Session 30: General Ichthyology IRoom: Ballroom 111C2022-07-30 08:15 - 09:30 |
| Moderator: Brian Sidlauskas |
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1. 08:15 Three New Species of Electric Fishes (Paramormyrops: Mormyridae: Osteoglossomorpha) with Unbalanced Electric Organ Discharges (EODs). Matthew A. Burnett*, Cornell University College of Agriculture and Life Sciences; John P. Sullivan, Cornell University Museum of Vertebrates; Carl D. Hopkins, Cornell University Museum of Vertebrates mb2483@cornell.edu
Mormyrid electric fishes in the genus Paramormyrops constitute a riverine species flock with eight described species in the Lower Guinea ichthyofaunal province of West-Central Africa. We describe three new cryptic species of Paramormyrops from Gabon first discovered because of their distinctive unbalanced and predominantly head-negative electric organ discharges (EODs) with significant Fourier spectral energy at frequencies below 100 Hz. Most mormyrids have balanced positive and negative phases with reduced energy at these low frequencies. Two of the new species are allopatric sister taxa, one from the Ivindo River of Gabon and a second from the Ntem River bordering Cameroon and Gabon. Although morphologically similar, their EODs differ in waveform and ontogeny. Their relation to each other and to described Paramormyrops is confirmed by molecular sequence data. A third new taxon found in sympatry with the Ivindo species differs in morphology, EODs, and molecular sequences. Its range extends beyond the Ivindo basin into the Upper Ogooué river of Gabon. All three new species have reduced lateral ethmoids, unfused ventral hypurals and 5 or 6 circumorbital bones. A phylogenetic tree of Paramormyropsspecies based on molecular data indicates that their unbalanced EODs arose independently in two separate lineages within Paramormyrops. We discuss the possible significance of unbalanced EODs in these and other electric fish species. |
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2. 08:30 Phylogeny of Alestidae and Evolution of Paedomorphosis: New Evidence from Genomic Data (Ostariophysi: Characiformes). Bruno Melo*, Department of Ichthyology, American Museum of Natural History; Melanie Stiassny, Department of Ichthyology, American Museum of Natural History brunfmelo@gmail.com
Paedomorphosis is a phenomenon of heterochrony-mediated retention of phenotypic features during development (i.e., adults retain the juvenile phenotype). This phenomenon is widespread among vertebrates and often observed in many families of teleost fishes. Characiform tetras of the family Alestidae contain at least two miniature groups, but no study has investigated the evolution of these features using a phylogenetic perspective. The 127 species in 19 genera are distributed in the Nile, Chad, Congo, Zambezi, Volta, and coastal rivers of West and East Africa. Species range from diminutive species of Micralestes and Lepidarchus maturing at ~2 cm standard length to the large predatory tigerfish Hydrocynus reaching ~130 cm standard length. Evolutionary studies in Alestidae are scarce and restricted to a multilocus phylogeny and species descriptions. Here, we reconstruct the evolutionary history of Alestidae using ~85% of the species and a new molecular dataset of >1,000 ultraconserved elements. The phylogeny indicates the paedomorphic Lepidarchus as the lineage sister to Hepsetus and remaining alestids, and shows at least three origins of paedomorphosis: the first in Lepidarchus, the second for the clade with Micralestes and Rhabdalestes, and the third for the clade Bathyaethiops and Phenacogrammus. Incorporation of key taxa in the analysis such as the miniature species of Clupeocharax, Ladigesia, Rhabdalestes, and Tricuspidalestes might reveal a more complex picture of convergent evolution. We hypothesize that the independent origins of paedomorphosis might have influenced the diversification of Micralestes and Phenacogrammus especially throughout the Congo and adjacent basins of central-west Africa. |
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3. 08:45 Does Ecological Opportunity Influence Patterns of Phenotypic Evolution Following the Invasion of Freshwaters in Fishes? Victor de Brito*, Western Michigan University; Devin Bloom, Western Michigan University victor.debrito@wmich.edu
