Browsing by Subject "Morphology"

Now showing 1 - 11 of 11
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    Experimental evolution of increased size and complexity in Anabaena variabilis
    (2014-05) Jacobsen, Kristin Alexa
    The evolution of multicellularity has occurred over 25 times in the history of life. Previously, we have shown the evolution of multicellular traits can readily be observed in laboratory populations across model unicellular organisms like yeast, chlamydomonas, and E. coli. Cyanobacteria are the oldest multicellular organisms, dating back 3.5 billion years. Many species appear morphologically unchanged, suggesting they have remained primitively multicellular. Are they incapable of evolving increased complexity? Model prokaryote Anabaena is a filamentous cyanobacteria, predating fossil records, existing as single strands or loose mats with three distinct cells types. Rapid settling was used to select for increased size advantage. Response to selection resulted in dramatic size increase; microscopic strands became inseparable macroscopic aggregates. Anabaena also became more complex; growth rate increased, two distinguishable morphologies developed, and growth and reproduction patterns changed. This shows that Anabaena, although primitively multicellular for billions of years, rapidly evolves increased size and complexity.
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    Improving the efficiency of a ceria reduction-oxidation cycle through the choice of operating conditions and ceria morphology
    (2014-05) De Smith, Robert Michael
    Pathways for improving the efficiency of ceria-based thermochemical cycling for solar-driven fuel production are investigated. First, the operating conditions of an isothermal CO2 splitting cycle are optimized to improve process efficiency. The optimum conditions are a sweep gas flow rate of 150 mL min-1 g-1, a CO2 flow rate of 50 mL min-1 g-1, a reduction time of 100 s, and an oxidation time of 155 s. A quasi-equilibrium model is developed to predict the rates of ceria reduction and oxidation. Finally, a new ceria morphology, wood templated ceria, is used to improve the heterogeneous oxidation reaction rates by maintaining a high surface area when exposed to the extreme temperatures required for ceria reduction. Wood templated ceria performs well at reduction temperatures up to 1400 °C, reaching peak CO production rates of 9 mL min-1 g-1, but rates decrease due to sintering when it is reduced at 1500 °C.
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    Intrinsically photosensitive retinal ganglion cells: diversity of form and function.
    (2010-12) Schmidt, Tiffany M.
    A subpopulation of retinal ganglion cells (RGCs) express the photopigment melanopsin, rendering them intrinsically photosensitive (ipRGCs). These ganglion cell photoreceptors are critical for several non-image forming behaviors including circadian entrainment and the pupillary light reflex. Initially thought to be a uniform population, later studies demonstrated that there was at least some degree of morphological and physiological diversity in the ipRGC population. Technical limitations, however, had prevented the comprehensive study of ipRGCs at the single cell level. The purpose of this project was to utilize a mouse model in which ipRGCs are labeled in vivo with enhanced green fluorescent protein to identify and target single ipRGCs for morphological and physiological analyses. The central hypothesis of the research presented herein is that distinct morphological ipRGC subtypes have distinct physiological properties and synaptic inputs, resulting in unique light information sent to target nuclei in the brain by the various ipRGC subpopulations. This work has confirmed the existence and further analyzed the morphological and physiological properties of at least three ipRGC subtypes: M1 cells with dendrites stratifying in the OFF sublamina of the inner plexiform layer (IPL), M2 cells with dendrites stratifying in the ON sublamina of the IPL, and M3 cells with dendrites bistratifying in both the ON and OFF sublaminas of the IPL. We find that these cell types do indeed possess distinct intrinsic light responses and intrinsic membrane properties. Furthermore, we find that these subpopulations are differentially influenced by cone-mediated signals. Finally, we find that the cation channel involved in ipRGC signal transduction is not composed solely of the canonical transient receptor potential channel (TRPC) subunit 3, 6, or 7. However, we do find that TRPC6 is involved in mediating the melanopsin-evoked light response in both M1 and M2 cells, with both subtypes showing a reduction in the magnitude of the intrinsic light response in TRPC6-/- animals. Collectively, the differential influence of intrinsic, melanopsin-mediated phototransduction and synaptically-evoked extrinsic inputs on the integrated light-evoked response of ipRGC subtypes indicates that these subtypes may serve as conduits for distinct light information sent to the brain. We discuss the implications of these findings and propose a model for the differential influence of distinct ipRGC subtypes on various non-image forming behaviors.
