The Dendropsophus decipiens clade comprises four species: D. berthalutzae, D. decipiens, D. haddadi, and D. oliveirai. Tadpoles of these species were described, but data on their internal morphology are lacking. We provide the first description of the buccopharyngeal anatomy, chondrocranial morphology, and cranial, hyoid and hyobranchial musculature of the tadpole of D. decipiens. Larvae of D. decipiens are characterized by the absence of lingual papillae, presence of fan-like papilla on the buccal floor, presence of a single-element suprarostral cartilage, presence of a small triangular process at the basis of the processus muscularis, m. levator mandibulae lateralis inserted on the nasal sac, and m. subarcualis rectus II-IV with a single, continuous slip. Tadpoles are likely macrophagous, although not as specialized as those of other species of the genus, suggesting some degree of diversification on the feeding habits within Dendropsophus.
Citation: Dias PHS, Araujo-Vieira K, Carvalho-e-Silva AMPTd, Orrico VGD (2019) Larval anatomy of Dendropsophus decipiens (A. Lutz 1925) (Anura: Hylidae: Dendropsophini) with considerations to larvae of this genus. PLoS ONE 14(7): e0219716. https://doi.org/10.1371/journal.pone.0219716
Editor: Claudia Patricia Tambussi, National Scientific and Technical Research Council (CONICET), ARGENTINA
Received: April 28, 2019; Accepted: June 28, 2019; Published: July 11, 2019
Copyright: © 2019 Dias et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript.
Funding: This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), procs # 2007/57067-9, 2012/10000-5, 2012/12500-5, 2013/20420-4, 2013/20423-3, 2013/50741-7, 2014/50342-8, 2015/11239-0 (http://www.fapesp.br/) to PHSD, KAV, VGDO; the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Grant # 310467/2017-9 (http://cnpq.br/) to VGDO; and the Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), PICT 404/2013 and 820/2015 (https://www.argentina.gob.ar/ciencia/agencia) to KAV. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Dendropsophini is a well-supported tribe of hylid treefrogs composed of the genera Dendropsophus and Xenohyla [1,2]. The relationships of Dendropsophini with other hylid tribes remain uncertain; it is poorly supported as sister taxon of Sphaenorhynchini  or as sister taxon of Pseudini [1,4–8]. Dendropsophus is a speciose clade of Neotropical treefrogs comprising 105 species distributed from Southern Mexico to Central-eastern Argentina , and the relationships between its species remain poorly known [1,3–8]. Three putative synapomorphies were suggested for the genus: diploid chromosome number of 30, the extreme reduction of quadratojugal, and labial tooth row formula 1/2 in tadpoles [3,10]. Nine species groups are recognized in Dendropsophus: the D. columbianus, D. garagoensis, D. labialis, D. leucophyllatus, D. marmoratus, D. microcephalus, D. minimus, D. minutus, and D. parviceps groups , whose composition have been slightly modified in the last few years (e.g. [11–13]).
The Dendropsophus microcephalus species group comprises more than 30 species, of which 13 are included in the two tentatively recognized clades: the D. decipiens and D. rubicundulus clades [3,11,13]. Two known morphological synapomorphies for this group are the absence of labial tooth rows and marginal papillae on the oral disc of larvae (with a reversal in the D. decipiens clade; [3,14]). The D. microcephalus group is the latest diverging taxon of Dendropsophus, and the relationship with other groups, as well as between its species remains controversial (e.g. [1,3,8]). The D. decipiens clade comprises four species: D. berthalutzae, D. decipiens, D. haddadi, and D. oliveirai. Dendropsophus berthalutzae is the only species of this clade included in molecular phylogenetic analyses (e.g. [1,3,15]), and therefore, the monophyly of the D. decipiens clade lacks a rigorous test. Putative synapomorphies for this clade are the presence of a posterior row of marginal papillae on the oral disc and oviposition on leaves overhanging water [3,16,17].
The external larval morphology in the Dendropsophus decipiens clade has been described for D. berthalutzae , D. decipiens , D. haddadi [19,20], and D. oliverai , but no aspect of their internal anatomy has been analyzed so far. We describe the buccopharyngeal anatomy, chondrocranial morphology, and cranial, hyoid and hyobranchial musculature of the tadpole of D. decipiens. We also provide comments on the larval internal morphology of Dendropsophus based on our observations complemented with data from the literature.
