The author's Thesis (M.S.)--University of California. / Cover title. "Literature cited": p. 97-98.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The author's thesis (M.S.)--Univ. of California. / Cover title. Description based on print version record. "Literature cited": p. 97-98.

Thesis (Ph. D.)--University of Missouri, 1920. / "Reprinted from the Journal of biological chemistry, vol. XLIX, no. 1, November, 1921." Bibliography: p. 56.

There are seven living species of gars in two genera (Lepisosteiformes: Actinopterygii). In my first chapter, I estimate phylogenetic relationships among six of them using DNA data generated from four complete mitochondrial loci (cytb, CR, 12S, and 16S) and a single, partial nuclear locus--recombination activating protein 1 (RAG1) intron. A single outgroup taxon, the bowfin (Amia calva), was included in my analyses. Regardless of optimality criterion (genetic distance, parsimony, maximum likelihood, and Bayesian inference), a single, well-supported phylogeny estimate emerged. Both sister genera (Atractosteus and Lepisosteus) were monophyletic. Within Atractosteus, A. spatula paired with A. tropicus in the absence of data from A. tristoechus. Within Lepisosteus I recovered two sister pairings of species: L. platyrhincus and L. oculatus; and L. ossues and L. platostomus. I estimated the phylogenetic position of the seventh gar species, A. tristoechus, using DNA data generated from several partial mitochondrial loci and 105 morphological characters. In this analysis, within a monophyletic Atractosteus I recovered a well-supported sister pairing between A. spatula and A. tristoechus, with A. tropicus sister to the pair. My molecular phylogenies largely agree with recent morphologically-based phylogenies aside from the positions of L. ossues and L. platostomus. Using dates associated with the best fossil data available (244 Ma minimal age of the node joining bowfins to gars, and 100 Ma for Lepisosteidae), I estimated divergence dates under a relaxed molecular clock model in a Bayesian framework. Estimated ages for lineages ranged from approximately 50 Ma for Lepisosteus, 23 Ma for the split between L. oculatus and L. platyrhincus, 28 Ma on the L. osseus and L. platostoms divergence, and 30 Ma for the node uniting A. spatula and A. tropicus--dates ranging from the Early Eocene to the Early Miocene. In my second chapter, I conducted basic phylogeographic investigations into the geographical structuring of gene genealogies built with mitochondrial D-loop sequences from 115 individual gars, belonging to five species (A. spatula, L. osseus, L. platostomus, L. platyrhincus and L. oculatus) and collected from a broad array of localities. Across species, across localities, I found some phylogeographic structuring in L. osseus and L. oculatus. I found one unique set of haplotypes confined to L. osseus in the Pee Dee River drainage of North Carolina. The level of molecular divergence between these and other L. osseus haplotypes was similar to that among gar species. I found evidence that there might be mixing of haplotypes across a contact zone between L. platyrhincus and L. oculatus in the Florida Panhandle. I found significant molecular divergence among populations of L. osseus and L. oculatus distributed among drainages to the Gulf of Mexico. However little genetic divergence was detected among populations of L. osseus, L. platostomus and L. oculatus within the Mississippi River basin. In my third chapter I present pilot work into characterizing the origins of a population of morphologically unusual gars in eastern Wisconsin. The longnose gar, Lepisosteus osseus, and the shortnose gar Lepisosteus platostomus are native to Wisconsin. In the Fox and Wolf River systems in eastern Wisconsin there is a third form that superficially resembles the spotted gar, L. oculatus (not previously reported to occur in Wisconsin) in that is exhibits heavy head and body pigmentation and a relatively short, broad snout. After initial molecular phylogenetic analyses showed that these gars did not belong to L. oculatus, results of more detailed molecular investigations, coupled with simple morphological findings, are consistent with the hypothesis that these unusual gars may be hybrids of L. platostomus and L. osseus. Further molecular and morphological investigations must be conducted to definitively infer hybrid status for these unusual gars.

