon, P. japonicus, P. aztecus, P. semisulcatus, P. pulchricaudatus, Litopenaeus vannamei, Fenneropenaeus merguiensis, and F. indicus, were introduced for aquaculture purposes in various countries outside their wild ranges. They have since been reported in natural environments, likely due to accidental escapes from aquaculture facilities or dispersion from adjacent areas (Kampouris et al., 2018; Scannella et al., 2017; Aguirre-Pabón et al., 2015; Wakida-Kusunoki et al., 2011; Quigley et al., 2013; Özcan et al., 2006).
The tiger shrimp, P. monodon, is a wild species of the Indo-Pacific Ocean, distributed from Japan to Mozambique, including the islands of Australia, Indonesia, the Philippines, Malaysia, Sri Lanka, and Madagascar. This species was highly successful in aquaculture production during the 1970s and 1980s, leading to its introduction into many countries outside its wild range. In the Atlantic Ocean, it was introduced to the United States from Hawaii, with Hawaii receiving stocks from the Philippines, Tahiti, and Taiwan (DIAS, 2018). Similarly, P. monodon was introduced into Mexico (from Taiwan; DIAS, 2018), and Central and South America, including Panama, Colombia, Venezuela, and Brazil, from Taiwan and the Philippines (Ferreira et al., 2009; Álvarez-León and Gutiérrez-Bonilla, 2007). Additionally, Cuba received stocks from Ecuador (FAO, 2005).
The first report of P. monodon outside its wild range was made in 1987 in Tutoia, Brazil (Fausto-Filho, 1987), followed by a second report in 1988 in South Carolina, Georgia, and Northeast Florida. In this area, approximately 300 individuals recovered following an accidental escape from aquaculture in South Carolina months earlier (Fuller et al., 2014). The species reappeared in 2000, and between that year and 2002, it was reported again in Tutoia (Brazil; Santos and Coelho, 2002), as well as in Alagoas and Pernambuco (Brazil; Coelho et al., 2001), Amapá (Silva et al., 2002), and Puerto Rico (Ramos, 2002).
In subsequent years (2004–2007), P. monodon was reported in Venezuela, Colombia, Cuba, and the United States. By 2012, reports began to emerge from Central America, including Mexico, Guatemala, and Costa Rica. As of 2018, sightings and capture frequencies have been increasing throughout the Caribbean (Fig. 1). The species is now considered established in most areas of the Caribbean due to the rising catch rates and the presence of both mature and juvenile individuals, indicating successful completion of its reproductive cycle (Aguirre-Pabón et al., 2015; Fuller et al., 2014).
Most studies on the invasion process of P. monodon in the Atlantic Ocean consist of reports (see above), descriptions of its spatiotemporal distribution (Fuller et al., 2014; Giménez et al., 2014; Sandoval et al., 2014), and analyses of size frequency (Fuller et al., 2014). The only study to date using molecular markers was conducted by Aguirre-Pabón et al. (2015, 2023), which reported low genetic diversity based on mitochondrial DNA but moderate diversity using microsatellites. These findings suggest multiple introductions and diverse origins of the invasive population within its wild range in the Pacific Ocean, highlighting the role of aquaculture-related translocations in shaping the genetic structure of these populations.
Since reconstructing and understanding invasion mechanisms are crucial for developing strategies to mitigate future impacts (Pyšek and Richardson, 2010), this study employed mitochondrial DNA (COI) and microsatellites to reconstruct the invasion scenario of P. monodon in the Atlantic Ocean. The specific objectives were: (i) to infer the phylogenetic relationships of selected species within the Penaeidae family, with a primary focus on the divergence of P. monodon; (ii) to determine the genetic diversity and structure of the invasive population and its relationship to wild and domestic populations; and (iii) to decipher the role of aquaculture in the invasion process of P. monodon in the Atlantic Ocean.