Materials and methods
Tadpoles were collected (ICMBio/RAN permit # 13256–1) in a dam of Rio Borboleta (22°59'19"S, 44°06'13"W) at Reserva Rio das Pedras, Mangaratiba, Rio de Janeiro, Brazil. Specimens were euthanized by topical application of 20% benzocaine anesthetic mixed with water, preserved in 5% formaldehyde and deposited in the Coleção de Anfíbios do Laboratório de Biossistemática de Anfíbios da Universidade Federal do Estado do Rio de Janeiro (Lot UNIRIO 3635). Some tadpoles were raised in the laboratory to corroborate species identification. Developmental stages were determined according to Gosner .
Two individuals (stages 34 and 35) were dissected according to Wassersug  to expose the buccopharyngeal cavity. One individual (stage 34) was submitted to the protocol of Alcalde and Blotto  for scanning electron microscopy (SEM). Descriptive terminology follows Wassersug [22,24]. For observations of the chondrocranium and cranial muscles, six individuals (stages 30–36) were treated following the protocol of Dingerkus and Uhler  for clearing and staining; we interrupted the procedure just after the staining with alcian blue for two individuals (stage 36) which were then dissected manually for the study of larval muscles. After observations and illustrations, we finished the clearing protocol. Terminology for the chondrocranium and muscles follows Haas [26–28]. The character-states discussed through the text were optimized on the phylogenetic hypothesis proposed by Duellman et al.  with the software TNT v1.5 .
The tadpole of Dendropsophus decipiens (stage 37) was described by Pugliese et al. . It is characterized by having a triangular body, high tail fins with brown stripes, and a reduced oral disc with blunt marginal papillae and absence of labial teeth.
Buccal floor triangular with two pairs of infralabial papillae; medial pair conical; lateral pair flap-like (Fig 1A). Lingual bud elliptical, lacking lingual papillae. Buccal floor arena U-shaped, laterally delimited by single fan-shaped papilla, with few pustulations. Prepocked pustulations present. Buccal pocket deep, oriented transversely. Glandular zone well-developed, with evident secretory pits, and well-marked spicular support. Ventral velum arch-shaped, lacking marginal projections; medial notch discreet. Branchial basket triangular, with three well-developed filter cavities. Filter plates unconnected, bearing many filter rows. Glottis exposed.
(A) Buccal floor and (B) buccal roof. Abbreviations: BFA, buccal floor arena; BFAP, buccal floor arena papillae; BP, buccal pocket; BRA, buccal roof arena; DV, dorsal velum; G, glottis; GZ, glandular zone; IL, infralabial papillae; IN, internal nares; LB, lingual bud; LRP, lateral ridge papillae; MR, median ridge; VV, ventral velum. Scale bars = 400 μm.
Buccal roof triangular (Fig 1B). Prenarial arena half-circle shaped, with few pustulations. Internal nares elliptical, oriented transversely; anterior border with four to five conical pustulations; posterior margin lacking valve. Postnarial papillae absent. Median ridge triangular, low. Lateral ridge papillae conical. Buccal roof arena poorly defined, delimited posterolaterally by two conical papillae. Glandular zone undistinguished. Dorsal velum arch-shaped, smooth, medially interrupted.
Suprarostral cartilage single (Fig 2D); suprarostral alae and suprarostral corpus completely fused. Suprarostral alae triangular, bearing two processes: processus posterior dorsalis and anterior dorsalis. Cornu trabeculae short, thin, uniform along their extension, and parallel to each other; articulates with suprarostral (Fig 2A and 2B). Planum ethmoidale developed and distinct. Foramen nasalis present, elliptical. Fenestra basicranialis not occluded; planum intertrabeculare not formed in medial region; pierced by the foramen caroticum primarium.
