The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Craig E Franklin - One of the best experts on this subject based on the ideXlab platform.

  • salt water acclimation of the estuarine crocodile Crocodylus porosus involves enhanced ion transport properties of the urodaeum and rectum
    The Journal of Experimental Biology, 2020
    Co-Authors: Martin Grosell, Rebecca L. Cramp, Ross G Dwyer, Rachael M Heuer, Nicholas C Wu, Yadong Wang, Edward M Mager, Craig E Franklin
    Abstract:

    Estuarine crocodiles, Crocodylus porosus, inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo-osmotic and hyperosmotic environments, little is known about the role of the cloaca in coping with changes in salinity. We report here that, in addition to the well-documented functional plasticity of the lingual salt glands, the middle of the three cloacal segments (i.e. the urodaeum) responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short-circuit current (an indicator of active ion transport) compared with freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na/K-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na channel (ENaC) and/or the apical Na/H exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and probably does not contribute to solute-coupled water absorption in this cloacal segment. As C. porosus does not appear to drink water of salinities above 18 ppt, observations of elevated short-circuit current in the rectum as well as a trend for increased NHE2 expression in the oesophagus, the anterior intestine and the rectum suggest that dietary salt intake may stimulate salt and possibly water absorption by the gastrointestinal tract of C. porosus living in hyperosmotic environments.

  • salt water acclimation of the estuarine crocodile Crocodylus porosus involves enhanced ion transport properties of the urodaeum and rectum
    The Journal of Experimental Biology, 2020
    Co-Authors: Martin Grosell, Rebecca L. Cramp, Ross G Dwyer, Rachael M Heuer, Yadong Wang, Edward M Mager, Craig E Franklin
    Abstract:

    Estuarine crocodiles Crocodylus porosus inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo- and hyperosmotic environments, little is known on the role of the cloaca in coping with changes in salinity. In addition to the well-documented functional plasticity of the lingual salt glands, we report here that the middle of the three cloacal segments (i.e. the urodaeum), responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short circuit current (indicator of active ion transport) compared to freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na+/K+-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na+ channel (ENaC) and/or the apical Na+/H+ exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and likely does not contribute to solute-coupled water absorption in this cloacal segment. Since C. porosus does not appear to drink water of salinities above 18 ppt, observations of elevated short circuit current in the rectum as well as a trend for increased NHE2 expression in the esophagus, the anterior intestine, and the rectum, suggests that dietary salt intake may stimulate salt, and possibly water absorption by the gastro-intestinal tract of C. porosus living in hyperosmotic environments.

  • feeding across the food web the interaction between diet movement and body size in estuarine crocodiles Crocodylus porosus
    Austral Ecology, 2015
    Co-Authors: Jeffrey O Hanson, Steven W Salisbury, Hamish A Campbell, Ross G Dwyer, Timothy D Jardine, Craig E Franklin
    Abstract:

    The estuarine crocodile (Crocodylus porosus) is an apex predator across freshwater, estuarine and coastal environments. The impact of a changing C. porosus population upon the ecosystem is unknown, but due to large ontogenetic changes in body mass (>1000-fold) their impact may be wide reaching and substantial. Here we investigated the relationship between diet, movement and body size in a population of C. porosus inhabiting a tidal river in northern Australia. Subcutaneous acoustic transmitters and fixed underwater receivers were used to determine the activity space and movement patterns of 42 individuals (202–451 cm in total length). There was no size-related spatial partitioning among different sized crocodiles. Large individuals (snout–vent length (SVL): 160 cm   160 cm). Tissue δ13C composition on the other hand was positively correlated with body size, indicating that different size classes were trophically linked to primary producers in different habitats. Individual-level analyses showed that small crocodiles were generalist feeders while medium and large size classes specialized on particular prey items within the food webs they fed. The findings further our understanding of ontogenetic variation in C. porosus diet, and suggest that change in C. porosus population size or demographics may be influential at various levels across the local food web.

