Browsing by Subject "Ontogeny"
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Item Developmental Osteology of Two Species of Economically Important Sciaenids, Sciaenops ocellatus and Cynoscion nebulosus (Teleostei: Sciaenidae)(2014-04-22) Kubicek, KoleThe red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus) are two ecomomically important sciaenids currently cultured for stock enhancement in Texas. 237 specimens of S. ocellatus, ranging in size from 2.5-26.3mm SL, and 214 specimens of C. nebulosus, ranging in size from 2.6-27.7 mm SL, were investigated and utilized to create ossification sequences depicting development of the entire skeleton for both species. Development of the skeleton, excluding the basisphenoids and sclerotic bones, was complete in S. ocellatus and C. nebulosus at 14.4 mm SL and 13.5 mm SL, respectively. The basisphenoid did not appear until later in development (21.9 mm SL in S. ocellatus and 19.5 mm SL in C. nebulsosus), while the sclerotic bones were not present in the material examined. No major differences were identified between the ossification sequences compiled for each species. Cynoscion nebulosus exhibited variation in the presence/absence of two elements, supraneural 1 and the coronomeckelian. Development of the skeleton in S. ocellatus and C. nebulosus was compared with Agyrosomus meagre and Micropogonias furnieri, two other species of sciaenid for which information on skeletal development is available. No major differences were identified in the development of the axial skeleton between A. meagre, S. ocellatus or C. nebulosus. Several notable differences were identified in the development of the neurcranium between M. furnieri and that of S. ocellatus and C. nebulosus, suggesting that variation may exist in the development of the neurocranium across Sciaenidae. Lastly, the ossification sequence compiled here for S. ocellatus was compared to that of Danio rerio, the only other species of teleost for which an ossification sequence is available for development of the entire skeleton, and Chanos chanos, for which an ossification sequence is available for the cranial skeleton. Several differences were identified between all three species, suggesting variation of skeletal development exists across Teleostei. The information provided herein will benefit the culture of S. ocellatus and C. nebulosus by providing information on normal skeletal development and a standard reference sequence of skeletal development for both species that will facilitate identification of skeletal malformations should they become an issue in the future.Item The evolution of skeletal development in early tetrapods : anatomy and ontogeny of microsaurs (Lepospondyli)(2011-05) Olori, Jennifer Catherine; Bell, Christopher J., 1966-; Rowe, Timothy B.; Cannatella, David C.; Sprinkle, James T.; Anderson, Jason S.Because the ancestry of extant amphibians remains highly controversial, under traditional perspectives, amphibians and amniotes often are distinguished by differences in developmental mode rather than their evolutionary relationships. Resolution of relationships is important, however, because phylogeny affects interpretations of biology, including the evolution of development. To address those issues, I documented the growth and development of two extinct lepospondyls, Microbrachis pelikani and Hyloplesion longicostatum, and compared the patterns in those taxa to data from other tetrapods. I quantified allometry in the skeleton using both measurement-based and geometric morphometric analyses. I applied Ontogenetic Sequence Analysis (OSA), a size-independent method, to the reconstruction of ossification sequences based on fossils. I also documented skeletal morphogenesis and used Parsimov Analysis and Parsimov-based Genetic Inference of ossification sequence data to evaluate the three hypotheses of extant amphibian ancestry, the Lepospondyl (LH), Temnospondyl (TH), and Polyphyletic (PH) hypotheses. Skeletal growth in Microbrachis pelikani and Hyloplesion longicostatum is primarily isometric. Comparisons with data from other Paleozoic taxa suggest that isometry was the ancestral pattern of growth in tetrapods. All regression analyses had a linear fit indicating lack of an abrupt metamorphosis. Absence of metamorphosis is also supported by the possession of lateral lines in both taxa throughout ontogeny, and Microbrachis pelikani additionally retained gills. However, ossification of the skeleton was completed at small body size. The greatest resolution in ossification sequence reconstruction was achieved with OSA, but results from all reconstruction methods indicated advanced ossification of the pubis and delayed ossification of the scapula in the lepospondyls. In terms of total number of sequence shifts optimized across each hypothesis of amphibian relationships, the TH had the