“…[ 18 , 19 ]). As shown in other studies, neither under breeding conditions nor after gonadal regression was the EOD waveform sexually dimorphic in either species [ 31 , 32 ]. Figure 1.…”
Section: Methodsmentioning
confidence: 48%
“…The communication cues facilitating species recognition are often fixed and unique to a species, and necessary for attracting a mate [ 30 ]. Among Campylomormyrus weakly electric fishes, the EOD is a species-specific but not sexually dimorphic component of electrocommunication [ 31 , 32 ]. We were therefore interested in investigating if the EOD waveform is necessary and sufficient for conspecific association and potentially mate recognition under both breeding and non-breeding (i.e.…”
Section: Discussionmentioning
confidence: 99%
“…All males showed a kink in their anal fin base indicating sex and maturity [ 26 ]. Concluding breeding condition experiments, the water conductivity was slowly increased to 700 ± 20 µS cm −1 to induce gonadal regression [ 32 , 34 ].…”
Effective communication among sympatric species is often instrumental for behavioural isolation, where the failure to successfully discriminate between potential mates could lead to less fit hybrid offspring. Discrimination between con- and heterospecifics tends to occur more often in the sex that invests more in offspring production, i.e. females, but males may also mediate reproductive isolation. In this study, we show that among two Campylomormyrus African weakly electric fish species, males preferentially associate with conspecific females during choice tests using live fish as stimuli, i.e. when all sensory modalities potentially used for communication were present. We then conducted playback experiments to determine whether the species-specific electric organ discharge (EOD) used for electrocommunication serves as the cue for this conspecific association preference. Interestingly, only C. compressirostris males associated significantly more with the conspecific EOD waveform when playback stimuli were provided, while no such association preference was observed in C. tamandua males. Given our results, the EOD appears to serve, in part, as a male-mediated pre-zygotic isolation mechanism among sympatric species. However, the failure of C. tamandua males to discriminate between con- and heterospecific playback discharges suggests that multiple modalities may be necessary for species recognition in some African weakly electric fish species.
“…[ 18 , 19 ]). As shown in other studies, neither under breeding conditions nor after gonadal regression was the EOD waveform sexually dimorphic in either species [ 31 , 32 ]. Figure 1.…”
Section: Methodsmentioning
confidence: 48%
“…The communication cues facilitating species recognition are often fixed and unique to a species, and necessary for attracting a mate [ 30 ]. Among Campylomormyrus weakly electric fishes, the EOD is a species-specific but not sexually dimorphic component of electrocommunication [ 31 , 32 ]. We were therefore interested in investigating if the EOD waveform is necessary and sufficient for conspecific association and potentially mate recognition under both breeding and non-breeding (i.e.…”
Section: Discussionmentioning
confidence: 99%
“…All males showed a kink in their anal fin base indicating sex and maturity [ 26 ]. Concluding breeding condition experiments, the water conductivity was slowly increased to 700 ± 20 µS cm −1 to induce gonadal regression [ 32 , 34 ].…”
Effective communication among sympatric species is often instrumental for behavioural isolation, where the failure to successfully discriminate between potential mates could lead to less fit hybrid offspring. Discrimination between con- and heterospecifics tends to occur more often in the sex that invests more in offspring production, i.e. females, but males may also mediate reproductive isolation. In this study, we show that among two Campylomormyrus African weakly electric fish species, males preferentially associate with conspecific females during choice tests using live fish as stimuli, i.e. when all sensory modalities potentially used for communication were present. We then conducted playback experiments to determine whether the species-specific electric organ discharge (EOD) used for electrocommunication serves as the cue for this conspecific association preference. Interestingly, only C. compressirostris males associated significantly more with the conspecific EOD waveform when playback stimuli were provided, while no such association preference was observed in C. tamandua males. Given our results, the EOD appears to serve, in part, as a male-mediated pre-zygotic isolation mechanism among sympatric species. However, the failure of C. tamandua males to discriminate between con- and heterospecific playback discharges suggests that multiple modalities may be necessary for species recognition in some African weakly electric fish species.
