PHYLOGENETIC ANALYSIS OF THE SOUTH-AMERICAN ELECTRIC FISHES (ORDER GYMNOTIFORMES) AND THE EVOLUTION OF THEIR ELECTROGENIC SYSTEM - A SYNTHESIS BASED ON MORPHOLOGY, ELECTROPHYSIOLOGY, AND MITOCHONDRIAL SEQUENCEDATA
Ja. Alvesgomes et al., PHYLOGENETIC ANALYSIS OF THE SOUTH-AMERICAN ELECTRIC FISHES (ORDER GYMNOTIFORMES) AND THE EVOLUTION OF THEIR ELECTROGENIC SYSTEM - A SYNTHESIS BASED ON MORPHOLOGY, ELECTROPHYSIOLOGY, AND MITOCHONDRIAL SEQUENCEDATA, Molecular biology and evolution, 12(2), 1995, pp. 298-318
The order Gymnotiformes (South American electric fishes) is a fascinat
ing assemblage of freshwater fishes that share the unusual ability to
produce and sense electric fields used for electrolocation and social
communication. In the last few decades, the electrogenic and electrose
nsory systems (EES) of these fish have served as an excellent model to
study motor and sensory physiology in vertebrates. In an attempt to a
ddress the evolution of characters associated with the EES in the grou
p, we applied maximum-parsimony (MP), minimum-evolution (ME), and maxi
mum-likelihood (ML) methods to analyze 302 aligned bases of the mitoch
ondrial 12S rRNA and 416 bases of the mitochondrial 16S rRNA of 19 gym
notiform genera representing all six recognized families. Six catfish
genera (order Siluriformes) were also sequenced and used as outgroups.
The phylogenetic hypothesis resultant from molecular data analysis di
ffers in some respects from previous hypotheses based on morphological
studies. Our results were most informative within the family level, a
s we were unable to elucidate the relationships among deeper branches
in this order with sufficient confidence by using molecular data alone
. The phylogenetic information of both mitochondrial DNA segments appe
ars to be affected by functional constraints, and the resultant topolo
gies were sensitive to different weighting schemes and the algorithm u
sed. Nonetheless, we found unanimous support for the following phyloge
netic relationships: (1) the family Sternopygidae is an unnatural grou
p, and Sternopygus is the sole representative of a unique lineage with
in the order; (2) the family Hypopomidae is not monophyletic; and (3)
the order Gymnotiformes is composed of at least six natural clades: St
ernopygus, family Apteronotidae, a new clade consisting of the remaini
ng sternopygids, families Hypopomidae + Rhamphichthyidae, family Elect
rophoridae, and family Gymnotidae. By combining molecular, morphologic
al, and physiological information, we propose a new hypothesis for the
phylogeny of this group and suggest a new family Eigenmanniidae n. (o
rder Gymnotiformes).