Review of Ancistrus (Siluriformes: Loricariidae) from the northwestern Guiana Shield, Orinoco Andes, and adjacent basins with description of six new species

Abstract

The Orinoco Andes and northwestern Guiana Shield (Essequibo, Orinoco, Branco, and upper Negro) were found to contain 11 species of Ancistrus, six of which are new. We additionally examine A. brevifilis from the Río Tuy of Venezuela and A. trinitatis from the island of Trinidad. The species in the region can be broken up into dorsoventrally flattened species (A. leoni new species, A. lithurgicus, and A. macropthalmus), white to yellow-dotted species (A. kellerae new species, A. nudiceps, and A. patronus new species), wide-jawed species (A. amaris new species and A. yutajae new species), and white-spotted species (A. brevifilis, A. leucostictus, A. trinitatis, A. saudades new species, and A. triradiatus). Distributions of Ancistrus support the Proto-Berbice hypothesis as A. saudades is found in the upper reaches of the Ventuari, Caura, and Caroni rivers, which were thought to have once flowed into the Proto-Berbice. In addition, although A. nudiceps does not appear to have split once the Takutu River was captured by the Branco, the progenitor of A. leucostictus and A. saudades did speciate with the populations on either side of the Rupununi Portal differing by 7% sequence divergence of the mitochondrial Cytochrome b gene. Besides the descriptions of the new species, we redescribe the others occurring in the area, and adjacent watersheds. We provide a key for their identification, and a preliminary hypothesis of relationships based on DNA sequences of the few species for which tissue samples are available.

A new distinctively striped species of bushynose catfish (Siluriformes: Loricariidae: Ancistrus) from the Pachitea River drainage, Pasco, Peru

“…Yet, in the original description, Steindachner (1876) comments that A. jelskii has the dorsum of head slightly mottled, body indistinctly marbled, and very small eyes (vs. conspicuous black stripes over the body and normal‐sized eyes in A. yanesha ). Most species of Ancistrus have mean orbital diameter (OD) >15% HL (i.e., de Souza et al, 2019; Taphorn et al, 2013), like A. yanesha (OD mean = 21.1% HL; Table 1). On the other hand, some Andean species have what we can consider as very small eyes, like A. greeni (Isbrücker, 2001) (OD mean = 11%; Bifi & Ortega, 2020) and A. occloi (OD =10.9% HL, CAS‐ICH 071818).…”

Connectivity of Neotropical River Basins in the Central Guiana Shield Based on Fish Distributions

“…The combination of increased acidity and low dissolved oxygen results in a greater degree of air-breathing fishes in tropical systems relative to temperate, reflecting selective pressure due to the hypoxic conditions (Lowe-Mcconnell, 1975;Kramer, 1983), and sites with these conditions were dominated by predatory species and species tolerant of these conditions, including Pygocentrus natteri, Acestrorhynchus falcirostris, Hoplias malabaricus, and Megalechis thoracata (Figure 6). These hypoxia-tolerant fishes are those that we would predict would move more easily across the Rupununi Portal, and such has been shown for needlefish (Potamorrhaphis; Lovejoy and De Araújo, 2000;de Souza et al, 2012), the trahira (Hoplias malabaricus; de Souza et al, 2012), the peacock bass (Cichla; Willis et al, 2010), the eartheater cichlid (Geophagus surinamensis; de Souza et al, 2012), the flannel-mouth characin (Prochilodus; Turner et al, 2004); two species of suckermouth armored catfish (Ancistrus nudiceps and Hypostomus emarginatus; de Souza et al, 2012Souza et al, , 2019. Meanwhile, the slow waters of the flooded savanna likely limit some fishes from crossing.…”

“…Species cognates (sister species pairs found either in the Rupununi or the Takutu) have been identified in species that appear to be intolerant of still waters including some suckermouth armored catfishes (Peckoltia cavatica vs. P. braueri and Ancistrus leucostictus vs. A. saudades), some species of pencil catfishes (two probably undescribed species of Acanthopoma and two of Branchioica), some wood catfishes (Auchenipterus demerarae vs. A. ambyiacus), and some toothless characins (Curimata sp. vs. C. roseni) (de Souza et al, 2012(de Souza et al, , 2019.…”

“…Its dynamic and complex paleogeographic history has contributed to the tremendous biodiversity, spectacular table-top mountains called tepuis and remarkable waterfalls often cascading 500 m or more off the face of escarpments throughout the Shield (i.e., Angel Falls, Kaieteur Falls, Yutajé Falls). High levels of endemism are characteristic for the region particularly among several taxonomic groups (including cichlids, gymnotiform knifefishes, and siluriform catfishes) in the Guiana Shield with percentages as high as 80-95% (GAHEF, 1992;Duellman, 1999;Lopez-Fernandez et al, 2012;Maldonado Ocampo et al, 2013;Potapov et al, 2017;de Souza et al, 2019;Paz et al, 2019). Intriguing explorers for centuries, these highland regions of the Guiana Shield continue to remain poorly known due to remoteness and isolation.…”

Range extension of the miniature pencil‐catfish Potamoglanis wapixana (Siluriformes: Trichomycteridae) into the Essequibo River basin, Guyana

“…The proto-Berbice has been invoked to explain distributions of various rheophilic fish species occurring in headwaters of the Orinoco, the upper Branco and/or throughout the Essequibo, whose occurrences on opposite sides of the modern Rupununi Savannahs are hypothesized to be relicts of a once-contiguous distribution throughout the proto-Berbice (e.g., Armbruster et al, 2021). This provides one possible hypothesis to , 2019Lovejoy & De Araújo, 2000;Sabaj et al, 2020;Willis et al, 2012). This is the first report of a miniaturized fish species having a range spanning portions of both the Branco and Rupununi river basins, possibly indicating that other very small-bodied fishes can also cross this drainage divide.…”