Biogeography of Phallusia nigra: is it really black and white?
Invasive invertebrate species often have a large effect on native organisms by shifting species interactions and community organization (Strayer et al., 2011). The correct identification of invasive species is critical for their management and eradication given that unique biological characteristics of the species, such as timing of reproduction and physiological tolerances, are important for management strategies. Ascidians (Chordata, Tunicata) are invertebrate chordates that compose a major part of benthic ecosystems globally and have recently been a major focus of invasive species studies due to increasing numbers of reported invasions (Lambert, 2007; Rius et al., 2008; Dupont et al., 2009; Lejeusne et al., 2011). Ascidians are potent biofoulers and effective invaders because sessile adults and free-swimming tadpole larvae can be transported to new areas through human vectors such as boat hulls, ballast waters, and aquaculture (Lambert, 2002, 2007).
Efforts to correctly identify species in this group are not trivial. Historical taxonomic descriptions of species within the ascidians are not always straightforward (Stefaniak et al., 2009), and there may be significant morphological variation within a single species (Lopez-Legentil and Turon, 2006). Additionally, present taxonomic descriptions may be inadequate for the separation of some ascidian species, as molecular data have uncovered unexpected cryptic diversity even in well-studied ascidian species (Tarjuelo et al., 2001; Caputi etal., 2007; Iannelli et al., 2007b; Perez-Portela and Turon, 2008; Bock et al., 2012; Perez-Portela et al, 2013). However, rigorous morphology-based taxonomy is still central to the initial identification of an organism and can be utilized in conjunction with molecular studies (Schlick-Steiner et al, 2007; Shenkar and Swalla, 2011). Genetic markers combined with morphological character analysis have been instrumental in distinguishing native ascidians from invaders (Nishikawa et al, 2014).
Phallusia nigra is one example of a widely distributed species. It is a solitary ascidian with a striking smooth black tunic usually devoid of epibionts, and a large size, up to 10 cm (see Fig. 1). It lives in tropical waters at shallow depths on hard or rocky substrates, and is very common on artificial substrates. P. nigra was originally described in the early 1800s from the Red Sea, but has been reported in many tropical and subtropical locations since then. It has been reported in the Mediterranean Sea (Izquierdo-Munoz et al, 2009), the Red Sea (Savigny, 1816; Shenkar et al, 2008; Shenkar, 2012), the Pacific Ocean (Abbott et al, 1997; Hirose, 1999; Lambert, 2003), the Indian Ocean (Michaelson, 1919; Monniot and Monniot, 1997; Subba Rao, 2005; Abdul Jaffar Ali and Sivakumar, 2007; Abdul Jaffar Ali et al, 2009), Gulf of Guinea (Millar, 1965), Angola (Millar, 1965), and widely in the west Atlantic Ocean and the Caribbean (Rocha et al, 2005; Mendiola et al, 2006; Bonnet and Rocha, 2011; Carman et al., 2011) (see Fig. 3A). Though its native range is not known, P. nigra has been described as an introduced species in the Pacific (De Felice et al, 2001), in the Indian Ocean (Abdul Jaffar Ali et al, 2009), and in the Mediterranean Sea (Cinar et al, 2006; Shenkar et al. 2008; Izquierdo-Munoz et al, 2009; Kondi-latos et al., 2010), and it has been labeled as either native (Galil, 2007) or cryptogenic (Galil, 2007; Rocha et al, 2012) in the western Atlantic.
Reports of the geographical distribution of P. nigra are complicated by this species' many synonyms: Ascidia nigra Heller, 1878, Ascidia atra Lesueur, 1823, Ascidia somalensis Sluiter, 1905, Phallusia atra Traustedt, 1882, Phallusia violacea Gould, 1852, Phallusiopsis nigra Hartmeyer, 1909, Thallusia nigra Hartmeyer, 1908, Tunica nigra Hilton, 1913; but most reports in the last 70 years have used either Ascidia nigra or Phallusia nigra, with a preference for Phallusia in recent years (Shenkar and Swalla, 2011). Further compounding the difficulty of identifying P. nigra in the field are two other species in the genus Phallusia that also have darkly pigmented tunics and whose geographical range partially overlaps with that of P. nigra: Phallusia philippinensis (Millar, 1975) and Phallusia fumigata (Gruber, 1864) (see Fig. 1). Phallusia fumigata has been described as native to the Mediterranean (Peres, 1958), though it is also found in the Atlantic, on the French coast along the English Channel (Harant and Vernieres, 1933) where it is typically found in shallow waters (up to 50-m depth) in rock crevasses among sponges (Hircinia spp.) or algae (Codium bursa). P. fumigata is referred to as the black bottle tunicate (Harant and Vernieres, 1933), and its dark pigmentation can be seen all over the body or concentrated in the anterior or exposed area (though very young specimens may have a predominantly light coloration). P. philippinensis also has a tunic that is dark (from black-brown to gray), but usually not as opaque as that of P. nigra. It is found on coarse sediment of coral habitats in the Indo-Pacific (Monniot and Monniot, 2001).