This study investigates early life stages of the southern sea garfish (Hyporhamphus melanochir) and their association with seagrass in Gulf St Vincent, South Australia. The overall aims were to identify and describe the early life stages of H. melanochir and to explore the possible relationship(s) between these life stages and seagrass habitat with the emphasis on seagrass as a requirement for spawning or as a food source. The reproductive biology of female H. melanochir from the commercial fishery was assessed by microscopic examination of ovaries, oocyte size distributions, gonadosomatic indices, and macroscopic ovarian stages. Five stages of oocyte development were identified and described: perinucleolar, yolk vesicle, yolk globule, migratory nucleus and hydrated. A coherence between histological and whole oocyte descriptions is demonstrated. Hyporhamphus melanochir are characterised as multiple spawners with group-synchronous oocyte development and indeterminate fecundity. A protracted spawning season from October to March was indicated by the occurrence of ripe ovaries and increases in gonadosomatic index. Females reach sexual maturity at 193 mm standard length, and batch fecundity ranged from 201-3044 oocytes depending on fish size. Spawning shoals are segregated by sex, as indicated by commercial samples, with a biased female-to-male ratio of 4.5:1 during the spawning season (1.2:1 during the non-spawning season). In addition, features of the oocyte surface were closely examined, which revealed that the filaments on the chorion of the hydrated oocyte are adhesive. These adhesive filaments presumably allow the fertilised egg to become attached to vegetative substrate by adhesion and/or entanglement. H. melanochir larvae were discriminated from another hemiramphid species, river garfish (H. regularis), which is also known to occur in the study area, based on species-specific amplification of part of the mitochondrial control region using a multiplex polymerase chain reaction (PCR) assay. The species were easily discerned by the number and distinct sizes of PCR products [H. melanochir, 443 bp; river garfish (H. regularis), 462 and 264 bp]. Although based on a single gene, this molecular method will correctly identify the species of individuals in at least 96% and 94% of tests for H. melanochir and H. regularis, respectively. Subsequent to verifying the identification of species by molecular discrimination, the larval development of H. melanochir and H. regularis were described. Larvae of H. melanochir and H. regularis had completed notochord flexion at hatching and are characterized by their elongate body with distinct rows of melanophores along the dorsal, lateral and ventral surfaces; small to moderate head; heavily pigmented, long straight gut; persistent preanal finfold; and extended lower jaw. Fin formation occurs in the sequence: caudal, dorsal and anal (almost simultaneously), pectoral, pelvic. Despite the similarities between both species and among hemiramphid larvae in general, H. melanochir larvae are distinguishable from H. regularis by: having 58-61 vertebrae (v. 51-54 for H. regularis); having 12-15 melanophore pairs in longitudinal rows along the dorsal margin between the head and origin of the dorsal fin (v. 19-22 for H. regularis); and the absence of a large ventral pigment blotch anteriorly on the gut and isthmus (present in H. regularis). A logistic regression analysis of body measurements also revealed interspecies differences in the combined measurements of eye diameter and pre-anal fin length. Both species can be distinguished from morphologically similar larvae found in southern Australia (other hemiramphids and a scomberosocid) by differences in meristic counts and pigmentation. Hyporhamphus melanochir larvae were successfully collected throughout Gulf St Vincent using a neuston net; however, attempts to sample eggs were unsuccessful. Abundances of larvae in the gulf averaged 4.8 and 12.3 larvae 1000⁻ ² of surface water in December 1998 and December 2000, respectively. Larvae exhibit fast growth, as indicated by otolith growth increments, with backcalculated spawning dates falling within the October-March spawning season. Spatial analysis of larval distributions revealed a positive spatial autocorrelation, i.e. non-randomness or clustering of similar abundance values. Most larvae were found in the upper region of the gulf, and the prevalence of seagrass habitat throughout this region supports the view that the demersal eggs of H. melanochir become attached to seagrass and/or algae following spawning. A gyre in waters of the upper gulf, influenced by prevailing southerly