  • diving in a warming world the thermal sensitivity and plasticity of diving performance in juvenile estuarine crocodiles Crocodylus porosus
    Conservation Physiology, 2015
    Co-Authors: Essie M Rodgers, Jonathon J Schwartz, Craig E Franklin
    Abstract:

    Air-breathing, diving ectotherms are a crucial component of the biodiversity and functioning of aquatic ecosystems, but these organisms may be particularly vulnerable to the effects of climate change on submergence times. Ectothermic dive capacity is thermally sensitive, with dive durations significantly reduced by acute increases in water temperature; it is unclear whether diving performance can acclimate/acclimatize in response to long-term exposure to elevated water temperatures. We assessed the thermal sensitivity and plasticity of 'fright-dive' capacity in juvenile estuarine crocodiles (Crocodylus porosus; n = 11). Crocodiles were exposed to one of three long-term thermal treatments, designed to emulate water temperatures under differing climate change scenarios (i.e. current summer, 28 degrees C; 'moderate' climate warming, 31.5 degrees C; 'high' climate warming, 35 degrees C). Dive trials were conducted in a temperature-controlled tank across a range of water temperatures. Dive durations were independent of thermal acclimation treatment, indicating a lack of thermal acclimation response. Acute increases in water temperature resulted in significantly shorter dive durations, with mean submergence times effectively halving with every 3.5 degrees C increase in water temperature (Q(10) 0.17, P < 0.001). Maximal dive performances, however, were found to be thermally insensitive across the temperature range of 28-35 degrees C. These results suggest that C. porosus have a limited or non-existent capacity to thermally acclimate sustained 'fright-dive' performance. If the findings here are applicable to other air-breathing, diving ectotherms, the functional capacity of these organisms will probably be compromised under climate warming.

  • Hormone-dependent dissociation of blood flow and secretion rate in the lingual salt glands of the estuarine crocodile, Crocodylus porosus
    Journal of Comparative Physiology B, 2010
    Co-Authors: Rebecca L. Cramp, Inga Vries, W. Gary Anderson, Craig E Franklin
    Abstract:

    Salt and water balance in the estuarine crocodile, Crocodylus porosus , involves the coordinated action of both renal and extra-renal tissues. The highly vascularised, lingual salt glands of C. porosus excrete a concentrated sodium chloride solution. In the present study, we examined the in vivo actions of vasoactive intestinal peptide (VIP), B-type natriuretic peptide (BNP) and angiotensin II (ANG II) on the secretion rate and blood perfusion of the lingual salt glands. These peptides were selected for their vasoactive properties in addition to their reported actions on salt gland activity in birds and turtles and rectal gland activity in elasmobranchs. The femoral artery was cannulated in seven juvenile crocodiles for delivery of peptides and measurement of mean blood pressure and heart rate. In addition, secretion rate of, and blood flow to, the salt glands were recorded simultaneously using laser Doppler flowmetry. VIP stimulated salt secretion was coupled to an increase in blood flow and vascular conductance of the lingual salt glands. BNP was a potent stimulant of salt gland secretion, resulting in a maximal secretion rate of more than 15-fold higher than baseline; however, this was not coupled to an increase in perfusion rate, which remained unchanged. ANG II failed to stimulate salt gland secretion and there was a transient decrease in salt gland blood flow and vascular conductance. It is evident from this study that blood flow to, and secretion rate from, the lingual salt glands of C. porosus are regulated independently; indeed, it is apparent that maximal secretion from the salt glands may not require maximal blood flow.

Sally R Isberg - One of the best experts on this subject based on the ideXlab platform.

