Diapoma pampeana, Ito & Carvalho & Pavanelli & Vanegas-Ríos & Malabarba, 2022

Ito, Priscila Madoka M., Carvalho, Tiago P., Pavanelli, Carla S., Vanegas-Ríos, James A. & Malabarba, Luiz R., 2022, Phylogenetic relationships and description of two new species of Diapoma (Characidae: Stevardiinae) from the La Plata River basin, Neotropical Ichthyology (e 210115) 20 (1), pp. 1-30 : 6-12

Diapoma pampeana , new species

urn:lsid:zoobank.org:act:4B4370D0-0662-4B0B-9D40-6AA1AC0DE842

( Figs. 1–4 ; Tab. 1 )

Diapoma sp. n. —Bertaco et al., 2016:413 (listed, UFRGS 12642, Uruguay River drainage).

Holotype. UFRGS 28705 , male, 29.6 mm SL, Brazil, Rio Grande do Sul, Bagé, road between Aceguá and Bagé, BR-153, Cinco Saltos creek, affluent of Negro River , 31°36’53”S 54°08’42”W, 29 Mar 2006, L. R. Malabarba & students.

Paratypes. All from the Negro River basin. Brazil, Rio Grande do Sul State: MCP

16400, 17, 24.5–32.1 mm SL (2 males, 26.4–26.5 mm SL, 13 females, 24.5–32.1 mm SL, 1 male c&s, 30.0 mm SL, 1 female c&s, 28.9 mm SL), Bagé , Negro River, road ca. 14 km from Bagé , 31°28’37”S 54°08’20”W, 9 Dec 1992, P. H. Wimberger, R. E. Reis & J. F. Pezzi. UFRGS 8429 , 28 , 17.0– 28.1 mm SL (1 male, 25.7 mm SL, 27 juveniles /females 17.0– 28.1 mm SL), Bagé , road between Aceguá and Bagé, Negro River, 31°28’37”S 54°08’20”W, 29 Mar 2006, L. R. Malabarba & students. UFRGS 8464 , 93 , 17.6–33.6 mm SL (2 males, 27.6–28.8 mm SL, 89 juveniles /females 17.6–33.6 mm SL), 2 c&s, 30.8–31.9 mm SL, same locality and collector as holotype. UFRGS 12642 , 16 , 26.9–31.8 mm SL, TEC 1377 , Bagé , BR-153 between Bagé and Aceguá, Negro River, 31°28’37”S 54°08’19”W, 3 Mar 2005, M. A. Azevedo, J. Ferrer, L. R. Malabarba & C. Oliveira. UFRGS 27318 , 6 , 24.3–29.7 mm SL, Aceguá , stream affluent of Negro River, 31°30’42.12”S 54°05’46.85”W, 12 Apr 2019, M. Camana, P. M. Ito, M. Souza & F. Collar. UFRGS 27336 , 1 , 27.8 SL, Aceguá , stream affluent of Negro River at Linha do Silêncio , 31°39’24.41”S 54°19’03.35”W, 15 Apr 2019, M. Camana, P. M. Ito, M. Souza & F. Collar. Uruguay. UFRGS 8119 , 7 , 24.7–33.5 mm SL (1 male 33.5 mm SL, 6 females 24.7–33.0 mm SL, Melo, Departamento de Cerro Largo, small stream at Route 26, ca. 59 km from Melo, between Sauce Creek and Fraile Muerto Creek, 32°17’39”S 54°44’59”W, 28 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera. UFRGS 8120 , 9 , females 23.0–29.0 mm SL, Departamento de Tacuarembó, Tacuarembó River, at Route 26, Villa Ansina, 31°58’33”S 55°28’13”W, 28 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera. UFRGS 8121 , 1 , female 24.3 mm SL, Departamento de Rivera, Negro River, Mazangano Bridge at Route 44, 32°06’33”S 54°40’08.6”W, 27 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera. UFRGS 8122 , 123 , 17.7 –32.0 mm SL (13 males 22.9–32.0 mm SL, 110 juveniles /females 17.7–31.1 mm SL), 2 c&s, 30.4–31.5 mm SL, Departamento de Rivera, lateral puddles and Corrales Creek , affluent of Tacuarembó River, Route 27, 31°23’26”S 55°15’14”W, 27 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera. UFRGS 8123 , 245 , 17.3–29.7 mm SL (3 males 27.7–29.3 mm SL, 242 juveniles /females 17.3–29.7 mm SL), Departamento de Tacuarembó, Caraguatá creek , tributary to Tacuarembó River, Route 26, Las Toscas, 32°09’29”S 55°01’27”W, 28 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera. ZVCP 15417 , 21 , 19.7–32.2 mm SL (6 males 25.0– 28.9 mm SL, 15 juveniles /females 19.7–32.2 mm SL), Departamento de Rivera, lateral puddles and Corrales Creek, affluent of Tacuarembó River, Route 27, 31°23’26”S 55°15’14”W, 27 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera. ZVCP 15418 , 15 , 24.3–27.9 mm SL (3 males 26.1–26.5 mm SL, 12 juveniles /females 24.3–27.9 mm SL), Departamento de Tacuarembó, Caraguatá creek, tributary to Tacuarembó River, Route 26, Las Toscas, 32°09’29”S 55°01’27”W, 28 May 2005, L. R. Malabarba, V. A. Bertaco, P. Lehmann & F. Cantera .