winds, the Coriolis effect, and land boundaries, may explain retention of larvae. The importance of seagrass beds to H. melanochir spawning is also supported by anecdotal evidence and available literature on eggs of other Beloniformes, which are also demersal and attach to marine plants. Dual stable isotope analysis (δ¹³ and δ¹⁵N) of larval, juvenile and adult H. melanochir and several potential food sources from the Bay of Shoals was carried out to estimate the importance of zosteracean seagrass towards the assimilated diet of H. melanochir. Although the diet of H. melanochir larvae is probably planktonivorous, their isotopic signatures partly reflect the parental diet due to the influence of pre–existing tissue in addition to growth. According to mixing model calculations, the signatures of juveniles can be explained by a diet consisting of 23–37% Zostera, 0–10% Halophila and the remainder zooplankton, whilst the diet of adults consists of 53–58% Zostera and the remainder zooplankton. These findings indicate an increasing dependence upon Zostera with growth of H. melanochir. The results of this study enhance the completeness of our understanding of the fisheries biology and ecology of H. melanochir. Significant contributions are provided in reproductive biology and larval biology, seagrass beds (in combination with mixed algae) are demonstrated to be an important habitat for spawning, and Zostera seagrass is shown to be a necessary food source in the diet of juveniles and adults. / Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2005.

This study investigates early life stages of the southern sea garfish (Hyporhamphus melanochir) and their association with seagrass in Gulf St Vincent, South Australia. The overall aims were to identify and describe the early life stages of H. melanochir and to explore the possible relationship(s) between these life stages and seagrass habitat with the emphasis on seagrass as a requirement for spawning or as a food source. The reproductive biology of female H. melanochir from the commercial fishery was assessed by microscopic examination of ovaries, oocyte size distributions, gonadosomatic indices, and macroscopic ovarian stages. Five stages of oocyte development were identified and described: perinucleolar, yolk vesicle, yolk globule, migratory nucleus and hydrated. A coherence between histological and whole oocyte descriptions is demonstrated. Hyporhamphus melanochir are characterised as multiple spawners with group-synchronous oocyte development and indeterminate fecundity. A protracted spawning season from October to March was indicated by the occurrence of ripe ovaries and increases in gonadosomatic index. Females reach sexual maturity at 193 mm standard length, and batch fecundity ranged from 201-3044 oocytes depending on fish size. Spawning shoals are segregated by sex, as indicated by commercial samples, with a biased female-to-male ratio of 4.5:1 during the spawning season (1.2:1 during the non-spawning season). In addition, features of the oocyte surface were closely examined, which revealed that the filaments on the chorion of the hydrated oocyte are adhesive. These adhesive filaments presumably allow the fertilised egg to become attached to vegetative substrate by adhesion and/or entanglement. H. melanochir larvae were discriminated from another hemiramphid species, river garfish (H. regularis), which is also known to occur in the study area, based on species-specific amplification of part of the mitochondrial control region using a multiplex polymerase chain reaction (PCR) assay. The species were easily discerned by the number and distinct sizes of PCR products [H. melanochir, 443 bp; river garfish (H. regularis), 462 and 264 bp]. Although based on a single gene, this molecular method will correctly identify the species of individuals in at least 96% and 94% of tests for H. melanochir and H. regularis, respectively. Subsequent to verifying the identification of species by molecular discrimination, the larval development of H. melanochir and H. regularis were described. Larvae of H. melanochir and H. regularis had completed notochord flexion at hatching and are characterized by their elongate body with distinct rows of melanophores along the dorsal, lateral and ventral surfaces; small to moderate head; heavily pigmented, long straight gut; persistent preanal finfold; and extended lower jaw. Fin formation occurs in the sequence: caudal, dorsal and anal (almost simultaneously), pectoral, pelvic. Despite the similarities between both species and among hemiramphid larvae in general, H. melanochir larvae are distinguishable from H. regularis by: having 58-61 