  • identification and characterization of micrornas mirnas and their transposable element origins in the saltwater crocodile Crocodylus porosus
    Analytical Biochemistry, 2020
    Co-Authors: Arnab Ghosh, Roy N Platt, Michael W Vandewege, Rabia Tabassum, John W Finger, Daniel G. Peterson, Sally R Isberg
    Abstract:

    Abstract MicroRNAs (miRNAs) are 18-24 nucleotide regulatory RNAs. They are involved in the regulation of genetic and biological pathways through post transcriptional gene silencing and/or translational repression. Data suggests a slow evolutionary rate for the saltwater crocodile (Crocodylus porosus) over the past several million years when compared to birds, the closest extant relatives of crocodilians. Understanding gene regulation in the saltwater crocodile in the context of relatively slow genomic change thus holds potential for the investigation of genomics, evolution, and adaptation. Utilizing eleven tissue types and sixteen small RNA libraries, we report 644 miRNAs in the saltwater crocodile with > 78% of miRNAs being novel to crocodilians. We also identified potential targets for the miRNAs and analyzed the relationship of the miRNA repertoire to transposable elements (TEs). Results suggest an increased association of DNA transposons with miRNAs when compared to retrotransposons. This work reports the first comprehensive analysis of miRNAs in Crocodylus porosus and addresses the potential impacts of miRNAs in regulating the genome in the saltwater crocodile. In addition, the data suggests a supporting role of TEs as a source for miRNAs, adding to the increasing evidence that TEs play a significant role in the evolution of gene regulation.

  • a high quality reference genome assembly of the saltwater crocodile Crocodylus porosus reveals patterns of selection in crocodylidae
    Genome Biology and Evolution, 2020
    Co-Authors: Arnab Ghosh, Sally R Isberg, Travis C Glenn, Matthew G Johnson, Austin B Osmanski, Swarnali Louha, Natalia J Bayonavasquez, Jaime Gongora, Richard E Green
    Abstract:

    : Crocodilians are an economically, culturally, and biologically important group. To improve researchers' ability to study genome structure, evolution, and gene regulation in the clade, we generated a high-quality de novo genome assembly of the saltwater crocodile, Crocodylus porosus, from Illumina short read data from genomic libraries and in vitro proximity-ligation libraries. The assembled genome is 2,123.5 Mb, with N50 scaffold size of 17.7 Mb and N90 scaffold size of 3.8 Mb. We then annotated this new assembly, increasing the number of annotated genes by 74%. In total, 96% of 23,242 annotated genes were associated with a functional protein domain. Furthermore, multiple non-coding functional regions and mappable genetic markers were identified. Upon analysis and overlapping the results of branch length estimation and site selection tests for detecting potential selection, we found 16 putative genes under positive selection in crocodilians, ten in C. porosus and six in A. mississippiensis. The annotated C. porosus genome will serve as an important platform for osmoregulatory, physiological and sex determination studies, as well as an important reference in investigating the phylogenetic relationships of crocodilians, birds, and other tetrapods.

  • a high quality reference genome assembly of the saltwater crocodile Crocodylus porosus reveals patterns of selection in crocodylidae
    Genome Biology and Evolution, 2020
    Co-Authors: Arnab Ghosh, Sally R Isberg, Travis C Glenn, Matthew G Johnson, Austin B Osmanski, Swarnali Louha, Natalia J Bayonavasquez, Jaime Gongora, Richard E Green
    Abstract:

    Crocodilians are an economically, culturally, and biologically important group. To improve researchers' ability to study genome structure, evolution, and gene regulation in the clade, we generated a high-quality de novo genome assembly of the saltwater crocodile, Crocodylus porosus, from Illumina short read data from genomic libraries and in vitro proximity-ligation libraries. The assembled genome is 2,123.5 Mb, with N50 scaffold size of 17.7 Mb and N90 scaffold size of 3.8 Mb. We then annotated this new assembly, increasing the number of annotated genes by 74%. In total, 96% of 23,242 annotated genes were associated with a functional protein domain. Furthermore, multiple noncoding functional regions and mappable genetic markers were identified. Upon analysis and overlapping the results of branch length estimation and site selection tests for detecting potential selection, we found 16 putative genes under positive selection in crocodilians, 10 in C. porosus and 6 in Alligator mississippiensis. The annotated C. porosus genome will serve as an important platform for osmoregulatory, physiological, and sex determination studies, as well as an important reference in investigating the phylogenetic relationships of crocodilians, birds, and other tetrapods.