Since P. nigra has been repeatedly reported as introduced in many localities and a morphological comparison between populations of black Phallusia from Japan and the Caribbean coast of Panama by the authors has revealed important distinctive characteristics, we hypothesized that some of the previous reports might not be accurate. In this study, we compared individuals from different populations of the three darkly pigmented Phallusia species and detail major morphological characters to distinguish them. We also sequenced the 18S ribosomal subunit DNA and cytochrome oxidase B (cyt-B) from individual ascidians from populations of P. nigra, P. fumigata, and P. philippinensis. Published genetic data for this genus are limited, with only 6 of the 19 recognized species in this genus represented in GenBank, and there has not been wide-scale sequencing of mitochondrial or nuclear genes of Phallusia until now.
Our results show that Phallusia nigra occurs in the Red Sea, Singapore, and the West Atlantic, but it has been confused with both P. fumigata and P. philippinensis in other regions. In Japan and Hawaii, what has been reported as P. nigra is actually P. philippinensis. We provide molecular sequences as well as detailed taxonomic descriptions of the three darkly pigmented Phallusia species, which we hope will be useful for future studies seeking to report occurrences and locations of P. nigra, P. fumigata, and P. philippinensis.
Materials and Methods
Morphological comparisons included individuals of Phallusia with dark tunics from Brazil (Rio de Janeiro), Panama (Bocas del Toro, Caribbean coast), Israel (Eilat), Singapore, Japan (Okinawa), Taiwan, Hawaii, Australia, and the Mediterranean (Spain and France). All specimens were deposited at the Ascidiacea collection of the Zoology Department, Federal University of Parana, Brazil (DZUP). We obtained samples for molecular analysis from the Atlantic and greater Caribbean (Florida, Brazil, and Panama), the Mediterranean Sea (Greece), Singapore, Japan, and the Red Sea (Eilat, Israel). The specimens from the Red Sea can be regarded as topotype specimens of Phallusia nigra. Tissue samples were stored in 95% ethanol until DNA was extracted.
DNA extraction, polymerase chain reaction, and sequencing
Genomic DNA was extracted using DNeasy Blood and Tissue Kit (Qiagen, Valencia, CA). Though cytochrome oxidase subunit I (COI) is a commonly used mitochondrial gene in barcoding studies, it did not readily amplify in our samples; however, we successfully amplified cytochrome oxidase B, another commonly used mitochondrial marker. Cytochrome oxidase B (cyt-B) was amplified by modifying PCR conditions previously described (Stefaniak et al, 2009), using forward primer 5'TGRGGNCARATGWSNTTYTG3' and reverse primer 5'GCKAANARRAARTAYCAYTC3'. 18S ribosomal DNA was amplified utilizing primers as previously described (Swalla et al., 2000): 18S-A 5'CAGCAGCGCGGTAA TTCCAGCTC3', 18S-BS 5'CCTGGTTGATCCTGCCAG3' 18S-B 5'AAAGGGCAGGGACGTAATCAACG3', 18S-PH 5'TAATGATCCATCTGCAGGTTCACCT3'. PCR amplifications were carried out in 25-[micro]J reactions containing 0.2 mmol [l.sup.-1] each dNTP (Qiagen, Valencia CA), 1.0 [micro]g each primer, 1X GoTaq Flexi buffer (Promega Corp. Madison, WI), 1.5 mmol [l.sub.2] Mg[Cl.sub.2], 0.5 [micro]l of GoTaq Flexi polymerase (Promega Corp. Madison, WI), and 25-50 ng total DNA. Samples that did not amplify initially were amplified in 25-[micro]l reactions containing 12.5 [micro]l of PrimeSTAR MAX DNA Polymerase Premix (Clontech Laboratories, Mountain View, CA), 5.5 [micro]l water, 1.0 [micro]g each primer, and 25-50 ng total DNA. Cycling conditions for PrimeSTAR MAX reactions are 35 cycles of 10 s denaturing at 98 [degrees]C, 15 s annealing at 48 [degrees]C, and 10 s elongation at 72 [degrees]C. Cycling conditions for GoTaq Flexi polymerase amplifications of cyt-B consist of an initial denaturing step of 4 min at 94 [degrees]C, followed by 60 cycles of 10 s denaturing at 94 [degrees]C, 30 s annealing at 47 [degrees]C, and 50 s elongation at 72 [degrees]C, with a final elongation of 10 min at 72 [degrees]C. Cycling conditions for GoTaq Flexi polymerase amplifications of 18S ribosomal DNA consist of an initial denaturing step of 4 min at 94 [degrees]C, followed by 35 cycles of 1 min denaturing at 94 [degrees]C, 1 min annealing at 47 [degrees]C, and 1.5 min elongation at 72 [degrees]C, with a final elongation of 10 min at 72 [degrees]C. PCR product was extracted from the agarose gel using Illustra GFX PCR DNA and Gel Band Purification Kit (GE Healthcare, Pittsburgh, PA). DNA sequencing was performed using BigDye3.1 (Life Technologies, Carlsbad, CA) with a 3130 DNA analyzer (Life Technologies, Carlsbad, CA) in the UW Biology Department Comparative Genomics Center.