Diagnosis. Diapoma pampeana can be distinguished from its congeners by the presence of a narrow and conspicuous black line along horizontal septum, never forming a wide lateral stripe (vs. lateral dark stripe thick at horizontal septum, usually covering one row of scales at vertical through anal-fin origin); by having a longitudinal black stripe extending posteriorly on middle caudal-fin rays (vs. lack of a black stripe on middle caudal-fin rays in D. alegretense and D. uruguayense ); by the presence of a small black blotch, restricted on the base of the middle caudal-fin rays (vs. presence of a large black blotch extending from the caudal peduncle to the base of most branched caudal-fin rays in D. guarani ). Diapoma pampeana can be differentiated from D. alegretense , D. guarani , D. lepiclastum , D. obi , D. tipiaia , and D. uruguayense by having distal border of the anal fin concave in males (vs. convex in males of D. alegretense , D. tipiaia , and D. uruguayense ; and nearly straight in D. guarani , D. lepiclastum , and D. obi ). It can be distinguished from D. alegretense , D. lepiclastum and D. uruguayense by the number of scales forming sheath along anal-fin base (5–12 vs. 12–18 in D. alegretense , 13–20 in D. lepiclastum , and 20–28 in D. uruguayense ); and from D. uruguayense by the number of branched anal-fin rays (21–25 vs. and 29–35). Diapoma pampeana can be distinguished from D. nandi , D. obi and D. potamohadros by the smaller number of vertebrae (34–35 vs. 36–37 in D. nandi , 36 in D. potamohadros , and 37 in D. obi ); and can be differentiated from D. nandi and D. obi by the lower body depth at dorsal-fin origin (27.7–33.3% SL vs. 32.4–38.8% SL in D. nandi and 34.5–40.8% SL in D. obi ). Diapoma pampeana is distinguished from D. alburnum , D. dicropotamicus and D. itaimbe by the presence of an incomplete lateral line (vs. usually complete in D. alburnum , D. dicropotamicus and D. itaimbe ). Diapoma pampeana can be distinguished from D. pyrrhopteryx , D. speculiferum , D. terofali , and D. thauma by the absence of modified scales in the caudal fin (vs. presence), and additionally, from D. pyrrhopteryx and D. speculiferum by the lack of posterior elongation of the opercle and subopercle bones (vs. presence).

Description. Morphometric data are given in Tab. 1 . Largest specimen 33.6 mm SL. Body laterally compressed, maximum depth at vertical through dorsal-fin origin or at posterior tip of pelvic-fin rays when adnate to body. Dorsal head profile slightly convex or straight, dorsal body profile slightly concave at supraoccipital and straight to slightly convex from tip of supraoccipital spine to dorsal-fin origin, posteroventrally straight from terminus of dorsal fin to adipose-fin origin. Dorsal profile of caudal peduncle somewhat straight to slightly concave. Ventral body profile convex from tip of lower jaw to pelvic-fin origin, straight between pelvic- and anal-fin origins, and posterodorsally slightly straight from this point to caudal peduncle. Ventral profile of caudal peduncle nearly straight. Head with anterior region rounded. Anterior and posterior nostrils rounded, separated by skin fold; posterior nostril opening larger, twice size of anterior nostril.

Mouth terminal, anterior tip of premaxilla slit at the horizontal through upper half of eye. Premaxilla with two rows of teeth ( Fig. 2 ). Outer row with two (2), three (15), or four* (18) teeth; usually conical (27) but sometimes tricuspid (8). Inner row with four* (34) or rarely five (1) tricuspid teeth. Maxilla toothless (1) or with one (10), two (11), three (11), or four* (2) conical teeth ( Fig. 2 ). Posterior tip of maxilla reaching vertical through anterior margin of eye, but not surpassing. Dentary with six (1), seven (2), eight (8), nine (15), 10 (7), 11 (1), or 14* (1) teeth; four anterior-most teeth large and tricuspid, followed by conical teeth ( Fig. 2 ). Third anterior tooth with same size, not aligned and more ventrally located than other teeth of dentary. First gill arch with four (1), six (7), seven* (18), eight (6), or nine (3) gill rakers on epibranchial, 13* (13), 14 (14), or 15 (8) on ceratobranchial.