  • crocodilepox virus evolutionary genomics supports observed poxvirus infection dynamics on saltwater crocodile Crocodylus porosus
    Viruses, 2019
    Co-Authors: Subir Sarker, Lorna Melville, Sally R Isberg, Jasmin Moran, Rachel De Araujo, Nikki Elliott, Travis Clarke Beddoe, Karla J Helbig
    Abstract:

    Saltwater crocodilepox virus (SwCRV), belonging to the genus Crocodylidpoxvirus, are large DNA viruses posing an economic risk to Australian saltwater crocodile (Crocodylus porosus) farms by extending production times. Although poxvirus-like particles and sequences have been confirmed, their infection dynamics, inter-farm genetic variability and evolutionary relationships remain largely unknown. In this study, a poxvirus infection dynamics study was conducted on two C. porosus farms. One farm (Farm 2) showed twice the infection rate, and more concerningly, an increase in the number of early- to late-stage poxvirus lesions as crocodiles approached harvest size, reflecting the extended production periods observed on this farm. To determine if there was a genetic basis for this difference, 14 complete SwCRV genomes were isolated from lesions sourced from five Australian farms. They encompassed all the conserved genes when compared to the two previously reported SwCRV genomes and fell within three major clades. Farm 2′s SwCRV sequences were distributed across all three clades, highlighting the likely mode of inter-farm transmission. Twenty-four recombination events were detected, with one recombination event resulting in consistent fragmentation of the P4c gene in the majority of the Farm 2 SwCRV isolates. Further investigation into the evolution of poxvirus infection in farmed crocodiles may offer valuable insights in evolution of this viral family and afford the opportunity to obtain crucial information into natural viral selection processes in an in vivo setting.

  • a pilot study to understand tooth replacement in near harvest farmed saltwater crocodiles Crocodylus porosus implications for blemish induction
    Aquaculture, 2019
    Co-Authors: John W Finger, P C Thomson, Sally R Isberg
    Abstract:

    Abstract Saltwater crocodiles (Crocodylus porosus) are farmed in Australia primarily for their belly skin. The desirability and ultimately the value of each skin depends on the extent and location of various industry-defined defects. Anecdotal observations suggest that conspecific interactions are the main contributors with the protrusive 4th dentary teeth (i.e. eye teeth) the most likely cause. It is well known that crocodilians undergo continual tooth replacement, yet no study has investigated tooth replacement rates or tooth growth dynamics in juvenile saltwater crocodiles. In this pilot study, we repeatedly measured eye tooth crown height and observed eye tooth replacement in individually-housed juvenile saltwater crocodiles (n = 98) accounting for 290 individual teeth. The majority of teeth were replaced every three to six months (n = 172) but nine teeth were not replaced over the 15-month study period. After a tooth was lost, the need to replace it quickly was evidenced by a faster tooth growth rate in the first three months (11.07 ± 0.17 mm) but subsequently slowed to a model-adjusted asymptote of 14.03 ± 0.27 mm (p

Rebecca L. Cramp - One of the best experts on this subject based on the ideXlab platform.

  • salt water acclimation of the estuarine crocodile Crocodylus porosus involves enhanced ion transport properties of the urodaeum and rectum
    The Journal of Experimental Biology, 2020
    Co-Authors: Martin Grosell, Rebecca L. Cramp, Ross G Dwyer, Rachael M Heuer, Nicholas C Wu, Yadong Wang, Edward M Mager, Craig E Franklin
    Abstract:

    Estuarine crocodiles, Crocodylus porosus, inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo-osmotic and hyperosmotic environments, little is known about the role of the cloaca in coping with changes in salinity. We report here that, in addition to the well-documented functional plasticity of the lingual salt glands, the middle of the three cloacal segments (i.e. the urodaeum) responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short-circuit current (an indicator of active ion transport) compared with freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na/K-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na channel (ENaC) and/or the apical Na/H exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and probably does not contribute to solute-coupled water absorption in this cloacal segment. As C. porosus does not appear to drink water of salinities above 18 ppt, observations of elevated short-circuit current in the rectum as well as a trend for increased NHE2 expression in the oesophagus, the anterior intestine and the rectum suggest that dietary salt intake may stimulate salt and possibly water absorption by the gastrointestinal tract of C. porosus living in hyperosmotic environments.