(A) Dorsal and (B) ventral views, (C) hyobranchial, (D) suprarostral cartilage, and (E) infrarostral and Cartilago Meckeli. Abbreviations: AS, arcus subocularis; BH, basihyal; CA, capsula auditivae; CB I-IV, ceratobranchials I-IV; CH, ceratohyal; CM, Cartilago Meckeli; CQA, commissura quadratocranialis anterior; CT, cornua trabeculae; FAH, facies articularis; FBC, fenestra basicranialis; FCA, foramen caroticum primarium; FS, fenestra subocularis; IC, infrarostral cartilage; NC, notochord; PAB, processus anterior branchiale; PAH, processus anterior hyalis; PALH, processus anterolateralis hyalis; PHB, planum hypobranchiale; PM, processus muscularis; PPH, processus posterior hyalis; RAP, retroarticular processus; SA, suprarostral alae; SC, suprarostral corpus; SP, spicules; TS, tectum synoticum. Scale bars = 0.5 mm.
Cartilago orbitalis tall, reaching the capsula auditivae posteriorly, forming the dorsal margin of the foramen prooticum; foramina oculomotorium, opticum, and prooticum pierce the cartilago orbitalis. Frontoparietal fontanelle large, rectangular and open (Fig 2A and 2B); laterally bordered by taenia tecti marginales, anteriorly by the planum ethmoidale, and posteriorly by the tectum synoticum. Capsula auditivaes robust, rhomboid-shaped, representing c.a. 28% of chondrocranium length. Anterolateral process of crista parotica absent. Jugulare and inferior perilymphaticum foramina present, visible in ventral view.
Palatoquadrate thin, long, slightly curved (Fig 2A and 2B); articular process articulate with cartilago Meckeli. Processes quadratoethmoidalis and pseudopterygoideus absent. Processus muscularis triangular, lower than cartilago orbitalis; triangular process present at the anterior margin of the process muscularis, triangular, anteriorly directed. Commissura quadratoorbitalis absent. Processus antorbitalis reduced. Subocular bar with small, triangular, lateral expansions. Processus ascendens attached to cranial floor with an angle of approximately 90°. Hyoquadrate process evident on ventral surface of processus muscularis. Cartilago Meckeli sigmoid-shaped, orientated almost perpendicular to chondrocranium axis (Fig 2E). Infrarostral cartilages rectangular, curved, joined medially by connective tissue.
Ceratohyals long, flat, and subtriangular (Fig 2C); their anterior margin bearing two triangular, well-developed processes: processus anterior hyalis and processus anterolateralis hyalis. Posterior processes triangular, tall. Ceratohyals are joined by a pars reuniens, which is chondrified. Basibranchial rectangular, bearing a rounded processus urobranchialis. Basihyal present, slim, cylindrical. Planum hypobranchiale long, triangular, contacting each other along their anterior half. Branchial basket has four curved ceratobranchials with numerous lateral projections. Ceratobranchial I continuous with the planum hypobranchiale; dorsally, it bears a triangular processus anterior branchialis. Ceratobranchials II and III also fuse to the planum hypobranchiale plate and bear round branchial processes. Ceratobranchial IV is shorter, wider, and fused to the planum hypobranchiale. Four long, curved spicules develop dorsally; the third and fourth spicules are connected to the planum hypobranchiale by a thin cartilaginous bridge. Ceratobranchials are distally joined by terminal commissures.
Cranial, hyoid and hyobranchial musculature
We found a total of 31 muscles in larvae of Dendropsophus decipiens (origins and insertions in Table 1; Figs 3 and 4). Interhyoideus posterior and diaphragmatopraecordialis absent. Subarcualis obliquus present in two slips, inserting on the processus branchialis II and III. Subarcualis rectus II-IV continuous, inserting on the ceratobranchial I. Mandibulolabialis with single slip, corresponding to mandibulolabialis inferior. Intermandibularis arch-shaped. Larval levator mandibulae externus with two slips, superficialis and profundus. Levator mandibulae lateralis inserting in the nasal sac. Ramus mandibularis (cranial nerve V3) runs dorsally to longus and externus groups.
Abbreviations: CB I, II, and III = Ceratobranchial I, II, and III. c.n. = cranial nerve. LMLP = m. levator mandibulae longus profundus. n. = nerve.
