Boana stellae ( Kwet, 2008 )

Widholzer, Ronaldo Libardi & Castroviejo-Fisher, Santiago, 2018, The tadpole of Boana stellae (Anura: Hylidae), Zootaxa 4508 (4), pp. 582-586 : 582-585

Boana stellae ( Kwet, 2008)

was allocated within the B. pulchella species group and, presumably, is closely related to B. caipora ( Antunes, Faivovich, and Haddad, 2008) , B. curupi ( Garcia, Faivovich, and Haddad, 2007) , B. joaquini ( Lutz, 1968) , and B. semiguttata ( Lutz, 1925) due to the similarity of the external morphology of adult specimens ( Kwet 2008). Boana stellae is currently only known from adult specimens and embryos from the type locality in Rio Grande do Sul, southeastern Brazil, and from a single locality in Misiones, Argentina ( Ferro et al. 2018). Although the embryo morphology has been described in detail (Navarro Acosta et al. 2017; Navarro Acosta & Vera Candioti 2017, as Hypsiboas sp. gr. pulchellus), the tadpole of B. stellae has not been yet described.

We collected three tadpoles at the type locality (i.e., stream confluent of rio Pardinho, about 15 km N of Sinumbú , Rio Grande do Sul, RS; 29.56425 S, 52.567333 W; 400 m a.s.l.) on 0 4 October 2016 and deposited them at the amphibian collection of Museu de Ciências e Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul ( MCP) . Tadpoles were found inside the water of a small stream (average width ~ 1 m), at ~ 10 cm depth. The predominant substrate of the stream was gravel and large rocks ( Fig. 1A, B ). The tadpoles were at Stages 25 (n = 1; MCP 13201) and 30 (n = 2; MCP 13202) of Gosner (1960). Tadpoles were euthanized with lidocaine diluted in water and fixed and preserved in 10 % formalin. A sample of muscle tissue of MCP 13201was preserved in 95 % ethanol. We sequenced the barcoding fragment of the 16S mitochondrial gene following described procedures and primers ( Vences et al. 2005) of five adults and one tadpole of B. stellae ( MCP 13201), all topotypic (Appendix). Sequences were aligned using Muscle ( Edgar 2004) as implemented in Mega 6.06 ( Tamura et al. 2013) with default parameters, the later software was also used to calculate uncorrected pairwise genetic distances. We also studied 14 tadpoles from the type locality of B. stellae that were already available at MCP (Appendix). For comparisons with other species, we used the available descriptions of the external morphology of tadpoles of B. caipora , B. curupi , B. semiguttata , and B. joaquini ( Faivovich 1996; Garcia et al. 2003, 2007; Antunes et al. 2008). We studied the 23 discrete morphological characters (see results) following Altig & McDiarmid (1999) and measured 22 morphometric variables in preserved tadpoles using a digital caliper or a stereo microscope Zeis SV11 with graduated lenses (precision 0.1 mm). Variables follow Altig (1970), Altig & McDiarmid (1999), and Gonçalves (2014): Total length (TL); internarinal distance ( IND); interorbital distance ( IOD); snout length ( SNL); eye diameter ( ED); eye-naris distance ( EN); head width ( HW); body width ( BW); body height (BH); body length ( BL); tail length ( TAL); maximum tail height ( MTH); tail muscle height ( TMH); tail muscle width ( TMW); height of upper tail fin ( UTAIL); height of lower tail fin ( LTAIL); snout-spiracle distance ( SSD); spiracle length ( SPL); height of spiracle ( HS); spiracle width ( SW); maximum width of nostril ( MWN); Oral disc width ( OW).

Uncorrected pairwise genetic distances of 16S (565–567 bp) among five adult topotypic specimens of Boana stellae and the tadpole MCP 13201 are 0.0–0.1 %. Based on these molecular results, we identified this tadpole as B. stellae . Below, we describe the external morphology of MCP 13201 and MCP 13202, Gosner Stages 25 and 30 ( Fig. 1 C–E), followed by comments on variation corresponding to the other 16 topotypic tadpoles ( Table 1).