  • salt water acclimation of the estuarine crocodile Crocodylus porosus involves enhanced ion transport properties of the urodaeum and rectum
    The Journal of Experimental Biology, 2020
    Co-Authors: Martin Grosell, Rebecca L. Cramp, Ross G Dwyer, Rachael M Heuer, Yadong Wang, Edward M Mager, Craig E Franklin
    Abstract:

    Estuarine crocodiles Crocodylus porosus inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo- and hyperosmotic environments, little is known on the role of the cloaca in coping with changes in salinity. In addition to the well-documented functional plasticity of the lingual salt glands, we report here that the middle of the three cloacal segments (i.e. the urodaeum), responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short circuit current (indicator of active ion transport) compared to freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na+/K+-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na+ channel (ENaC) and/or the apical Na+/H+ exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and likely does not contribute to solute-coupled water absorption in this cloacal segment. Since C. porosus does not appear to drink water of salinities above 18 ppt, observations of elevated short circuit current in the rectum as well as a trend for increased NHE2 expression in the esophagus, the anterior intestine, and the rectum, suggests that dietary salt intake may stimulate salt, and possibly water absorption by the gastro-intestinal tract of C. porosus living in hyperosmotic environments.

  • Hormone-dependent dissociation of blood flow and secretion rate in the lingual salt glands of the estuarine crocodile, Crocodylus porosus
    Journal of Comparative Physiology B, 2010
    Co-Authors: Rebecca L. Cramp, Inga Vries, W. Gary Anderson, Craig E Franklin
    Abstract:

    Salt and water balance in the estuarine crocodile, Crocodylus porosus , involves the coordinated action of both renal and extra-renal tissues. The highly vascularised, lingual salt glands of C. porosus excrete a concentrated sodium chloride solution. In the present study, we examined the in vivo actions of vasoactive intestinal peptide (VIP), B-type natriuretic peptide (BNP) and angiotensin II (ANG II) on the secretion rate and blood perfusion of the lingual salt glands. These peptides were selected for their vasoactive properties in addition to their reported actions on salt gland activity in birds and turtles and rectal gland activity in elasmobranchs. The femoral artery was cannulated in seven juvenile crocodiles for delivery of peptides and measurement of mean blood pressure and heart rate. In addition, secretion rate of, and blood flow to, the salt glands were recorded simultaneously using laser Doppler flowmetry. VIP stimulated salt secretion was coupled to an increase in blood flow and vascular conductance of the lingual salt glands. BNP was a potent stimulant of salt gland secretion, resulting in a maximal secretion rate of more than 15-fold higher than baseline; however, this was not coupled to an increase in perfusion rate, which remained unchanged. ANG II failed to stimulate salt gland secretion and there was a transient decrease in salt gland blood flow and vascular conductance. It is evident from this study that blood flow to, and secretion rate from, the lingual salt glands of C. porosus are regulated independently; indeed, it is apparent that maximal secretion from the salt glands may not require maximal blood flow.