Evolutionary transitions between marine and freshwater ecosystems are an extreme ecological shift and expose lineages to novel abiotic and biotic settings. Yet, it remains unclear how these habitat transitions and the interaction with the invaded communities have altered the macroevolutionary dynamics of fish clades. Exploring the effects of marine/freshwater transitions across multiple fish clades, and how varying species richness in incumbent communities can influence morphological diversification patterns, will help elucidate the effect of species interaction over short and deep time scales. In this project, we will test if rates of phenotypic diversification following marine/freshwater transitions in Atheriniformes (silversides and rainbowfishes), Clupeiformes (anchovies, sardines, and herrings), and Sciaenidae (drums) are influenced by different levels of competition. Collectively, these include approximately 1,300 valid species, with 317 freshwater taxa resulting from more than 20 independent transitions to freshwaters around the globe. The wide range of species diversity and the different ecologies of these groups offer a prime opportunity to explore how ecological opportunity may drive macroevolutionary processes. We will use phylogenetic comparative analyses to test if species richness of incumbent freshwater fish species drives functional trait diversity and causes phenotypic divergence across lineages that invaded different freshwater regions. We predict that rates of phenotypic diversification following transitions to freshwaters are higher in clades that invaded species-poor regions than in highly diverse regions. |
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4. 09:00 Genetic variation among populations of Tlaloc hildebrandi (Profundulidae). Kyle Piller*, Southeastern Louisiana University; Chantal Parker, Yale University; Diego Elias, Louisiana State University; Caleb McMahan, The Field Museum; Wilfredo Matamoros, Universidad de Ciencias y Artes de Chiapas kyle.piller@selu.edu
Traditionally, the study of diversification of Middle American fishes largely focus on broadly distributed species, whereas narrowly distributed species receive less attention. Tlaloc hildebrandi (Profundulidae), El popoyote de San Cristóbal or the Chiapas Killifish, is an endangered species that has a limited distribution in the Valley of San Cristobal de las Casas in Chiapas, Mexico. It is a microendemic with one of the smallest ranges of any species in the family. Recent fieldwork has shown that T. hildebrandi is more widespread than previously known, as specimens have been collected in lower elevation areas in the region. These recently discovered populations dramatically expands the range of T. hildebrandi to areas outside of the endorheic basin and therefore leads to questions about the evolutionary colonization dynamics of the species. Therefore, the objective of this study was to examine genetic variation among populations of T. hildebrandi from historic and newly discovered populations in the Grijalva and Usumacinta basins. We collected ultraconserved elements (UCEs; >1,000 loci) from 18 populations. We conducted multiple phylogenetic and population genetic analyses to compare genetic variation among the populations. The UCE phylogeny shows a pattern of lowland to upland diversification. Single nucleotide polymorphism data (SNPs) pulled from the UCE data show genetic differences between high and low elevation areas indicating some level of reduced gene flow that may be explained by elevational differences among localities. The conservation implications of these results will be presented. |
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5. 09:15 Turning a Skate into a Ray: The Genetic Basis of Modified Pectoral Fins in Manta Rays and their Relatives. Emily McFarland*, San Francisco State University; Karen Crow-Sanchez, San Francisco State University emcfarland1@mail.sfsu.edu
Batoids possess a unique body plan associated with a benthic lifestyle that includes dorsoventral compression and anteriorly expanded pectoral fins that fuse at the rostrum. Members of the family Myliobatidae, including manta, eagle, and cownose rays, exhibit further modifications to the standard batoid body plan that are associated with invasion of the pelagic environment, including a redistribution of pectoral fin rays, a shifted center of mass, and a high aspect ratio, that facilitate underwater flight. Most notably, the pectoral fins are split into two discrete domains with independent functions--the anterior cephalic fins are used for feeding while the remainder is dedicated to oscillatory locomotion. Domain splitting during paired fin development is driven by an interruption of the AER around the fin margins that is maintained by Wnt3/a. Dkk1 is a known Wnt3 antagonist that is differentially expressed in the anterior pectoral fin of myliobatids. Here, we provide functional evidence that Dkk1 is sufficient to initiate fin domain splitting. Agarose beads soaked in DKK1 protein were implanted in the pectoral fins of little skate (Leucoraja erinacea) embryos resulting in interruption of the AER compared to implantation of control beads. This disruption creates an indent in the fin resembling that of a developing myliobatid. These results provide functional evidence for the underlying genetic pathway associated with the evolution of a novel paired fin/limb modification in manta rays and their relatives. |