Session 34: General Ichthyology IIRoom: Ballroom 111C2022-07-30 10:00 - 11:30 |
| Moderator: Luke Tornabene |
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1. 10:00 Alternating Regimes of Shallow and Deep Diversification in Marine Fishes. Elizabeth Miller*, University of Oklahoma; Christopher Martinez, UC Irvine; Sarah Friedman, UC Davis; Peter Wainwright, UC Davis; Samantha Price, Clemson University; Luke Tornabene, University of Washington lizmiller2633@gmail.com
The deep sea contains a surprising diversity of life including iconic fish groups such as anglerfishes and lanternfishes. Still, ~70% of marine teleost fish species are restricted to the photic zone above 200 meters, which comprises <10% of the ocean’s total volume. From a macroevolutionary perspective, this dramatic asymmetry may be explained by three hypotheses: (a) shallow lineages have had more time to diversify than deep lineages, (b) shallow lineages have faster rates of speciation than deep lineages, or (c) shallow-to-deep transition rates limit deep-sea richness. Here we use phylogenetic comparative methods to test among these three non-mutually exclusive hypotheses. We found support for all hypotheses, but the disparity in species richness is best described as the outcome of alternating phases that favored shallow or deep diversification over the past 200 million years. Shallow diversification was favored during times of warm temperatures and high sea level suggesting the importance of reefs and epicontinental settings. Conversely, deep-sea colonization and diversification was favored during times such as the present day when colder temperatures increased the efficiency of the biological pump. Finally, we show that time-variable ecological filters limited shallow-to-deep colonization for much of teleost history and helped maintain higher shallow richness. A pelagic lifestyle and large jaws were associated with early deep-sea colonists, while a demersal lifestyle and a tapered body plan were dominant among later colonists. Therefore, we also suggest for the first time that some hallmark characteristics of deep-sea fishes are exaptations. |
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2. 10:15 Scale shape vs Trophic position: Testing form and function relationships in an assemblage of reef fishes. Sean Trainor*, Rice University; Kory Evans, Rice University st78@rice.edu
Fish scales and integuments represent an understudied system which can yield insights into form-function relationships that may govern how these organisms interact with their environments. They also offer a diverse and varied source of bioinspiration whether looking at shape, internal structure, or location along the fish. In this study, we have examined the scales of 24 reef fish species using computed tomography and 3D segmentation software to test the relationship between scale shape and trophic level collected via stable isotope analysis. We hypothesize that we will find that reef species in lower trophic levels will have a scale shape that allows for higher mobility in the reef, which would allow them to escape predation more effectively and locomote their feeding areas. |
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3. 10:30 Burrowing Constrains Patterns of Skull Shape Evolution in Wrasses. Kory Evans*, Rice University; Olivier Larouche, Rice University; JoJo West, Rice University; Samantha Gartner, University of Chicago; Mark Westneat, University of Chicago kory.evans@rice.edu
The evolution of ecological specialization can have marked effects on the tempo and mode of phenotypic evolution. Head-first burrowing has been shown to exert powerful selective pressures on the head and body shapes of many vertebrate and invertebrate taxa. In wrasses, burrowing behaviors have evolved multiple times independently, and are commonly used in foraging and predator avoidance behaviors. While recent studies have examined the kinematics and body shape morphology associated with this behavior, no study to-date has examined the macroevolutionary implications of burrowing on patterns of phenotypic diversification in this clade. Here, we use three-dimensional geometric morphometrics and phylogenetic comparative methods to study the evolution of skull shape in fossorial wrasses and their relatives. We test for skull shape differences between burrowing and non-burrowing wrasses and evaluate hypotheses of shape convergence among the burrowing wrasses. We also quantify rates of skull shape evolution between burrowing and non-burrowing wrasses to test for whether burrowing constrains or accelerates rates of skull shape evolution in this clade. We find that while burrowing and non-burrowing wrasses exhibit similar degrees of morphological disparity, for burrowing wrasses, it took nearly twice as long to amass this disparity. Furthermore, while the disparities between groups are evenly matched, we find that most burrowing species are confined to a particular region of shape space with most species exhibiting narrower heads than many non-burrowing species. These results suggest head-first burrowing constrains patterns of skull shape diversification in wrasses by potentially restricting the range of phenotypes that can perform this behavior. |
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4. 10:45 MYTHBUSTERS: refining what we understand about anal fin variation in surfperches
. Breana Goldman*, San Francisco State University; Karen Crow, San Francisco State University breanagoldman@gmail.com
Phenotypic diversity is defined by the evolution of novel traits, and because reproduction is the currency of fitness, reproductive structures and associated secondary sex traits exhibit a high degree of variation. The embiotocids, or surfperches, exhibit novel, sexually dimorphic, medial fin modifications that are likely associated with internal fertilization, but their function is currently unknown. These structures have been loosely characterized, in taxonomic keys and papers that are 100 years old, as bony hooks and serrated plates (Amphisticinae), or enlarged fleshy protuberances (Embiotocinae). We found divergence between subfamilies, species, and sex that have not been previously described. Including a fin ray modification, an ancestral feature present in embiotocines as well as amphisticines, and sexual dimorphism that is not fully penetrant-manifest as diminished character states in females. Six species were evaluated using clear and stain methods. We compared placement and developmental stage of fin ray modifications between species and sexes. |
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5. 11:00 Cranial Evolution of Sculpin Fishes (Superfamily Cottoidea) Shows Rapid Acceleration After Invading Freshwater. Thaddaeus Buser*, Rice University; Olivier Larouche, Rice University; Andres Aguilar, California State University, Los Angeles; Michael Sandel, Univeristy of Western Alabama; Brian Sidlauskas, Oregon State University; Adam Summers, University of Washington; Kory Evans, Rice University thaddaeus.buser@gmail.com
Evolutionary habitat transitions can trigger explosive diversification as taxa colonize new areas and evolve to exploit the resources that they subsequently encounter. For example, several groups of marine fishes have invaded freshwater habitats, with varying degrees of subsequent diversification. Sculpins (superfamily Cottoidea) represent an interesting case of this phenomenon, as they are a primarily marine group, with a large freshwater clade nested therein. The freshwater species are broadly distributed geographically but are generally morphologically and ecologically conserved. The exception to this generality however is an incredibly diverse clade that evolved in Lake Baikal, Siberia, and this group has frequently been described as an adaptive radiation. However, the morphological diversity of freshwater and marine sculpins has yet to be considered in a quantitative framework. We compared the cranial bones of 107 species of cottoid fishes, with a representative sample of marine and freshwater (including Baikal) species. We quantified the shape of the major bones of the cranium with 3D geometric morphometric techniques applied to reconstructions from micro-CT scans of members of each species. We characterized the morphospace of cranial bones within cottoids and compared rates of morphological evolution across the various sculpin families. We found that morphological diversification is driven primarily by the neurocranium and the weaponized preopercle. We further found that the freshwater sculpins have undergone a remarkably rapid diversification, driven especially by the Baikal radiation. The marine sculpins are more diverse overall, but their diversification was not nearly as rapid. |