Evolution and Biodiversity of Electric Animals

Electroreception is the ability to detect weak electric fields. This exotic sense for humans is widespread in vertebrates (animals with a spine). There are several cases in each class of fish: lamprey in fish without jaw; Sharks, rays and ratfish in cartilaginous fish; Sturgeons, spatulas, polyptera and coelacanths ; And in teleosts, mormyriformes, and gymnotiforms. There are also electroreceptive animals in two classes of amphibians (salamanders and caecilians ) and even in mammals (platypus). Electroreception appears to be an ancestral feature of vertebrates as it is present in lampreys and cartilaginous fish.

However, the scattered presence of electroreception in various groups of vertebrates indicates that electroneception has been “reinvented” a number of times during evolution. A particularly striking proof of independent evolution of electreception is its existence in African mormyriformes and South American gymnotiforms, two distant orders (osteoglossomorphs and ostariophyses) of modern osseous fishes (teleosteens), as well as in the platypus mammal. In all cases, the ancestors do not seem to possess the capacity of electreception. The modern holosteens , who have given the teleost line, including mormyriforms and gymnotiforms, are not electroreceptive. Similarly, reptiles, the ancestors of mammals, Do not possess this sense of which the ornithorynque could evolve. Thus, the mormyriformes, the gymnotiforms and the platypus have had to invent electreception again during their evolutions.

In addition, in each group of electroreceptive animals, the organs responsible for electroreception have unique anatomical structures and properties. From one group to another, the electroreceptors present in the skin exhibit a great variation in sensitivity (from 0.005μV -1 to 0.1mVcm -1 ) , different frequency responses (almost continuous current at a frequency of 1500 Hz ) And very variable distributions at the surface of the skin. Different structures and functions are in favor of independent evolution histories ( see 19 e ).

All electroneceptive animals have ampullar electroreceptors on the surface of their skin, which are very sensitive and more easily excitable at low frequencies (<30Hz). Mormyriforms and gymnotiforms also have tuberous electroreceptors that respond to low natural high frequency currents (> 50Hz) ( see Electroreceptor ).

Electrogeneous fish, capable of producing an electric field, produce electrical signals through their electrical organs consisting of columns of modified muscle cells (electrocytes). But again, these structures and their functions differ greatly from one group of fish to another.

Some species of electrogeneous fish produce large discharges of hundreds of volts to kill prey, while others produce low discharges (a few millivolts) used as signals of communication and localization. These latter species are both electrogenic (producing) and electreceptive (receptor). Electrogenic species that produce low landfills do so in two ways: some species do so intermittently (species with pulsating discharges) which they repeat as necessary to “scan” their environment, while other species produce periodically (Species with wavy discharges) and “scanning” their surroundings continuously.

In teleosts, bone fish, the distribution of species is interesting. Thus, mormyriformes have developed in the fresh waters of African lakes and rivers, while gymnotiforms have developed in South America.

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