Austrolebias ayoreode, Drawert & Ergueta, 2024

Drawert, Heinz Arno & Ergueta, Carlos, 2024, Redescription of Austrolebias accorsii (Cyprinodontiformes: Rivulidae) and description of a new species of the genus from the upper Paraguay River basin, Neotropical Ichthyology (e 240001) 22 (2), pp. 1-29 : 13-20

Austrolebias ayoreode , new species urn:lsid:zoobank.org:act:292472BD-D4D6-4081-B92F-F535584DF1F1

( Figs. 5–7 ; Tab. 2)

Holotype. MNKP 16612 , male, 50.7 mm SL, Bolivia, Santa Cruz, Charagua Iyambae Guarani Autonomous Territory, Ñembi Guasu Conservation and Ecological Importance Area , temporary pool within low dry forest (Abayoy) on side of dirt road between San Jorge and Ponderosa ranches ca. 10 km west of San Jorge , hydrologic unit 6424726 (Pfafstetter), San Miguel watershed , upper Paraguay River drainage, La Plata basin, 19°08’46”S 59°55’44”W, 10 Jun 2021, C. Ergueta & H. A. Drawert.

Paratypes. MNKP 16587 , 12 males (21.2–34.7 mm SL), 11 females (19.7–38.1 mm SL), collected with holotype . MNKP 16590 , 2 males (34.7–34.8 mm SL), 1 female (26.1 mm SL), c&s, collected with holotype .

Non-types. MNKP 16589 , female, Bolivia, Santa Cruz, Charagua Iyambae Guarani Autonomous Territory, Ñembi Guasu Conservation and Ecological Importance Area , temporary pool within low dry forest (Abayoy) ca. 1 km southwest of Ponderosa ranch, hydrologic unit 6424726 (Pfafstetter), San Miguel watershed , upper Paraguay River drainage, La Plata basin, 19°10’35”S 59°57’24”W, 10 Jun 2021, C. Ergueta .

Diagnosis. Austrolebias ayoreode males differs from all congeners, except A. accorsii , A. ephemerus , and A. vandenbergi , by presence of 1–3 transverse rows of scales on basal anterior and median portion of anal fin. Males of A. ayoreode can be distinguished from A. accorsii , A. ephemerus , A. melanoorus , A. queguay , and A. vandenbergi by presence of whitish to pale yellowish dots on flanks usually vertically aligned in unarranged rows (vs. absent in A. accorsii ; mostly coalesced in vertical bars in A. ephemerus , A. melanoorus , and A. queguay ; absent or, when rarely present, sparse and scattered in A. vandenbergi ); from A. accorsii and A. vandenbergi by urogenital papilla mostly attached to anal fin (70–80% adhered vs. only on base and maximum 10% adhered), medial pelvic fin membranes 75–100% coalesced (vs. less than 75% coalesced), and less transversal series of scales (11–13 vs. 14–18, 13–18 [14–17 on comparative material examined, Tab. S1], respectively); from A. ephemerus by shorter pelvic fin (5.0–8.1% SL vs. 8.6–11.1%), wider head width (65.0–83.5% SL vs. 55.3–61.1%), and more anterior rostral neuromasts (2–3 vs. 1); from A. melanoorus and A. univentripinnis by lower pre-pelvic length (38.4–46.7% SL vs. 48.8–52.8%, 47.0–49.4%, respectively); from A. melanoorus by more longitudinal series of scales (30–33 vs. 26–29), more posterior dorsal-fin origin (vertical between of 4 th and 5 th anal-fin ray vs. anterior of 1 st anal-fin ray); from A. univentripinnis by posterior tip of pelvic fins reaching between 1 st and 2 nd anal-fin ray (vs. between 3 rd and 4 th anal-fin ray); from A. vandenbergi by shorter body depth (32.6–38.6% SL vs. 39.6–46.7%). Females of the new species differ from A. bellottii , A. melanoorus , A. univentripinnis , and A. vandenbergi by more posterior dorsal-fin origin (vertical between 4 th and 5 th anal-fin ray vs. anterior of 4 th anal-fin ray); from A. melanoorus and A. univentripinnis by shorter pre-dorsal length (49.0–58.1% SL vs. 60.8–64.4%, 58.7–63.5%, respectively); from A. melanoorus , A. queguay , and A. univentripinnis by posterior tip of pectoral fin reaching between 1 st and 4 th anal-fin ray (vs. not reaching over anal-fin origin); from A. melanoorus and A. univentripinnis by shorter pre-pelvic length (42.6–48.3% SL vs. 52.6–59.2%, 52.5–57.7%, respectively); from A. bellottii by shorter length of anal-fin base (23.7–29.9% SL vs. 32.6–38.1%) and shorter pelvic-fin length (6.6–12.2% SL vs. 12.3–16.8%); from A. ephemerus by greater head width (66.8–82.3% SL vs. 58.4–62.8%) and by posterior tip of pectoral fin reaching between 1 st and 4 th anal-fin ray (vs. reaching between 5 th and 7 th anal-fin ray); from A. queguay by higher anal-fin rays count (28–32 vs. 24–27).