Sequence alignments and phylogenetic analysis
18S ribosomal DNA and cyt-B sequences were edited in MacVector (MacVector Inc., Cary, NC) and aligned using MAFFT (Katoh and Standly, 2013). Bayesian analysis was performed using Mr. Bayes 3.1.2 (Ronquist and Huelsenbeck, 2003) using a general time reversible (GTR) model (nst = 6) with gamma-distributed rate variation across sites and a proportion of invariable sites (rates = invgamma) run for 1,000,000 Markov chain Monte Carlo generations, sampling every 5000 generations with a burn-in of 25%. Resulting trees were visualized in FigTree ver. 1.3.1 (Rambaut, 2009). Numbers of variable and informative sites were generated using PAUP (*) ver. 4.0b10 (Swofford, 2002). Divergences of cyt-B sequences within and between clades were estimated using uncorrected pairwise distances (p-distances) calculated in MEGA 5.2.2 (Tamura et al, 2011). Outgroups and other Phallusia sequences were obtained from GenBank. GenBank accession numbers for cyt-B: Ciona intestinalis, NC_004447.2; Ciona savignyi, NC_004570.1; Phallusia nigra (India), JN791272; Phallusia mammillata, NC_009833; Phallusia fumigata, NC_009834; Ascidiella aspersa, NC_021469. GenBank accession numbers for 18S ribosomal DNA: Phallusia nigra (Mediterranean coast of Israel), FM244845.1; Phallusia nigra (India), JN791272.1; Phallusia mammillata, AF236803.2; Phallusia fumigata, FM244844.1; Corella eumyota, FM244846.1; Ascidia ceratodes, L12378.2; Chelyosoma siboja, AF165821.2; Megalodicopia hians, AB075543.1; Corella inflata, AY903930.1.
Based on morphological and molecular characters, the Phallusia reported in the Pacific (Hawaii, Japan, Taiwan, and Australia) are Phallusia philippinensis. We have no evidence that Phallusia nigra is present in Hawaii or Okinawa, Japan, while P. nigra and P. philippinensis co-occur in Singapore. Atlantic populations of dark Phallusia, as well as the Red Sea populations, were all P. nigra. Mediterranean specimens from Spain and France were Phallusia fumigata.
Although P. nigra, P. philippinensis, and P. fumigata show external resemblance when fixed (Fig. 1), the dissection and study of internal characters revealed morphological differences that made the identification of the species straightforward, including the musculature pattern on the right side of the body, presence of projections on the peripharyngeal groove, presence of secondary papillae on the pharynx, and size and position of the alimentary canal (Table 1).
A close observation of living adult specimens also shows some differences (Fig. 1, Table 1): P. nigra is really black, with short siphons positioned close, the oral siphon curved dorsally and almost touching the atrial siphon, the lobes of the siphons rarely seen. P. philippinensis is more brownish, with more distant siphons and conspicuous siphon lobes. P. fumigata is also brownish or grayish, has a wrinkled tunic with small papillae around the oral siphon, the siphons are longer and distant from each other, and part of the body is usually found inside crevices. Since descriptions available in the literature are not detailed, especially for P. nigra and P. fumigata, we describe the three species based on the material studied.
Phallusia nigra Savigny, 1816 (Fig. 1, top row)
Examined material. DZUP-PHA-34 Marina Bocas, Bocas del Toro, Panama--7 ind; 20/vi/2011; Collector Rosana Rocha. DZUP-PHA-33 Meia-Lua Bay, Pargos Island, Cabo Frio, Rio de Janeiro, Brazil--7 ind; 30/iii/2011; Col. Rosana Rocha. DZUP-PHA-01 Forno Beach, Arraial do Cabo, Rio de Janeiro, Brazil--2 ind; 04/2002; Col. Rosana Rocha. DZUP-PHA-35 St John Island, Singapore--1 ind.; 1l/vii/2012; Col. Serina Lee. DZUP-PHA 048-051 Kisoski Marina, Eilat, Israel--4 ind.; 20/iii/2014; Col. Gretchen Lambert.
Individuals are up to 10 cm long with the oral siphon usually curved dorsally. The animals attach themselves by the posterior left region and usually attain a vertical upright position. The tunic is black and smooth without encrustations. The oral siphon is apical with 8-10 lobes and the atrial siphon is very close to it, with 8-12 lobes, but in some specimens these lobes are very shallow or absent. The right side musculature is formed by both longitudinal and transverse fibers, the longitudinal wider and running toward both the endostyle and the posterior region, the transverse forming a dense mat underneath the longitudinal fibers. There are oblique fibers extending from the atrial siphon and from the region posterior to it, which cross transverse fibers. On the left side, there are only short longitudinal muscles extending from the oral and atrial siphons and ending before the gut loop. There are 35-115 oral tentacles of three sizes, the larger 2.5-5.5 mm long. There are papillae in the prepharyngeal area. The peripharyngeal groove has two smooth margins and forms a rounded area around the dorsal tubercle, which has a U-shaped opening. The neural gland duct has 10-40 accessory apertures on the left side, and only two animals (in 16) had 79 and 136. The pharynx has 75-121 longitudinal vessels on the right side. The alimentary canal is large and occupies more than 2/3 of the left side. The anterior margin of the intestinal loop reaches the base of the atrial siphon. The intestine is isodiametric, though some individuals have a slightly dilated secondary loop or rectum; however, this may be due to the presence of food in the gut, and the intestine never forms a sac-like structure.
