Biology subjects

Gallant, J. R.

Publications and source records attributed to Gallant, J. R..

6 recordsLinked to original sources

bioRxiv2026

Electric signal polymorphism predicts dietary niche partitioning in a weakly electric fish

Electric organ discharge (EOD) waveform diversity in African elephantfish is often attributed to sexual selection, yet EODs also mediate active electrolocation during prey detection, raising the possibility that natural selection on foraging ecology contributes to waveform divergence. Paramormyrops kingsleyae exhibits an intraspecific polymorphism where certain populations emit biphasic EODs whereas other populations emit triphasic waveforms. The genes underlying this polymorphism show signatures of selection; the polymorphism persists despite gene flow and is behaviorally discriminable by the fish themselves. If waveform differences influence prey detection during active electrolocation, biphasic and triphasic fish should consume systematically different prey. We tested this prediction using DNA metabarcoding of gut contents from 186 mormyrids representing 16 species across eight sites in Gabon, employing two independent COI primer sets for cross-validation and pairing dietary data with environmental invertebrate sampling to distinguish active prey preference from passive availability. At the community level in the diverse Bale Creek mormyrid assemblage, species identity was the dominant predictor of diet composition (R{superscript 2} {approx} 24%), consistent with phylogenetic signal in foraging ecology. Within P. kingsleyae, waveform type was the strongest independent predictor of dietary composition (R{superscript 2} = 5-6%), explaining variance independently of geographic region, sex, body size, and parasitism status -- a result concordant across both primer sets. Dietary differences were driven by prey species turnover rather than differential abundance of shared prey, and prey selectivity analyses confirmed that waveform types differ in which prey they actively prefer, not merely in what is locally available. These findings are consistent with natural selection on foraging ecology contributing to the maintenance of EOD waveform polymorphism, though the sensory mechanisms linking subtle waveform differences to prey detection remain an open question.

ecology↗

bioRxiv2026

The Genomic Basis of Electric Signal Diversity

Behavioral diversity is a striking result of species diversity, shaped by intertwined mechanisms, developmental pathways, and evolutionary histories. Yet the genetic underpinnings of behavioral evolution remain obscure, even though they are key to understanding how organisms adapt and diversify. Weakly electric African elephantfishes provide a rare opportunity to dissect the genetics of behavior because their electric communication signals are quantifiable, stereotyped, and directly tied to identifiable cellular mechanisms. Among elephantfishes, electric organ discharges (EODs) vary widely across species and populations, shaping mate choice, social interactions, and reproductive isolation. A key axis of this diversity is the presence or absence of an initial phase in the EOD waveform--a discrete, repeated evolutionary transition whose genetic basis has remained unresolved. Here we show, using whole-genome resequencing, population-genomic analyses, transcriptomics, and histology from 306 specimens, that biphasic EODs in Paramormyrops kingsleyae have evolved repeatedly through independent de novo regulatory mutations at distinct genomic loci. These population-specific mutations occur exclusively in noncoding regions, show localized signatures of selection, and are associated with differences in gene expression and protein localization in the electric organ, indicating that they act through cis-regulatory mechanisms affecting electrocyte development. These findings challenge the expectation that repeated within-species adaptations primarily draw from standing ancestral variation, revealing instead that the developmental program underlying electric signaling contains multiple points of regulatory sensitivity. Distinct genetic changes can therefore produce the same behavioral phenotype, enabling repeated evolutionary transitions even within a single species. More broadly, our results show how developmental architecture shapes the evolutionary pathways available to behavior, helping explain why communication signals in elephantfishes--and in other radiations--diversify so rapidly.

evolutionary biology↗

bioRxiv2024

Mechanistic insights into gene expression changes and electric organ discharge elongation in mormyrid electric fish

Electric organ discharge (EOD) duration in African weakly electric fish (Mormyridae) is the most variable waveform component between species and the basis for distinguishing species-specific signals. EOD duration is thought to be influenced by morphological and physiological features of electrocytes (the cells that comprise the electric organ), but the mechanistic details are poorly understood. It has long been known that EOD duration is modulated by androgen hormones, affording an opportunity to identify gene expression correlates of EOD duration differences. We induced EOD elongation in the mormyrid Brienomyrus brachyistius by administering 17-methyltestosterone (17MT) to three treatment groups: control (no 17MT exposure), T1day and T8day (samples taken one and eight days after a single exposure to 17MT, respectively). We then performed RNAseq, differential gene expression, and functional enrichment analysis to detect gene expression changes during EOD duration change. Our analyses indicate 44 genes whose expression changed in tandem with EOD elongation and include genes responsible for actin filaments and microtubules, extracellular matrix organization, and membrane lipid metabolism. Additionally, we found expression changes in one Na+ channel beta subunit, and five K+ voltage-gated channels. Together, these genes point toward specific cellular processes that contribute to morphological and physiological changes that contribute to EOD duration changes.