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    The morphology and evolution of tooth replacment in the combtooth blennies (Ovalentaria: Blenniidae)
    (2020-07) Williams, Keiffer
    This research investigates the morphology and evolution of tooth replacement in the combtooth blennies. Blennies exhibit complex dentition that is not easily categorized by previously established metrics of teleost tooth replacement (extraosseous and intraosseous replacement). Most blennies are heterodont, possessing a single row of comb-shaped feeding teeth on the anterior portion of their jaws, and enlarged canines on the posterior portion of their lower jaws used for agonistic interactions. However, this bizarre dentition has been intentionally overlooked in classic surveys of teleost dentition due to its complexity. In Chapter 1, I investigate how feeding teeth are replaced in salariin blennies by establishing a descriptive model of tooth replacement for the Pacific Leaping Blenny, Alticus arnoldorum. This fish exhibits tooth replacement and tooth attachment that defy the discrete categorizations used for most other teleost dentitions. Using my descriptive model, I then propose hypotheses of how feeding teeth function in this fish. In chapter 2, I investigate how modes of tooth replacement have evolved in blennies. I find that canines in blennies are consistently replaced intraosseously, while feeding teeth across the family vary from intraosseous to a derived form of extraosseous replacement. These results further support the concept of teleost tooth replacement as a continuum rather than discretely classified modes. My results also suggest teleost tooth replacement needs to be carefully examined within a phylogenetic context to better understand how trophic morphological novelties evolve, as modes of tooth replacement likely play a key role in ecological and functional morphological shifts in teleosts.
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    Morphology and Mechanical Properties of High Density Polyethylene Exposed to Chlorinated Water
    (2018-07) Majewski, Kelly
    High density polyethylene (HDPE) is often used in applications that include both structural loads and oxidative environmental conditions. In this study, the effect of an oxidative environment on HDPE morphology and mechanical performance is evaluated. Extruded thin 70 micron HDPE samples (as-extruded and heat treated) are exposed to 5ppm chlorinated water at 70 degrees Celsius for up to 1250 hours. Changes in semicrystalline polymer morphology as a function of exposure time are evaluated and compared with tensile and creep test data. Additionally, data are evaluated as a function of molecular weight, to eliminate variations in sample thickness, processing, or variation in oxidative environment conditions. IR spectrum data indicate an increase in the carbonyl functional groups with increased exposure time and decreased molecular weight, with the largest peak change in the carbonyl band being the ketone group, and a 300% increase in the carbonyl index. Molecular weight data reveal no change in molecular weight of 200 kg/mol from 0-250 hours, with over a 50% decrease in Mw after 750 hours, and a slower decrease with further exposure. Molecular weight distribution data and determination of chain scissions and crosslinking reveal preferential chain scission of high molecular weight chains as the underlying mechanism for this decrease in molecular weight. Heat treated samples exhibit more resistance to a decrease in molecular weight. The critical molecular weight is observed at ~83-86 kg/mol for the as-extruded HDPE. Crystallinity measurements using Differential Scanning Calorimetry and X-Ray Diffraction (XRD) differ by up to 10% but show a steady increase in crystallinity as exposure time increases, due to chemicrystallization. Molecular weight is determined to be the primary characteristic governing ultimate tensile strength, while percent crystallinity and molecular weight both govern the strain at break. In a preliminary study of lamellar morphology, a decrease in the interlamellar spacing, lamella thickness, and long period is observed with increased degradation. The critical interlamellar spacing from the ductile to brittle transition for as-extruded HDPE is observed to occur at ~85Å, determined using the XRD crystallinity results, and ~38Å determined using the DSC results. The data presented in this study demonstrate the correlation between morphology changes and a loss in ductility in HDPE. These data are the basis for a predictive model for lifetime of HDPE components exposed to oxidative environments.
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    Network morphologies in monodisperse and polydisperse multiblock terpolymers.
