Research Article
Research Article
Molecular and morphological identification of Biomphalaria species from the state of São Paulo, Brazil
expand article infoRaquel Gardini Sanches Palasio§, Marisa Cristina de Almeida Guimarães§, Fernanda Pires Ohlweiler§, Roseli Tuan§
‡ University of São Paulo, São Paulo, Brazil
§ Superintendency for the Control of Endemic Diseases, São Paulo, Brazil
Open Access


DNA barcoding and morphological characters were used to identify adult snails belonging to the genus Biomphalaria from 17 municipalities in the state of São Paulo, Brazil. The DNA barcode analysis also included twenty-nine sequences retrieved from GenBank. The final data set of 104 sequences of the mitochondrial cytochrome oxidase I (COI) gene was analyzed for K2P intraspecific and interspecific divergences, through tree-reconstruction methods (Neighbor-Joining, Maximum Likelihood and Bayesian inference), and by applying different models (ABGD, bPTP, GMYC) to partition the sequences according to the pattern of genetic variation. Twenty-seven morphological parameters of internal organs were used to identify specimens. The molecular taxonomy of Biomphalaria agreed with the morphological identification of specimens from the same collection locality. DNA barcoding may therefore be a useful supporting tool for identifying Biomphalaria snails in areas at risk for schistosomiasis.


Biomphalaria, COI, DNA barcoding, morphological taxonomy, schistosomiasis, species identification


Brazil contains one of the richest faunas of freshwater snails of the genus Biomphalaria (Agostinho et al. 2005, Scholte et al. 2012). The state of São Paulo, in southeast Brazil, is of enormous epidemiological importance, as all the three Neotropical intermediate hosts of Schistosoma mansoni (Sambon, 1907), Biomphalaria glabrata (Say, 1818), B. straminea (Dunker, 1848), B. tenagophila (d’Orbigny, 1835), are distributed in streams, ponds, dams and reservoirs in this municipality. Biomphalaria occidentalis (Paraense, 1981), B. peregrina (d’Orbigny, 1835), B. intermedia (Paraense & Deslandes, 1962), B. oligoza (Paraense, 1975) and B. schrammi (Crosse, 1864) are also distributed in São Paulo state (Vaz 1989; Teles 2005; Ohlweiler et al. 2010).

Identification of Biomphalaria specimens to the species level and analysis of infection by S. mansoni are key elements of surveillance strategies for schistosomiasis control and elimination (PAHO 1968, WHO 2013). Shell morphology is of limited use for identifying different species of snails in this genus (Paraense 1966; Jarne and Théron 2001), and therefore the anatomical characters described by Paraense (1961, 1975, 2001) are used instead. However, identification of Biomphalaria solely based on morphological characters is constrained by phenotypic plasticity, the limited descriptions of cryptic species, and the difficulty in applying species-diagnostic characters to juvenile specimens (Carvalho et al. 2008; Teodoro et al. 2010). The issue of how useful molecular tools may be in the identification of Biomphalaria snails has become particularly important in recent years as there is consensus among malacologists that morphological identification using internal anatomical parameters is susceptible to error, especially when the snails being analyzed belong to complexes of morphologically similar species (Paraense 1972, 1974, 1988; Spatz et al. 1999; Vidigal et al. 2000). To overcome these limitations and difficulties associated with traditional taxonomy, various methodologies based on molecular markers have been developed.

PCR-RFLP analysis of mitochondrial and nuclear genes (Spatz et al. 1999; Vidigal et al. 1998, 2000; Caldeira et al. 2000, 2009), fingerprinting techniques using nonspecific primers (Abdel-Hamid et al. 1999; Al-Quraishy et al. 2014) and sequence analysis of COI and r16RNA genes and ITS-1 and ITS-2 sequences (Woolhouse and Chandiwana 1989; Langand et al. 1998; Vidigal et al. 2000; Campbell et al. 2000; DeJong et al. 2003; Wethington et al. 2007; Tuan and Santos 2007; Tuan et al. 2012) have all produced results that allowed significant genetic differences in species and populations to be identified.

