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Xander Combrink - One of the best experts on this subject based on the ideXlab platform.
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organochlorine pesticide bioaccumulation in wild nile crocodile Crocodylus niloticus fat tissues environmental influences on changing residue levels and contaminant profiles
Science of The Total Environment, 2021Co-Authors: Marc S Humphries, Jan G. Myburgh, Robert Campbell, Archibold Buahkwofie, Xander CombrinkAbstract:Abstract Biologically significant concentrations of organochlorine pesticides (OCPs) continue to be reported in wildlife populations and are of particular concern in species that occupy the highest trophic levels. Nile crocodiles (Crocodylus niloticus) are important apex predators occurring throughout much of tropical and subtropical sub-Saharan Africa, where they inhabit estuarine and freshwater habitats often impacted by contamination. In this study we examined pesticide residue accumulation in fat tissue from Nile crocodiles at Lake St Lucia, South Africa, where historically large quantities of OCPs have been used for agriculture and disease control. During 2019, we collected tail fat samples from wild (n = 21) and captive (n = 3) individuals to examine the influence of habitat, body size and sex on variations in bioaccumulation. The principal contaminant found was p,p′-DDE, a major persistent metabolite of DDT, which continues to be used in the region for combating malaria. Tissue p,p′-DDE concentrations in wild crocodiles (95–1200 ng g−1 ww) were significantly (p 0.70) to body length. Male (n = 14) and female (n = 7) wild crocodiles exhibited similar contaminant body burdens, however, total concentrations were substantially lower than those measured in the same population during 2016/2017. Marked differences in residue levels and profiles appear to reflect changes in food availability and dietary exposure associated with a shift in environmental conditions. These findings suggest that periods of environmental stress may be associated with enhanced toxicological risk in crocodiles. Additional work is needed to better understand contaminant accumulation and elimination mechanisms in crocodiles, and their potential effects on reproductive health.
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synthesizing nile crocodile Crocodylus niloticus attack data and historical context to inform mitigation efforts in south africa and eswatini swaziland
Oryx, 2020Co-Authors: Simon Pooley, Xander Combrink, Hannes Botha, George PowellAbstract:Conflicts with wildlife are a major challenge for conservation across Africa, and Nile crocodiles Crocodylus niloticus are allegedly responsible for more attacks on people than any other species; however, there is a lack of data regarding such attacks. We analysed reported attacks on people by Nile crocodiles in South Africa and eSwatini (Swaziland) during 1949–2016, identifying spatial and temporal patterns in attack incidence, as well as victim demographics. Through a literature review and archival searches we identified records of 214 attacks. Most attacks occurred in natural water bodies, with attacks in dams increasing since 2000. Most victims were attacked while swimming or bathing, others while fishing, doing domestic chores, and crossing waterways. There was a significant relationship between gender and activity when attacked. Children (< 16 years old) accounted for 51% of all attacks, with a higher fatality rate compared to adults. Most victims were male (65%), with teenage boys being the largest individual category. We make recommendations for conservation policy and management to mitigate attacks by Nile crocodiles.
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nest site selection nesting behaviour and spatial ecology of female nile crocodiles Crocodylus niloticus in south africa
Behavioural Processes, 2017Co-Authors: Xander Combrink, Jonathan K. Warner, Colleen T. DownsAbstract:Abstract Nesting biology and ecology have been investigated for Nile crocodiles (Crocodylus niloticus), but information on behaviour and movement patterns of nesting females during nest guarding is scant. Consequently, we investigated the home ranges, nest-site selection strategies, movement patterns, activity levels and nest fidelity of four nesting females using telemetry. Gravid females selected winter basking/breeding areas close (351 ± 2 m) to nest-sites. Mean home range and core-use areas of nesting females were 8539 ± 4752 m2, and 4949 ± 3302 m2 respectively. Mean home range (0.85 ha) was significantly smaller than those of non-nesting females (108.4 ha) during nesting season. Activity levels and mean daily movements while nesting were 8.1 ± 2.5% and 213 ± 64 m, respectively, and increased to 47.9 ± 11.7% and 2176 ± 708 m post-nesting. Overall levels of nest fidelity were 82.8 ± 11.7%, (day 78.1 ± 15.9%; night 87.3 ± 7.8%). Highest nest fidelity recorded during incubation was 99.7% over 96 days. Telemetry data from nesting females were helpful for elucidating spatial and behavioural patterns during the nest guarding period, and provided novel insights into this biologically important event.