    (2009-02) Meuler, Adam James
    Multiply continuous network morphologies were previously identified in “monodisperse” (polydispersity index (PDI) < ~1.1 in all blocks) poly(isoprene-bstyrene- b-ethylene oxide) (ISO) triblock terpolymers. This work extends the investigation of multiply continuous network structures to two other classes of multiblock terpolymers: i) “monodisperse” OSISO pentablocks and ii) polydisperse ISO triblocks. The OSISO pentablocks are synthesized using a protected initiation strategy that required the development of the functional organolithium 3-triisopropylsilyloxy-1- propyllithium (TIPSOPrLi). TIPSOPrLi may be used to prepare α-hydroxypolystyrene with narrower molecular weight distributions (PDI ~ 1.1) than are attainable using the commercially available 3-tert-butyldimethylsilyloxy-1-propyllithium. A telechelic triblock terpolymer (HO-SIS-OH) with narrow molecular weight distributions in all blocks is prepared using TIPSOPrLi. A series of OSISO pentablocks is synthesized from this parent triblock, and a stable region of O70 (the orthorhombic Fddd network) is identified between two-domain lamellae (LAM2) and three-domain lamellae (LAM3) in OSISO materials. This sequence of morphologies was previously reported in ISO triblocks with comparable compositions. Mechanical tensile testing reveals that an OSISO sample with a lamellar mesostructure fractures in a brittle fashion at a strain of 0.06. An OSISO containing the O70 network, in contrast, has a strain at failure of 1.3, even though the crystallinity of the terminal blocks is above the brittle threshold established in other multiblock materials. This improved toughness is attributed to the combined effects of a triply continuous morphology and an intrinsically tough SIS core. The ISO triblock studies probe the stability of network morphologies with respect to polydispersity in the polystyrene and poly(ethylene oxide) chains. Three series of ISO triblocks with polydisperse (PS PDI = 1.16, 1.31, 1.44) polystyrene blocks are prepared by anionic polymerization. While the network “window” in the PS PDI = 1.16 series is comparable in width and location to the window reported in the “monodisperse” ISO materials, it apparently shrinks for the higher PS PDI values. Only lamellar mesostructures are reported in the PS PDI = 1.31 materials, and network morphologies are identified over only a narrow range of compositions in the PS PDI = 1.44 samples. Polydispersity does not always destabilize network morphologies, however, as broadening the molecular weight distribution of the terminal poly(ethylene oxide) block drives a morphological transition from lamellae to the coreshell gyroid network. This result demonstrates that polydispersity can be used to tune block terpolymer phase behavior and stabilize technologically useful network mesostructures. Self-consistent field theory calculations augment the experimental analysis and offer insight into the physics underlying the polydispersity-driven morphological changes.
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    Noun Composition in Ojibwe
    (2021-06) Johnson, Hunter, F
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    Reconstructing Past Craft Networks: A Case Study using 3D scans of Late Bronze Age Swords to reconstruct Specialized Craft Networks
    (2016-05) Golubiewski-Davis, Kristina
    As the collection of 3d data proliferates in the archaeological community, new methods integrating analysis of those data must also be developed. This dissertation project approaches the problem of observing social networks by examining decisions made by specialized craft workers: specifically, Late Bronze Age smiths (~1200-800BC). The data examined include shape data collected from 3D scans of bronze swords. These data were used to group the blades using cluster analysis based on different aspects of the swords including blade profile, hilt profile, and various decorative shape data. Those clusters create links between the swords which were then used to examine the network of bronze smiths. This project is a case study of how one might go about studying the way individuals with specialized knowledge were connected in the past by studying the results of that knowledge expressed through tangible differences between artifacts.
