Elachistocleis matogrosso Caramaschi, 2010

Novaes-E-Fagundes, Gabriel, Lyra, Mariana L., Loredam, Vinicius S. A., Carvalho, Thiago R., Haddad, Célio F. B., Rodrigues, Miguel T., Baldo, Diego, Barrasso, Diego A., Loebmann, Daniel, Ávila, Robson W., Brusquetti, Francisco, Prudente, Ana L. C., Wheeler, Ward C., Orrico, Victor Goyannes Dill & Peloso, Pedro, 2023, A tale of two bellies: systematics of the oval frogs (Anura: Microhylidae: Elachistocleis), Zoological Journal of the Linnean Society 197, pp. 545-568 : 557-558

Elachistocleis matogrosso Caramaschi, 2010 as junior subjective synonym of Elachistocleis bicolor ( Guérin-méneville, 1838)

The two topotypical samples of E. matogrosso were recovered in E. bicolor ( Fig. 1 ). Although some SDM analyses grouped those samples as a different putative species (see ASAP-16S-splitter and mPTP, Fig. 1 ), their morphological variation falls in what we observed for E. bicolor , as delimited herein. Caramaschi (2010) distinguished E. bicolor and E. matogrosso by subtle differences in four morphological traits: head proportions (HL/HW about 0.92 in E. matogrosso vs. HL/HW below 0.90 in E. bicolor ); the mid-dorsal white line (present in E. matogrosso vs. absent in E. bicolor ); loreal region colouration (same grey colour of dorsum in E. matogrosso and white in E. bicolor ); and shape of the femoral line (broad in E. matogrosso vs. thin in E. bicolor ). None of these differences listed by Caramaschi (2010) holds for the voucher specimens we examined. All are in the range of variation of those characters: the HL/HW ratio varies significantly from 0.76 to 0.93 (N = 24), and the specimens from Cuiabá (type locality of E. matogrosso ) have the ratio of 0.84 and 0.88; the mid-dorsal line may be present or absent ( Fig. 1 ); all vouchers have the loreal region with the same colour of the dorsum, which varies from shades of grey to brown; the femoral line is usually thin, but at least one voucher from Argentina (LGE 10782) has a broad line, as does one voucher from Cuiabá originally assigned to E. matogrosso (AAG-UFU 5954). Therefore, due to its phylogenetic position, and genetic and morphological similarity, we formally propose that Elachistocleis matogrosso Caramaschi, 2010 is a junior subjective synonym of Elachistocleis bicolor (GuérinMéneville, 1838) .

Elachistocleis bicolor has a long and complex nomenclatural history (for a summary and references see: Frost, 2022). Currently, E. bicolor is recognized as a species with an immaculate yellow venter and dorsum lacking the mid-dorsal white line ( Lavilla et al., 2003; Caramaschi, 2010). Lavilla et al. (2003) argued that the type locality of E. bicolor is Buenos Aires, Argentina; although it is not clear if they were referring to the city of Buenos Aires or the Province of Buenos Aires. Our conclusions would not change either way, as all the nearest samples to both regions belong to the same species ( Figs 1 , 3 ).

It is important to remark that, although most of the vouchers we examined indeed fit into the current understanding of E. bicolor morphology, some of them do not. Several specimens have the mid-dorsal line, others have the venter with a finely spotted pattern and one specimen (AAG-UFU 5953) has both a dorsal line and a maculate belly ( Figs 1 , 4E ). Even though the ventral colour pattern of this specimen is not as evident as the pattern seen in specimens of the E. surinamensis group, it is certainly not equal to the uniformly immaculate pattern historically described for E. bicolor . What is even more remarkable is that another syntopic and genetically identical (p -distance = 0.0%) specimen (AAG-UFU 5954) has the classical immaculate yellow belly ( Marinho et al., 2018: fig. 6). We note that ontogenetic variation has been recorded for the ventral colour pattern in at least one species ( Elachistocleis haroi ; Bueno-Villafañe et al., 2020). Juveniles and subadults of E. haroi present a venter translucent grey with small black specks and white stains, while the yellow colouration develops gradually with growth and sexual maturation of the individuals (see: Bueno-Villafañe et al., 2020: fig. 1). Curiously, the three vouchers of E. bicolor with spotted venters are one juvenile and two small-sized males (SVL ≈ 23 mm). This, of course, is not indisputable evidence of a consistent pattern (the other two smaller males have uniform immaculate yellow venter), but certainly requires further investigation.

Figures

Figure 1. Species delimitation in Elachistocleis. The tree shown is from the maximum likelihood (ML) analysis with only 16S + COI from only Elachistocleis samples (tree rooted in E. araios). Numbers on branches are SH-aLRT/UFBoot support values. Asterisks represent support above 80/95. The terminals of the tree are named as: original labelling of

Figure 3. Geographic location of sampled specimens (symbols) and type-localities of the nominal species (numbers). 1, Elachistocleis araios; 2, E. bicolor (here illustrated as the city of Buenos Aires; see Discussion); 3, E. bumbameuboi; 4, E. carƲalhoi; 5, E. cesarii; 6, E. corumbaensis; 7, E. erythrogaster; 8, E. haroi; 9, E. helianneae; 10, E. magna; 11, E. matogrosso; 12, E. muiraquitan; 13, E. nigrogularis; 14, E. panamensis; 15, E. pearsei; 16, E. piauiensis; 17, E. sikuani; 18, E. skotogaster; 19, E. surinamensis; 20, E. surumu; 21, E. tinigua.

Figure 4. Variation of ventral colour pattern among sample vouchers of different species of Elachistocleis of the bicolor group. A, B, E. helianneae; MPEG 29416, 29419. C, E. haroi; IIBPH 2947. D–F, E. bicolor; CFBH 10117, AAGUFU 5953, IIBPH 0285. G, H, E. nigrogularis; CAS 231811, 245101.