When used in conjunction with bioinformatics tools and sequence databases, DNA barcoding routinely facilitates the identification of biological species (Ratnasingham and Hebert 2007; Casiraghi et al. 2010). This technique is based on the polymorphism of a short region (approximately 600 bp long) of the mitochondrial cytochrome c oxidase 1 (COI) gene (Hebert et al. 2003). DNA barcode includes a series of strategies for delimiting species into molecular operational taxonomic units (MOTUs) using a combination of laboratory and bioinformatics methods (Fontaneto et al. 2013). The most important strategies for identifying MOTUs include analysis of intraspecific and interspecific genetic distances, and analyses based on population and phylogenetic models. These approaches include (ABGD) (Puillandre et al. 2012) and the barcode index number (BIN) system (Ratnasingham and Hebert 2013), which use algorithms based on the partition of molecular data according distance methods, and the generalized mixed Yule coalescent (GMYC) method (Fujisawa and Barraclough 2013) and Bayesian Poisson Tree Processes (bPTP) method (Zhang et al. 2013).

DNA barcoding has been used to augment morphological identification of Bulinus in Africa (Kane at al. 2008; Stothard et al. 2013; Standley et al. 2014), and yielded better results than identifications based on shell characters. Although there are over 500 COI sequences in GenBank from snails of the genus Biomphalaria found in African and Neotropical regions, most DNA barcoding studies use African species. There is therefore a dearth of knowledge about the effectiveness of DNA barcoding in taxonomic identification of Neotropical species of Biomphalaria (Standley et al. 2011; Tuan et al. 2012).

Here, we investigate the utility of analysis of distributions of intraspecific and interspecific COI divergences based on genetic distances, tree reconstruction methods based on Bayesian inference, Maximum Likelihood (ML), and K2P-Neighbor-Joining (NJ) grouping of sequences, and the ABGD, GMYC and bPTP methods for delimitation of Biomphalaria species in conjunction with schistosomiasis field surveys.

Materials and methods

Experimental design

Planorbids were collected in 17 municipalities in the state of São Paulo, Brazil between May 2012 and January 2013 (Fig. 1). The collection points were georeferenced with a Garmin ETrex Summit® GPS (Table 1).

Figure 1.

Locations of the 17 municipalities in São Paulo (Brazil) where the snails were collected. 1 Aparecida 2 Ilhabela 3 Caraguatatuba 4 Biritiba Mirim 5 Mogi das Cruzes 6 Santa Isabel 7 Franco da Rocha 8 Embu das Artes 9 São Lourenço da Serra 10 Juquitiba 11 Itariri 12 Juquiá 13 Ipaussu 14 Ourinhos 15 Martinópolis 16 Novais 17 Araraquara (coordinates are detailed in Table 1).

Collection localities, sample information, and GenBank accession numbers for COI sequences used in this study.