vertebrae (v. 51-54 for H. regularis); having 12-15 melanophore pairs in longitudinal rows along the dorsal margin between the head and origin of the dorsal fin (v. 19-22 for H. regularis); and the absence of a large ventral pigment blotch anteriorly on the gut and isthmus (present in H. regularis). A logistic regression analysis of body measurements also revealed interspecies differences in the combined measurements of eye diameter and pre-anal fin length. Both species can be distinguished from morphologically similar larvae found in southern Australia (other hemiramphids and a scomberosocid) by differences in meristic counts and pigmentation. Hyporhamphus melanochir larvae were successfully collected throughout Gulf St Vincent using a neuston net; however, attempts to sample eggs were unsuccessful. Abundances of larvae in the gulf averaged 4.8 and 12.3 larvae 1000⁻ ² of surface water in December 1998 and December 2000, respectively. Larvae exhibit fast growth, as indicated by otolith growth increments, with backcalculated spawning dates falling within the October-March spawning season. Spatial analysis of larval distributions revealed a positive spatial autocorrelation, i.e. non-randomness or clustering of similar abundance values. Most larvae were found in the upper region of the gulf, and the prevalence of seagrass habitat throughout this region supports the view that the demersal eggs of H. melanochir become attached to seagrass and/or algae following spawning. A gyre in waters of the upper gulf, influenced by prevailing southerly winds, the Coriolis effect, and land boundaries, may explain retention of larvae. The importance of seagrass beds to H. melanochir spawning is also supported by anecdotal evidence and available literature on eggs of other Beloniformes, which are also demersal and attach to marine plants. Dual stable isotope analysis (δ¹³ and δ¹⁵N) of larval, juvenile and adult H. melanochir and several potential food sources from the Bay of Shoals was carried out to estimate the importance of zosteracean seagrass towards the assimilated diet of H. melanochir. Although the diet of H. melanochir larvae is probably planktonivorous, their isotopic signatures partly reflect the parental diet due to the influence of pre–existing tissue in addition to growth. According to mixing model calculations, the signatures of juveniles can be explained by a diet consisting of 23–37% Zostera, 0–10% Halophila and the remainder zooplankton, whilst the diet of adults consists of 53–58% Zostera and the remainder zooplankton. These findings indicate an increasing dependence upon Zostera with growth of H. melanochir. The results of this study enhance the completeness of our understanding of the fisheries biology and ecology of H. melanochir. Significant contributions are provided in reproductive biology and larval biology, seagrass beds (in combination with mixed algae) are demonstrated to be an important habitat for spawning, and Zostera seagrass is shown to be a necessary food source in the diet of juveniles and adults. / Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2005.

This study investigates early life stages of the southern sea garfish (Hyporhamphus melanochir) and their association with seagrass in Gulf St Vincent, South Australia. The overall aims were to identify and describe the early life stages of H. melanochir and to explore the possible relationship(s) between these life stages and seagrass habitat with the emphasis on seagrass as a requirement for spawning or as a food source. The reproductive biology of female H. melanochir from the commercial fishery was assessed by microscopic examination of ovaries, oocyte size distributions, gonadosomatic indices, and macroscopic ovarian stages. Five stages of oocyte development were identified and described: perinucleolar, yolk vesicle, yolk globule, migratory nucleus and hydrated. A coherence between histological and whole oocyte descriptions is demonstrated. Hyporhamphus melanochir are characterised as multiple spawners with group-synchronous oocyte development and indeterminate fecundity. A protracted spawning season from October to March was indicated by the occurrence of ripe ovaries and increases in gonadosomatic index. Females reach sexual maturity at 193 mm standard length, and batch fecundity ranged from 201-3044 oocytes depending on fish size. Spawning shoals are segregated by sex, as indicated by commercial samples, with a biased female-to-male ratio of 4.5:1 during the spawning season (1.2:1 during the non-spawning season). In addition, features of the oocyte surface were closely examined, which revealed that the filaments on the chorion