Description. Morphometric and meristic data presented in Tab. 2. Males larger than females; largest examined male 50.7 mm SL, largest female 38.1 mm SL. Body elongated, moderately deep, and laterally compressed. Highest body depth approximately on vertical between origins of dorsal and anal fins in males, and on vertical through pelvic-fin base in females. On lateral view, dorsal profile of head in males slightly convex to almost straight, and in females straight to slightly concave, from snout to vertical between eye and superior limit of operculum, from this point to posterior end of dorsal-fin base convex with increased curvature, and on caudal peduncle straight; ventral profile convex from lower jaw to pelvic-fin base, from there to end of anal-fin base in males slightly convex to almost straight and in females straight to slightly concave, and straight on caudal peduncle. Snout blunt, mouth superior and jaws short.

Tip of dorsal and anal fins rounded in both sexes; in females, anteromedial anal-fin rays longer than the remaining rays, resulting in triangular shaped anal fin; dorsal-fin origin on vertical between 4 th and 5 th anal-fin ray; dorsal-fin origin between neural spines of 8 th to 9 th vertebrae in males and 11 th to 12 th in females; anal-fin origin between pleural ribs of 5 th to 6 th vertebrae in males and 7 th to 8 th in females. Caudal fin rounded. Pectoral fin elliptical; posterior margin reaching vertical between 4 th and 6 th anal-fin ray in males, and between 1 st and 4 th in females. Pelvic fins membranes medially coalesced in 75–100% of its length, posterior tip reaching between 1 st and 2 nd anal-fin ray when folded. Urogenital papilla in males attached to anal fin in 70–80% of its basal portion. Prominent in females. Dorsal-fin rays 23–29 in males and 18–22 in females; anal-fin rays 28–32 in males and 24–28 in females; caudal-fin rays 23–26; pectoral-fin rays 12– 13; pelvic-fin rays 4–5.

Scales cycloid, large. Trunk and head completely scaled, except ventral surface of head. Frontal squamation H-patterned, no scales anterior to H-scale, E-scales usually overlapping medially; scales transversally arranged on trunk. In both sexes, no scales surpassing base of dorsal, pectoral, and pelvic fins; up to 3 rows of scales surpassing anal-fin base on anterior and median portion; 3 rows of scales on caudal-fin base. Longitudinal series of scales 30–33, transversal series of scales 11–13, and circumpeduncular rows of scales 14–16 (two males with 17 and one female with 13), in both sexes. Males with 1 or 2 contact organs per scale on anterior central and ventral section of flanks and opercular region; rows of contact organs on 3–5 uppermost pectoral-fin rays and on anterior distal anal-fin rays; no contact organs on other fins and not present on females.

Cephalic neuromasts: supraorbital 16–18 (one with 15), parietal 1–3 (usually 3), anterior rostral 2–3 (usually 2 or 5 adding both sides of head), posterior rostral 1–2 (usually 1), infraorbital 2 + 22–27, preorbital 2 (one with 1), otic 1–3 (usually 2), post-otic 2–4 (usually 3–4), lateral supratemporal 1 (sometimes absent), median opercular 1–4 (usually 1), ventral opercular 3–5 (usually 3), preopercular 19–23 (usually 21–22), mandibular 11–18 (usually 15–16), lateral mandibular 6–8, post-temporal 1–2 (usually 1). Lateral line complete, with one neuromast per scale.

Total number of vertebrae 30–32. Hypurals ankylosed in a single plate without visible fissure. Six branchiostegal rays, arranged in 3 pairs. Gill-rakers on 1 st branchial arch 6–8 + 16–18.