Dorsal-fin rays ii (35), seven (2), eight* (32), or nine (1). Nine pterygiophores in dorsal fin (4 c&s). Dorsal-fin origin at vertical through slightly anterior to anal-fin origin, often reaching vertical through tip of pelvic-fin rays. Adipose-fin origin at vertical through origin of posteriormost two to three anal-fin rays. Anal-fin rays iv* (10), v (22), or vi (3), 21 (3), 22* (12), 23 (11), 24 (7), or 25 (2). Twenty-two (1), 23 (2), or 24 (1) pterygiophores in anal fin (4 c&s). Anal-fin origin at posterior half of body, posterior to vertical through dorsal-fin origin. Pectoral-fin rays i (35), seven (4), eight* (27), or nine (4). Pectoral-fin inserted immediately after the opercle, posterior tip surpassing pelvic-fin origin, usually reaching the half of elongated scale covering pelvic-fin origin. Pelvic-fin rays i, six* (35). Caudal fin forked with 10/9 principal rays.

Scales cycloid, almost all with the same size and form. Lateral line incomplete, with five (2), six (5), seven* (11), eight (14), or nine (3) anterior pored scales and a total of 32 (1), 33 (2), 34 (8), 35* (9), 36 (12), or 37 (3). Terminal lateral-line tube absent on caudal-fin interradial membrane. Predorsal scales 10 (1), 11 (3), 12* (17), 13 (12), or 14 (2), forming with irregular row of scales. Five* (14) or six (21) longitudinal scale rows between dorsal-fin origin and lateral line. Four (18) or five* (17) longitudinal scale rows between lateral line and pelvic-fin origin. Circumpeduncular scales 11 (1), 12 (10), 13* (12), 14 (11), or 15 (1). One row of scales forming sheath along anal-fin base (eight individuals less than five scales probably lost their scales) five* (3), six (2), seven (3), eight (1), nine (10), 10 (3), 11 (3), or 12 (2) scales. Caudal-fin lower lobe covered by a set of four or five large unmodified scales, not extending beyond anterior one-third of caudal-fin rays. Total number of vertebrae 34 (1), or 35 (3) (4 c&s); 16 (4) precaudal and 18 (1), or 19 (3) caudal.

Coloration in alcohol. Ground color pale yellowish in preserved specimens.Dorsal and dorsolateral portions of body with small black dark chromatophores. Abdominal region lacking pigment. Scattered black dark chromatophores above anal fin. Chromatophores

delineating scale margins above horizontal septum and forming a chevron pattern below and above thin midlateral line. Head darkly pigmented dorsally. Black chromatophores around border of orbit. Opercle with black scattered chromatophores, mostly on its dorsal portion. Infraorbitals pale yellowish (somewhat silvery in some specimens), with scattered black chromatophores. Humeral blotch vertically elongate, covering at least four series of scales, with diffuse black chromatophores in some specimens. Black midlateral line, more diffuse at the humeral area forming a conspicuous narrow line from this region to caudal-fin base. Small caudal peduncle blotch with scattered brown chromatophores, concentrated from middle region of caudal peduncle to interradialis muscles, and faintly through interradial membranes of middle caudal-fin rays. Dorsal fin with chromatophores concentrated on interradial membranes proximally, and hyaline on distal tips. Adipose fin with few scattered black chromatophores. Anal fin dusky, with black chromatophores more concentrated on interradial membranes than on rays; distal border of fin darkly pigmented. Pectoral and pelvic fins mostly hyaline with black chromatophores on interradial membranes and rays. Coloration just after fixation in formalin ( Fig. 3 ) with similar pattern described above, but with dorsal, anal and caudal fins reddish-orange.

Sexual dimorphism. Males have tiny hooks on the distal portion of the anterior three or four branched rays of the anal fin (more clearly visualized in c&s specimens). We observed gill glands on the ten anteriormost filaments of the first branchial arch in sexually dimorphic males, and absence of gill glands on juveniles and females (up to 25 mm SL). No conspicuous morphometric differences between males and females ( Tab. 1 ).

Geographical distribution. Diapoma pampeana is apparently endemic to the Negro River basin, a tributary to the Uruguay River, in Brazil and Uruguay countries ( Fig. 4 ).

Ecological notes. Diapoma pampeana occurs in sympatry with the congeners D. terofali , D. uruguayense , and D. alburnum .