Sample Sites/ Country Map locality Municipality Latitude; Longitude COI sequence GenBank accession number
São Paulo, Brazil 1 Aparecida 22°51'52.0"S; 45°15'46.0"W 589, 588, 591 KF926184, KF926196, KF926186
2 Ilhabela
23°49'17.5"S; 45°22'01.4"W 564,555 KF926191, KF926187
23°47'56.4"S; 45°21'44.0"W 593,554 KF926213, KF926212
3 Caraguatatuba 23°37'55.7"S; 45°25'08.7"W 563 KF926218
23°37'59.6"S; 45°25'11.4"W 517 KF926105
23°38'04.2"S; 45°25'14.7"W 579, 580 KF926221, KF926217
23°38'3.25"S; 45°25'14.3"W 516 KF926106
23°40'26.1"S; 45°26'54.3"W 592 KF926215
23°40'42.2"S; 45°27'18.5"W 568 KF926214
23°41'34.8"S; 45°26'58.1"W 569 KF926216
23°41'46.4"S; 45°28'57.9"W 565, 571 KF926219, KF926220
23°41'49.5"S; 45°26'30.8"W 523 KF926222
4 São Paulo 23°33'43.0"S; 45°59'66.0"W 551 KF926204
23°33'44.0"S; 46°02'35.0"W 548, 549 KF926203, KF926205
5 23°33'95.0"S; 46°09'24.0"W 547 KF926202
6 Santa Isabel 23°17'16.8"S; 46°12'16.1"W 544 KF926174
23°17'00.2"S; 46°12'59.1"W 545, 546, 550, 552 KF926177, KF926189, KF926195, KF926190
7 Franco da Rocha 23°20'02.0"S; 46°40'28.0"W -
8 Embu das Artes 23°38'50.5"S; 46°51'11.3"W 524 KF926197
23°40'08.5"S; 46°51'41.7"W 640 KF926198
9 Embu-Guaçu 23°48'11.0"S; 46°55'27.0"W 630 KF926201
10 Juquitiba 24°00'21.0"S; 47°08'52.0"W -
11 Itariri 24°17'53.6"S; 47°08'55.0"W 537 KF926188
24°17'55.0"S; 47°08'06.8"W 536 KF926211
24°18'26.3"S; 47°03'58.9"W 618 KF926207
24°18'39.9"S; 47°07'31.4"W 503 KF926206
24°18'11.8"S; 47°04'04.1"W 532, 627, 534 KF926209, KF926185, KF926208
24°18'13.5"S; 47°04'31.7"W 535 KF926210
São Paulo, Brazil 12 Juquiá 24°18'55.1"S; 47°37'58.6"W 650, 651, 653 KT225577, KT225578, KT225579
24°19'39.5"S; 47°40'25.0"W 655 KT225580
13 Ipaussu 23°05'39.6"S; 49°39'01.5"W 756, 761, 755 KX354441-KX354442, KX354440
14 Ourinhos 22°57'00.2"S; 49°52'33.1"W 764 KX354435
22°58'02.5"S; 49°52'27.1"W 572, 543, 573 KF926181, KF926182, KF926183
22°58'03.4"S; 49°52'28.9"W 735, 733, 766 KX354437-KX354438, KX354433
22°59'08.0"S; 49°50'59.9"W 577 KF926192
22°58'29.5"S; 49°53'29.4"W 538, 578 KF926165, KF926193
23°00'24.8"S; 49°51'48.7"W 739 KX354444
23°00'32.2"S; 49°52'21.9"W 763, 765 KX354436, KX354434
23°00'11.5"S; 49°51'41.4"W 747 KX354443
22°57'11.6"S; 49°52'41.9"W 636, 540 KF926194, KF926166
22°57'11.6"S; 49°52'41.9"W 575, 542 KF926168, KF926167
22°59'42.4"S; 49°52'27.6"W 541 KF926178
15 Martinópolis 22°14'04.4"S; 51°09'36.4"W 581, 582 KX354445, KF926180
16 Novais 20°59'30.0"S; 48°55'05.0"W 570, 586, 587 KF926179, KF926169, KF926171
17 Araraquara 21°45'37.9"S; 48°07'40.1"W 595, 599, 601 KF926170, KF926173, KF926172
21°47'30.3"S; 48°08'41.1"W 594, 596 KF926199, KF926200
21°48'57.1"S; 48°10'13.1"W 602 KF926175
Argentina ARG_1, ARG_2, ARG_3, ARG_4 JN621901, JN621902
JN621903, GU168593
Brazil BRA_1 AF199090
RS_BRA_2, RS_BRA_3, RS_BRA_4, MG_BRA_5, BRA_6, BRA_7, BRA_8, BRA_9 KF926107, KF926108
AF199091 , AF199092,
AF199095 , AF199096
RS_BRA_10 KX354439
BRA_11 AF199084
Brazil RS_BRA_12, RS_BRA_13, RS_BRA_14, RS_BRA_15, RS_BRA_16 KF926155-KF926156
RS_BRA_18, RS_BRA_19
EF433576, NC010220
Egypt EGY_2, EGY_1 DQ084823
Hong Kong HKG AF199085
M-Line * AY380567
Puerto Rico PUR DQ084824
Venezuela VEN AF199093

Samples were collected from freshwater habitats in the Paranapanema, Tietê, Ribeira do Iguape and Paraíba do Sul River basins and the northern coast of São Paulo that had been previously surveyed and classified according to the risk for schistosomiasis transmission as part of a program to monitor snails that are intermediate hosts of S. mansoni (Biomphalaria).

In accordance with the methods described in the Brazilian Ministry of Health Schistosomiasis Surveillance and Control Program (Ministry of Health 2008), snails were collected at sampling stations in each freshwater body and grouped into batches according to their origin. Most of the snails in each batch were then exposed to artificial light in the laboratory to determine whether they were infected with cercariae. At least two specimens from each batch were used for morphological analysis and at least two for the DNA barcode analysis.

