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  1. Article ; Online: A Spark in the Dark

    Stefan Mucha / Franziska Oehlert / Lauren J. Chapman / Rüdiger Krahe

    Frontiers in Ecology and Evolution, Vol

    Uncovering Natural Activity Patterns of Mormyrid Weakly Electric Fish

    2022  Volume 10

    Abstract: To understand animal ecology, observation of wildlife in the natural habitat is essential, but particularly challenging in the underwater realm. Weakly electric fishes provide an excellent opportunity to overcome some of these challenges because they ... ...

    Abstract To understand animal ecology, observation of wildlife in the natural habitat is essential, but particularly challenging in the underwater realm. Weakly electric fishes provide an excellent opportunity to overcome some of these challenges because they generate electric organ discharges (EODs) to sense their environment and to communicate, which can be detected non-invasively. We tracked the EOD and swimming activity of two species of mormyrid weakly electric fishes (Marcusenius victoriae and Petrocephalus degeni) over diel cycles in the laboratory, and we recorded EODs and environmental dissolved oxygen (DO) concentration and temperature over several months in a naturally hypoxic habitat in Uganda. Under laboratory conditions, both species showed increases of activity and exploration behavior that were closely synchronized to the onset of the dark phase. In the wild, fish preferred structurally complex habitats during the day, but dispersed toward open areas at night, presumably to forage and interact. Nocturnal increase of movement range coincided with diel declines in DO concentration to extremely low levels. The fact that fish showed pronounced nocturnal activity patterns in the laboratory and in the open areas of their habitat, but not under floating vegetation, indicates that light intensity exerts a direct effect on their activity. We hypothesize that being dark-active and tolerant to hypoxia increases the resistance of these fish against predators. This study establishes a new technology to record EODs in the field and provides a window into the largely unknown behavior of mormyrids in their natural habitat.
    Keywords behavioral activity ; habitat use ; electric organ discharge ; hypoxia ; swim behavior ; Evolution ; QH359-425 ; Ecology ; QH540-549.5
    Subject code 590
    Language English
    Publishing date 2022-06-01T00:00:00Z
    Publisher Frontiers Media S.A.
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Predation and Crypsis in the Evolution of Electric Signaling in Weakly Electric Fishes

    Philip K. Stoddard / Alex Tran / Rüdiger Krahe

    Frontiers in Ecology and Evolution, Vol

    2019  Volume 7

    Abstract: Eavesdropping by electroreceptive predators poses a conflict for weakly electric fish, which depend on their Electric Organ Discharge (EOD) signals both for navigation and communication in the dark. The EODs that allow weakly electric fish to ... ...

    Abstract Eavesdropping by electroreceptive predators poses a conflict for weakly electric fish, which depend on their Electric Organ Discharge (EOD) signals both for navigation and communication in the dark. The EODs that allow weakly electric fish to electrolocate and communicate in the dark may attract electroreceptive predators such as catfishes and Electric Eels. These predators share with their prey the synapomorphy of passive electric sense supported by ampullary electroreceptors that are highly sensitive to low-frequency electric fields. Any low-frequency spectral components of the EOD make weakly electric fish conspicuous and vulnerable to attack from electroreceptive predators. Accordingly, most weakly electric fish shift spectral energy upwards or cloak low-frequency energy with compensatory masking signals. Subadults and females in particular emit virtually no low-frequency energy in their EODs, whereas courting males include a significant low-frequency component, which likely attracts females, but makes the signals conspicuous to predators. Males of species that coexist with the most predators tend to produce the least low-frequency signal energy, expressing sexual dimorphism in their signals in less risky ways. In these respects, electric signals follow the classic responses to opposing forces of natural and sexual selection, as exemplified in the visual signals of guppies and the acoustic signals of Túngara frogs. Unique to electric fish is that the electric signal modifications that help elude detection by electroreceptive predators are additions to the basal signal rather than losses of attractive components. These enhancements that enable crypsis are energetically costly, but have also provided the evolutionary substrates for subsequent sexual selection and species identity characters.
    Keywords catfish ; electroreception ; Gymnotiformes ; Mormyridae ; predation ; sensory drive ; Evolution ; QH359-425 ; Ecology ; QH540-549.5
    Subject code 590
    Language English
    Publishing date 2019-07-01T00:00:00Z
    Publisher Frontiers Media S.A.
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article: Hypoxia acclimation increases novelty response strength during fast-starts in the African mormyrid, Marcusenius victoriae

    Ackerly, Kerri L / Lauren J. Chapman / Rüdiger Krahe

    Comparative biochemistry and physiology. 2017 Nov., v. 213

    2017  

    Abstract: Many fishes perform quick and sudden swimming maneuvers known as fast-starts to escape when threatened. In pulse-type weakly electric fishes these responses are accompanied by transient increases in the rate of electric signal production known as novelty ...

