Sexual dimorphism in longnose gar Lepisosteus osseus

The present study of Lepisosteus osseus dimorphism expands upon previous work by examining a broader array of morphometric characters while removing the bias associated with overall body length. A stepwise discriminant function analyses (swDFA) found that five characters best distinguish the sexes: head width, mid-snout width, anal-fin height, anal-fin width and prepectoral-fin length. Discriminant function analyses (DFA) with the five characters yields misclassification rates of 23·5% for females and 9·7% for males. Subsequent DFA using these five characters plus standard length yields misclassification rates of only 8·8% for females and 6·2% for males. The data presented here reveal differences in head and anal-fin shape between male and female L. osseus that may have evolved to enhance predatory abilities or competitive abilities during reproduction. This study is the first to find that L. osseus exhibits sexual dimorphism in characters without the biases of overall size.     

Formation of the genome of the alligator gar Lepisosteus osseus (Ganoidomorpha) genome

Genome structure of the alligator gar was studied by means of a comparison of reassociation kinetics of short and long DNA fragments, an estimation of hyperchromicity of reassociated repetitive DNA as a function of fragments length, and length estimation of S1-resistant duplexes by gel filtration. It was shown that most of the repeated sequences in the alligator gar DNA are no less than 2000 b.p. long and weakly divergent. Little or no interspersion of unique and short repeated sequences were observed in this genome. No highly divergent repeats were found in the alligator gar genome.     

Prey composition and ontogenetic shift in coastal populations of longnose gar Lepisosteus osseus

Longnose gar Lepisosteus osseus were collected from May 2012 to July 2013 in the Charleston Harbor and Winyah Bay estuaries (SC, U.S.A.). This study examined trends in stomach fullness, described major prey components and their importance in the diet of L. osseus, compared stomach content‐based trophic level estimates with the stable‐isotope‐based proxy: δ¹⁵N and tested for the occurrence of an ontogenetic diet shift using stomach content analysis and stable C and N isotopes (δ¹³C and δ¹⁵N). Dominant prey families were Clupeidae, Sciaenidae, Penaeidae, Fundulidae and Mugilidae, with the highest consumption rates in autumn. Trophic levels calculated using stomach contents did not correspond to δ¹⁵N (P > 0·05). Stomach contents and stable‐isotope signatures indicate ontogenetic prey composition shifts from low trophic level benthic prey (fundulids) to higher trophic level pelagic prey (clupeids) as the fish grow between 400 and 600 mm in standard length. Due to their biomass, abundance and top predator status, L. osseus play a significant ecological role in the estuarine community composition, although this effect has often been overlooked by past researchers and should be considered in future estuarine community studies.     

Characterization of erythrocyte carbonic anhydrase in an ancient fish,the longnose gar ( Lepisosteus osseus)

This study investigates the evolutionary history of vertebrate red blood cell carbonic anhydrase (CA) by characterizing the isozyme properties and nucleotide sequence of an ancient fish, the longnose gar ( Lepisosteus osseus). The inhibitor sensitivities of gar rbc CA closely resembled those for mammalian CA II, as well as those for CAs from more recently evolved fishes. The kinetic properties of gar rbc CA were not closely aligned with either mammalian CA I and CA II, but fit well into an emerging phylogenetic pattern for early vertebrates. Gar rbc CA cDNA was also amplified from mRNA using 5' and 3'-RACE and the open reading frame consisted of 786 bp. This sequence shares approximately 65% identity with the nucleotide and amino acid sequences of both mammalian CA I and CA II. When the amino acid sequences within the active site are compared, gar rbc CA differs from mammalian CA I, CA II and CA VII by 9, 4 and 3 of the 36 amino acids, respectively. Phylogenetic analyses suggest that gar rbc CA diverged before the amniotic CAs (CA I, CA II and CA III), but after CA V and CA VII.     