“…Indeed, previous studies already showed differential gene expression among C. tshokwe and C. compressirostris [30,40], indicating the impact of transcriptional regulation on EOD waveforms. Transcriptional regulation would provide also a feasible explanation for the remarkable changes in EOD waveforms during the ontogeny of a Campylomormyrus fish [64], as expression levels may change during ontogeny [65,66]. Experimental evidence on ontogenetic expression levels is however still lacking for our target taxa.…”
Background: African weakly electric fish generate weakly electric organ discharges (EODs) for orientation and communication. In the mormyrid genus Campylomormyrus, waveform and duration of discharges are species-specific and elongated pulses (> 4ms) are a derived trait. Pulse duration is presumed to depend on electrocyte geometry/excitability or hormonal signaling.Tissue-specific transcriptome analyses across species with different pulse durations have revealed differential expression of genes related to electrocyte excitability. There are also point mutations in ion channel genes which relate to pulse duration. However, a comprehensive assessment of expressed Single Nucleotide Polymorphisms (SNPs) throughout the entire transcriptomes of African weakly electric fish, with the potential to identify further genes influencing EOD duration, is still lacking. This is of particular value, as discharge duration is likely based on multiple cellular mechanisms and various genes. Here, we want to identify non-synonymous SNPs in transcriptomes of Campylomormyrus species differing by EOD duration.
Results: We identified 27 candidate genes with inferred positive selection among Campylomormyrus species and at least one non-synonymous substitution specific to Campylomormyrus tshokwe, a species with elongated EODs. Inferred candidate genes had mainly functions linked to transcriptional regulation, cell proliferation, cell differentiation and apoptosis. Further, we identified 27 GO terms and 2 KEGG categories ('Transcription' and 'Cancer: Specific types') for which C. tshokwe (derived elongated EOD) significantly more frequently exhibited a species-specific expressed substitution than C. compressirostris (ancestral short EOD).
Conclusion: We performed the first transcriptome-wide SNP analysis among weakly electric fish species (genus Campylomormyrus) and provide putative candidate genes and cellular mechanisms potentially involved in the determination of an elongated discharge in C. tshokwe. Most likely, transcriptional regulation as well cell proliferation, cell differentiation and apoptosis take part in the determination of pulse durations. The processes of cell growth and density are pivotal for tissue morphogenesis and might determine the shape of electric organs. This supports the observed correlation between cell geometry/tissue structure of the electric organ and discharge duration. The inferred expressed SNPs putatively related to EOD duration are a valuable resource for future investigations on this peculiar trait, which may focus on their functional implications.
“…The three Campylomormyrus species used in this study are: the short snouted C. tamandua (n = 9), the medium snouted C. compressirostris (n = 10) and the long snouted C. rhynchophorus (n = 11). All experimental fish were imported from Kinshasa (Democratic Republic of the Congo) or are F1 descendants of imported fish (Nguyen et al 2017).…”
Under an ecological speciation scenario, the radiation of African weakly electric fish (genus Campylomormyrus) is caused by an adaptation to different food sources, associated with diversification of the electric organ discharge (EOD). This study experimentally investigates a phenotype-environment correlation to further support this scenario. Our behavioural experiments showed that three sympatric Campylomormyrus species with significantly divergent snout morphology differentially react to variation in substrate structure. While the short snout species (C. tamandua) exhibits preference to sandy substrate, the long snout species (C. rhynchophorus) significantly prefers a stone substrate for feeding. A third species with intermediate snout size (C. compressirostris) does not exhibit any substrate preference. This preference is matched with the observation that long-snouted specimens probe deeper into the stone substrate, presumably enabling them to reach prey more distant to the substrate surface. These findings suggest that the diverse feeding apparatus in the genus Campylomormyrus may have evolved in adaptation to specific microhabitats, i.e., substrate structures where these fish forage. Whether the parallel divergence in EOD is functionally related to this adaptation or solely serves as a prezygotic isolation mechanism remains to be elucidated. by Tonio Pieterek. Matlab scripts were inspired by Volker Hofmann.Author's contribution RA participated in the design of the study, carried out the experiments, analysed the data and drafted the manuscript; RN participated in the design of the experiment and critically revised the manuscript; MH carried out the feeding experiments of the C. tamandua individuals under the supervision of RA and RT. RT and FK conceived, participated in the design and coordinated the study. RA and RT revised the manuscript after an initial review. All authors have read and approved the manuscript for publication.
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