Phallusia philippinensis (Millar, 1975) (Fig. 1, middle row)
Examined material. DZUP-PHA-32 Kaneohe, Hawaii--7 ind; 14/iii/2012. Col. Euichi Hirose. DZUP-PHA-30 Penghu, Taiwan--1 ind; 09/iii/2011; Col. Shih-Wei Su. DZUP-PHA-36; DZUP-PHA-37; DZUP-PHA-38; DZUP-PHA-39 Padang Buoy, Singapore--4 ind; 23/vii/2012; Col. Serina Lee. DZUP-PHA-31 Toya Fishery Port, Okinawa-Jima, Japan--7 ind; 08/iv/2011; Col. Euichi Hirose. DZUP-PHA-44 Magnetic Island, Australia--3 ind., 18/xi/2011; Col. Mari Carmen Pineda.
Individuals are up to 6.5 cm long and attach themselves by the posterior left region, usually attaining a vertical upright position. The tunic is dark or light brown, with encrustations only at the fixation base. The oral siphon is apical with 6-10 lobes and the atrial siphon is in the mid dorsal line, with 6-8 lobes. The right side musculature is formed mainly by longitudinal fibers extending from both oral and atrial siphons. From the oral siphon, the ventral ones are shorter and end in the first 1/3 of the body length, while the middle are longer and end before the base of the atrial siphon. The longitudinal fibers extending from the atrial siphon end in the posterior margin. The transverse fibers are more internal and extend between the dorsal and ventral margins. On the left side, there are longitudinal muscles extending only from the oral siphon and ending before the gut loop. There are 30-57 oral tentacles of four sizes with very small ones (not counted) among the larger, which are 2.5-5.5 mm long. There are papillae in the prepharyngeal area. The peripharyngeal groove has two margins, the anterior one with projections. It forms a V around the dorsal tubercle, which has a U-shaped opening with inrolled ends. The neural gland duct has 20-45 accessory apertures on the left side, with four individuals (in 17) having less than 20. The pharynx has 46-63 longitudinal vessels. The alimentary canal is large and occupies more than 2/3 of the left side. The anterior margin of the intestinal loop reaches beyond the base of the atrial siphon. The intestine is isodiametric, though some individuals have a slightly dilated secondary loop; this may be due to the presence of food in the gut, and the intestine never forms a sac-like structure.
Phallusia fumigata (Grube, 1864) (Fig. 1, bottom row)
Examined material. CRBA-3353 Punta Sarnella, Port de la Selva, Spain--1 ind.; 12/iv/1981; CRBA-3084 Punta Sarnella, Port de la Selva, Spain--1 ind; 22/iii/1981; Col. Joan Cervantes. DZUP PHA47, Port Vendres, France-1 ind.; 28/vii/1992; Col. Rosana M. Rocha.
Individuals are up to 8 cm long. The animals attach themselves inside crevices by the posterior region, leaving only the siphons projecting above the substrate. The tunic is dark brown or gray only in exposed parts, with thicker left side and small papillae along the oral siphon. The oral siphon is apical with 8 lobes, and the atrial siphon is posterior to the mid dorsal line, with 6 lobes. The right side musculature is formed mainly by transverse fibers extending between the dorsal and ventral margins, in the first half. Posterior to the base of the atrial siphon, the transverse fibers are shorter and divide in two marginal bands lining the central region without muscles. Longitudinal fibers extending from the oral siphon are very delicate and end before the level of the atrial siphon. There are 31-33 oral tentacles of four sizes, the larger 2.5-4 mm long. There are papillae in the prepharyngeal area. The peripharyngeal groove has two smooth margins. It forms a V around the dorsal tubercle, which is heart-shaped. We counted 32 and 48 accessory apertures on the left side in the two animals from Spain. The pharynx has 58-67 longitudinal vessels on the right side, with intermediate small papillae between transverse vessels. The alimentary canal occupies half of the left side and is covered by numerous renal vesicles. The anterior margin of the intestinal loop reaches the base of the atrial siphon. The intestine is isodiametric.
The detailed descriptions given in this study show that the position of the atrial siphon, pattern of body musculature, and size of the digestive tract are easily identifiable characters that can be observed by removing the animal from its tunic. A further character to differentiate P. nigra from P. philippinensis is the presence of small projections along the peripharyngeal groove in the latter, while P. fumigata is the only of these three species to have intermediate papillae inside the pharynx. All the mentioned characters are constant in all individuals dissected. The number of oral tentacles and longitudinal vessels were larger in P. nigra, but these characters usually increase in number as animals get larger, and smaller P. nigra could have the same numbers as the other species. The number of accessory apertures proved to be too variable to be reliable as a distinguishing character and its range overlaps among species.
Figure 2 shows a phylogenetic tree constructed with cyt-B sequences (see Table 2 for GenBank accessions). The samples that are the true P. nigra are from the Red Sea, Singapore, and Caribbean Panama, Florida, and Brazil; they form a monophyletic clade with high support. The Phallusia samples we obtained from Greece genotyped as P. fumigata when compared to sequences from GenBank (Iannelli et al, 2007a). Sequences of P. philippinensis cyt-B obtained from the two locations in Japan (East Okinawa: Atta Fishery Port, dark gray boxes; West Okinawa: Toya Fishery Port, light gray boxes) do not fall into discrete clades on the tree, indicating that gene flow between the western and eastern sides of the island of Okinawa may be occurring or has occurred in the recent past. There is also a clade from West Okinawa that clusters with high support and may be indicative of a separate population or subspecies of P. philippinensis, but further genetic analysis may be needed to confirm whether this clade of Phallusia in West Okinawa is distinct.