  • activity abundance distribution and expression of na k atpase in the salt glands of Crocodylus porosus following chronic saltwater acclimation
    The Journal of Experimental Biology, 2010
    Co-Authors: Rebecca L. Cramp, Nicholas J. Hudson, Craig E Franklin
    Abstract:

    Saltwater crocodiles, Crocodylus porosus, possess lingual salt glands which function to remove excess Na(+) and Cl(-) accumulated as a consequence of living in salt water. Little is known about the nature of ion transport systems in C. porosus salt glands and how these systems respond to an osmotic challenge. In the present study, we examined the distribution and regulation of the Na(+)/K(+)-ATPase (NKA) pump, specifically the alpha-(catalytic) subunit in the salt glands of C. porosus chronically acclimated (6 months) to freshwater (FW) or 70% seawater (SW). We hypothesised that in the SW-acclimated C. porosus there would be an up-regulation of the abundance, activity and gene expression of the NKA transporter. NKA was immunolocalised to the lateral and basal membrane of secretory cells. As predicted, the NKA alpha-subunit was 2-fold more abundant in SW-acclimated C. porosus salt glands. NKA gene expression was also elevated in the salt glands of SW- vs FW-acclimated crocodiles. There was no increase in the specific activity of NKA in SW-acclimated animals and the in vitro rate of oxygen consumption by salt gland slices from SW-acclimated animals was not significantly different from that of FW-acclimated animals. The proportion of tissue oxygen consumption rate attributable to NKA activity was not different between SW- and FW-acclimated animals (approximately 50%). These data suggest that either chronic SW acclimation does not affect NKA in crocodile salt glands in the same manner as seen in other models or crocodiles possess the capacity to moderate NKA activity following prolonged exposure to SW.

  • Functional and morphological plasticity of crocodile (Crocodylus porosus) salt glands.
    The Journal of experimental biology, 2008
    Co-Authors: Rebecca L. Cramp, Edward A Meyer, Nicole Sparks, Craig E Franklin
    Abstract:

    The estuarine crocodile, Crocodylus porosus, inhabits both freshwater and hypersaline waterways and maintains ionic homeostasis by excreting excess sodium and chloride ions via lingual salt glands. In the present study, we sought to investigate the phenotypic plasticity, both morphological and functional, in the lingual salt glands of the estuarine crocodile associated with chronic exposure to freshwater (FW) and saltwater (SW) environments. Examination of haematological parameters indicated that there were no long-term disruptions to ionic homeostasis with prolonged exposure to SW. Maximal secretory rates from the salt glands of SW-acclimated animals (100.8+/-14.7 micromol 100 g(-0.7) body mass h(-1)) were almost three times greater than those of FW-acclimated animals (31.6+/-6.2 micromol 100 g(-0.7) body mass h(-1)). There were no differences in the mass-specific metabolic rate of salt gland tissue slices from FW- and SW-acclimated animals (558.9+/-49.6 and 527.3+/-142.8 microl O(2) g(-1) h(-1), respectively). Stimulation of the tissue slices from SW-acclimated animals by methacholine resulted in a 33% increase in oxygen consumption rate. There was no significant increase in the metabolic rate of tissues from FW-acclimated animals in response to methacholine. Morphologically, the secretory cells from the salt glands of SW-acclimated animals were larger than those of FW-acclimated animals. In addition, there were significantly more mitochondria per unit volume in secretory tissue from SW-acclimated animals. The results from this study demonstrate that the salt glands of C. porosus are phenotypically plastic, both morphologically and functionally and acclimate to changes in environmental salinity.

Edward M Mager - One of the best experts on this subject based on the ideXlab platform.

  • salt water acclimation of the estuarine crocodile Crocodylus porosus involves enhanced ion transport properties of the urodaeum and rectum
    The Journal of Experimental Biology, 2020
    Co-Authors: Martin Grosell, Rebecca L. Cramp, Ross G Dwyer, Rachael M Heuer, Nicholas C Wu, Yadong Wang, Edward M Mager, Craig E Franklin
    Abstract:

    Estuarine crocodiles, Crocodylus porosus, inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo-osmotic and hyperosmotic environments, little is known about the role of the cloaca in coping with changes in salinity. We report here that, in addition to the well-documented functional plasticity of the lingual salt glands, the middle of the three cloacal segments (i.e. the urodaeum) responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short-circuit current (an indicator of active ion transport) compared with freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na/K-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na channel (ENaC) and/or the apical Na/H exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and probably does not contribute to solute-coupled water absorption in this cloacal segment. As C. porosus does not appear to drink water of salinities above 18 ppt, observations of elevated short-circuit current in the rectum as well as a trend for increased NHE2 expression in the oesophagus, the anterior intestine and the rectum suggest that dietary salt intake may stimulate salt and possibly water absorption by the gastrointestinal tract of C. porosus living in hyperosmotic environments.