    Abstract Many fishes perform quick and sudden swimming maneuvers known as fast-starts to escape when threatened. In pulse-type weakly electric fishes these responses are accompanied by transient increases in the rate of electric signal production known as novelty responses. While novelty responses may increase an individual's information about their surroundings, they are aerobically powered and may come at a high energetic cost when compared to fast-starts, which rely primarily on anaerobic muscle. The juxtaposition between two key aspects of fast-starts in these fishes – the aerobic novelty response and the anaerobic swimming performance – makes them an interesting model for studying effects of hypoxia on escape performance and sensory information acquisition. We acclimated the hypoxia-tolerant African mormyrid Marcusenius victoriae to either high or low dissolved oxygen (DO) levels for 8weeks, after which fast-starts and novelty responses were quantified under both high (normoxic) and low-DO (hypoxic) test conditions. Hypoxia-acclimated fish exhibited higher maximum curvature than normoxia-acclimated fish. Displacement of normoxia-acclimated fish was not reduced under acute hypoxic test conditions. Novelty responses were given upon each startle, whether or not the fish performed a fast-start; however, novelty responses associated with fast-starts were significantly stronger than those without, suggesting a functional link between fast-start initiation and the motor control of the novelty response. Overall, hypoxia-acclimated individuals produced significantly stronger novelty responses during fast-starts. We suggest that increased novelty response strength in hypoxia-acclimated fish corresponds to an increased rate of sensory sampling, which may compensate for potential negative effects of hypoxia on higher-level processing.
    Keywords acclimation ; dissolved oxygen ; fish ; hypoxia ; Marcusenius ; models ; muscles ; swimming
    Language English
    Dates of publication 2017-11
    Size p. 36-45.
    Publishing place Elsevier Inc.
    Document type Article
    ZDB-ID 121246-1
    ISSN 1531-4332 ; 0300-9629 ; 1095-6433
    ISSN (online) 1531-4332
    ISSN 0300-9629 ; 1095-6433
    DOI 10.1016/j.cbpa.2017.08.008
    Database NAL-Catalogue (AGRICOLA)

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  4. Article ; Online: Tempo and mode of allopatric divergence in the weakly electric fish Sternopygus dariensis in the Isthmus of Panama

    Celestino Aguilar / Matthew J. Miller / Jose R. Loaiza / Rigoberto González / Rüdiger Krahe / Luis F. De León

    Scientific Reports, Vol 9, Iss 1, Pp 1-

    2019  Volume 11

    Abstract: Abstract Spatial isolation is one of the main drivers of allopatric speciation, but the extent to which spatially-segregated populations accumulate genetic differences relevant to speciation is not always clear. We used data from ultraconserved elements ( ...

    Abstract Abstract Spatial isolation is one of the main drivers of allopatric speciation, but the extent to which spatially-segregated populations accumulate genetic differences relevant to speciation is not always clear. We used data from ultraconserved elements (UCEs) and whole mitochondrial genomes (i.e., mitogenomes) to explore genetic variation among allopatric populations of the weakly electric fish Sternopygus dariensis across the Isthmus of Panama. We found strong genetic divergence between eastern and western populations of S. dariensis. Over 77% of the UCE loci examined were differentially fixed between populations, and these loci appear to be distributed across the species’ genome. Population divergence occurred within the last 1.1 million years, perhaps due to global glaciation oscillations during the Pleistocene. Our results are consistent with a pattern of genetic differentiation under strict geographic isolation, and suggest the presence of incipient allopatric species within S. dariensis. Genetic divergence in S. dariensis likely occurred in situ, long after the closure of the Isthmus of Panama. Our study highlights the contribution of spatial isolation and vicariance to promoting rapid diversification in Neotropical freshwater fishes. The study of spatially-segregated populations within the Isthmus of Panama could reveal how genetic differences accumulate as allopatric speciation proceeds.
    Keywords Medicine ; R ; Science ; Q
    Subject code 590
    Language English
    Publishing date 2019-12-01T00:00:00Z
    Publisher Nature Publishing Group
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article ; Online: First record of Gymnotus henni (Albert, Crampton and Maldonado, 2003) in Panama

    Fernando Alda / Sophie Picq / Luis León / Rigoberto González / Henriette Walz / Eldredge Bermingham / Rüdiger Krahe

    Check List, Vol 9, Iss 3, Pp 655-

    phylogenetic position and electric signal characterization

    2013  Volume 659

    Abstract: We present the first record of the weakly electric fish Gymnotus henni in Panama, which also represents the first record of Gymnotus in the Pacific slope of the country. One specimen was collected in a tributary of the Chucunaque River in the Tuira basin. ...

    Abstract We present the first record of the weakly electric fish Gymnotus henni in Panama, which also represents the first record of Gymnotus in the Pacific slope of the country. One specimen was collected in a tributary of the Chucunaque River in the Tuira basin. The species showed a monophasic electric organ discharge. Molecular analyses indicated that G. henni from Panama and Colombia are closely related and represent an independent and basal lineage to the Central American G. cylindricus and South American G. carapo groups. Evolutionary and biogeographic implications are discussed.
    Keywords Biology (General) ; QH301-705.5
    Language English
    Publishing date 2013-06-01T00:00:00Z
    Publisher Pensoft Publishers
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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