of the hydrated oocyte are adhesive. These adhesive filaments presumably allow the fertilised egg to become attached to vegetative substrate by adhesion and/or entanglement. H. melanochir larvae were discriminated from another hemiramphid species, river garfish (H. regularis), which is also known to occur in the study area, based on species-specific amplification of part of the mitochondrial control region using a multiplex polymerase chain reaction (PCR) assay. The species were easily discerned by the number and distinct sizes of PCR products [H. melanochir, 443 bp; river garfish (H. regularis), 462 and 264 bp]. Although based on a single gene, this molecular method will correctly identify the species of individuals in at least 96% and 94% of tests for H. melanochir and H. regularis, respectively. Subsequent to verifying the identification of species by molecular discrimination, the larval development of H. melanochir and H. regularis were described. Larvae of H. melanochir and H. regularis had completed notochord flexion at hatching and are characterized by their elongate body with distinct rows of melanophores along the dorsal, lateral and ventral surfaces; small to moderate head; heavily pigmented, long straight gut; persistent preanal finfold; and extended lower jaw. Fin formation occurs in the sequence: caudal, dorsal and anal (almost simultaneously), pectoral, pelvic. Despite the similarities between both species and among hemiramphid larvae in general, H. melanochir larvae are distinguishable from H. regularis by: having 58-61 vertebrae (v. 51-54 for H. regularis); having 12-15 melanophore pairs in longitudinal rows along the dorsal margin between the head and origin of the dorsal fin (v. 19-22 for H. regularis); and the absence of a large ventral pigment blotch anteriorly on the gut and isthmus (present in H. regularis). A logistic regression analysis of body measurements also revealed interspecies differences in the combined measurements of eye diameter and pre-anal fin length. Both species can be distinguished from morphologically similar larvae found in southern Australia (other hemiramphids and a scomberosocid) by differences in meristic counts and pigmentation. Hyporhamphus melanochir larvae were successfully collected throughout Gulf St Vincent using a neuston net; however, attempts to sample eggs were unsuccessful. Abundances of larvae in the gulf averaged 4.8 and 12.3 larvae 1000⁻ ² of surface water in December 1998 and December 2000, respectively. Larvae exhibit fast growth, as indicated by otolith growth increments, with backcalculated spawning dates falling within the October-March spawning season. Spatial analysis of larval distributions revealed a positive spatial autocorrelation, i.e. non-randomness or clustering of similar abundance values. Most larvae were found in the upper region of the gulf, and the prevalence of seagrass habitat throughout this region supports the view that the demersal eggs of H. melanochir become attached to seagrass and/or algae following spawning. A gyre in waters of the upper gulf, influenced by prevailing southerly winds, the Coriolis effect, and land boundaries, may explain retention of larvae. The importance of seagrass beds to H. melanochir spawning is also supported by anecdotal evidence and available literature on eggs of other Beloniformes, which are also demersal and attach to marine plants. Dual stable isotope analysis (δ¹³ and δ¹⁵N) of larval, juvenile and adult H. melanochir and several potential food sources from the Bay of Shoals was carried out to estimate the importance of zosteracean seagrass towards the assimilated diet of H. melanochir. Although the diet of H. melanochir larvae is probably planktonivorous, their isotopic signatures partly reflect the parental diet due to the influence of pre–existing tissue in addition to growth. According to mixing model calculations, the signatures of juveniles can be explained by a diet consisting of 23–37% Zostera, 0–10% Halophila and the remainder zooplankton, whilst the diet of adults consists of 53–58% Zostera and the remainder zooplankton. These findings indicate an increasing dependence upon Zostera with growth of H. melanochir. The results of this study enhance the completeness of our understanding of the fisheries biology and ecology of H. melanochir. Significant contributions are provided in reproductive biology and larval biology, seagrass beds (in combination with mixed algae) are demonstrated to be an important habitat for spawning, and Zostera seagrass is shown to be a necessary food source in the diet of juveniles and adults. / Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2005.