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Nest predation and maternal care in the Nile crocodile (Crocodylus niloticus) at Lake St Lucia, South Africa.
Behavioural processes, 2016Co-Authors: Xander Combrink, Jonathan K. WarnerAbstract:Abstract Information regarding nest predation, nest abandonment, and maternal care in the Nile crocodile (Crocodylus niloticus) is largely restricted to anecdotal observations, and has not been studied quantitatively. Consequently, we investigated their nesting biology using camera-traps over four years at Lake St Lucia, South Africa. We obtained 4305 photographs (daylight captures = 90.1%, nocturnal = 9.9%) of 19 nest-guarding females. Of 19 monitored nests, 37% were raided by predators (mean = 12.1 ± 6.2 days subsequent to camera placement). All females returned to their nests following first predation, and on average returned three times between predator raids before nest abandonment. Water monitors (Varanus niloticus) and marsh mongoose (Atilax paludinosus) were the main egg predators. Nesting raids lasted 5.9 ± 1.6 days. Diurnally females were seldom on the nest, except during cool/cloudy weather or rain, preferring to guard from nearby shade. Females defended nests aggressively against non-human intruders. Five Nile crocodile females were observed liberating their hatchlings from nests. A detailed sequence of a mother excavating and transporting hatchlings revealed 13 excursions between nest and water over 32.5 h. This, after months of continual nest attendance and defence, is illustrative of the high level of maternal care in Nile crocodiles. Camera-trapping is an effective, non-invasive method for further crocodile nesting behaviour research.
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morphometrics sex ratio sexual size dimorphism biomass and population size of the nile crocodile Crocodylus niloticus at its southern range limit in kwazulu natal south africa
Zoomorphology, 2016Co-Authors: Jonathan K. Warner, Xander Combrink, Peter M Calverley, Garreth ChampionAbstract:Animal body size and sex are requisite data for understanding population structure and demography. Little information exists regarding Nile crocodile, Crocodylus niloticus, morphometrics, sex ratios of wild populations, sexual size dimorphism and standing crop biomass. We captured 322 C. niloticus at Lake St Lucia and Ndumo Game Reserve, South Africa, the two largest crocodile populations at the southern extent of the species’ range in Africa, and measured a suite of physical characteristics to create predictive models of body length from other morphological attributes and body mass. Our sample included 118 hatchlings, 91 subadults and 113 adults. Strong positive allometric relationships were found between body length metrics (total length and snout-vent length) and other morphometrics. All morphometric regressions were linear, with the exception of the relationship of body length to body mass, which was logarithmic. Among relationships of cranial morphology and body length, we found considerable individual variation among all size classes. The mean head width-to-head length ratio was 1.9 ± 1.6, and mean head length-to-total length ratio was 0.14 ± 0.005. The sex ratios for non-hatchling individuals at both populations were essentially 1:1, but adult sex ratios were male biased. We calculated a total standing crop biomass of 96,867.18 kg (161.45 kg/km) and 52,640.40 kg (1504.01 kg/km) for C. niloticus at Lake St Lucia and Ndumo Game Reserve, respectively, and an estimated 3650 non-hatchling individuals for the province of KwaZulu-Natal. The data presented here will help inform crocodile management and population surveys in South Africa, where C. niloticus is an important apex predator that partitions aquatic resources and occasionally comes into conflict with human beings.
Jan G. Myburgh - One of the best experts on this subject based on the ideXlab platform.
