Phylogenetic systematics and historical biogeography of the Neotropical electric fish Sternopygus (Teleostei: Gymnotiformes)

Abstract

Interrelationships among 10 extant species of the Neotropical electric fish Sternopygus are inferred from phylogenetic analysis of 66 morphological characters, including features of pigmentation, body proportions, meristics and osteology. A total of 287 lots containing 677 specimens were examined. The important findings of this study are: (1) S. branco is the most basal species unique among congeners in being restricted to whitewater rivers in the Central Amazon Basin, (2) S. sp. ‘cau’ from the Rio Caura of Venezuela is the sister taxon to (S. obtusirostris + S. astrabes), (3) S. castroi is a junior synonym of S. astrabes, (4) S. macrurus is the sister taxon to (S. arenatus + S. xingu + S. aequilabiatus species group) and (5) S. arenatus is the sister taxon to (S. xingu + S. aequilabiatus species group). A key to the adults of Sternopygus species is provided. Several features of S. astrabes previously thought to be plesiomorphic are now considered derived, including: short body cavity, paedomorphic cranial osteology, and the habitat restriction to terra firme streams. Sternopygus species assemblages in the Pacific (trans‐Andean) and Atlantic (cis‐Andean) slopes of northwestern South America are not monophyletic and do not result exclusively from local or regional radiations. The clade composed of S. macrurus, S. arenatus, S. xingu and the S. aequilabiatus species group is inferred to predate the Middle Miocene uplift of the Eastern Cordillera (c. 11.8–12.2 Ma). As currently recognized S. macrurus is the most widely distributed and most eurytopic gymnotiform species, inhabiting all hydrogeographical regions of tropical South America and most lowland aquatic habitats. Other Sternopygus species have much more restricted geographic and ecological distributions. Perceptions of phylogenetic patterns in Sternopygus are shown to be highly sensitive to taxon sampling.

Keywords:

• biodiversity
• classification
• comparative osteology
• evolution
• South America
• ontogeny

Notes

Corresponding author. Email: [email protected]