The structure of the gas bladder of the spotted gar,Lepisosteus oculatus

We report here on the macroscopic, light microscopic, and electron microscopic structure of the gas bladder (GB) of the spotted gar, Lepisosteus oculatus. The GB opens into the pharynx, dorsal to the opening of the oesophagus, through a longitudinal slit bordered by two glottal ridges. Caudal to the ridges, the GB is an elongated sac divided into a central duct and right and left lobes. The lobes are formed by a cranio‐caudal sequence of large air spaces that open into the central duct. The structure of the GB is that of a membranous sac supported by a system of septa arising from the walls of a central duct. The septa contain variable amounts of striated and smooth muscle might function to maintain the bladder shape and in providing contractile capabilities. The presence of muscle cells, nerves, and neuroepithelial cells in the wall of the GB strongly suggests that GB function is tightly regulated. The central duct and the apical surface of the thickest septa are covered by mucociliated epithelium. Most of the rest of the inner bladder surface is covered by a respiratory epithelium which contains goblet cells and a single type of pneumocyte. These two cell types produce surfactant. The respiratory barrier contains thick areas with fibrillar material and cell prolongations, and thin areas that only contain basement membrane material between the capillary wall and the respiratory epithelium. Lungs and GBs share many anatomical and histological features. There appears to be no clear criterion for structural distinction between these two types of respiratory organs. J. Morphol. 276:90–101, 2015. © 2014 Wiley Periodicals, Inc.     

The metabolic organization of a primitive air-breathing fish, the Florida gar (Lepisosteus platyrhincus)

The metabolic organization of the air-breathing Florida gar, Lepisosteus platyrhincus, was assessed by measuring the maximal activities of key enzymes in several metabolic pathways in selected tissues, concentrations of plasma metabolites including nonesterified fatty acids (NEFA), free amino acids (FAA) and glucose as well as tissue FAA levels. In general, L. platyrhincus has an enhanced capacity for carbohydrate metabolism as indicated by elevated plasma glucose levels and high activities of gluconeogenic and glycolytic enzymes. Based upon these properties, glucose appears to function as the major fuel source in the Florida gar. The capacity for lipid metabolism in L. platyrhincus appears limited as plasma NEFA levels and the activities of enzymes involved in lipid oxidation are low relative to many other fish species. L. platyrhincus is capable of oxidizing both D- and L-beta-hydroxybutyrate, with tissue-specific preferences for each stereoisomer, yet the capacity for ketone body metabolism is low compared with other primitive fishes. Based on enzyme activities, the metabolism of the air-breathing organ more closely resembles that of the mammalian lung than a fish swim bladder. The Florida gar sits phylogenetically and metabolically in an intermediate position between the "primitive" elasmobranchs and the "advanced" teleosts. The apparently unique metabolic organization of the gar may have evolved in the context of a bimodal air-breathing environmental adaptation.     

Scanning electron microscopy of the air bladder in the spotted gar,Lepisosteus occulatus

The surface of the gar respiratory epithelium was examined by scanning electron microscopy. Nonciliated and ciliated cells constitute the epithelium. Puffs appear to be an unusual feature of the ciliated cells as well as nonciliated cells. There appears to be a transition from nonciliated to puff ciliated cells through a puff stage. The role of the cell types as related to oxygen available in the air bladder is discussed.     

Immunoreactivity of the corpuscles of Stannius of the garpike,Lepisosteus osseus,to antisera against salmon and trout stanniocalcins

Stanniocalcin-immunoreactive cells were localized in the corpuscles of Stannius of a holostean fish, the garpike (Lepisosteus osseus), using antisera against salmon and trout stanniocalcins and the peroxidase-antiperoxidase and protein A-gold immunohistochemical methods. The stanniocalcin-immunoreactive cells were periodic acid-Schiff-positive, and antibody staining was abolished if the antiserum was preabsorbed with corpuscle homogenate. Immunocytochemistry revealed two reactive cell types in the glandular parenchyma, and immunoreactivity was confined to the secretory granules. Staining of the granules was also abolished when the antisera were blocked with crude corpuscle homogenate. When corpuscle extracts from garpike were subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Western blot analysis, a single dense band was evident with a molecular weight of 68 kDa under non-reducing conditions, whereas three bands were observed (29, 31, and 34 kDa) under reducing conditions. Staining of all bands disappeared following preabsorption of the antiserum with salmon stanniocalcin, trout stanniocalcin, or garpike corpuscle extract. The results are compared with stanniocalcins from another extant holostean, the bowfin (Amia calva), and from more modern bony fishes, the teleosts.     

