Abstract
The native ranges and invasion histories of many marine species remain elusive due to a dynamic dispersal process via marine vessels. Molecular markers can aid in identification of native ranges and elucidation of the introduction and establishment process. The supralittoral isopod Ligia exotica has a wide tropical and subtropical distribution, frequently found in harbors and ports around the globe. This isopod is hypothesized to have an Old World origin, from where it was unintentionally introduced to other regions via wooden ships and solid ballast. Its native range, however, remains uncertain. Recent molecular studies uncovered the presence of two highly divergent lineages of L. exotica in East Asia, and suggest this region is a source of nonindigenous populations. In this study, we conducted phylogenetic analyses (Maximum Likelihood and Bayesian) of a fragment of the mitochondrial 16S ribosomal (r)DNA gene using a dataset of this isopod that greatly expanded previous representation from Asia and putative nonindigenous populations around the world. For a subset of samples, sequences of 12S rDNA and NaK were also obtained and analyzed together with 16S rDNA. Our results show that L. exotica is comprised of several highly divergent genetic lineages, which probably represent different species. Most of the 16S rDNA genetic diversity (48 haplotypes) was detected in East and Southeast Asia. Only seven haplotypes were observed outside this region (in the Americas, Hawai’i, Africa and India), which were identical or closely related to haplotypes found in East and Southeast Asia. Phylogenetic patterns indicate the L. exotica clade originated and diversified in East and Southeast Asia, and only members of one of the divergent lineages have spread out of this region, recently, suggesting the potential to become invasive is phylogenetically constrained.
Highlights
Numerous marine species have dispersed and established extensively throughout the world via marine vessels over the past several centuries (Banks et al, 2015; Carlton, 1987; Carlton & Iverson, 1981)
The final 16S rDNA gene dataset excluding redundant sequences consisted of 81 taxa (51 in the L. exotica clade and 30 in the L. cinerascens clade)
The best model selected for the 16S rDNA + 12S rDNA concatenated dataset was TPM2uf + I + (BIC weight 0.31)
Summary
Numerous marine species have dispersed and established extensively throughout the world via marine vessels over the past several centuries (Banks et al, 2015; Carlton, 1987; Carlton & Iverson, 1981). The native ranges and invasion histories of a large number of them, remain elusive (i.e., they are cryptogenic), as a result of one or more of the following: inadequate taxonomy; poor historical documentation ( for older introductions); presence of cryptic lineages; and multiple inputs of invaders (Carlton, 1996; Carlton, 2009). The supralittoral isopod Ligia exotica Roux, 1828 represents a case of a widespread cryptogenic taxon with an old, albeit poorly documented, history of human-assisted dispersal (recognized as exotic in the type locality since its original description), as well as a highly problematic taxonomy. Known as wharf roach, this isopod has a wide tropical and subtropical distribution, and is considered an alien species in different regions of the world, where it is frequently found in harbors, and ports, and other man-made structures (Schmalfuss, 2003; Taiti et al, 2003; Van Name, 1936; Yin et al, 2013). With the exception of Ligia oceanica, an endemic of the Atlantic coast of Europe that has been introduced into some localities in the northern Atlantic coast of the US (Richardson, 1905), all other coastal species of Ligia (∼30) do not appear to have been moved by humans, or at least not to as many geographically distant places as L. exotica (Schmalfuss, 2003)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
