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Mormyroids
Also known as: Mormyroid
Facts (24)
Sources
Comparable Ages for the Independent Origins of Electrogenesis in ... journals.plos.org 24 facts
claimThe small eye sizes of many mormyroids and gymnotiforms may be a direct result of their active electrosensory systems superseding the importance of vision.
claimThe lack of gymnotiform and mormyroid fossils older than 35 million years limits inferences about their geographical origins and early diversification.
claimMormyroid and gymnotiform fishes share morphological similarities including elongate bodies, extended tube-like snouts, reduced eyes, and small mouth sizes.
claimGymnotiforms and mormyroids both possess high-frequency electroreceptors, which are derived from similar lateral line receptor precursors and underlie active electrolocation and electrocommunication.
perspectiveThe authors refer to gymnotiforms and mormyroids as a textbook example of convergent evolution to highlight their independent origins from phylogenetically unrelated and phenotypically dissimilar teleost ancestors.
measurementThe estimated time interval between the origins of teleost electroreception and the origins of electrogenesis is 22.7 million years for mormyroids and 25.6 million years for gymnotiforms under reconstruction #2.
claimGymnotiforms and mormyroids evolved novel myogenic electric organs (EOmyo) that are developmentally derived from skeletal muscle progenitor cells known as myoblasts.
claimH.W. Lissmann proposed that the convergence upon an anguilliform body form with ribbon fin propulsion, seen in all gymnotiforms and some mormyroids, may have evolved to minimize body axis bending during active electrolocation.
claimSimilar patterns of amino acid substitution occurred in regions of the sodium channel α-subunit in both gymnotiforms and mormyroids, which are thought to contribute to electric signal variation.
claimGymnotiforms and mormyroids originated independently from non-electrogenic ancestors at approximately the same period in Earth's history.
referenceZakon et al. and Arnegard et al. demonstrated that in both gymnotiforms and mormyroids, the same sodium channel α-subunit paralog (gene duplicate) was co-opted from skeletal muscle for exclusive expression in myogenic electric organs (EOmyo).
measurementBoth mormyroids and gymnotiforms have diversified to a similar degree, with each group comprising approximately 200 named species.
claimElectrical communication and its associated neural traits in mormyroids increase the number of axes of variation in signal space, which positively influences signal evolution.
measurementThe estimated time interval between the origins of teleost electroreception and the origins of electrogenesis is 16.6 million years for mormyroids and 18.7 million years for gymnotiforms under reconstruction #1.
claimThe ability to produce "strong" electric discharges for prey capture or defense has evolved once in the gymnotiform Electrophorus electricus (the electric eel) and once in the African electric catfish family Malapteruridae, but has not evolved in African mormyroids.
claimReduced mouth sizes and restricted gill openings in mormyroids and gymnotiforms likely evolved to reduce interfering electrical emissions from electrically active epithelial tissues.
claimElectrical communication in mormyroids may augment the rate of signal divergence and the tempo of species radiation.
claimMormyroids and gymnotiforms, with the exception of Electrophorus electricus, are classified as "weakly" electric fishes because the external potentials they produce are typically imperceptible to humans without amplification.
claimWhole genome duplication (WGD) occurring just prior to the radiation of teleosts contributed to the origin of novel electrogenic systems in mormyroids and gymnotiforms.
claimSimilar periods of time elapsed between the origin of passive electroreception and the appearance of the myogenic electric organ (and active electroreception) in both the mormyroid and gymnotiform lineages of weakly electric fishes.
claimMormyroid and gymnotiform fishes exhibit phenotypic convergence in body form, swimming behavior, reproductive behavior, ecology, nocturnal activity patterns, electric signals, and the neuronal algorithms used to avoid jamming of active electrolocation and communication.
claimMyogenic electric organs in mormyroids and gymnotiforms are similar in many ways, but also exhibit significant differences between lineages and great diversity in structure and function among species.
claimThe elongate snouts or trunks of some mormyroids and gymnotiforms may have arisen secondarily as an adaptation to the specific types and habits of prey organisms found in the ecological niches exploited by active electrosensory predators.
claimThe two groups of weakly electric fishes, mormyroids and gymnotiforms, originated at nearly the same time in evolutionary history, with similar time intervals passing between the whole genome duplication (WGD) at the base of the teleost radiation and the origins of novel myogenic electric organs in each lineage.