evolutionary biology↗

bioRxiv2022

Molecular evolution of the ependymin-related gene epdl2 in African weakly electric fish

Gene duplication and subsequent molecular evolution can give rise to taxon-specific gene specializations. In a previous study, we found evidence that African weakly electric fish (Mormyridae) may have as many as three copies of the epdl2 gene, and the expression of two epdl2 genes is correlated with electric signal divergence. Epdl2 belongs to the ependymin-related family (EPDR), a functionally diverse family of secretory glycoproteins. In this study, we first describe vertebrate EPDR evolution and then present a detailed evolutionary history of epdl2 in Mormyridae with emphasis on the speciose genus Paramormyrops. Using Sanger sequencing, we confirm three apparently functional epdl2 genes in P. kingsleyae. Next, we developed a nanopore-based amplicon sequencing strategy and bioinformatics pipeline to obtain and classify full-length epdl2 gene sequences (N = 34) across Mormyridae. Our phylogenetic analysis proposes three or four epdl2 paralogs dating from early Paramormyrops evolution. Finally, we conducted selection tests which detected positive selection around the duplication events and identified ten sites likely targeted by selection in the resulting paralogs. These sites locations in our modeled 3D protein structure involve four sites in ligand binding and six sites in homodimer formation. Together, these findings strongly imply that epdl2 genes display signatures of selection-driven functional specialization after tandem duplications in the rapidly speciating Paramormyrops. Considering previous evidence, we propose that epdl2 may contribute to electric signal diversification in mormyrids, an important aspect of species recognition during mating.

evolutionary biology↗

bioRxiv2019

The transcriptional correlates of divergent electric organ discharges in Paramormyrops electric fish

BackgroundUnderstanding the genomic basis of phenotypic diversity can be greatly facilitated by examining adaptive radiations with hypervariable traits. In this study, we focus on a rapidly diverged species group of mormyrid electric fish in the genus Paramormyrops, which are characterized by extensive phenotypic variation in electric organ discharges (EODs). The main components of EOD diversity are waveform duration, complexity and polarity. Using an RNA-sequencing based approach, we sought to identify gene expression correlates for each of these EOD waveform features by comparing 11 specimens of Paramormyrops that exhibit variation in these features.\n\nResultsPatterns of gene expression among Paramormyrops are highly correlated, and 3,274 genes (16%) were differentially expressed. Using our most restrictive criteria, we detected 71-144 differentially expressed genes correlated with each EOD feature, with little overlap between them. The predicted functions of several of these genes are related to extracellular matrix, cation homeostasis, lipid metabolism, and cytoskeletal and sarcomeric proteins. These genes are of significant interest given the known morphological differences between electric organs that underlie differences in the EOD waveform features studied.\n\nConclusionsIn this study, we identified plausible candidate genes that may contribute to phenotypic differences in EOD waveforms among a rapidly diverged group of mormyrid electric fish. These genes may be important targets of selection in the evolution of species-specific differences in mate-recognition signals.

evolutionary biology↗

bioRxiv2017

Microevolutionary processes underlying macroevolutionary patterns of electric signal diversity in mormyrid fish

The mormyrid fish species Paramormyrops kingsleyae emits an electric organ discharge (EOD) with a dual role in communication and electrolocation. Populations of P. kingsleyae have either biphasic or triphasic EODs, a feature which characterizes interspecific signal diversity among the Paramormyrops genus. We quantified variation in EODs of 327 P. kingsleyae from 9 populations throughout Gabon and compared it to genetic variation estimated from 5 neutral microsatellite loci. We found no correlation between electric signal and genetic distances, suggesting that EOD divergence between populations of P. kingsleyae cannot be explained by drift alone. An alternative hypothesis is that EOD differences are a cue for assortative mating, which would require P. kingsleyae be capable of differentiating between divergent EOD waveforms. Using a habituation-dishabituation assay, we found that P. kingsleyae can discriminate between triphasic and biphasic EOD types. Nonetheless, patterns of genetic and electric organ morphology divergence provide evidence for hybridization between signal types. Although reproductive isolation with respect to signal type is not absolute, our results suggest that EOD variation in P. kingsleaye has the potential to serve as a cue for assortative mating and point to selective forces rather than drift as important drivers of signal evolution.

evolutionary biology↗