shortest tree length. However, the values for the three hypotheses did not differ significantly, demonstrating that none was supported strongly. Based on my synthesis of new developmental data, I propose that Microbrachis pelikani and Hyloplesion longicostatum expressed a mosaic pattern of skeletal development. That pattern included a gradual transition to an adult morphology, and a lack of an amphibian-like metamorphosis. A similar pattern is common to most early tetrapods and Eusthenopteron, supporting the hypothesis that metamorphosis is not ancestral for Tetrapoda.Item An integrated evaluation of costs and benefits of corticosterone secretion through development(2007) Wada, Haruka; Jansen, Robert; Breuner, CreaghGlucocorticoids (GCs) play critical roles during development: transient increases in GCs facilitate anticipatory physiological changes and trigger ontogenetic transitions such as promoting fetal/embryonic organ maturation and initiating birth/hatching. In contrast, chronically elevated GCs can be detrimental to growth, cognition, and survival. Thus, animals going through substantial growth may have higher corticosteroid binding globulin (CBG) levels, or enhance negative feedback/tonic inhibition on the hypothalamic-pituitary-adrenal (HPA) axis to keep GCs levels low. Here I investigated these hypotheses using altricial white-crowned sparrow nestlings. I examined 1) the ontogeny of the corticosterone (CORT) response (both total and free hormone levels), 2) changes in corticosteroid receptor levels in brain with age, and 3) effects of acute and extended elevation of CORT on behavior and growth. In response to acute stress, nestlings showed a low HPA reactivity in total CORT during the first 1/3 of the nestling period. When free CORT is considered, this hyporesponsive period was extended to 2/3 of the nestling period, suggesting CBG is one of the mechanisms to keep free CORT low. These periods coincided with rapid mass gain and acquiring thermoregulatory ability. The low reactivity was partly due to a dampened sensitivity at pituitary level or higher as all stages of nestlings responded to adrenocorticotropic hormone challenges; however it was not due to an enhanced negative feedback/tonic inhibition on hypothalamus or hippocampus. When CORT levels were artificially elevated, I only observed detrimental effects on begging behavior and growth. These series of data elucidated the ontogeny of the HPA axis in altricial nestlings regarding CORT, binding globulin, and receptor levels. In addition, I found that measured effects of exogenous CORT are primarily costly and highly age-specific.Item An integrated evaluation of costs and benefits of corticosterone secretion through development(2007-05) Wada, Haruka, 1976-; Jansen, Robert K., 1954-; Breuner, Creagh W.Glucocorticoids (GCs) play critical roles during development: transient increases in GCs facilitate anticipatory physiological changes and trigger ontogenetic transitions such as promoting fetal/embryonic organ maturation and initiating birth/hatching. In contrast, chronically elevated GCs can be detrimental to growth, cognition, and survival. Thus, animals going through substantial growth may have higher corticosteroid binding globulin (CBG) levels, or enhance negative feedback/tonic inhibition on the hypothalamic-pituitary-adrenal (HPA) axis to keep GCs levels low. Here I investigated these hypotheses using altricial white-crowned sparrow nestlings. I examined 1) the ontogeny of the corticosterone (CORT) response (both total and free hormone levels), 2) changes in corticosteroid receptor levels in brain with age, and 3) effects of acute and extended elevation of CORT on behavior and growth. In response to acute stress, nestlings showed a low HPA reactivity in total CORT during the first 1/3 of the nestling period. When free CORT is considered, this hyporesponsive period was extended to 2/3 of the nestling period, suggesting CBG is one of the mechanisms to keep free CORT low. These periods coincided with rapid mass gain and acquiring thermoregulatory ability. The low reactivity was partly due to a dampened sensitivity at pituitary level or higher as all stages of nestlings responded to adrenocorticotropic hormone challenges; however it was not due to an enhanced negative feedback/tonic inhibition on hypothalamus or hippocampus. When CORT levels were artificially elevated, I only observed detrimental effects on begging behavior and growth. These series of data elucidated the ontogeny of the HPA axis in altricial nestlings regarding CORT, binding globulin, and receptor levels. In addition, I found that measured effects of exogenous CORT are primarily costly and highly age-specific.Item Morphometric analysis of phytosaur premaxillae and maxillae(2013-08) Siegel, Elizabeth Rose; Wilson, Clark R.; Bell, Christopher J., 1966-When it