(A) Ventral and (B) dorsal views. Abbreviations: CB (II-IV), constrictor branchialis; GH, genyohioideus; HA, hyoangularis; IH, interhyoideus; IM, intermandibularis; LBI, levator arcuum branchialium I; LBIV-TP, levator arcuum branchialium IV + tympanopharyngeus; LMA, levator mandibulae articularis; LMEP, levator mandibulae externus profundus; LMES, levator mandibulae externus superficialis; LMI, levator mandibulae internus; LMLP, levator mandibulae longus profundus; LMLS, levator mandibulae longus superficialis; ML, mandibulolabialis; OH, orbitohyoideus; RC, rectus cervicis; SO, subarcualis obliquus; SRI, subarcualis rectus I; SRII-IV, subarcualis II-IV. Scale bars = 0.5 mm.
Larval internal morphology
Dendropsophus has been repeatedly found as sister taxon of Xenohyla (always well supported) in molecular phylogenetic analyses for Hylidae (e.g. [1,3,6,8]). However, the phylogenetic relationships of the tribe Dendropsophini (Dendropsophus + Xenohyla; sensu ) within Hylidae remain controversial. It is recovered as sister taxon of Sphaenorhynchini, closely related to Pseudini and Scinaxini  or alternatively, as sister taxon of Pseudini, distantly related to Scinaxini and Sphaenorhynchini (e.g. [1,8]).
Descriptions of the internal larval anatomy are scarce for Dendropsophus. The buccopharyngeal anatomy is known for D. ebraccatus, D. garagoensis, D. minutus, D. microcephalus, D. nanus, D. padreluna, D. phlebodes, D. sarayacuensis, D. stingi, and D. virolinensis [24,30–32]. Similarly, descriptions of cranial muscles and the chondrocranium morphology are only available for D. ebraccatus, D. microcephalus, and D. nanus [28,32–34]. Dendropsophus ebraccatus was included in the phylogenetic analyses of Haas . Aside from those studies, there is some scattered information available as the relative size of the buccal depressors muscles of D. microcephalus and D. phlebodes , buccal pumping anatomy and secretory ridges of D. microcephalus [36,37], hyobranchial morphology of D. nanus , and some character-states of chondrocranium for D. microcephalus .
The controversial phylogenetic position of the tribe Dendropsophini (e.g. [1,3]) within Hylidae, added to the poor knowledge about on internal larval anatomy in Dendropsophus prevents us to assess the polarity of most character-states and, therefore, to enhance broad discussions about larval character evolution in Dendropsophus; however, there are some interesting exceptions that deserve comments.
Several species of Dendropsophus have a reduced number of elements in the buccopharyngeal cavity [24,30–32]. For example, the median ridge is missing in D. ebraccatus and D. nanus [24,32], and a lower number of papillae in both buccal floor and roof and the absence of lingual papillae were also reported for larvae of Dendropsophus (e.g. [31,32]). Faivovich et al.  suggested the absence of lingual papillae as a putative synapomorphy for the clade composed of Dendropsophus, Lysapsus, Pseudis, Scarthyla, Scinax, and Sphaenorhynchus (the former Dendropsophini tribe sensu ), with reversion in Lysapsus and Pseudis. Our observations showed that lingual papillae are also present at least in some species of Sphaenorhynchus (S. dorisae, S. lacteus, S. prasinus; P.H.S. Dias and K. Araujo-Vieira personal observations). This character-state is unknown for Xenohyla. The absence of lingual papillae optimizes ambiguously in the phylogenetic hypothesis of Duellman et al.  due to the unknown character-state of Xenohyla; it is a synapomorphy of Dendropsophus or of a more inclusive clade, the tribe Dendropsophini (Dendropsophus + Xenohyla sensu ).
Dendropsophus decipiens (D. microcephalus group) has a fan-like papilla on the buccal floor, adjacent to the buccal pockets. This character was first described by Kaplan and Ruíz-Carranza  for D. garagoensis, D. padreluna, D. virolinensis (D. garagoensis group), and D. stingi (D. parviceps group) and illustrated for D. minutus (D. minutus group; ). Fan-like papillae are absent in larvae of D. ebraccatus, D. microcephalus, D. nanus, D. phlebodes, and D. sarayacuensis [24,28,32]. The presence of a fan-like papilla on the buccal floor in members of the D. garagoensis, D. microcephalus, D. minutus, and D. parviceps groups suggest that it could be a putative synapomorphy of the genus Dendropsophus; however, the taxonomic distribution of this character-state within Dendropsophus remains poorly known.