The number of variable characters in available cyt-B sequences of phlebobranch ascidians was 260 out of 419 characters, with 220 sites being parsimony-informative. The number of variable sites in available 18S sequences of phlebobranch ascidians was 256 out of 1715 characters, with 166 sites being parsimony-informative. Because there were so few parsimony-informative characters in phlebobranch 18S sequences, the tree has less resolution, but is available in the appendix (Fig. Al). The maximum genetic divergence (uncorrected p-distances) observed among all taxa was 0.3808 between the Ciona clade and P. nigra. Genetic distances between each Phallusia species ranged from 0.2653 between P. nigra and P. philippinensis to 0.3288 between P. philippinensis and the clade that includes P. mammillata (Table 3). There was little variation within cyt-B for P. nigra (0.0053), whereas P. philippinensis had the highest within-species variation in the Phallusia (0.0941).
The phylogenetic tree of relationships using 18S ribosomal subunit sequences shows P. nigra from the western Atlantic and P. philippinensis from Okinawa as a polytomy with two Phallusia samples from GenBank from India and the Mediterranean coast of Israel, while P. philippinensis from Singapore clusters with P. fumigata in the tree (appendix Fig. A1). We believe that the lack of informative sites in the 18S gene sequences of the available plebobranchs (166 out of 1715 characters) is the reason that the relationships within the Phallusia in the I8S tree differ from those in the cyt-B tree (220 parsimony-informative sites out of 419 characters). We analyzed concatenated sequences using both genes with the same prior probabilities and models of Bayesian inference. The concatenated sequences recovered the relationships between taxa that are well-supported in the cyt-B tree, and the monophyly of P. philippinensis was restored (data not shown). We conclude that the relationships between the three black Phallusia species shown in the cyt-B tree are the best phylogenetic reconstruction hypothesis available with our data.
An investigation of the reported distribution of the three s pec ies revealed that although P. nigra has been reported worldwide, P. philippinensis has been found only in the Indo-Pacific, and P. fumigata is a European species (Fig. 3A). Figure 3B shows the di stribution of s peci mens th at were sequenced for this study, with their identification confirm ed by rigorous morphological or genetic analyses. Note the co-occurrence of P. nigra and P. philippinensis in Singapore (Lee et al., 2013). All other populations formerly identified as P. nigra in the Indo-Pacific as ide from those in Singapore are actually P. philippin ensis, and the specimens from Greece are P. fumigata. We also report the first confirmed occurrence of P. philippinen sis in Australia, where it was found in a marina in Magnetic Island, Queensland.
The detection of introduced species is not a trivial quest and may be hampered by the lack of historical surveys in a region to the date of arrival of a new species. Poor taxonomy has been recognized as a primary source of the non-recognition of the introduced status of a species (Chapman and Carlton, 1991). In some cases, isolated populations of a widespread species are described as different "native" species; in others, similar species are named as one cosmopolitan invasive species (exampl es in Carlton, 2009). Ascidians are a prevalent group of invaders in both tropical and temperate marine habitats (Lambert, 2007; Pineda et al., 2011), but invasions by this group are often difficult to characterize because morphological plasticity within a species is not unusual (Olson, 1986 ; Marks, 1996 ; Tarjuelo et al., 2004; Lopez-Legentil et al., 2005 ; Hirabayashi et al., 2006). Additionally, studies analyzing mitochondrial markers and other molecular method s have revealed cryptic speciation in a number of well-known species (Tarjuelo et al., 2001 ; Caputi et al., 2007; Hirose et al., 2009; Bock et al., 201 2; Perez-Portela et al., 2013).
Using a combination of morphological characters and molecular data, we show that the putatively cosmopolitan phlebobranch ascidian Phallusia nigra is not as widespread as previously thought and that reports of this species in Greece, Japan, Taiwan, and Hawaii are likely to be incorrect. Morphology and the genetic markers s howed that West Atlantic and Red Sea animals belong to the same species, and since Phallus ia nigra is the only Phallus ia species listed in the Red Sea (Shenkar, 2012) (type locality), there is no doubt in the identificati on of Atlantic samples.
Given morphological distinctions and amounts of genetic variance between Phallusia clades (between 0.2755 and 0.3288), we are confident that the three dark Phallusia included in our study represent different species. Pairwise distances have been used to analyze differences between and within mitochondrial gene sequences to distinguish ascidian species or confirm that individuals from multiple sampling localities represent the same species (Nydam and Harrison, 2010; Smith et al., 2012). Within-species variation of the dark Phallusia was relatively low (p-distances: 0.0053 for P. nigra, 0.0181 for P. fumigata, and 0.0941 for P. philippinensis). It is interesting to note that P. nigra specimens have the lowest p-distances between individuals but the broadest geographical range of the dark Phallusia (Red Sea, West Atlantic, and Singapore).