Isolation and characterization of microsatellite loci for alligator gar (Atractosteus spatula) and their variability in two other species (Lepisosteus oculatus and L. osseus) of Lepisosteidae

We report on the isolation of 17 polymorphic microsatellite loci from alligator gar (Atractosteus spatula), a large-bodied species that has experienced population declines across much of its range. These loci possessed 2-19 alleles and observed heterozygosities of 0-0.974. All loci conformed to Hardy-Weinberg equilibrium expectations, and none exhibited linkage disequilibrium. Nine and eight of these loci were found to be polymorphic in the related species Lepisosteus oculatus and L. osseus, respectively. These microsatellite loci should prove useful in conservation efforts of A. spatula through the study of population structure and hatchery broodstock management.     

Comparative ultrastructure of ureteric innervation

The distribution and structure of the ureteric nerves in a small series of mammals was compared with that previously demonstrated in the rat. There was marked interspecies variation in the extent to which the nerves penetrated the wall of the ureter and in the degree of development of the deep submucous plexus. In animals with a highly developed deep submucous plexus, terminal arterioles frequently passed through the muscle coat before breaking up into capillaries. These vessels were surrounded by a fine periarteriolar plexus and were accompanied in their course through the muscle coat by one or more branches of the adventitial nerves. Intramuscular nerves not related to arterioles contained few axons with terminals classifiable as either adrenergic or cholinergic, and in animals in which the muscle cells were arranged in fascicles rather than in sheets, the nerves were typically interfascicular in position. As in the rat, only the periarteriolar plexuses contained large numbers of adrenergic axons. Cholinergic axons were generally few, but were not uncommon in the deep submucous plexus when this was well-developed. The majority of the terminals encountered in the intramural nerves contained variable and usually small numbers of both clear and large dense-cored vesicles. The relationship between these terminals and those defined in the submucous nerves of the rat ureter was discussed and it was suggested that the marked variations in the diameter of the axons in the terminal areas and in the number of vesicles in the terminals were related to the effects of the mechanical and other derangements which occur during processing.     

The ultrastructure and innervation of muscles controlling chromatophore expansion in the squid,Loligo vulgaris

Squid chromatophores are organs of colour change, consisting of a pigment sac opened by contraction of 10–24 radial muscle fibres. The ultrastructure and innervation of these muscle fibres were examined by electron microscopy and diagramatic reconstructions made on the basis of serial ultra-thin sections. At the proximal end of the fibre, nearest the pigment sac a cortical myofilament zone surrounds 2 cores containing mitochrondria; further along the fibre these merge to form one central core. The myofilament zone forms a groove containing a nerve bundle consisting of 2 to 4 axons per muscle fibre. The axons are surrounded by glial cell processes, and either originate from a neighbouring fibre, or join the fibre at some point along its length. Axons twist around each other, forming a series of synapses with the muscle fibre. As many as 6–37 synapses exist along the length of each muscle fibre; the mean synapse interval is 9.05 m, but the largest may be 123 m. At the distal end of the muscles, the nerve is located towards the middle of the fibre, which it penetrates as the muscle splits up. Electron-lucent vesicles are present in all synaptic regions, but electron-dense vesicles are only found towards the distal end of the fibre. There is thus a possibility that more than one neurotransmitter is present in the nerves innervating chromatophores. Electron-lucent and dense-cored vesicles are not colocalised.This work was carried out during the tenure of a BBSRC CASE studentship     

Comparative neurochemical features of the innervation patterns of the gut of the basal actinopterygian,Lepisosteus oculatus,and the euteleost,Clarias batrachus

The structure and physiology of enteric system are very similar in all classes of vertebrates, although they have been investigated only occasionally in non‐mammalian vertebrates. Very little is known about the distribution of the neurotransmitters in the gut of actinopterygian fishes. Anatomical and physiological studies of enteric nervous systems in the spotted gar (Lepisosteus oculatus) and airbreathing catfish (Clarias batrachus), a non‐teleost and teleost actinopterygian, respectively, have not been undertaken. This study provides the first comprehensive characterization of the range of neurochemical coding in the enteric nervous system of these two species, including the chemical diversity of the mucosal endocrine cells in the pyloric stomach of Clarias. Autonomic innervation of the secretory glands is also described and reported herein for the first time for fishes. We also report splanchnic (spinal) innervation of the stomach, submucosal ganglia (that also colocalize with nNOS) and caudal intestine of Clarias. In both fish species, numerous 5HT, ChAT, nNOS and TH‐positive nerve fibres have been observed. These discoveries demonstrate that much more physiological and pharmacological data are needed before a comprehensive model of enteric nervous system control in vertebrates can be developed.