Etymology. The name of the new species is an allusion to the Pampa, a peculiar biome distributed along lowlands of Rio Grande do Sul State, Brazil, Uruguay, and Argentina countries. The new species is apparently endemic to this biome.

Conservation status. There are no clear specific threats detected for this species in the Negro River basin. Based on collecting sites of Diapoma pampeana , we estimate the extent of occurrence ( EOO) to be 6,509.329 km ² and for area of occupancy ( AOO) applying a 2 km ² area for each locality, to be ca. 32.000 km ², which are beyond the minimum limits defined for International Union for Conservation of Nature ( IUCN) for threatened categories under the criteria B (B1: EOO <5,000 km ²; B2: AOO <500 km ²). Therefore, this species can be classified as Least Concern ( LC) according to IUCN categories and criteria ( IUCN Standards and Petitions Subcommittee, 2019).

Figures

FIGURE 1 | Holotype of Diapoma pampeana, male, UFRGS 28705, 29.6 mm SL, Brazil, Rio Grande do Sul, Bagé, Sanga Cinco Saltos, affluent of Negro River, BR-153, between Aceguá and Bagé.

FIGURE 2 | Left premaxilla, maxilla and dentary of Diapoma pampeana, UFRGS 8464, 31.9 mm SL, paratype.

FIGURE 3 | Diapoma pampeana, paratypes, UFRGS 8123, A. Male, 27.2 mm SL, B. Female, 26.0 mm SL, Caraguatá creek, tributary of the Tacuarembó River, Ruta 26, Las Toscas, Tacuarembó, Uruguay. Photograph taken just after fixation in formalin.

FIGURE 4 | Map of part of southern Brazil, Paraguay, Uruguay, and east Argentina showing the geographic distributions of Diapoma pampeana (white squares) and D. potamohadros (paratypes with pink circles, and non-types with plus sign in red). Stars indicate type localities.

Tables

TABLE 1 | Morphometric data for holotype and 34 paratypes of Diapoma pampeana.

	Holotype		Males (N = 12)		Females and juveniles		(N = 22)
		Range	Mean	SD	Range	Mean	SD
Standard length (mm)	29.6	25.1–33.3	28.8		25.9–33.6	29.6	–
Percentages of standard length
Head length	25.2	21.4–25.2	23.0	1.0	21.3–24.7	23.1	0.1
Depth at dorsal-fin origin	31.8	29.7–33.7	31.6	1.2	27.7–32.6	30.6	1.2
Snout to dorsal-fin origin	51.5	48.9–54.5	52.0	1.8	50.8–56.2	53.2	1.6
Snout to pectoral-fin origin	25.8	23.2–26.1	25.0	0.9	23.7–27.5	25.2	0.9
Snout to pelvic-fin origin	45.8	41.9–46.4	44.6	1.4	42.5–47.0	45.1	1.1
Snout to anal-fin origin	59.2	53.9–59.0	57.4	1.5	53.8–60.6	58.7	1.4
Distance between dorsal- and adipose-fin origins	37.7	34.9–39.9	37.0	1.3	33.0–39.5	37.2	1.5
Dorsal- fin origin to caudal-fin base	49.9	46.2–54.8	49.5	2.4	45.9–51.6	48.8	1.8
Dorsal-fin length	25.2	23.2–26.7	25.1	1.0	22.7–26.3	24.2	1.1
Dorsal-fin base length	14.0	10.1–13.7	11.9	1.0	10.4–12.7	11.5	0.8
Pectoral-fin length	24.8	21.9–25.8	23.7	1.0	23.7–27.5	25.2	0.9
Pelvic-fin length	14.4	12.0–15.6	14.1	1.0	12.2–15.7	13.7	0.9
Anal-fin base-length	35.8	32.5–36.1	34.8	1.1	32.1–36.6	34.2	1.4
Caudal peduncle depth	9.2	8.2–10.0	9.1	0.6	7.8–9.7	8.9	0.5
Caudal peduncle length	11.5	9.6–12.4	11.3	0.8	8.9–13.4	11.2	1.1
Percentages of head length
Snout length	17.3	16.3–21.7	19.5	1.6	16.9–22.1	19.1	1.6
Horizontal eye length	43.0	39.5–45.0	43.3	1.8	40.3–46.8	43.6	1.6
Postorbital head length	40.8	36.2–41.6	38.7	1.6	35.6–43.1	39.4	2.1
Least interorbital width	29.8	29.3–34.5	31.9	1.6	28.6–38.7	32.5	2.0
Upper jaw length	34.5	34.6–39.1	36.6	1.5	32.4–38.6	35.3	1.9
Dentary length	36.5	36.7–42.2	39.2	1.8	36.5–41.1	38.8	1.5