A putative synapomorphy of the Dendropsophus garagoensis group is the presence of two pairs of infralabial papillae, which were reported for D. garagoensis and D. padreluna —with independent evolution in D. decipiens [this work]. Other species of Dendropsophus that have been studied present a single pair of infralabial papillae (e.g. D. minutus, D. nanus, D. phlebodes; [24,30,32]).
Larvae of Dendropsophus decipiens differ from those of its related species D. microcephalus and D. nanus (characters in parenthesis) in having generalized processus muscularis (broad processus muscularis), marginal projections on arcus subocularis of palatoquadrate (smooth margin), thin ceratohyals (stout and thick ceratohyals), regular branchial basket (reduced branchial basked), and presence of spicules on the ceratobranchialia (absence of spicules) [32–34]. However, D. decipiens share with those species short and narrow cornu trabeculae, the presence of a small triangular process at the basis of the processus muscularis, and a single-element suprarostral cartilage. The latter could be a synapomorphy of Dendropsophus (with one reversion to a separated element suprarostral cartilage in D. ebraccatus within the D. leucophyllatus group; ) or of the D. microcephalus group. In larvae of Lysapsus, Pseudis, and some Scinax, the suprarostral corpora are fused distally, but with a medial indentation that allow the identification of both elements; several other hylids have completely separated suprarostral cartilage (e.g. [32,33,40–43]). This character-state is still unknown for Scarthyla, Sphaenorhynchus, and Xenohyla.
It is worth to note that a single-element suprarostral cartilage is not very common in anuran larvae. Besides some Dendropsophus, such morphological condition have been reported in some microhylids , Occidozyga baluensis (Dicroglossidae) , and Ceratophrys and Lepidobatrachus (Ceratophryidae) [32,45–47]. It is interesting to point that, regarding Ceratophryidae, Chacophrys pierotti possesses the suprarostral alae and corpora completely fused (with a small fenestra), but both corpora have a medial indentation . Lavilla and Fabrezi  suggested that the complete fused suprarostral could be a synapomorphy of Ceratophrys + Lepidobatrachus. Given the phylogenetic relationships within Ceratophryidae —Chacophrys and Lepidobatrachus are sister taxa, and both sister to Ceratophrys—this is not possible. However, the complete fusion between the alae and corpora could be a synapomorphy for the family. While microhylids are filter-feeders, Ceratophrys, Lepidobatrachus, and Occidozyga are macrophagous larvae. Further information are still needed to understand the relationship between macrophagy and the fusion of the elements of the suprarostral cartilage.
Dendropsophus decipiens shares with D. ebraccatus the m. subarcualis rectus II-IV with a single, continuous slip; whereas D. microcephalus and D. nanus have this muscle discontinued at the processus branchialis II [28,32,41]. Larvae of Scinax and distantly related hylids (e.g. Agalychnis, Boana, Osteocephalus, Trachycephalus; [28,32,42]) have a single subarcualis rectus II-IV, while larvae of Lysapsus and Pseudis have a discontinued subarcualis rectus II-IV [28,32,34]. The taxonomic distribution of these character-states on the phylogenetic hypothesis of Duellman et al.  suggests that D. decipiens and D. ebraccatus have the plesiomorphic condition (single subarcualis rectus II-IV), being the m. subarcualis rectus II-IV discontinued at the processus branchialis II a putative synapomorphy of Lysapsus + Pseudis, with instances of homoplasy in D. microcephalus and D. nanus.