comes to studying organisms, having size independent measures for maturity are important for many aspects of organismal biology, and may be crucial for determining taxonomic affinity, and morphological signals associated with ontogenetic age (i.e., juvenile vs. adult) and sexual dimorphism. This is because the size of an organism can be the result of many factors that are not necessarily indicators of maturity (Chabreck and Joanen, 1979; Ferguson, 1984; Mazzotti et al., 1986; Deeming and Ferguson, 1989; Brandt, 1991). This problem is particularly pronounced when researchers are studying extinct species. The purpose of my research project was to investigate and understand patterns of morphological variation in the phytosaur premaxilla and maxilla and to determine the degree to which morphological variation is a result of ontogeny. For example, such patterns might include the number, size and location of alveoli or the presence of prenarial crests. I conducted this research by gathering information on the premaxilla and maxilla of all phytosaur elements present in the University of Texas at Austin Vertebrate Paleontology Lab collection. I then performed statistical analysis on the data, and compared my results to those of previous authors to see if I could identify any ontogenetic signal. I did not identify size-independent ontogenetic influence on morphology with certainty but I did find some possible features that merit additional investigation in future studies. Those include the presence of one to three diastemas located primarily at the anterior end of the premaxilla, a wide interpremaxillary fossa but small alveolar ridge, and alveoli whose size mirror the width of the premaxilla (for example wide areas in the premaxilla are associated with larger alveoli whereas narrow areas in the premaxilla are associated with smaller alveoli). My study also confirmed the previous findings of Hungerbühler (2002) that the alveoli of phytosaurs are heterodont and exist in three distinct location-specific patterns, and the work of other researchers that prenarial crests are present only in larger specimens (Camp, 1930; Ballew, 1986; Hungerbühler, 2002; Stocker, 2010).Item Ontogenetic changes in orangutan brain evolution: Is it heterochrony?(2012-05) Creel, Jody; Durband, Arthur C.; Rice, Sean H.; Walter, Tamra L.During the last 40 million years of primate brain evolution, intriguing changes have arisen. A problem faced by large bodied primates is the issue of how to birth a large brained offspring from a relatively small birth canal. This study analyzes the ontogenetic changes in the evolution of the orangutan brain that aids in the birthing of large brained offspring. The growth of the orangutan brain is plotted and compared with the growth trajectories of humans, macaques, squirrel monkeys and chimpanzees.Item Ontogeny and evolutionary morphology of the skeleton in frogs(2001-08) Yeh, Jennifer Jean; Dudley, Robert, 1961-; Cannatella, David C.Ontogenetic studies, or studies of development, have repeatedly proven insightful in exploring questions of morphological evolution. Here, two projects illuminate the relationship between ontogeny and the evolution of skeletal morphology in frogs. In the first part of this dissertation, I examine the evolution of skull development in pipoid frogs, a group that is exceptional in both morphology and life history. Two methods are used. First, skull bone ossification sequences are examined within a phylogenetic context. Second, studies are made of ontogenetic shape change in the skull using thin-plate spline morphometrics. Important differences between pipoid skull development and that of other frogs are uncovered. These include the convergent evolution of primitive ossification patterns still retained in extant salamanders, and the elaboration of novel trajectories of ontogenetic shape change which create the unusual pipoid morphology. The second part of this dissertation examines the phenomenon of miniaturization in frogs. Because miniaturization has evolved numerous times in frogs and has reached impressive extremes, frogs make an ideal group in which to study the effects of miniaturization on morphological evolution. I use qualitative presence/absence characters in the skull and limbs, as well as shape variables from thin-plate spline morphometrics to identify patterns of morphological change which are statistically associated with the evolution of miniaturization. These statistically significant patterns are discussed in the context of functional constraints and paedomorphosis.Item Ontogeny of bipedalism : pedal mechanics and trabecular bone morphology(2013-12) Zeininger, Angel Diane; Shapiro, Liza J.A unique pattern of pedal loading from heel-strike at touchdown to hallucal propulsion at toe-off is a distinct feature of mature human bipedalism, however, its first