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ontogenetic dependence of nile crocodile Crocodylus niloticus isotope diet to tissue discrimination factors
Rapid Communications in Mass Spectrometry, 2021Co-Authors: Stephan Woodborne, Jan G. Myburgh, Hannes Botha, David Huchzermeyer, Grant Hall, Albert MyburghAbstract:Rationale The diet of wild Nile crocodiles (Crocodylus niloticus) is difficult to assess because they are cryptic, nocturnal predators that are extremely sensitive to disturbance by observers, and stomach content analysis is challenging, especially in large specimens. Stable light isotope analysis provides a means of assessing their diet but diet-to-tissue discrimination factors have yet to be established for the species. Methods Isotope ratio (15 N/14 N and 13 C/12 C expressed as δ15 N and δ13 C) analyses of scutes, claws and blood of farmed crocodile of a range of sizes were compared with the isotope values of their lifelong diet, which comprises chickens from a single supplier. Results Systematic size dependence in the diet-to-tissue discrimination factors for scute collagen, scute keratin, and claw keratin, is described in regression relationships against the snout to vent length. Fixed values are presented for erythrocytes and blood plasma because blood was not sampled from juveniles. Conclusions The diet-to-tissue discrimination factors allow an assessment of the diet of wild crocodiles. The diet of crocodiles from Lake Flag Boshielo shows a clear ontogenic shift, as has been seen in other studies, and the results strongly indicate a dependence on the terrestrial food web rather than a fish diet. That this population may exploit a terrestrial diet highlights potential conflicts for conserving Nile crocodiles outside of protected areas.
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organochlorine pesticide bioaccumulation in wild nile crocodile Crocodylus niloticus fat tissues environmental influences on changing residue levels and contaminant profiles
Science of The Total Environment, 2021Co-Authors: Marc S Humphries, Jan G. Myburgh, Robert Campbell, Archibold Buahkwofie, Xander CombrinkAbstract:Abstract Biologically significant concentrations of organochlorine pesticides (OCPs) continue to be reported in wildlife populations and are of particular concern in species that occupy the highest trophic levels. Nile crocodiles (Crocodylus niloticus) are important apex predators occurring throughout much of tropical and subtropical sub-Saharan Africa, where they inhabit estuarine and freshwater habitats often impacted by contamination. In this study we examined pesticide residue accumulation in fat tissue from Nile crocodiles at Lake St Lucia, South Africa, where historically large quantities of OCPs have been used for agriculture and disease control. During 2019, we collected tail fat samples from wild (n = 21) and captive (n = 3) individuals to examine the influence of habitat, body size and sex on variations in bioaccumulation. The principal contaminant found was p,p′-DDE, a major persistent metabolite of DDT, which continues to be used in the region for combating malaria. Tissue p,p′-DDE concentrations in wild crocodiles (95–1200 ng g−1 ww) were significantly (p 0.70) to body length. Male (n = 14) and female (n = 7) wild crocodiles exhibited similar contaminant body burdens, however, total concentrations were substantially lower than those measured in the same population during 2016/2017. Marked differences in residue levels and profiles appear to reflect changes in food availability and dietary exposure associated with a shift in environmental conditions. These findings suggest that periods of environmental stress may be associated with enhanced toxicological risk in crocodiles. Additional work is needed to better understand contaminant accumulation and elimination mechanisms in crocodiles, and their potential effects on reproductive health.