This study investigates early life stages of the southern sea garfish (Hyporhamphus melanochir) and their association with seagrass in Gulf St Vincent, South Australia. The overall aims were to identify and describe the early life stages of H. melanochir and to explore the possible relationship(s) between these life stages and seagrass habitat with the emphasis on seagrass as a requirement for spawning or as a food source. The reproductive biology of female H. melanochir from the commercial fishery was assessed by microscopic examination of ovaries, oocyte size distributions, gonadosomatic indices, and macroscopic ovarian stages. Five stages of oocyte development were identified and described: perinucleolar, yolk vesicle, yolk globule, migratory nucleus and hydrated. A coherence between histological and whole oocyte descriptions is demonstrated. Hyporhamphus melanochir are characterised as multiple spawners with group-synchronous oocyte development and indeterminate fecundity. A protracted spawning season from October to March was indicated by the occurrence of ripe ovaries and increases in gonadosomatic index. Females reach sexual maturity at 193 mm standard length, and batch fecundity ranged from 201-3044 oocytes depending on fish size. Spawning shoals are segregated by sex, as indicated by commercial samples, with a biased female-to-male ratio of 4.5:1 during the spawning season (1.2:1 during the non-spawning season). In addition, features of the oocyte surface were closely examined, which revealed that the filaments on the chorion of the hydrated oocyte are adhesive. These adhesive filaments presumably allow the fertilised egg to become attached to vegetative substrate by adhesion and/or entanglement. H. melanochir larvae were discriminated from another hemiramphid species, river garfish (H. regularis), which is also known to occur in the study area, based on species-specific amplification of part of the mitochondrial control region using a multiplex polymerase chain reaction (PCR) assay. The species were easily discerned by the number and distinct sizes of PCR products [H. melanochir, 443 bp; river garfish (H. regularis), 462 and 264 bp]. Although based on a single gene, this molecular method will correctly identify the species of individuals in at least 96% and 94% of tests for H. melanochir and H. regularis, respectively. Subsequent to verifying the identification of species by molecular discrimination, the larval development of H. melanochir and H. regularis were described. Larvae of H. melanochir and H. regularis had completed notochord flexion at hatching and are characterized by their elongate body with distinct rows of melanophores along the dorsal, lateral and ventral surfaces; small to moderate head; heavily pigmented, long straight gut; persistent preanal finfold; and extended lower jaw. Fin formation occurs in the sequence: caudal, dorsal and anal (almost simultaneously), pectoral, pelvic. Despite the similarities between both species and among hemiramphid larvae in general, H. melanochir larvae are distinguishable from H. regularis by: having 58-61 vertebrae (v. 51-54 for H. regularis); having 12-15 melanophore pairs in longitudinal rows along the dorsal margin between the head and origin of the dorsal fin (v. 19-22 for H. regularis); and the absence of a large ventral pigment blotch anteriorly on the gut and isthmus (present in H. regularis). A logistic regression analysis of body measurements also revealed interspecies differences in the combined measurements of eye diameter and pre-anal fin length. Both species can be distinguished from morphologically similar larvae found in southern Australia (other hemiramphids and a scomberosocid) by differences in meristic counts and pigmentation. Hyporhamphus melanochir larvae were successfully collected throughout Gulf St Vincent using a neuston net; however, attempts to sample eggs were unsuccessful. Abundances of larvae in the gulf averaged 4.8 and 12.3 larvae 1000⁻ ² of surface water in December 1998 and December 2000, respectively. Larvae exhibit fast growth, as indicated by otolith growth increments, with backcalculated spawning dates falling within the October-March spawning season. Spatial analysis of larval distributions revealed a positive spatial autocorrelation, i.e. non-randomness or clustering of similar abundance values. Most larvae were found in the upper region of the gulf, and the prevalence of seagrass habitat throughout