appearance in the fossil record is debated. The main goal of this dissertation is to identify anatomical correlates to a modern human heel-strike, rigid foot, and propulsive hallucal toe-off. First, a biomechanical analysis of toddler walking is used as a 'natural experiment' to investigate the influence of non heel-strike (NHS, n = 11) and immature heel-strike (IHS, n = 7) on the location of the center of pressure and orientation of the ground reaction force resultant in relation to specific foot bones during stance phase. With an expanded knowledge of foot bone loading in toddlers, a microarchitectural approach is used to test the influence of a heel-strike, rigid foot, and propulsive hallucal toe-off on trabecular bone fabric properties in an ontogenetic series of human and African ape (chimpanzee, bonobo, and gorilla) calcanei, tali, first metatarsal heads and hallucal distal phalanges. This dissertation presents the first ontogenetic analysis of pedal trabecular bone in primates. Heel-strike and toe-off are developmentally independent from one another. Although most toddlers lack a hallucal toe-off, NHS and IHS apply equally high propulsive forces when the entire width of their forefoot is in contact with the ground. Biomechanical and fossil evidence suggest that a generalized active propulsion may have preceded the evolution of a propulsive hallucal toe-off. Although pedal trabecular fabric properties are more complex than predicted, trabecular correlates to heel-strike and hallucal toe-off are identified within adult human foot bones. Compared to toddlers and African apes, adult humans have a unique combination of relatively thick trabecular struts and an anteroplantar to posterodorsal primary trabecular orientation in the plantar aspect of the calcaneal tuber. In the calcaneal tendon volume of interest, adult humans have a unique anteroplantar to posterodorsal primary trabecular orientation associated with a propulsive hallucal toe-off. This dissertation provides the comparative context necessary to begin assessing the evolution and developmental timing of foot function and specific bipedal gait events in juvenile and adult fossil hominins.Item Skeletal ontogeny of Monodelphis domestica (Mammalia: Didelphidae) : quantifying variation, variability, and technique bias in ossification sequence reconstruction(2013-12) Morris, Zachary Stephen; Rowe, Timothy, 1953-The field of evolutionary developmental biology (evo-devo) focuses on understanding the evolution of ontogeny and mechanisms of evolutionary change. Recently, taxonomic comparisons of the sequence of skeletal ossification have become prominent in evo-devo. However, most of these studies fail to consider two major issues: how the technique used to assay ossification and ontogenetic variation and variability may affect comparisons among taxa. This study focuses on the onset of ossification in the skeleton of Monodelphis domestica and quantifies the affects of variation, variability, and technique bias on reconstructions of ontogeny. Previous comparisons among mammalian taxa have used both computed tomography (CT) and clearing-and-staining (CS) to assess the presence or absence of skeletal elements (i.e., skeletal maturity). In this study, CT and CS were used on the same specimen to compare how these methods assess skeletal maturity. The comparisons of the same individual under reveal significant differences in how skeletal maturity is assessed by CT and CS techniques. Further, significant biases were recovered between techniques. CT is more likely to reveal cranial elements that CS does not, whereas CS is more likely to reveal appendicular elements that CT does not. To assess levels of variation and variability, Ontogenetic Sequence Analysis (OSA) was used to characterize the ontogeny of Monodelphis domestica. This revealed significant levels of variation with over 800 different ontogenetic pathways recovered for the onset of ossification of all skeletal elements studied. Additionally, high levels of variability were also reconstructed because the majority of specimens were found to exhibit non-modal ontogenetic sequences. This variability is more highly concentrated in the sequence of cranial ossification, suggesting potential modularity in ontogenetic variation and variability. Finally, OSA revealed that technique bias could importantly affect reconstructions of skeletal ossification sequences because no identical sequences were recovered by the CT and CS datasets. The results of this study demonstrate the importance of considering the primary nature of developmental studies, the specimen. Only by recognizing and quantifying the complexities of evo-devo research, especially natural variation and methodological biases, can more complete understandings of the evolution of ontogeny be had.Item The eastern box turtle (Terrapene