Larvae of Dendropsophus, Lysapsus, and Pseudis that have been studied share the m. levator mandibulae lateralis inserted on the nasal sac [32,41] [this work]—although Haas  mentioned that it inserted on the processus posterior dorsalis of the suprarostral or in the rostral tissue in D. ebraccatus [28: ch. 57.0]. In larvae of Scinax, the m. levator mandibulae lateralis inserts on the pars alaris of the suprarostral cartilage [32,34,42]. The taxonomic distribution of these character-states on the phylogenetic hypothesis of Duellman et al.  suggests that the m. levator mandibulae lateralis inserted on the nasal sac could be a synapomorphy of the Dendropsophini + Pseudini clade (sensu ) or arose twice independently in Dendropsophus and the Lysapsus + Pseudis clade. Other character-state, the absence of the superior slip of the m. mandibulolabialis also optimize ambiguously as a synapomorphy of the Dendropsophini + Pseudini clade or of Dendropsophus and the Lysapsus + Pseudis clade (with some instances of reversion within Pseudis; [28,41]). Larvae of Scinax have the superior slip of the m. mandibulolabialis . The optimizations of both character-states mentioned above are dependent on the conditions, still unknown, present in larvae of Scarthyla, Sphaenorhynchus, and Xenohyla.
Tadpoles can be distinguished regarding their deeding habits accordingly with the size of their prey (macrophagous or microphagous) and the nature of the feeding items (herbivore, carnivore, or omnivore). Larvae of Dendropsophus have been described as macrophagous feeders (e.g. ), or macrophagous herbivores according to Wassersug . However, other reports suggest that tadpoles of Dendropsophus could be omnivorous. For example, Vera Candioti  described the presence of entire oligochaetes in the digestive system of D. nanus. Ruas et al.  observed tadpoles of D. novaisi chasing and preying on tadpoles of Rhinella crucifer. Also, larvae of D. minutus were observed attacking and preying on living tadpoles of Physalaemus sp.—although it was considered a facultative behavior, given that D. minutus feeds commercial fish food and plant residues in captivity .
Most of the macrophagous tadpoles (both herbivorous or carnivores) have terminal mouth, reduced branchial basket, well-developed orbitohyoideus, reduced labial tooth rows, reduced or lost elements of the buccopharynx, massive jaw sheaths, fused elements of suprarostral cartilages, and short intestines [32,35–36,44–47,54] [P.H.S. Dias personal observation]. Almost all these character-states are present, with different combinations, in larvae of Dendropsophus. Wassersug  pointed out several buccopharyngeal characters associated with macrophagy in larvae of Dendropsophus, and also reported that D. phlebodes “presented the most extreme reduction in structures associated with fine suspended matters”.
We observed that larvae of Dendropsophus decipiens have some character associated with a macrophagy as a terminal mouth lacking labial teeth, reduction in the elements of the buccopharyngeal cavity, such as papillation and secretory tissue, and single-element suprarostral cartilage. Nevertheless, tadpoles of D. decipiens differ from those of D. microcephalus and D. nanus, which have marked reduction of branchial baskets (well-formed and bearing spicules in D. decipiens) and massive orbitohyoideus  that is correlated with powerful suction capacity . This combination of characters suggests that larvae of D. decipiens feed on large elements and have reduced filter capacity, although they are not as specialized for predation (carnivory/omnivory) as the tadpoles of D. microcephalus and D. nanus. Morphological and behavioral observations for more species, as well as the usage of techniques such as stable isotope (see ) are necessary for a fully appreciation of the evolution of feeding habits in Dendropsophus.
Our results suggest that larval internal morphology could provide interesting insights into the evolution and diversification of Dendropsophus. However, additional studies on other species of Dendropsophus and its related taxa (e.g. Scarthyla, Sphaenorhynchus, and Xenohyla) are required to corroborate the different putative synapomorphies mentioned in this work. Further, the feeding habits of tadpoles of the genus are, putatively, more diverse than previously observed, with variable degrees of specialization for a macrophagous diet.
We thank J. Faivovich and F. Vera Candioti for their comments on earlier drafts of the manuscript. Ênio Mattos and Phillip Lenktatis assisted us with the SEM procedures. Financial support and fellowships were provided by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP; Procs. # 2007/57067-9, 2012/10000-5, 2012/12500-5, 2013/20420-4, 2013/20423-3, 2013/50741-7, 2014/50342-8, 2015/11239-0), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq; Grant # 310467/2017-9), and Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT, PICT 404/2013 and 820/2015).
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