Body depressed (BH/BW = 0.9); longer than one third of total length (BL/TL = 0.3); body shape oval in dorsal view, widest at spiracle level. In lateral view, ventral contour of body flat in gular and concave in branchial regions, slightly convex in abdominal region. Dorsal contour of body slightly convex from the nostrils to beginning of dorsal fin. Snout rounded in dorsal and lateral views. Nostrils oval, with slightly elevated marginal rim and a rounded projection in medial margin; nostrils dorsolaterally located, as closer to eyes as to the tip of snout (SNL/EN = 1), visible in dorsal and lateral views. Eyes large (ED/B = 0.2), dorsolaterally positioned and dorsolaterally directed, not visible in ventral view. Spiracle single, lateral and sinistral, its inner wall fused to body except for its distal end; its opening oval, elevated, more longer than wide (SPL/SW = 1.7), diameter smaller than or equal to tube diameter, located in posterior third of body (SSD/BL = 0.7), visible in dorsal and lateral views. White spots on antero and posteroventral portions of the body ( Kolenc et al. 2008) not observed. Vent tube starts at midline, at posterior end of body, vent tube and tail welded, opening dextral. Tail long (TAL/TL = 0.7), with both fins higher than body height (MTH/ BH = 1.2). Dorsal fin originates before of body-tail junction. Ventral fin origin concealed by vent tube. Dorsal fin contour slightly convex; ventral fin contour almost flat, both fins tapering to tip of tail in last third. Tail axis straight, end acute; tail musculature reaching tail tip. Oral disc ( Fig. 1E ) ventral (OW/ BW = 0.5, disc measured folded) with a well-marked infra-angular emargination on each side. Marginal papillae simple, straight; those at anterior lip short and blunt, while the ones at posterior lip longer and thinner, with pointed tip. Dorsal gap present. Row of marginal papillae single, disposed in angular and infra-angular regions. Presence of short ridges with teeth in the commissures. Upper jaw sheath widely arch-shaped. Lower jaw sheath Vshaped. Labial tooth row formula 3(1,3)/5(1). A2 slightly longer than A1 and A3. P3 as longer than P2, P1 and P4 respectively. P5 is the smaller one with 2/3 of P3.

In life, yellowish-brown body with golden spots; dorsum darker than venter, with small spots in the form of dark spots; ventral skin opaque, with many golden spots; caudal muscle clearer than the body, transparent fins with yellowish tones; few melanophores on caudal fin, more numerous in the dorsal side; iris golden. In preservative, whitish body with small darker points in the eye region and larger spots on the posterior half of the body; venter partially translucent, allowing partial visualization of gills and intestine; caudal muscle white, which brown spots.

Variation in qualitative characters is scarce and seems associated with development. The ocular lateral line becomes visible at stage 36 and the snout becomes truncated in dorsal view at stage 42. Variation in coloration is subtle and related to the number of spots on body and tail with no obvious pattern. Morphometric variation is summarized in Table 1.

Kwet (2008) referred to a lot of 38 tadpoles from Arvorezinha, RS (approximately 53 km in straight line from the type locality) as Boana cf. stellae (Appendix) . However, those specimens have not been further studied. Herein, we compared the tadpoles of B. stellae with those from Arvorezinha, RS. The only noteworthy difference is related to the external morphology of the oral disc ( Table 2). While we found no variation in the number of tooth rows among 17 tadpoles of B. stellae from Sinimbú, the number of anterior and posterior tooth rows among 38 tadpoles from Arvorezinha varied (2–3 and 3–5, respectively). With the data at hand, the observed variation between the tadpoles of two localities could be explained as intraspecific polymorphism, local adaptation, phenotypic plasticity, and developmental changes. Thus, we prefer to leave the identification of the tadpoles from Arvorezinha as B. cf. stellae .

In general, the tadpole of Boana stellae is similar to the larva of Boana caipora , B. curupi , B. joaquini , and B. semiguttata . However, there are differences among them ( Table 2). The only of these tadpoles that has the same tooth row formula than B. stellae is B. curupi ; however, the later has two rows of papillae and lack a dorsal diastema. Nonetheless, one should keep in mind that marginal papillae may appear as in a single, single-alternated, and double array depending of the developmental stage and the sector of the margin and the dorsal gap may or may not be evident depending on the developmental stage and on how papillae bear teeth forming the extra anterior row.

We wish to thank Fernando J.M. Rojas-Runjaic and Adriana Becerra-Rondón for help during fieldwork, Glaucia Maria Funk-Pontes for help with museum specimens and Henrique Zanette-De Castilhos for help with photos of tadpoles. We are thankful to Florencia Vera Candioti and an anonymous reviewer for comments on a previous version on the manuscript that helped to improve it. This study had financial support from CNPq (project # 442981/2014-7, PI: SC- F) and Programa de Excelência Acadêmica of Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (PROEX- CAPES, project #1030/2014). Ronaldo L. Widholzer performed research while on a scholarship from CAPES to complete his master degree.

Figures

FIGURE 1. General aspect of the stream where tadpoles of Boana stellae were found (A) and exact pond in which the tadpoles were collected (B). General ventral and dorsal view of the preserved tadpole of B. stellae, MCP 13202 stage 30 (C, D), and detail of the oral disc of MCP 13201 stage 25 (E).