Coloration in life. Males ( Figs. 5–6 ). Head greenish gray, opercular region bluish gray to bluish dark green. Broad black bar crosses vertically the eye; subrectangular at suborbital portion, and subtriangular at supraocular portion rarely surpassing dorsally the line of parietal neuromasts. Iris yellow to dark yellow with black vertical bar through center of eye. Trunk and caudal peduncle ground color greenish gray, some paler at anteroventral region. Flanks and caudal peduncle sides with whitish to pale yellowish dots; sometimes, especially on anterior flanks, vertically elongated and usually vertically aligned in 5–11 unarranged rows. At anteromedial portion of flanks, approximately on center of linear axis between anal- and dorsal-fin bases, 1–2 vertically elongated black humeral blotches with size of eye diameter or larger, sometimes coalesced or unconspicuous. Pectoral fins hyaline to pale gray, with black margin at least ventrally, sometimes also distally and dorsally, and usually with a bluish gray iridescent band at ventral submargin. Pelvic fins pale gray to greenish gray, usually with black tip. Dorsal and anal fins greenish gray at basal half, usually with some whitish to yellowish spots following vertical alignment of spots on flanks; dorsal fin distal half hyaline to pale gray, sometimes posterodistal section dark gray to almost black and with black margin; anal fin distal half pale gray to greenish gray, submargin usually dark gray to almost black with black margin. Caudal fin basal half greenish to bluish gray, sometimes with metallic shine, and marginal section hyaline.

Females ( Figs. 5 , 7 ). Head pale greenish gray with golden greenish iridescent postocular and opercular region. Iris yellow to dark yellowish with black vertical bar through center. Trunk and caudal peduncle ground color yellowish brown, greenish darker dorsally, on anteroventral and pectoral region pale yellowish turning whitish ventrally, sometimes golden iridescent on anterior flanks. Posterior flanks and caudal peduncle sides with dark grayish brown to pale black blotches irregularly distributed, turning inconspicuous with age. On anteromedial flanks, some anterior to the center of the linear axis between anal- and dorsal-fin bases, 1 to 4 black, sometimes greenish iridescent, vertical elongated humeral blotches. Fins hyaline; dorsal fin sometimes pale yellowish at basal half and with some black dots at posterior basal section; anal fin sometimes pale yellowish at anterior and median basal section and/or with some black dots at posterior basal section.

Coloration in alcohol. Overall color pattern similar to that of live specimens, but less intense and faded, without iridescence and shines, or color hues. Body background color in males brown to grayish brown, in females yellowish gray to pale yellowish brown. Dorsal and anal fins in males dark gray to pale black.

Geographical distribution. This species is only known from two temporary pools in an unnamed watershed ( HU 6424726 ) that drains its waters through an intermittent stream into the San Miguel River , part of the upper Paraguay River drainage in the La Plata basin ( Fig. 3 ). The locality is situated in the Cordillera Province of the Santa Cruz Department in Bolivia, in close proximity to the Paraguayan border. With such a restricted known distribution, the species can be considered microendemic to the area. Ecological notes. The species is found in two distinct types of aquatic ecosystems within the xeric woodlands of the Dry Chaco ecoregion, in the Chiquitano transitional to Chaco sector, locally known as “Abayoy”. The first is a residual temporary pool of an intermittent watercourse with clear water ( Fig. 8 ), not exceeding 30 cm in depth ,

featuring a thin layer of plant litter and debris (1 to 2 cm) over gray clay as substratum.

It is situated in dense vegetation, with some low trees and shrubs growing in it, and includes submerged aquatic plants (Echinodorus sp., Najas sp., Cabomba sp. and Riccia fluitans Linnaeus, 1753), emergent species (mainly Poaceae species, and Echinodorus sp.)

and abundant floating plants ( Nymphaea sp. , Limnolobium sp., Lemna sp. , Pistia stratiodes

Linnaeus, 1753, Azolla sp., and Heteranthera aff. peduncularis), which, in some wellilluminated areas, completely cover the water surface. The second aquatic ecosystem,

located a few kilometers away from the first, is a temporary clearwater lagoon with a depth of up to 1.5 m and a detritus layer (ca. 5 cm) over sandy substrate. It exhibits a considerable diversity of aquatic vegetation, including submerged species ( Najas

sp., Sagittaria sp., Echinodorus sp., Eleocharis aff. vivipara, Macaya sp., and R. fluitans), floating species (P. stratiodes, Salvinia sp., Lemna sp., Limnolobium sp., Nymphoides sp., and Nymphaea sp.), and emergent plants (Poaceae and Cyperaceae species, Eleocharis sp., Echinodorus sp., and Sagittaria sp.) in the riparian zone. This waterbody has extensions that extend into the surrounding shrubland, forming aquatic ecosystems with characteristics similar to those of the first described ecosystem where A. ayoreode inhabits. The only sympatric fish species in these ecosystems is Neofundulus paraguayensis (Eigenmann & Kennedy, 1903). The minimum annual temperature varies from 2.1 to 10.2°C (average 6.2°C), and the maximum ranges from 38.8 to 44.3°C (average 41.4°C), with minimums concentrated in the months of May to August and maximums from September to November. The accumulated annual precipitation can vary from 443 to 1334 mm, concentrating in the months of November to March, with a pronounced dry season between June and September.