carolina) in time and space(2013-05) Vitek, Natasha Slonim; Bell, Christopher J., 1966-; Rowe, Tim B; Clarke, Julia A; LaDuc, Travis JVariation is a key component of the evolutionary process. However, variation often is poorly understood within species. The eastern box turtle (Terrapene carolina) presents an excellent opportunity to study that topic because extant populations have high levels of variation in soft-tissue characters as well as morphological variation in skeletal characters. To explore patterns of spatiotemporal variation, I used geometric morphometrics to quantify shape within three datasets. First, I asked to what extent size explained total shape variation using an ontogenetic series of 101 specimens. Next, I examined to what extent subspecies were morphologically distinct and identifiable in the modern record, and to what degree they explained overall variation using a dataset of 200 modern specimens. Finally, I compared the patterns in the modern biota to those from the fossil record using the previous datasets as well as a fossil dataset of 44 Pleistocene shells of T. carolina. I found that in four views of the turtle shell (dorsal, ventral, posterior, and lateral), size significantly explains 10% - 31% of the variation in shape. Some of the characters correlated with size were historically ascribed to characters of subspecies. Studying the extent to which size explains overall variation in different subsamples of my data allowed me to discover a new way of classifying segments of a population in order to account for size in future studies. Subspecies identification also explained a statistically significant amount of overall shape variation. However, the results of assignments tests and CVAs indicated insignificant or unreliable differences. Results indicate that differences between putative subspecies are more statistically significant than they are biologically significant. They do not support the recognition of subspecies in T. carolina. The inability of statistical analyses to identify individuals of a subspecies based on shell shape means that subspecies cannot be identified in the fossil record. Some of the same relationships between shape and size are present in the fossil record and the modern biota, but other morphological patterns are unique to fossil specimens. Two of the morphotypes co-occur in the same strata, and represent a unique evolutionary pattern not seen in the modern biota.Item Trends in evolutionary morphology : a case study in the relationships of angel sharks and batoid fishes(2010-05) Claeson, Kerin Michele; Bell, Christopher J., 1966-; Rowe, Timothy B.; Hendrickson, Dean; Sprinkle, James; McEachran, John D.Chondrichthyans are cartilaginous fishes that include the extant chimaeras, sharks, and batoids, and their extinct relatives. In this dissertation, I examined the growth, development, and relationships of extinct and extant chondrichthyans. I reexamined the skeleton of fossil and fetal specimens of the angel sharks (Squatiniformes) and reanalyzed the current morphologically based hypothesis of chondrichthyan evolution, which conflicts with the current molecular based hypothesis. I did this by including extinct taxa and new characters based on dentition, and the ethmoid, occipital, pectoral, and vertebral skeleton. My results supported the pre-existing morphological hypothesis that angel sharks, saw sharks, and batoids form a clade. However, some of my new characters, particularly those based on the vertebral morphology, indicate that fetal and juvenile angel sharks do not share as many apomorphies with batoids as previously hypothesized from the examination of adults. I also examine the relationships of major groups within batoids, beginning with the construction of a hypothesis of the evolutionary history of electric rays (Torpediniformes). My results are consistent with previous rank-based classifications. However, they deviate from previous classifications depending on the criteria used to generate the hypothesis and on which taxon, or combination of taxa, were used to root the ingroup phylogeny. Because pectoral and vertebral morphology are so critical to morphological hypotheses, I also examined the growth and development of the synarcual cartilage in batoid fishes, with particular emphasis on the synarcual of skates (Rajiformes). My results demonstrate that calcification and chondrification do not proceed in the same order, temporally and spatially. Finally, I redescribe the extinct batoid †Cyclobatis, known only from the Cretaceous, and evaluate its phylogenetic position. My results indicate that †Cyclobatis, the oldest known rajid, is also the sister taxon to a clade of all known extant members of Rajidae. Furthermore, the inclusion of new characters, mainly derived from the synarcual, help to resolve the interrelationships of Rajidae.