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histological investigation of the nile crocodile Crocodylus niloticus phallic glans
South American Journal of Herpetology, 2020Co-Authors: Brandon C Moore, Herman B Groenewald, Jan G. MyburghAbstract:The male crocodylian phallus, an intromittent organ, transfers sperm to the female cloaca during reproduction. During copulation, the distal phallic glans inflates via blood-filled spongiform tissues; it enlarges into an elaborate shape that directly interacts with the female urodeum—the cloacal chamber that contains the female reproductive tract openings. Alas, the specific mechanics of crocodylian insemination and gamete transfer remain unclear. To that end, we investigated the gross and cellular morphology of the Nile crocodile (Crocodylus niloticus) glans characterizing tissues types and structural morphologies to better predict how these male tissues may interact with those of the female. We tracked blood flow from the descending aorta to the phallic glans by way of sulcus spermaticus-adjacent blood vessels. Utilizing an artificial inflation technique, we documented how the glans tissue shape changes with increased hydrostatic pressure in spongiform tissues including increases in height and width and the enlargement of a cup-like distal lumen. Sectioning the glans, we traced the decrease in dense collective tissues and the proliferation of inflatable tissues moving from proximal to distal. Concomitant with the development of the inflatable glans, we identified elastin-rich tissues around the inflatable glans regions and the deep sulcus spermaticus semen conduit. Together, these observations demonstrated the dynamic nature of the tissues, where collagen fibers supply mechanical strength and elastin fibers provide resilience and recoil. We hypothesize how these glans characteristics may interact with female tissues during copulation to increase the chance of successful gamete transfer.
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nile crocodile Crocodylus niloticus egg mass relative to egg component mass in unbanded and fertile eggs
Aquaculture, 2019Co-Authors: Geoffrey James Brown, Jan G. Myburgh, Patricia B C Forbes, J O NothlingAbstract:Abstract Crocodylus niloticus eggs are a useful starting point to study reproduction in this species. Using samples collected from a single farm during a single breeding season, the present research aimed to describe and compare the masses of unbanded and fertile eggs and their components. The clustering effect of clutch on egg and egg component mass was investigated, and the relationship between the mass of unbanded eggs and their components, together with the effect of possible confounding variables was explored. Estimated egg volume (ellipsoid volume) was strongly positively correlated with egg mass. A strong positive linear relationship existed between egg mass and the combined mass of the foetus and intra-abdominal yolk, as well as between egg mass and the isolated yolk-free foetal mass. If egg mass and incubation period were kept constant, foetal mass increased by 1.1 g for each gram that yolk decreased. The wet yolk and dried shell masses of fertile eggs were significantly lower than those of size-matched unbanded eggs. Clutch had a strong clustering effect on all component masses, particularly total egg mass and hatchling mass. Unbanded egg mass and its individual component masses tended to be similar within a clutch, however some variability existed which should not be discounted. The mass of an egg was strongly positively linearly correlated with the mass of each of its components. The period within the laying season an egg was laid had no effect on its mass nor the mass of any of its components, whereas the breeding pond in which the female resided did affect these measurements. The strong clustering effect of clutch on total egg mass and the masses of all egg components must be accounted for when selecting samples for future studies. The potential confounding effect of breeding pond of origin (which related to female size in the current study) should be considered, particularly where the age or size of females differ among ponds.
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Vertical transmission of microcystins to Nile crocodile (Crocodylus niloticus) eggs.