DNA barcoding was applied to 75 adult snails taken from samples collected in the field. Only snails that did not have any parasite larvae in their digestive gland and ovotestis were used for molecular identification. Shells were removed by compressing each snail between two slides. After removing the shell fragments, each crushed snail was transferred to a clean Petri dish. The portion of the cephalopodal mass corresponding to the foot was excised under a stereo microscope with forceps and scissors and used as starting material for isolation of total DNA. To maximize the efficiency of genomic DNA purification we used fresh material that had not been fixed. Each specimen was then dissected and identified to the species level based on the presence or absence of the renal ridge and the most informative characters of the male and female copulatory organs. DNA barcoding was carried out in a blind fashion, i.e., without prior knowledge of the general morphological characteristics identified in the animal.

An additional 118 adult specimens were taken from the same field samples (at least two per batch) and scored for 27 morphological characters used by Paraense (1975, 1981, 1984, 2001) in his descriptions of Neotropical species of the genus Biomphalaria. The soft parts were removed from the shell after placing the snails in 70°C for 40 seconds and then fixing them in Railliet-Henry’s solution (distilled water 930 mL, sodium chloride 6 g, formalin 50 mL and glacial acetic acid 20 mL). After at least 24 hours of fixation, the specimens were dissected following Deslandes’ (1951) protocols to examined the renal tube and reproductive system. Specimens were not anesthetized prior to fixation to ensure that the procedure followed was the same as that used in our malacology laboratories.

The longitudinal renal ridge is considered the gold-standard character for differentiating B. glabrata (Paraense and Deslandes 1959) from other species in the genus, in which the ridge is absent. The anterior and posterior regions of the vagina were examined. The proportions for the diameter and length of the oviduct were based on the nidamental gland; for the diameter of the uterus, the cephalic portion of the nidamental gland was used, for the length of the uterus, the posterior region of the vagina; for the length of the spermathecal duct, the body of the spermatheca; and for the length of the anterior region of the vagina, the posterior region of the vagina. The relative proportions of the organs or structures were used for comparisons together with the shell and mantle pigmentation pattern.

DNA extraction, amplification and sequencing

DNA isolation was carried out with the DNeasy Tissue Kit (Qiagen®). A fragment of the COI gene (~600 bp) was amplified with the LCO/HCO primers (Folmer et al. 1994). Polymerase chain reaction (PCR) was carried out in a total volume of 50 µL and the following reaction mixture: 10-100 ng of DNA, 0.2 mM of each dNTP, 0.10 μM of each primer and 1 U of Taq DNA polymerase in the supplied reaction buffer. The cycling conditions consisted of an initial 3 min step at 95°C for denaturation; 25 cycles of 1 min at 95°C, 1 min at 47°C and 1 min 30 s at 72°C and a final extension step of 7 min at 72°C (Tuan et al. 2012). PCR products were purified with a Qiagen purification kit and then sequenced in the Biotechnology Center at the Butantan Institute in an ABI3100 automated sequencer (Applied Biosystems®).

Molecular data analysis

The electropherograms obtained from forward and reverse sequencing of each specimen were corrected using CHROMAS (Technelysium Pty Ltd.) and then aligned with CLUSTALX version 1.8 (Thompson et al. 1997). The aligned sequences were edited with BIOEDIT version 7.0 (Hall 1999), and the general polymorphism of the sequences was calculated in DNAsp version 5 (Librado and Rozas 2009).

The final alignment consisted of a matrix of 75 COI sequences from the collected specimens (36 B. tenagophila, 12 B. occidentalis, 10 B. glabrata, 9 B. straminea, 1 B. intermedia, 7 B. peregrina) and 29 COI sequences of Biomphalaria from other Neotropical areas that were retrieved from GenBank (Table 1).

