Title

A new species of electric knifefish, genus Compsaraia (Gymnotiformes: Apteronotidae) from the Amazon River, with extreme sexual dimorphism in snout and jaw length

Authors

Authors

J. S. Albert;W. G. R. Crampton

Comments

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Abbreviated Journal Title

Syst. Biodivers.

Keywords

comparative morphology; mosaic evolution; neotropical biodiversity; osteology; phenotypic evolution; taxonomy; GHOST KNIFEFISH; COLOMBIA GYMNOTIFORMES; FISHES GYMNOTIFORMES; BASIN; DIVERSITY; BRAZIL; PHYLOGENY; TELEOSTEI; COMPONENT; BEHAVIOR; Biodiversity Conservation; Biology

Abstract

Anew species of the neotropical electric fish genus Compsaraia is described from the western Amazon of Peru and Brazil. Compsaraia samueli is distinguishable from all other apteronotids by sexual dimorphism in which mature males exhibit extreme elongation and slenderness of the snout and jaws. Compsaraia samueli is readily distinguishable from its only congener, C. compsa, by more caudal-fin rays (17-18 vs. 13-16), a shorter caudal peduncle (mean length 9% vs. 34% body length to end of anal fin), a less tapering body shape in lateral profile (mean ratio of body depth at origins of anal fin and dorsal organ 93% vs. 75%), and a smaller maximum adult body size (230 vs. 305 mm). The genus Compsaraia is readily separated from other apteronotids by a pate antorbital stripe and a pale L-shaped patch over the supratemporal canal. The phylogenetic position of C. samueli is estimated by inclusion in a previously published data matrix of osteological and other morphological characters. Comparisons of the cranial bones in apteronotids shows the derived morphology of C. samueli to be a composite of three developmentally and phylogenetically discrete characters: (1) positive allometric growth before sexual maturity in both sexes of the pre-orbital region of the neurocranium, (2) positive allometric growth of the (oral) jaws, and (3) secondary sexual dimorphism of snout and jaw morphology. The genus Compsaraia represents one of at least three phylogenetically independent cases of snout elongation and one of at least four cases of jaw elongation within the Apteronotidae. Compsaroia samueli also represents one of at least four cases of secondary sexual dimorphism in snout and jaw length within the Apteronotidae. The phylogenetic distribution of snout and jaw characters within the Apteronotidae suggests the influence of both sexual and trophic functional influences on the evolution of head morphology.

Journal Title

Systematics and Biodiversity

Volume

7

Issue/Number

1

Publication Date

1-1-2009

Document Type

Article

Language

English

First Page

81

Last Page

92

WOS Identifier

WOS:000264359600007

ISSN

1477-2000

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