Although the original description of P. nigra from the Red Sea (type locality) is very simple, a few characters permit its identification: the brilliant black tunic, smooth and without incrustations; the pattern of left body musculature; and the position of the atrial siphon in relation to the intestinal loop (Savigny, 1816: 163, pl. II, fig 2; pl. IX, fig 1). Further, Monniot (1972) compared P. nigra specimens from Bermuda and Suez Canal and found the only difference to be a lobed anus rim in the Suez samples, while the Bermuda P. nigra had a smooth anus rim. The anus was found to be lobed in P. nigra from both Panama and Brazil, which is more similar to the characteristics of P. nigra from the Suez Canal.
We report that although P. philippinensis is found exclusively in the Pacific, its geographical range may be increasing via human vectors. It was described from the Philippines, and in the same study Millar (1975) comments that samples from Arafura Sea (Tokioka, 1952) and Singapore resembled his specimens slightly. Kott (1985) did not agree and created the species P. millari that accommodated both Arafura and Singapore specimens. In 1997 this species was collected again outside the Philippines, this time in Palau on a boat hull (Monniot and Monniot, 2001). The first report in Japan was by Hirose (1999) of animals collected in Gi-nowan Port Marina, Okinawa Island (as P. nigra in that study). Previous monographs on ascidian fauna of Japan did not mention any Phallusia species (Tokioka, 1963; Nishikawa, 1991). In Hawaii the first evidence of the presence of a black ascidian is a picture taken in Pearl Harbor in the 1930s (Carlton and Eldredge, 2009). Abbott et al. (1997) did not explicitly categorize the black Phallusia as introduced or invasive to the Hawaiian Islands, though others have (De Felice et al., 2001). Recently (2011) P. philippinensis was collected from a pier in Magnetic Island, Australia. The species had already been listed by Kott (2005) in the Great Barrier Reef (Queensland) as a junior synonym of P. arabica, but her description of P. arabica shows many differences between those species, mainly in the color of the animal, muscular pattern, presence of a rectum dilation, and a very lobed anus. Thus, it seems that the synonymy does not hold and this is the first report of P. philippinensis in Australia. Evidence accumulated up to this point (lack of previous reports of this animal in well-studied areas and the prominent presence of the species in marinas and on piers) suggests that P. philippinensis is an introduced species in most of its current known Pacific range (Hawaii, Palau, Japan, and Australia).
The first report of P. nigra in the Mediterranean was by Peres (1958) for the Israeli coast, and the species seems to have slowly spread toward the north since then. Recently Izquierdo-Munoz et al. (2009) reviewed the reports of introduced ascidians in the Mediterranean and concluded that P. nigra occurred only in Israel, Lebanon, and Turkey. Kondilatos et al. (2010) report the presence of P. nigra in Rhodes Island, Greece, but they did not describe the specimens in sufficient detail for us to confirm this report. The picture provided by Kondilatos et al. is more similar to P. nigra than to P. fumigata, but the perils of identifying these species by photographs are obvious. We did not obtain any samples from the Mediterranean that were P. nigra; instead, the samples that we sequenced from Greece were P. fumigata, although they were sent to us labeled as P. nigra, which demonstrates the difficulty of identifying these darkly pigmented Phallusia using external features (e.g., coloration). A study similar to what we have done in the Pacific should be undertaken in the Mediterranean since P. nigra seems to be slowly spreading from the initial establishment in the Israeli coast. The single "P. nigra" cytochrome oxidase B sequence in GenBank (which is unpublished) is from India and groups in our molecular trees with P. mammillata, suggesting that this sequenced taxa may be another case of mistaken ascidian identity.
The conspicuous dark tunic of these three darkly pigmented Phallusia species has likely induced researchers to identify populations of P. philippinensis and P. fumigata as P. nigra, because it is the most commonly known of the three. Several studies discussing the occurrence of P. nigra in the Pacific have used Abbott et al. (1997) as a taxonomic guide. But the pattern of the body musculature, the position of the siphons on their figure 11, and their comments that juveniles and adults in shade lose the dark color clearly show that they have misidentified the species. Hirose (1999) and Hirose et al. (2001) also followed the description in Abbott et al. (1997) to identify specimens and incurred the same error. Of the darkly pigmented Phallusia, only P. philippinensis adults change color when moved from shade to light, wherein they become darker (Hirose, 1999). Juvenile individuals of P. nigra (less than 1.5 cm) are light gray but rapidly acquire the characteristic black pigment and never lose it (Van Name, 1945; RMR, pers. obs.).
At this point, we are unable to ascertain the native range of either P. nigra or P. philippinensis. The fact that P. nigra is found extensively throughout the western Atlantic Ocean favors this region as its hypothetical native range, although it was first described from the Red Sea. Considering the Red Sea as its native region would indicate either a massive recent Atlantic invasion without the colonization of most Mediterranean coasts, or that this species had a much wider distribution in the past with present locally extinct populations in the East Atlantic and Mediterranean. The fact that most known populations of P. philippinensis can be recognized as introduced favors the Philippines as its hypothetical native range. The more restricted geographical range of P. fumigata indicates that this species is native to Europe, though the disjunctive distribution between Atlantic and Mediterranean populations suggests possible human regional transport (e.g., Turon et al., 2003). These hypotheses should be further tested with population genetics on a global scale (Rius et al., 2008; Pineda et al., 2011).
