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    ASIH Stoye Award, Ichthyology III

    2021-07-21   13:45 - 15:15

    Moderator: Luiz Rocha

    2.  14:00  VIRTUAL    Rapid Morphological Divergence in Three Introduced Cichlid Species. Khalil Russell*, William & Mary; Eric Hilton, Virginia Institute of Marine Science

    Cichlids are well-known for their capacity to exploit trophic niches in their environments through rapid speciation and morphological diversification; the best-documented case of such diversification in cichlids occurred in the African Rift Valley. With numerous species established in Florida, the purpose of this study was to explore how members of the family Cichlidae have managed to invade so successfully by focusing on morphological differences between native and non-native (Floridian) populations of three cichlid species: Pelmatolapia mariae, Mayaheros urophthalmus, and Parachromis managuensis. Using both linear measurements and 2D landmark geometric morphometry, I found that all three species have diverged in multiple characteristics. Additionally, P. mariaeand P. managuensis have developed morphology beyond the range exhibited by endemic populations. The findings reported herein demonstrate that rapid morphological change has taken place among introduced populations of three cichlid species. The results suggest the observed morphological change may be the result of natural selection; however, further work is needed to test this hypothesis. Nevertheless, this study suggests that the conditions exist to promote rapid morphological evolution in introduced populations of cichlids in Florida.

    3.  14:15  VIRTUAL    Chew on This: Oral Jaw Shape is not Correlated to Diet Type in Loricariid Catfishes. Corinthia Black*, Auburn University; Jonathan Armbruster, Auburn University

    The correlation between form and function is influenced by biomechanical constraints, natural selection, and ecological interactions. In many species of suction-feeding fishes, jaw shape has shown to be closely associated with diet. However, these correlations have not been tested in fishes that contain more complex jaw functions. For example, the neotropical loricariid catfishes (commonly known as suckermouth armored catfishes or plecos) possess a ventrally facing oral disk, which allows for the oral jaws to adhere to surfaces to conduct feeding. The upper jaw consists of a highly mobile premaxilla. The lower jaw comprises medially separated mandibles that rotate around the long axis within a shallow socket at the anteroventral articulation of the quadrate, which can be operated separately. Within Loricariidae, oral jaw shape is highly variable and structurally complex, ranging from short jaws with less than five teeth to long jaws with over 200 teeth. To determine if jaw shape is correlated to diet type, we assessed oral jaw shape across 36 species using CT scans. Shape was quantified with automated landmarking in 3DSlicer, and diet type correlation was calculated using the phylogenetic generalized least squares (PGLS) method. The PGLS analysis found that diet type did not correlate to jaw shape; however, there was a correlation between clades with diverse diets and fast evolutionary rates of shape. These results suggest that shape is not constrained to diet type, meaning there are many shapes loricariids can use to eat.

    4.  14:30  VIRTUAL    Variation and Diversity in Two Clades of Deep-channel Neotropical Electric Fishes (Gymnotiformes: Apteronotidae). Aaron H. Fronk*, University of Louisiana at Lafayette; James S. Albert, University of Louisiana at Lafayette

    The extent to which phenotypic differences among species (diversity) arise from differences within species (variation) can be studied directly by comparing patterns within and among closely related species. Under the theory of lines of least evolutionary resistance (LLER), diversity arises from the action of microevolutionary processes on standing heritable variation to produce new macroevolutionary changes; however, if macroevolutionary changes arise from the action of high-impact low-frequency (HILF) events, patterns of phenotypic diversity and variation are not expected to coincide. We compared patterns of variation and diversity in head and body shape among members of two clades of Neotropical electric fishes, Adontosternarchusand Sternarchella, that inhabit deep (>5 m) channels of large lowland rivers in northern South America (NSA), a system assembled through the action of HILF river capture events over the past 10 Ma. Using landmark-based 2D geometric morphometrics and principle component analysis (PCA) to characterize variation and diversity, we documented phylogenetic allometry in four sister species pairs. We estimated ancestral area evolution for both clades using a time-calibrated molecular phylogeny in the context of a Landscape Evolution Model (LEM) of changes in sedimentary basin connectivity across the NSA through the Neogene. We discovered strong discontinuities in variation and diversity of head and body shape in both clades, indicating speciation did not occur along intraspecific LLERs, illustrating a decoupling of micro- and macroevolutionary processes. The results also indicate the action of HILF river capture events as a major driver of phylogenetic diversification in these clades of deep-channel electric fishes.

    5.  14:45  VIRTUAL    Waking the Sleepers: Examining the Genetic Diversity of Eleotris (Eleotridae) in the Neotropics. Sheila Rodriguez-Machado*, Louisiana State University; Prosanta Chakrabarty, Louisiana State University

    A paucity of diagnostic characters exists to differentiate species of the widespread genus Eleotris. Recently, genetic tools have brought some light to the taxonomy and systematics of this group. Sleepers are among the most common freshwater fishes in Cuba. Nevertheless, they have been poorly studied and available information on their identification and distribution are not conclusive. We aimed to validate the taxonomic identity of Eleotris in Cuba and to analyze its phylogenetic relationship in the Neotropics, based on mitochondrial markers. Six clades were recovered from the Neotropics, four of which correspond to species of Eleotris described from the region: E. amblyopsis, E. pisonis, and E. perniger(Atlantic slope),andE. picta(Pacific slope). The Atlantic slope species form a clade but E. picta was recovered as the sister species to all other Eleotris except E. oxycephala (Japan). Cuba was found to have two species of sleepers, E. amblyopsis (only found in Isla de la Juventud) and Eleotris perniger(widespread on the island). Despite these two species having a wide distribution, from the United States to Northern Brazil and the Caribbean basin, we found few signs of phylogeographic patterns suggesting panmictic populations across the Americas: a predictable result for these amphidromous species that can disperse long distances. Based on our current molecular dataset and the low phenotypic diversity within Eleotris, our understanding of its phylogenetic relationships is far from being complete. Extensive sampling and more advanced genetic techniques are needed to better address the taxonomy of this group.

    6.  15:00  VIRTUAL    Evolution And Diversity In The Neotropical Freshwater Stingrays: A Phylogenomic Perspective. Joao Pedro Fontenelle*, University of Toronto; Fernando Marques, Universidade de São Paulo; Nathan Lovejoy, University of Toronto

    Comprising more than 20% of the whole described fish diversity, the Neotropical ichthyofauna is composed "ancient" freshwater groups and marine-derived lineages, which have recently evolved in freshwater environments. Among these lineages, the Neotropical freshwater stingrays (subfamily Potamotrygoninae) form a lineage that is hypothesized to have originated during the Miocene, associated with marine incursions from the Caribbean. However, this fairly young yet diverse group inhabits almost every major river basin in South America. Despite recent taxonomic studies and species descriptions, the diversity of this subfamily is still believed to be underestimated. Morphological and molecular studies struggle with overlapping morphological patterns for the former, and the apparent incomplete coalescence of genes for the latter. Here we provide the first phylogenomic study for the Potamotrygoninae, using a geographically and taxonomic dense dataset that includes 33 of 38 valid species, and more than 1500 loci and 8000 SNPs for 141 specimens. Our results resolve deep and shallow nodes in the phylogeny of the Potamotrygoninae subfamily, and provide evidence that closely-related species are genetically indistinguishable, suggesting hybridization among recently diverged species or extreme intraspecific variability within a single species. We also find evidence of geographically-based genetic distinctiveness in widespread species, suggesting underestimated diversity. We discuss possible convergent evolution of morphological patterns and propose that hybridization has occurred throughout the evolutionary history of potamotrygonines.

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