this region supports the view that the demersal eggs of H. melanochir become attached to seagrass and/or algae following spawning. A gyre in waters of the upper gulf, influenced by prevailing southerly winds, the Coriolis effect, and land boundaries, may explain retention of larvae. The importance of seagrass beds to H. melanochir spawning is also supported by anecdotal evidence and available literature on eggs of other Beloniformes, which are also demersal and attach to marine plants. Dual stable isotope analysis (δ¹³ and δ¹⁵N) of larval, juvenile and adult H. melanochir and several potential food sources from the Bay of Shoals was carried out to estimate the importance of zosteracean seagrass towards the assimilated diet of H. melanochir. Although the diet of H. melanochir larvae is probably planktonivorous, their isotopic signatures partly reflect the parental diet due to the influence of pre–existing tissue in addition to growth. According to mixing model calculations, the signatures of juveniles can be explained by a diet consisting of 23–37% Zostera, 0–10% Halophila and the remainder zooplankton, whilst the diet of adults consists of 53–58% Zostera and the remainder zooplankton. These findings indicate an increasing dependence upon Zostera with growth of H. melanochir. The results of this study enhance the completeness of our understanding of the fisheries biology and ecology of H. melanochir. Significant contributions are provided in reproductive biology and larval biology, seagrass beds (in combination with mixed algae) are demonstrated to be an important habitat for spawning, and Zostera seagrass is shown to be a necessary food source in the diet of juveniles and adults. / Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2005.

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder characterized by widespread loss of lower motor neurons from the spinal cord. Lower motor neuron degeneration leads to a progressive decline in motor development, manifesting as muscle atrophy and weakness. It is now well characterised that ubiquitin homeostasis is altered in SMA and that reduction of the ubiquitin-like modifier-activating enzyme 1 (UBA1) is central to this disruption. UBA1 is responsible for activating ubiquitin as the first step in the ubiquitin conjugation process, marking unwanted proteins for degradation by the proteasome. While it is known that therapies targeting UBA1 rescue neuromuscular phenotypes in SMA models, the mechanism by which UBA1 mediates neurodegeneration is unclear. In fact, very little is known about the function of UBA1 beyond its canonical role in the ubiquitin proteasome system. To better understand the role of UBA1 in motor neuron degeneration, a robust set of antibodies for both in vivo and in vitro work to study UBA1 have been identified. This enabled a novel characterisation of UBA1 distribution throughout disease progression in SMA spinal motor neurons to be performed, revealing that UBA1 reduction is an important pre-symptomatic molecular feature of SMA. To identify downstream targets of UBA1 critical for UBA1-mediated degeneration in SMA, label-free proteomics was performed on HEK293 cells after overexpression or knockdown of UBA1. The proteomics data was analysed across multiple platforms, including Biolayout, IPA and DAVID to identify UBA1-dependent pathways and demonstrated that modulation of UBA1 levels lead to disruption of key cellular pathways including translation elongation, nuclear transport, and tRNA synthetases. Validation of target proteins from these UBA1-dependent pathways identified that the tRNA synthetease GARS behaves in a UBA1-dependent manner across a range of model systems in vitro and in vivo. It was then identified that GARS expression is significantly dysregulated across a range of neuronal tissues in a mouse model of SMA. Interestingly, mutations in GARS cause Charcot-Marie-Tooth disease type 2D (CMT2D), an axonal neuropathy, in which a disruption to sensory neuron fate in dorsal root ganglia has recently been identified. In a mouse model of SMA we identified a phenotype consistent with that in the CMT2D mouse model and showed that disruption to sensory neuron fate is reversible and dependent on changes in UBA1 and GARS expression in SMA. In conclusion, modulation of UBA1 levels leads to disruption of key cellular pathways, with dysregulation of tRNA synthetases a prominent feature that is likely to play a role in the pathogenesis of SMA.