Previous to this paper there were no published genetic resources for P. philippinensis and very few sequences (if any) for P. nigra. P. philippinensis has also not previously been included in a published phylogenetic tree. The three darkly pigmented species (P. nigra, P. fumigata, P. philippinensis) form a clade that is a sister group to P. mammillata, which has a bumpy white tunic and occurs in more temperate waters. Whatever the source of the dark pigment found in the tunic (see Hirose, 1999), we believe that the dark appearance of P. fumigata and P. philippinensis has led to their misidentification as P. nigra in the Mediterranean and in the Pacific, respectively. Our results suggest that both P. nigra and P. philippinensis are transportable by human vectors and should be monitored for new introductions in the Pacific. Previous reports of P. nigra should be reviewed to confirm the identification of the species. Genetic resources have been shown to be essential for confirmation of provisional morphological identification (Darling and Blum, 2007), and the sequence data from this study can assist future identification efforts of the dark Phallusia species.
This manuscript is dedicated to the memory of Charley Lambert, who spent many years working on ascidians and inspired many others to do so. The authors thank Xavier Turon and Gretchen Lambert for many relevant discussions about ascidian taxonomy and for references on Phallusia fumigata. We also thank Gretchen Lambert for the collection and donation of. P nigra from the Eilat, Israel, gathered by Noa Shenkar and the participants of an ascidian workshop. The workshop and Gretchen Lambert's trip was sponsored by the Israeli Taxonomy Initiative. We thank Mari Carmen Pineda for the collection and donation of specimens (and 18S sequences) found at Magnetic Island, Australia; Dr. Sebastien Darras at Universite Pierre et Marie Curie for photos of living Phallusia fumigata; and Dr. Chryssanthi at Antoniadou, Aristotle University of Thessaloniki, for donation of Phallusia fumigata tissue samples. This collaboration was facilitated when the authors met at the Smithsonian Tropical Research Institute in Bocas del Toro, Panama, in 2011 to teach in the NSF: PASI: Advanced Tunicate Biology: Integrating Modern and Traditional Techniques for the Study of Ascidians. The course was funded by a National Science Foundation (NSF) grant (OISE-1034665), to Director Rachel Collin. We thank the government of Panama for permits for ascidian samples discussed in this manuscript. This material is based in part upon work supported by the National Science Foundation under Cooperative Agreement No. DBI-0939454. This research was also supported by an NSF grant (DEB 0816892) to BJS; NSF Graduate Research Fellowship (DGE1256082) to LEV; "International Research Hub Project" of University of the Ryukyus to EH; CNPq-National Counsel of Technological and Scientific Development grant (304768/2010-3) to RMR; and a Master of Science scholarship from CAPES--Coordenacao de Aperfeicoamento de Pessoal de Nfvel Superior to LMO.
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LAUREN E. VANDEPAS (1), LI VIA M. OLIVEIRA (2), SERINA S.C. LEE (3), EUICHI HIROSE (4), ROSANA M. ROCHA (2), AND BILLIE J. SWALLA1 (*)
Received 29 November 2013; accepted 27 October 2014
(1) Biology Department, University of Washington, and Friday Harbor Laboratories, Seattle, Washington;
(2) Departamento de Zoologia, Universidade Federal do Parana, Curitiba, Parana, Brazil; (3) Tropical Marine Science Institute, National University of Singapore, Singapore; and (4) Department of Chemistry, Biology, and Marine Science, University of the Ryukyus, Nishihara-cho, Okinawa, Japan
(*) To whom correspondence should be addressed. E-mail: email@example.com
Table 1 Morphological comparisons among dark of Phallusia P. nigra Color of living animals Black and shiny Tunic Smooth Oral siphon Bent dorsally, 8-10 lobes, usually not visible in living animals Atrial sphon Anterior to the middle of the body Right side Longitudinal transverse, and oblique fibers; longitudinal musculature wider and running toward both the endostyle and the posterior region Peripharyngel groove Both laminas smooth Pharyngeal papillae Absence of intermediate papillae Alimentary canal Occupies more than 2/3 of the left side; intestinal loop at the level of the base of the atrial siphon P. philippinesis Color of living animals Dark gray or brown; light color when in the shadow portions of the body Tunic Smooth Oral siphon Apical and upright, 6-10 visible lobes in living animals Atrial sphon In the middle of the body Right side Mainly longitudinal fibers extending from both oral musculature and atrial siphons, lonely the latter extending till the posterior margin Peripharyngel groove Anterior lamina with projections (arrows in Figure 1) Pharyngeal papillae Absence of intermediate papillae Alimentary canal Occupies more than 2/3 of the left side; intestinal loop anterior to the level of the base of the atrial siphon Peripharyngel groove Both laminas smooth Pharyngeal