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    Studies on the Assembly and Morphology of Human T-Cell Leukemia Virus Type 1
    (2019-08) Maldonado-Ortiz, José
    The group-specific antigen (Gag) polyprotein is an essential retrovirus structural protein required for the assembly and release of virus particles. Present knowledge of Gag biology has been limited to a few retroviruses. Furthermore, current understanding of the diversity in the nature of Gag structure and function in virus particle assembly is limited. Human T-cell leukemia virus type 1 (HTLV-1) is a deltaretrovirus that causes an adult T-cell leukemia/lymphoma (ATLL), HTLV-1-associated-myelopathy/tropical spastic paraparesis (HAM/TSP), and other neurotropic conditions. HTLV-1 has infected approximately 15 million individuals worldwide. A general knowledge gap exists regarding the details of HTLV-1 replication, including particle assembly. To address this, and to test the overarching hypothesis that HTLV-1 particle assembly is distinct from that of other retroviruses, this dissertation focused on investigating three key aspects of HTLV-1 immature and mature particle morphology. First, an analysis of the morphology and Gag stoichiometry of HTLV-1-like particles and authentic, mature HTLV-1 particles by using cryogenic transmission electron microscopy (cryo-TEM) and scanning transmission electron microscopy (STEM) was conducted. HTLV-1-like particles mimicked the morphology of immature authentic HTLV-1 virions. Importantly, it was observed for the first time that the morphology of these virus-like particles (VLPs) has the unique local feature of a flat Gag lattice that does not follow the curvature of the viral membrane, resulting in an enlarged distance between the Gag lattice and the viral membrane. Measurement of the average size and mass of VLPs and authentic HTLV-1 particles suggested a consistent range of size and Gag copy numbers in these two groups of particles. The unique local flat Gag lattice morphological feature observed suggests that HTLV-1 Gag could be arranged in a lattice structure that is distinct from that of other retroviruses characterized to date. Second, the effects of Gag proteins labeled at the carboxy terminus with a fluorophore protein were analyzed for their influence on particle morphology. In particular, a HTLV-1 Gag expression construct with the yellow fluorescence protein (YFP) fused to the carboxy-terminus was used as a surrogate for the HTLV-1 Gag-Pro to assess the effects of co-packaging of Gag and a Gag-YFP on virus-like particle morphology and particles were analyzed by cryo-TEM. STEM and fluorescence fluctuation spectroscopy (FFS) were also used to determine the Gag stoichiometry. Ratios of 3:1 (Gag:Gag-YFP) or greater were found to result in a particle morphology indistinguishable from that of VLPs produced with the untagged HTLV-1 Gag, i.e., a mean diameter of ~113 nm and a mass of 220 MDa as determined by cryo-TEM and STEM, respectively. This information is useful for the quantitative analysis of Gag-Gag interactions that occur during virus particle assembly and in released immature particles. Third, cryo-electron tomography (cryo-ET) was used to analyze mature HTLV-1 particle morphology. Particles produced from MT-2 cells were polymorphic, roughly spherical, and varied in size. Capsid cores, when present, were typically poorly defined polyhedral structures with at least one curved region contacting the inner face of the viral membrane. Most of the particles observed lacked a defined capsid core, which likely impacts HTLV-1 particle infectivity. Taken together, the findings of this dissertation provide new insights into the nature of immature and mature HTLV-1 assembly and morphology and provide foundational knowledge towards an advanced understanding of the HTLV particle assembly pathway.
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    Systematics of the family Polycentropodidae (Inseecta:Trichoptera: Psychomyioidea) and taxonomic revisions of New World Polyplectropus Ulmer.
    (2009-01) Chamorro, Maria Lourdes
    The monophyly and phylogenetic relationships of subfamilies and genera traditionally classified in Polycentropodidae Ulmer, 1903, one of the most diverse families in the suborder Annulipalpia, with more than 700 species in 3 subfamilies, were tested. Particular emphasis was placed on testing the monophyly of the cosmopolitan genus Polyplectropus. Larval information is unknown for 46% of the taxa included in this study. To understand the effects of including characters with large sets of missing data, three alternative datasets [TOTAL (all available data for all taxa)= 49 ingroup taxa, 122 characters (including highly incomplete characters); LPA (larval, pupal, adult) = 20 ingroup taxa, 122 characters; ADULT (only adult characters) = 49 ingroup taxa, 86 adult characters] were analyzed under parsimony and Bayesian methods. The