Intraspecific and interspecific genetic distances (Kimura 1980) were calculated by pairwise comparison of the sequences of all the individuals using the Kimura 2-parameter (K2P) method with the MEGA 6 (Molecular Evolutionary Genetics Analysis) package (Tamura et al. 2013). Three tree-based methods were performed for phylogenetic reconstructions. The K2P distance matrix was used to reconstruct a Neighbor-Joining (NJ) tree. MEGA 6 was also used to perform Maximum Likelihood analysis. In the ML analysis, the GTR+I+G model of sequence evolution was chosen using the Akaike information criterion as implemented in MODELTEST 2.3 (Nylander 2004). The reliability of NJ and ML topologies was evaluated using bootstrap support with 1000 replicates. The parameters estimated by MODELTEST were also used in a Bayesian Markov-Chain Monte Carlo (MCMC) analysis in MRBAYES 3.1 (Huelsenbeck and Ronquist 2001; Ronquist and Huelsenbeck 2003). Two simultaneous independent searches were run for 1.5 x 106 generations, with trees saved every 100 generations, and the first 1.500 sampled trees of each search discarded as “burn-in”.

The barcode gap analysis was performed with the ABGD (Puillandre et al. 2012), bPTP (Zhang et al. 2013) and GMYC methods (Fujisawa and Barraclough 2013). ABGD, bPTP and GMYC were run on the public/abgd/, and web servers, respectively, using default parameters.

All the molecular analysis was performed on the 104 sequences (39 B. tenagophila, 23 B. glabrata, 13 B. occidentalis, 11 B. straminea, 12 B. peregrina, 1 B. intermedia, and 5 sequences from B. tenagophila guaibensis) (Table 1). Biomphalaria oligoza was excluded from the analysis because we were unable to amplify its DNA.


Morphological analysis

The morphological identifications of the 118 adult snails that were studied are presented in Table 2. The results of morphological analysis revealed the following: Shell: the presence of a carina, the shape of the whorls and the shape of the shell aperture distinguished B. tenagophila and B. occidentalis from the other species in the group. Renal tube: The presence of renal ridge was observed in all the B. glabrata specimens studied. Pigmentation of the mantle: adult specimens of B. tenagophila, B. glabrata and B. occidentalis had more uniform pigmentation than the four other species studied, which had blotchy pigmentation. Reproductive system: the presence of a vaginal pouch in B. tenagophila and its absence in B. occidentalis differentiates these two species. Biomphalaria straminea and B. intermedia had marked variation in the posterior region of the vagina; in the former, the corrugation in this region was markedly wavy while in the latter it was swollen.

Morphological characters used to identify 118 Biomphalaria specimens from the state of São Paulo.

Morphological character B. glabrata
(n= 9)
B. tenagophila
(n= 56)
B. occidentalis
(n= 18)
B. oligoza
(n= 10)
B. peregrina
(n= 9)
B. intermedia
B. straminea
(n= 6)
Carinate shell Absent Present Present Absent Absent Absent Absent
Shape of the whorls on the shell Rounded Angular Angular Rounded Rounded Rounded Rounded
Shell aperture Rounded Transverse, low or deltoid Transverse, low or deltoid Rounded Rounded slightly to the right Rounded Rounded
Mantle pigmentation Tends to be homogeneous Tends to be homogeneous Tends to be homogeneous Spotted or blotchy Spotted or blotchy Spotted or blotchy Spotted or blotchy
Longitudinal renal ridge Present Absent Absent Absent Absent Absent Absent
Number of ovotestis diverticula More than 100 More than 100 More than 100 18 to 37 More than 100 Around 60 More than 100
Shape of the ovotestis diverticula Elongate, simple or subdivided Elongate, simple or subdivided Elongate, simple or subdivided Bulging and simple Elongate, simple or subdivided Elongate, simple or subdivided Elongate, simple or subdivided
Differentiation of the ovotestis diverticula Weakly differentiated Weakly differentiated Weakly differentiated Well differentiated Well differentiated Well differentiated Well differentiated
Diameter of the oviduct Narrow Narrow Narrow Wide Narrow Wide Wide
Length of the oviduct Long Long Long Short Long Long Short
Appearance of the oviduct pouch Clearly defined Clearly defined Clearly defined Bulky Clearly defined Clearly defined Bulky
Diameter of the uterus Narrow Narrow Narrow Wide Wide Narrow Wide
Length of the uterus Long Long Long Short Short Long Long
Length of the anterior region of the vagina Long Long Long Short Short Long Long
Corrugation on the dorsal wall of the posterior region of the vagina Absent Absent Absent Absent Absent Present Present
Type of vaginal Corrugation - - - - - Swollen Strongly wavy
Vaginal pouch on the ventral wall of the posterior region of the vagina Present Present Absent Present Present Present Absent
Shape of the vaginal pouch Elongate Bulging _ Elongate Elongate Elongate _
Appearance of the vaginal pouch Clearly defined Clearly defined _ Discrete Clearly defined Discrete _
Length of the spermathecal duct Long Long Long Short Short Long Long
Shape of the prostate diverticula Tree-like Tree-like Tree-like Simple or subdivided Tree-like Tree-like Tree-like
Number of prostate diverticula Around 30 Around 30 Around 20 1 to 4 Around 13 Around 13 Around 20
Length of the penial sheath Approx. the same length as the prepuce Approx. the same length as the prepuce Shorter than the prepuce Approx. the same length as the prepuce Longer than the prepuce Approx. the same length as the prepuce Longer than the prepuce
Diameter of the penial sheath Narrow Narrow Narrow Wide Wide Wide Wide
Shape of the prepuce Free end is wider Free end is wider Same diameter along its whole length Same diameter along its whole length Free end is wider Free end is wider Free end is wider
Seminal vesicle extensions Finger-like Finger-like Finger-like Nodular Finger-like Finger-like Finger-like
Appearance of the seminal vesicle Developed Developed Poorly developed Poorly developed Developed Developed Developed