Etymology. The name ayoreode is an eponym conferred in reference to the indigenous Ayoréode people, who historically occupied vast expanses of the northern Dry Chaco, and of whom a few groups still persist in the area of the type-locality of this species, standing as the last indigenous people in voluntary isolation outside of the Amazon in the Americas. Through this nomenclature, we intent to perpetuate the memory of the existence of the Ayoréode and emphasize the imperative of preserving their ancestral territory, which also is the habitat of the species described herein.

Conservation status. The species is known only from two closely situated (approximately 4 km) and isolated temporary water bodies in xeric woodlands and shrublands. Despite intensive sampling on multiple occasions in the area, the species was not found outside these specific waterbodies. Considering this, the estimated area of occupancy (AOO) is challenging due to the scarcity of small ephemeral and temporary water bodies in the xeric ecosystems of the Chiquitano transitional to Chaco sector near the border between Bolivia and Paraguay; detection and quantification with telemetric methods are difficult. Based on the currently known occurrences, the species has an AOO of less than 10 km ², but this estimate has a high degree of imprecision, and the AOO could potentially be higher, although unlikely to exceed 500 km ². Despite the entire AOO being within a subnational conservation unit (Ñembi Guasu Conservation and Ecological Importance Area), this does not exempt the species from threats to its conservation status and does not guarantee the stability of its population. On one hand, the legal security in Bolivia of subnational conservation areas, such as Ñembi Guasu, is fragile and uncertain, while, on the other hand, there is strong social demand for productive use of these territories. Additionally, the direct and indirect effects of climate change pose serious threats to both this species and the ecosystems it inhabits. Changes in hydrological regimes, such as prolonged and/or intense drought periods, can negatively affect the embryonic and/or ontogenetic development of species subpopulations. Indirectly, the increased incidence of wildfires, similar to those that occurred in the area in 2019, reaching sixth-generation levels and triggering firestorms, can rapidly degrade the habitat quality for these fish. Following the guidelines for categories and criteria of the IUCN, the species may be categorized as Endangered (EN) as it meets the criteria B2a,b(ii,iii) (IUCN Standards and Petitions Committee, 2022).

Figures

FIGURE 3 | Occurrence localities of Austrolebias species in the northern Chacoan province. Stars represent type-localities, colors differentiate the species (A. accorsii red, Austrolebias n. sp. yellow, A. ephemerus green, A. vandenbergi blue). Blue numbers indicate the Hydrologic Unit (Pfafstetter, level 5). Sources: Ecoregions from Olson et al. (2001); Hydrologic Units from Lehner, Grill (2013); Basemap ESRI World Topo (2022).

FIGURE 5 | Austrolebias ayoreode. Male and female (1 day after collection). Above: MNKP 16612, holotype, male, 50.7 mm SL, Bolivia, Santa Cruz, Cordillera, Charagua Iyambae Guarani Autonomous Territory, Ñembi Guasu Conservation and Ecological Importance Area. Below: MNKP 16587, paratype, female, 38.1 mm SL, collected with holotype.

FIGURE 6 | Austrolebias ayoreode. Males (immediately after collection). Two uppermost: MNKP 16590, paratypes, 34.7–34.8 mm SL, Bolivia, Santa Cruz, Cordillera, Charagua Iyambae Guarani Autonomous Territory, Ñembi Guasu Conservation and Ecological Importance Area. Lower six: MNKP 16587, paratypes, 21.2–34.7 mm SL, collected with uppermost.

FIGURE 7 | Austrolebias ayoreode. Females (immediately after collection). Above: MNKP 16590, paratype, 26.1 mm SL; Bolivia, Santa Cruz, Cordillera, Charagua Iyambae Guarani Autonomous Territory, Ñembi Guasu Conservation and Ecological Importance Area. Below: MNKP 16587 (vertically flipped), paratype, female, 38.1 mm SL, collected with MNKP 16590.

FIGURE 8 | Biotope at type-locality of Austrolebias ayoreode. Bolivia, Santa Cruz, Cordillera, Charagua Iyambae Guarani Autonomous Territory, Ñembi Guasu Conservation and Ecological Importance Area, 19°08’46”S 59°55’44”W, 10 Jun 2021. A. Well-illuminated area; B. Less illuminated area.