five outgroup taxa, representing all four extant families in the Psychomyioidea and the single family in the Hydropsychoidea, remained constant in all datasets. The TOTAL and ADULT datasets included all 20 currently recognized polycentropodid genera placed in 3 subfamilies, and the LPA and TOTAL datasets included characters interpreted from structures of the larvae, pupae, and adults. Results rejected the monophyly of Polycentropodidae, as currently defined; however, the monophyly of the three largest cosmopolitan genera, Polycentropus, Polyplectropus, and Nyctiophylax, could not be rejected nor confirmed. The monophyly of the following taxa was strongly supported in all analyses: Cernotina, Cyrnellus, Kambaitipsyche, Neureclipsis, Paranyctiophylax, New World Polyplectropus sensu stricto, Placocentropus, Neotropical Nyctiophylax, and in the outgroup, Psychomyia + Xiphocentron; while monophyly was strongly supported in some, but not all analyses for the following taxa: Cyrnus, Antillopsyche, Pseudoneureclipsis, Polycentropus sensu stricto, Pseudoneureclipsinae, New Zealand Polyplectropus, Polycentropodinae, Cyrnodes scotti + Pahamunaya jihmita. The implementation of two different analytical methods revealed some areas of conflict which would not have been detected under a single method of analysis. Contradictory results among the datasets were primarily due to either inclusion or exclusion of key sets of characters (i.e., immature characters); and second, missing data negatively affected phylogenetic reconstruction when proportions of characters with missing data were high and characters without missing data were unable to provide adequate phylogenetic signal due to high variation in rates of evolution among characters. Therefore, a combination of few overall characters that have high variation in rates of change, plus an abundance of missing data may be problematic and may lead to poorly resolved trees, thus decreased accuracy. This study also emphasized the importance in phylogenetic reconstruction of including data from all available sources. Several taxonomic changes were necessary in order for classification to properly reflect phylogeny. Three new genera, all from the Neotropical region, will be described in future publications. The redefinition of Paranyctiophylax as a valid genus in Polycentropodinae was confirmed. Additionally, the recommendation was made that North American Polycentropus species previously belonging in Plectrocnemia or Holocentropus be recognized as such (either Plectrocnemia or Holocentropus depending on original designation) and not as belonging in Polycentropus. Furthermore, species described in Polycentropus post-1944 in North America are transferred to either Holocentropus or Plectrocnemia to reflect previously hypothesized sister relationships. The following new or reinstated combinations were proposed: Plectrocnemia albipuncta Banks, 1930 combinatio revivisco; Plectrocnemia aureola Banks, 1930 comb. rev.; Plectrocnemia cinerea (Hagen), 1861 comb. rev.; Plectrocnemia clinei Milne, 1936 comb. rev.; Plectrocnemia crassicornis (Walker), 1852 comb. rev.; Plectrocnemia jenula (Denning), in Denning & Sykora, 1966 combinatio nova; Plectrocnemia icula (Ross), 1941 comb. nov.; Plectrocnemia nascotia (Ross), 1941 comb. nov.; Plectrocnemia remota (Banks), 1911 comb. rev.; Plectrocnemia sabulosa (Leonard & Leonard), 1949 comb. nov.; Plectrocnemia smithae (Denning), 1949 comb. nov.; Plectrocnemia vigilatrix Navás, 1933 comb. rev.; Plectrocnemia weedi (Blickle & Morse), 1955 comb. nov.; Holocentropus chellus (Denning), 1964 comb. nov.; Holocentropus flavus Banks, 1908 comb. rev.; Holocentropus glacialis Ross, 1938 comb. rev.; Holocentropus grellus Milne, 1936 comb. rev.; Holocentropus interruptus Banks, 1914 comb. rev.; Holocentropus melanae Ross, 1938 comb. rev.; Holocentropus milaca (Etnier), 1968 comb. nov.; Holocentropus picicornis (Stephens), 1836 comb. rev. Additional taxonomic changes proposed based on current findings were: 1) the elevation of Pseudoneureclipsinae to family status: Pseudoneureclipsidae Ulmer status novus; and 2) the resurrection of Placocentropus Schmid, nomen revivisco, to include the following species: Placocentropus aspinosus (Schmid), 1964 comb. nov.; Placocentropus chilensis (Yamamoto), 1966 comb. nov.; Placocentropus obtusus Schmid, 1955 comb. rev.; Placocentropus quadriappendiculatus (Schmid), 1964 comb. nov.; Placocentropus quadrispinosus (Schmid), 1964 comb. nov.; Placocentropus tuberculatus (Flint), 1983 comb. nov.; Placocentropus valdiviensis (Flint), 1983 comb. nov. A phylogeny of New World Polyplectropus species was inferred. Characters were interpreted from structures of the male and female genitalia as well as the fore- and hind wings. Parsimony and Bayesian phylogenetic analyses of 89 ingroup taxa (97% of the known New World diversity in the genus), two outgroup taxa, and 59 morphological characters