Biomphalaria peregrina differed from the species in the B. straminea complex (B. straminea and B. intermedia) in the width of the oviduct, the length of the uterus, the length of the spermathecal duct and the length of the anterior region of the vagina. Biomphalaria intermedia differed from B. straminea in the number of ovotestis diverticula, the length of the oviduct, the presence of an oviduct pouch, the number of prostate diverticula and the width of the uterus.

Biomphalaria oligoza, B. peregrina, B. intermedia and B. straminea are differentiated by the number and shape of the ovotestis diverticula, appearence and size of seminal vesicle, the number and shape of the prostate diverticula, and the shape of the prepuce. The 27 morphological characters used to identify Biomphalaria are detailed in Table 2.

All these findings are in agreement with Paraense and Deslandes (1959), Paraense (1961, 1974, 1975, 1981, 1984).

Molecular analysis

The final alignment matrix for the 104 sequences consisted of 549 characters including 25% polymorphic, 21% parsimony-informative and 12 unique sites (Table 3).

Sample size (N), number of haplotypes (H), haplotype diversity (Hd), nucleotide diversity (π, Nei 1987, equation 10.5) and average number of nucleotide differences (K, Tajima 1983, equation A3) calculated in DNAsp v.5 (Librado and Rozas 2009) for a 549 bp region of the COI gene in the six Biomphalaria species and one Biomphalaria subspecies.

Species N H Hd π K
Biomphalaria 104 36 0.946 0.06805
B. straminea 11 6 0.836 0.01199 6.582
B. occidentalis 13 1 0.000 0.00000 0.000
B. peregrina 12 6 0.848 0.01954 10.727
B. glabrata 23 10 0.862 0.01914 10.506
B. tenagophila 39 11 0.803 0.01222 6.707
B. t. guaibensis 5 1 0.000 0.00000 0.000
B. intermedia 1 1 - - -

The K2P sequence divergence for intraspecific comparisons ranged from 0.0% to 4.0%, while for interspecific comparisons the corresponding figure varied from 4.0% to 12% (Table 4). The greatest intraspecific genetic distances were observed between specimens of B. peregrina from SP and Rio Grande do Sul (southern Brazil) (4.0%) and specimens of B. glabrata from Rio Grande do Sul and Puerto Rico (3.9%).

Intraspecific and interspecific genetic distances (COI) generated using the Kimura 2-parameter model (K2P, Kimura 1980) in MEGA6 (Tamura et al. 2013).