papillae Absence of intermediate papillae Alimentary canal Occupies more than 2/3 of the left side; intestinal loop at the level of the base of the atrial siphon P. fumigate Color of living animals Dark grey with whitish tunic in buried Tunic Small projections around the oral siphon Oral siphon Apical and upright, 8 visible lobes in living animals Atrial sphon Posterior to the middle of the body Right side Mainly transverse fibers extending musculature between the dorsal and ventral margins in the first half and with an interruption in the central region in the second half Peripharyngel groove Both laminas smooth Pharyngeal papillae Presence of intermediate papillae Alimentary canal Occupies half of the left side; intestinal loop at the level of the base of the atrial siphon Table 2 Specimen collection locations and GenBank accession numbers Species Collection location Gene: Cytochrome oxidase B Phullusia nigra Red Sea, Israel Phallusia nigra Red Sea, Israel Phullusia nigra Red Sea, Israel Phallusia nigra Red Sea, Israel Phallusia nigra Rio de Janeiro, Brazil Phallusia nigra Rio de Janeiro, Brazil Phallusia nigra Rio de Janeiro, Brazil Phallusia nigra Rio de Janeiro, Brazil Phallusia nigra Bocas del Toro, Panama Phallusia nigra Bocas del Toro, Panama Phallusia nigra Bocas del Toro, Panama Phallusia nigra Bocas del Toro, Panama Phallusia nigra Bocas del Toro, Panama Phallusia nigra Florida, United States Phallusia nigra Florida, United States Phallusia nigra Florida. United States Phallusia nigra Singapore Phallusia philippinensis Singapore Phallusia philippinensis Singapore Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa. Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa, Japan Phallusia philippinensis Okinawa. Japan Gene: 18SrDA Phallusia fumigata Greece Phallusia fumigata Greece Gene: 18SrDNA Phallusia nigra Red Sea, Israel Phallusia nigra Red Sea, Israel Phallusia nigra Red Sea, Israel Phallusia nigra Rio de Janeiro, Brazil Phallusia nigra Rio de Janeiro, Brazil Phallusia nigra Bocas del Toro, Panama Phallusia nigra Florida, United States Phallusia nigra Singapore Phallusia philippinensis Singapore Phallusia philippinensis Okinawa. Japan Phallusia philippinensis Okinawa, Japan Phallusia fumigata Greece Species Collection site GenBank accession Gene: Cytochrome oxidase B Phullusia nigra Kisoski Marina, Eilat KJ87.<5967 Phallusia nigra Kisoski Marina, Eilat KJ875968 Phullusia nigra Kisoski Marina, Eilat KJ875969 Phallusia nigra Kisoski Marina, Eilat KJ875970 Phallusia nigra Cabo Frio KF302051 Phallusia nigra Cabo Frio KF302052 Phallusia nigra Cabo Frio KF302053 Phallusia nigra Cabo Frio KF302054 Phallusia nigra Marina Bocas KF302058 Phallusia nigra Marina Bocas KF302059 Phallusia nigra Marina Bocas KF302060 Phallusia nigra Town KF302061 Phallusia nigra Town KF302062 Phallusia nigra Indian River Lagoon KF302055 Phallusia nigra Cape Canaveral, FL KF302056 Phallusia nigra Indian River Lagoon KF302057 Phallusia nigra St. John Island KF302063 Phallusia philippinensis Padang Buoy KF302038 Phallusia philippinensis Padang Buoy KF302039 Phallusia philippinensis Okinawajima KF302043 Phallusia philippinensis Okinawajima KF302044 Phallusia philippinensis Okinawajima KF302045 Phallusia philippinensis Okinawajima KF302046 Phallusia philippinensis Okinawajima KF302047 Phallusia philippinensis Okinawajima KF302048 Phallusia philippinensis Okinawajima KF302049 Phallusia philippinensis Okinawajima KF302050 Phallusia philippinensis Toya Fishery Port KF302040 Phallusia philippinensis Toya Fishery Port KF302041 Phallusia philippinensis Toya Fishery Port KF302042 Gene: 18SrDA Phallusia fumigata Thermaikos Gulf KF302064 Phallusia fumigata Thermaikos Gulf KF302065 Phallusia nigra Kisoski Marina, Eilat KJ875971 Phallusia nigra Kisoski Marina, Eilat KJ875972 Phallusia nigra Kisoski Marina, Eilat KJ875973 Phallusia nigra Cabo Frio KF268455 Phallusia nigra Cabo Frio KF268456 Phallusia nigra Town KF268458 Phallusia nigra Indian River Lagoon KF268457 Phallusia nigra St. John Island KF268459 Phallusia philippinensis Padang Buoy KF268460 Phallusia philippinensis Okinawajima KF268462 Phallusia philippinensis Okinawajima KF268461 Phallusia fumigata Thermaikos Gulf KF268454 Table 3 Pairwise genetic distances (p-distances) between and within phlebobranch clades for cytochrome oxidase B Ciona int & Ascidiella Phallusia sav (*) aspersa spp. Within-clade 0.2414 N/A 0.0172 Ascidiella aspersa 0.3399 Phallusia spp. 0.3799 0.3190 Phallusia fumigata 0.3576 0.3112 0.2755 Phallusia philippinensis 0.3733 0.3094 0.3288 Phallusia nigra 0.3808 0.3344 0.3045 Phallusia Phallusia Phallusia fumigata philippinensis nigra Within-clade 0.0181 0.0941 0.0053 Ascidiella aspersa Phallusia spp. Phallusia fumigata Phallusia philippinensis 0.3004 Phallusia nigra 0.3106 0.2653
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|Author:||Vandepas, Lauren E.; Oliveira, Li Via M.; Lee, Serina S.C.; Hirose, Euichi; Rocha, Rosana M.; Swalla|
|Publication:||The Biological Bulletin|
|Date:||Feb 1, 2015|
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