were performed. Results of the parsimony and Bayesian analyses were similar, although the Bayesian tree was less resolved. Monophyly of the panamensis and charlesi Groups, as currently defined, was rejected. A total of 10 lineages, with varying amounts of support, were recognized. These groups are the alienus Group (2 species), annulicornis Group (11 species, 8 new), bredini Group (19, 7), charlesi Group (3), fuscatus Group (3, 2), guyanae Group (2, 2), manuensis Group (3, 3), narifer Group (5, 3), santiago Group (25, 6), and thilus Group (15, 7). Four species remain unassigned to any species-group: P. beccus, P. beutelspacheri, P. kanukarum, and P. nayaritensis. The distribution of the genus is mostly restricted to the Mexican and Brazilian subregions of the Neotropics. Most of the species and species-groups are regional endemics. The taxonomy of New World species of Polyplectropus Ulmer, 1905 was revised to include detailed male and female diagnoses, descriptions, illustrations, distribution records, and keys to males of all species and species-groups. A key to genera of New World Polycentropodidae, including a redescription of Polyplectropus, was provided. The homology of the male genitalia of species in the genus was discussed, as well as reassessment and diagnoses of 10 species groups, 6 newly established. A total of 92 species were treated, 39 described as new: Polyplectropus adamsae, sp. nov. (Peru), P. alatespinus, sp. nov. (Brazil), P. amazonicus, sp. nov. (Brazil), P. andinensis, sp. nov. (Argentina, Bolivia), P. blahniki, sp. nov. (Venezuela), P. bolivianus, sp. nov. (Bolivia), P. brasilensis, sp. nov. (Brazil), P. vii brborichorum, sp. nov. (Ecuador), P. cressae, sp. nov. (Venezuela), P. colombianus, sp. nov. (Colombia), P. corniculatus, sp. nov. (Peru), P. cuzcoensis, sp. nov. (Peru), P. ecuadoriensis, sp. nov. (Ecuador), P. flintorum, sp. nov. (Venezuela), P. gaesum, sp. nov. (Brazil), P. guyanae, sp. nov. (Guyana, Venezuela), P. holzenthali, sp. nov. (Brazil), P. hystricosus, sp. nov. (Brazil), P. insularis, sp. nov. (Panama), P. julitoi, sp. nov. (Brazil), P. kanukarum, sp. nov. (Guyana), P. maculatus, sp. nov. (Venezuela), P. manuensis, sp. nov. (Peru), P. matatlanticus, sp. nov. (Brazil), P. minensium, sp. nov. (Brazil), P. novafriburgensis, sp. nov. (Brazil), P. peruvianus, sp. nov. (Peru), P. petrae, sp. nov. (Brazil), P. pratherae, sp. nov. (Brazil), P. puyoensis, sp. nov. (Ecuador), P. robertsonae, sp. nov. (Bolivia), P. rodmani, sp. nov. (Brazil), P. rondoniensis, sp. nov. (Brazil), P. tragularius, sp. nov. (Brazil), P. tripunctatum, sp. nov. (Peru), P. venezolanus, sp. nov. (Venezuela), P. woldai, sp. nov. (Panama), P. zamoranoensis, sp. nov. (Honduras), and P. zuliae, sp. nov. (Venezuela). Polyplectropus buchwaldi is designated as a nomen dubium.
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    Systematics, Gill Raker Morphology, and Pharyngeal Arch Development of Suckers (Cypriniformes: Catostomidae)
    (2015-06) Hirt, Michael
    Morphological diversity is shaped by past evolutionary history, function, and ontogeny. Evolutionary history plays an important role in shaping morphological diversity and morphology itself can affect the future evolutionary trajectory of taxa. Morphology is shaped by function through selection and function can be constrained by morphology. Differences among taxa in their morphology arise due to changes in the pattern of development in those taxa. Therefore, a full understanding of morphological diversity requires knowledge about evolutionary history, morphological function, and ontogeny. Suckers, family Catostomidae, are a group of freshwater fish with interesting trophic morphology and feeding habits. I used molecular sequence data and fossil calibrations to reconstruct the phylogeny and divergence times of the families of Cypriniformes, including Catostomidae. I found evidence that gene choice, base compositional heterogeneity, and rate heterogeneity provide challenges to reconstructing the evolutionary history of the order and I found that body size is correlated with the rate of molecular evolution not only in Cypriniformes but in many groups of fishes. Suckers, like most fish, have gill rakers which are complex, repetitive, finger-like projections in the interior of the branchial arches that are important in feeding and vary among species. I quantified and compared gill raker morphology among sucker species and found that multiple aspects of gill raker morphology interact to predict function. Gill rakers are just one component of the complex trophic apparatus of suckers. I described and compared the sequence of chondrification and ossification of the paired elements of the pharyngeal arches and the histological development of the palatal organ, chewing pad, and pharyngeal teeth in five species of suckers and found several examples where heterochrony has shaped the trophic morphology of suckers.