Species 1 Species 2 Minimum distance Mean distance Maximum distance
B. glabrata 0.00 0.03 0.04
B. tenagophila 0.00 0.02 0.03
B. straminea 0.00 0.01 0.03
B. occidentalis 0.00 0.00 0.00
B. peregrina 0.00 0.02 0.04
B. intermedia 0.00 0.00 0.00
B. t. guaibensis 0.00 0.00 0.00
B. glabrata B. tenagophila 0.07 0.09 0.10
B. straminea 0.07 0.09 0.10
B. occidentalis 0.09 0.09 0.09
B. peregrina 0.10 0.12 0.15
B. intermedia 0.06 0.08 0.09
B. t. guaibensis 0.07 0.09 0.09
B. tenagophila B. straminea 0.08 0.09 0.10
B. occidentalis 0.04 0.05 0.06
B. peregrina 0.10 0.12 0.15
B. intermedia 0.05 0.08 0.09
B. t. guaibensis 0.04 0.04 0.05
B. straminea B. occidentalis 0.09 0.09 0.10
B. peregrina 0.09 0.01 0.10
B. intermedia 0.05 0.05 0.06
B. t. guaibensis 0.08 0.08 0.09
B. occidentalis B. peregrina 0.10 0.11 0.13
B. intermedia 0.08 0.08 0.08
B. t. guaibensis 0.03 0.03 0.03
B. peregrina B. intermedia 0.09 0.09 0.10
B. t. guaibensis 0.10 0.12 0.13
B. intermedia B. t. guaibensis 0.08 0.08 0.08

The frequency distribution of the 104 analyzed sequences indicates that although there were some extreme pairwise distances (>3%) in B. glabrata, B. tenagophila, B. peregrina and B. straminea; intraspecific and interspecific divergences did not overlap (Fig. 2A). Nevertheless, a typical barcode gap was not observed in this dataset. A closer inspection of the distances for each taxonomic group shows that there is a clear barcode gap between B. glabrata, B. straminea, B. peregrina and B. intermedia. There was no clear barcode gap between closely related B. tenagophila, B. t. guaibensis and B. occidentalis (interspecific distance 3-4%) (Fig. 2 C, D, E, F).

Figure 2.

A histogram showing pairwise Kimura 2-parameter intraspecific and interspecific distances for 104 Biomphalaria cytochrome oxidase I sequences B–H pairwise distances between each species and the other taxa analyzed.

The total number of MOTUs within the same taxon (Fig. 3) varied depending on the model used to partition the COI data (GMYC, bPTP or ABGD). Only bPTP recovered all seven groups identified by traditional morphology. GMYC revealed various sequences that were not consistent with morphological identifications: B. peregrina sequences from Rio Grande do Sul (BRA_10/KX354439) and São Paulo (756/KX354441), B. straminea sequences from Santa Isabel (SP) and Itariri (SP) (552/KF926190, 534/KF926185), one B. intermedia sequence (570/KF926179), two B. tenagophila sequences from Juquiá (SP) and four B. glabrata sequences from GenBank (RS_BRA_2/KF926107, RS_BRA_4/KF926109, BRA_6/AF199091 and PUR/DQ084824).

When run using the default settings, ABGD recovered five different subunits of B. glabrata. This result may be explained by the pronounced genetic variation in this species, but the possibility that these subgroups represent cryptic taxa cannot be ruled out.

The trees generated by the Bayesian, ML and NJ methods (Fig. 3) delineated six well supported groups (posterior probabilities and bootstrap values ≥90) congruent with the current classification of Biomphalaria. The only B. intermedia sequence appeared in a distinct branch supported by low Bayesian and bootstrap values.

Figure 3.

Bayesian phylogram. Support values for individual branches are given as Bayesian credibility/ML bootstrap/NJ bootstrap and are depicted above each node. The different shades of gray identify morphological species. The red, green and blue bars indicate species delimitations based on the distance-based (ABGD) and tree-based (bPTP and GMYC) models, respectively.


This study sought to determine the utility of DNA barcoding in delimiting species in freshwater snails of the genus Biomphalaria. The Bayesian, ML and NJ analyses (Fig. 3, Suppl. material 1) yielded trees with well-supported internal branches (≥90), resolving six out of the seven taxa as monophyletic groups.

The assessment of the potential of DNA barcode for species differentiation in Biomphalaria essentially revolves around the comparison of results of the morphological and molecular analysis of closely similar or taxonomically ambiguous species. In the case of the three taxa in the B. tenagophila complex, one character that is normally effective for specific identification is the vaginal pouch, which is present in B. tenagophila and B. t. guaibensis but not in B. occidentalis. (The anatomical features of these three taxa were illustrated by Tuan et al. 2012). Although we did not observe this in our material, in some specimens of B. occidentalis there is a slight projection of the ventral wall of the vagina (Paraense 1981), which raises questions regarding the distinctness of this taxon.