  • salt water acclimation of the estuarine crocodile Crocodylus porosus involves enhanced ion transport properties of the urodaeum and rectum
    The Journal of Experimental Biology, 2020
    Co-Authors: Martin Grosell, Rebecca L. Cramp, Ross G Dwyer, Rachael M Heuer, Yadong Wang, Edward M Mager, Craig E Franklin
    Abstract:

    Estuarine crocodiles Crocodylus porosus inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo- and hyperosmotic environments, little is known on the role of the cloaca in coping with changes in salinity. In addition to the well-documented functional plasticity of the lingual salt glands, we report here that the middle of the three cloacal segments (i.e. the urodaeum), responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short circuit current (indicator of active ion transport) compared to freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na+/K+-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na+ channel (ENaC) and/or the apical Na+/H+ exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and likely does not contribute to solute-coupled water absorption in this cloacal segment. Since C. porosus does not appear to drink water of salinities above 18 ppt, observations of elevated short circuit current in the rectum as well as a trend for increased NHE2 expression in the esophagus, the anterior intestine, and the rectum, suggests that dietary salt intake may stimulate salt, and possibly water absorption by the gastro-intestinal tract of C. porosus living in hyperosmotic environments.

John W Finger - One of the best experts on this subject based on the ideXlab platform.

  • identification and characterization of micrornas mirnas and their transposable element origins in the saltwater crocodile Crocodylus porosus
    Analytical Biochemistry, 2020
    Co-Authors: Arnab Ghosh, Roy N Platt, Michael W Vandewege, Rabia Tabassum, John W Finger, Daniel G. Peterson, Sally R Isberg
    Abstract:

    Abstract MicroRNAs (miRNAs) are 18-24 nucleotide regulatory RNAs. They are involved in the regulation of genetic and biological pathways through post transcriptional gene silencing and/or translational repression. Data suggests a slow evolutionary rate for the saltwater crocodile (Crocodylus porosus) over the past several million years when compared to birds, the closest extant relatives of crocodilians. Understanding gene regulation in the saltwater crocodile in the context of relatively slow genomic change thus holds potential for the investigation of genomics, evolution, and adaptation. Utilizing eleven tissue types and sixteen small RNA libraries, we report 644 miRNAs in the saltwater crocodile with > 78% of miRNAs being novel to crocodilians. We also identified potential targets for the miRNAs and analyzed the relationship of the miRNA repertoire to transposable elements (TEs). Results suggest an increased association of DNA transposons with miRNAs when compared to retrotransposons. This work reports the first comprehensive analysis of miRNAs in Crocodylus porosus and addresses the potential impacts of miRNAs in regulating the genome in the saltwater crocodile. In addition, the data suggests a supporting role of TEs as a source for miRNAs, adding to the increasing evidence that TEs play a significant role in the evolution of gene regulation.

  • a pilot study to understand tooth replacement in near harvest farmed saltwater crocodiles Crocodylus porosus implications for blemish induction
    Aquaculture, 2019
    Co-Authors: John W Finger, P C Thomson, Sally R Isberg
    Abstract:

