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    V: ASIH Symposium: Why are there so many kinds of fishes? A showcase of early-career ichthyologists, III

    2021-07-27   13:15 - 14:15

    Moderator: Prosanta Chakrabarty

    1.  13:15  VIRTUAL    Early Career: Evolutionary constraints, a double-edged sword: inhibitor or liberator of fish diversity? Jonathan Huie*, George Washington University

    There are many avenues by which fishes can diversify. In terms of ecology, fish have evolved to occupy the craziest of niches, from removing scales or parasites from other fishes to invading extreme habitats where the odds are not in their favor. With the transition towards new niches, existing traits are often repurposed or new traits are evolved altogether. However, biology is not perfect and there is often more than one way to accomplish the same task. As a result, there is immense morphological variation across taxa that have approached similar life-styles. In the era of big data, micro-computed tomography (micro-CT) scanning has enabled large-scale investigations of diverse fish forms. Coupled with open-source repositories, micro-CT scanning has proven to be an invaluable resource for myself and other early-career researchers. Here, I will highlight examples where my collaborators and I have used micro-CT scanning to investigate the evolution and morphological diversity of different groups of fishes. This includes both cleaner and ectoparasitic fishes, and how the heroes and villains of the fish world have evolved to remove food items from the surface of other fishes. Additionally, I will cover more recent work on fishes that have evolved suction cups from modified fin rays. We find that phylogenetic constraints may be a double-edged sword that limits diversity within clades, but facilitates variation between them and may help to explain why there are so many kinds of fish.

    2.  13:30  VIRTUAL    Early Career: Piscivory Spurs Kinematic Novelty and Diversity in Neotropical Cichlids. Christopher Martinez*, University of California; Sarah Williamson, University of California; Edward Burress, Yale University; Matthew McGee, Monash University; Samuel Borstein, University of Michigan; Peter Wainwright, University of California

    Neotropical cichlids have diversified broadly across Middle and South American freshwater habitats and display wide ecological and morphological diversity. Additionally, they feed on a variety of aquatic prey, from algae to other fishes, and have evolved a stunning range of functional variation in their feeding mechanisms. We used landmark morphometrics to examine cranial morphology and prey capture kinematics in over 80 species, spanning the diversity of neotropical cichlids. Feeding movements were studied with a combination of trajectory-based morphometric analyses as well as a suite of kinematic traits describing maximum excursions of key morphological features. We classified species into one of four dietary guilds that included herbivores, invertivores, omnivores, and piscivores. We then tested for differences in mean values, variances, and rates of evolution (the Brownian rate parameter) for morphological and kinematic traits. We found that piscivores differed in head shape and several kinematic variables, and that they were consistently among the most diverse and rapidly evolving trophic groups. These patterns were, in part, facilitated by the evolution of a functional innovation allowing extreme upper jaw protrusion in some piscivorous species. Interestingly, herbivores often had elevated rates of morphological and kinematic evolution, but were much more constrained in the diversity of their motions. Our results highlight the role of dietary specialization in the evolution of feeding systems in Neotropical cichlids and expands our understanding of motion diversity as it relates to trophic ecology.

    3.  13:45  VIRTUAL    Early Career: Why so many electric fishes? Mosaic Evolution of Craniofacial Morphologies in Apteronotidae (Gymnotiformes) and Mormyridae (Osteoglossiformes). Kassandra Ford*, University of Louisiana at Lafayette; Maxwell Bernt, American Museum of Natural History; Rose Peterson, George Washington University; James Albert, University of Louisiana at Lafayette

    What is convergent evolution, and how can it contribute to the diversification of organismal form and function? The independently-evolved electric fishes of tropical American and African freshwaters exhibit remarkable similarities and differences in aspects of their skull shape and electric signal design. These fishes occupy multiple habitat types (e.g. deep river channels, floodplains, non-flooded forest streams) where prey type and availability, water velocity, and habitat complexity likely influence the size and shape of the snout and oral jaws. Yet the relationships between environmental factors and craniofacial morphologies are incompletely understood. Here we examine head and skull shape in Neotropical apteronotid and Afrotropical mormyrid electric fishes for patterns of convergent and divergent evolution. Individuals from Apteronotidae (43 species, n=160 specimens) and Mormyridae (41 species, n=229 specimens) were CT-scanned and analyzed using 3D geometric morphometrics with 22 homologous landmarks in 3D-Slicerand the R package geomorph. We assessed phylogenetic patterns of evolution using phytools and tested for convergence using convevolin R. Our analyses show the presence of convergence, divergence, and stasis in craniofacial evolution within and between these families. This mosaic pattern of trait evolution allows for diverse and adaptive combinations of phenotypes across species. We interpret these patterns of morphological convergence and disparity among electric fishes as arising from the integration of organismal constraints on craniofacial development and functional constraints imposed by tropical aquatic environments.

    4.  14:00  VIRTUAL    Early Career: What Can and Can't Traits Tell Us About Why There are So Many Fishes? Kara Feilich*, University of Chicago

    Functional diversity describes the multitude of ways organisms interact with their ecosystems. However, direct measurement of function and behavior can be difficult, time-consuming, and expensive, especially for large samples. Instead, many researchers use easily measurable traits such as body shape or body size as proxies for functional diversity. These proxy traits allow us to explore how functional diversity is ecologically and evolutionarily distributed, generated, and maintained; questions that get to the heart of why there are so many kinds of fishes. But how do we know if we have chosen appropriate proxies for inferring function? Do these proxy traits capture the functional diversity that we think they do? And even if they do, do the functions represented by proxy traits matter with respect to fitness? In this talk, I will discuss some of the ways trait data are currently used to study functional diversity, how we assess the utility of traits as informative proxies, and what data we need to fill the gaps between traits, function, and evolution. While there are no perfect solutions to the challenges discussed here, interdisciplinary collaboration and persistent collection of natural history data are essential for understanding functional diversity.

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