The intraspecific genetic distance within B. tenagophila showed values with a range from 0 to 3% (Table 4, Figs 2, 3). A high level of genetic divergence within this species was obtained for sequences associated with specimens collected in Juquiá (650,651,653), Itariri (535), Embu das Artes (524,535) and São Paulo (549, 551). Due to these values we could not assign a clear barcode gap between B. tenagophila and B. occidentalis and B. t. guaibensis (Fig. 2 b, d, f). However, the Bayesian tree inferred from COI data (Fig. 3), as well as the ABGD and both bPTP and GMYC analyses recovered these close related taxa as distinct groups. We suggest that in geographical areas where B. tenagophila species complex have the same geographical distribution.

The application of the 3-4% cutoff value for maximum intraspecific divergence may be appropriate for our dataset as 36% of the intraspecific comparisons reached this value (Table 4). The highest values for intraspecific divergence (>3%) do not appear to be a consequence of geographic distance given that the greatest divergence in B. tenagophila was between closely proximal localities in São Paulo state (Fig. 3).

Biomphalaria glabrata and B. tenagophila, are differentiated by the renal ridge, which is present in the former and absent in the latter. Paraense and Deslandes (1959) described a false ridge that runs obliquely to the renal tube and is attached to the pneumostome, in specimens of B. tenagophila from Macaé, RJ. The presence of this false ridge in B. tenagophila may lead to incorrectly identify this species, particularly in juvenile specimens or specimens that have not been properly fixed. Five specimens of B. tenagophila in our study (three from São Lourenço da Serra and two from São Paulo) had a membrane on the renal tubes similar to that described by Paraense and Deslandes. The genetic distance of 9% between B. glabrata and B. tenagophila observed with both genetic distance and tree-based approaches show that DNA barcoding is an important tool for identifying these closely similar taxa.

The ABGD analysis partitioned B. glabrata into five distinct groups, while the GMYC analysis yielded a more cohesive group. Despite the pronounced COI divergence within B. glabrata, in all the specimens analyzed here the renal ridge has been considered a robust and consistent taxonomical character, suggesting that morphology is more effective than DNA barcode in this case. However, bBTP analysis and phylogenetic reconstruction supported B. glabrata as single and well supported MOTU, a result congruent with the morphological identification.

Another group of morphologically similar and frequently misidentified congeners includes B. intermedia and B. straminea; the latter a natural intermediate host of S. mansoni. Of the seventeen diagnostic characters common to B. straminea and B. intermedia, the degree of corrugation in the dorsal wall of the vagina has been used to these taxa as a species complex (Paraense 1975) . The vaginal corrugation, which is markedly wavy in B. straminea appears as swollen in B. intermedia. The large genetic divergence between B. straminea and B. intermedia, which was 9% greater than the intraspecific values in both species, indicates that these two species can be identified by DNA barcode. Note, however, that our study only included two of the three species in the B. straminea complex, as B. kuhniana does not occur in São Paulo state (Paraense 1988, Teodoro et al. 2010). In addition, we were unable to collect many specimens of B. intermedia owing to its rareness in São Paulo state.

Our findings show Biomphalaria species delimitation by phylogenetic approaches and bPTP yielded the same groups identified by traditional taxonomy. The use of DNA barcode to identify species in conjunction with Biomphalaria surveys requires the application of both evolutionary and bioinformatics criteria, making it a time-consuming approach that is dependent on specialist knowledge. Morphological identification also requires specialist knowledge. However, as shown in this study DNA barcoding can identify subtle (genetic) differences between intraspecific populations that are not detectable by traditional morphological study.

Furthermore, morphological identification of Biomphalaria species depends on subjective interpretation of anatomical variations, as these are measured in terms of relative rather than absolute sizes. We therefore agree with Hebert and Gregory (2005, p. 853), who stated that by reversing the logic of standard taxonomic approaches that “operate in an a priori fashion—seeking…morphological discontinuities”, DNA barcoding may, as “a posteriori approach”, direct the study of morphological variation in genetically divergent groups of Biomphalaria.


This work was supported by a grant from the Superintendency for the Control of Endemic Diseases (SUCEN) (ref. no. 0375/2012) to R. Tuan and M. C. A. Guimarães. The acquisition of equipment for the molecular analysis was funded by FAPESP grants to R. Tuan.


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