    Abstract Saltwater crocodiles (Crocodylus porosus) are farmed in Australia primarily for their belly skin. The desirability and ultimately the value of each skin depends on the extent and location of various industry-defined defects. Anecdotal observations suggest that conspecific interactions are the main contributors with the protrusive 4th dentary teeth (i.e. eye teeth) the most likely cause. It is well known that crocodilians undergo continual tooth replacement, yet no study has investigated tooth replacement rates or tooth growth dynamics in juvenile saltwater crocodiles. In this pilot study, we repeatedly measured eye tooth crown height and observed eye tooth replacement in individually-housed juvenile saltwater crocodiles (n = 98) accounting for 290 individual teeth. The majority of teeth were replaced every three to six months (n = 172) but nine teeth were not replaced over the 15-month study period. After a tooth was lost, the need to replace it quickly was evidenced by a faster tooth growth rate in the first three months (11.07 ± 0.17 mm) but subsequently slowed to a model-adjusted asymptote of 14.03 ± 0.27 mm (p

  • quantification of plasma corticosterone in juvenile farmed saltwater crocodiles Crocodylus porosus using current australian code of practice guidelines
    General and Comparative Endocrinology, 2018
    Co-Authors: Sally R Isberg, John W Finger, P C Thomson
    Abstract:

    : Saltwater crocodiles (Crocodylus porosus) across three size categories (hatchlings, grower and harvest-size) were repeatedly blood sampled on two farms in the Northern Territory, Australia to determine reference plasma corticosterone (CORT; crocodilian stress hormone) levels. The mean CORT values for hatchlings (<1 year old), growers (1-3 years) and harvest-size individuals (2 + years) were 1.65 ± 0.15 ng/ml, 2.73 ± 0.21 ng/ml and 2.19 ± 0.16 ng/ml, respectively. No inter-farm differences within the hatchling or harvest-size crocodiles were detected, but growers on Farm 2 had significantly lower plasma CORT than those on Farm 1. However, the grower growth rate coefficients were the same across both farms so the repeated blood sampling design most likely contributed to the difference in CORT values rather than any management procedures. Plasma corticosterone levels significantly increased with time of day. Substantial variation in plasma CORT was observed at each sampling which is not unprecedented in the literature but requires further elucidation. Irrespective, as CORT values were generally low, our results suggest that the farming environment and husbandry practices, as implemented under the Australian industry Code of Practice, are effective as baseline animal welfare measures although they should be viewed as a foundation for further welfare research and not considered static.

  • unexpected lower testosterone in faster growing farmed saltwater crocodile Crocodylus porosus hatchlings
    General and Comparative Endocrinology, 2016
    Co-Authors: John W Finger, P C Thomson, Sally R Isberg
    Abstract:

    Abstract Agricultural production of the saltwater crocodile (Crocodylus porosus) is an emergent industry in northern Australia with many of the factors affecting production remaining unknown. In this study, we sought to expand upon our previous findings of reference corticosterone and immune function by reporting baseline sex hormone levels [testosterone (TEST) and estradiol (ESTR)] and their association with growth. This was achieved by sampling 253 hatchling crocodiles repeatedly at 3, 6, and 9 months of age. Sampling age had a significant effect on both TEST (p

  • unexpected lower testosterone in faster growing farmed saltwater crocodile Crocodylus porosus hatchlings
    General and Comparative Endocrinology, 2016
    Co-Authors: John W Finger, P C Thomson, Sally R Isberg
    Abstract:

    Agricultural production of the saltwater crocodile (Crocodylus porosus) is an emergent industry in northern Australia with many of the factors affecting production remaining unknown. In this study, we sought to expand upon our previous findings of reference corticosterone and immune function by reporting baseline sex hormone levels [testosterone (TEST) and estradiol (ESTR)] and their association with growth. This was achieved by sampling 253 hatchling crocodiles repeatedly at 3, 6, and 9months of age. Sampling age had a significant effect on both TEST (p<0.001) and ESTR (p<0.001) suggesting climatic/abiotic factors have an influence even in prepubescent crocodiles. Stress, as measured by plasma corticosterone, had no detectable effect on plasma ESTR or TEST levels. Unexpectedly however, TEST was higher in slower-growing crocodiles, which is contrary to what has been reported for the American alligator. ESTR was not associated with growth.