Toxicon : official journal of the International Society on Toxinology, 2017Co-Authors: Alukhethi Singo, Jan G. Myburgh, Peter N. Laver, Elizabeth A. Venter, Gezina Catharina Helena Ferreira, Gertruida M. Rösemann, C.j. BothaAbstract:Abstract Cyanobacteria or blue green algae are known for their extensive and highly visible blooms in eutrophic, stagnant freshwater bodies. Climate change and global warming have also contributed to a rise in toxic cyanobacterial blooms. One of the most important cyanobacteria is Microcystis aeruginosa, which can synthesize various microcystins that can affect the health of terrestrial and aquatic animals. Commercial Nile crocodile (Crocodylus niloticus) farming in South Africa is based on keeping breeders (adult males and females) in big dams on farms (captive-bred approach). Unfortunately, cyanobacterial blooms in the breeder dams are a concern to farm owners, managers and veterinarians. The main objectives of this research project were to determine if microcystins were present in the contents of crocodile eggs and the liver and yolk of dead hatchlings, and to determine if the reduced hatchability on commercial farms might be caused by these toxins. Furthermore, the concentration of microcystins in the breeder dam was monitored on a monthly basis spanning the ovulation and egg laying period. During the hatching season microcystin concentrations in unfertilised eggs, egg shell membranes and in the yolk and liver of dead hatchlings were determined using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Microcystins were detected in Nile crocodile egg and hatchling samples. Microcystin (MC-LR, MC-RR, MC-YR) concentrations in the crocodile egg and hatchling samples collected from clutches with a good hatching rate (≥90%) ranged between 0 and 1.76 ng g−1, with the highest concentration in the egg shell membranes. Microcystin concentrations in samples collected from clutches with a bad hatching rate (≤10%) ranged from 0 – 1.63 ng g−1 with the highest concentration detected in the hatchling yolk. However, the concentrations were probably underestimated as the percentage recovery from spiked samples was very low with the extraction method employed. Bayesian analysis suggests that the liver, yolk and unfertilised egg all have similar microcystin concentrations, while the membranes have (with moderate to high certainty) higher microcystin concentrations. There appears to be no difference in microcystin concentrations among good and bad clutches across all tissue types or within a specific tissue type, but due to the small sample size, it was not possible to determine whether microcystin affected the hatchability of Nile crocodile eggs. However, vertical transmission of microcystin variants to the Nile crocodile egg does occur and the possible implications for the survival of wild Nile crocodile populations should be ascertained.
Lutgarde Arckens - One of the best experts on this subject based on the ideXlab platform.
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gnrh immunoreactive centrifugal visual fibers in the nile crocodile Crocodylus niloticus
Brain Research, 2005Co-Authors: Monique Medina, J Reperant, D Miceli, Roger Ward, Lutgarde ArckensAbstract:Abstract Thin varicose centrifugal visual fibers, between 30–45 in number and displaying cGnRH-I immunoreactivity, were identified in Crocodylus niloticus . Approximately 80% of these fibers were also FMRF-amide-like immunoreactive. The cGnRH-I fibers extended from the preoptic region to the retina where they appeared to terminate in the external portion of the inner plexiform layer. The location of their neurons of origin could not be determined precisely following the intraocular injection of the retrograde axonal tracer RITC. Nevertheless, the presence of cGnRH-I-immunoreactive neurons exclusively within the complex comprising the terminal nerve and the septo-preoptic region, and of several retinopetal fibers labelled retrogradely with the axonal tracer at the septo-preoptic junction, indicates that the cGnRH-immunoreactive centrifugal visual system originates from within this complex.
Roger Ward - One of the best experts on this subject based on the ideXlab platform.
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gnrh immunoreactive centrifugal visual fibers in the nile crocodile Crocodylus niloticus
Brain Research, 2005Co-Authors: Monique Medina, J Reperant, D Miceli, Roger Ward, Lutgarde ArckensAbstract:Abstract Thin varicose centrifugal visual fibers, between 30–45 in number and displaying cGnRH-I immunoreactivity, were identified in Crocodylus niloticus . Approximately 80% of these fibers were also FMRF-amide-like immunoreactive. The cGnRH-I fibers extended from the preoptic region to the retina where they appeared to terminate in the external portion of the inner plexiform layer. The location of their neurons of origin could not be determined precisely following the intraocular injection of the retrograde axonal tracer RITC. Nevertheless, the presence of cGnRH-I-immunoreactive neurons exclusively within the complex comprising the terminal nerve and the septo-preoptic region, and of several retinopetal fibers labelled retrogradely with the axonal tracer at the septo-preoptic junction, indicates that the cGnRH-immunoreactive centrifugal visual system originates from within this complex.
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retinal projections in two crocodilian species caiman crocodilus and Crocodylus niloticus
Anatomy and Embryology, 1999Co-Authors: Y Derobert, Monique Medina, J Reperant, Roger Ward, J P Rio, M J Marchand, D MiceliAbstract:The retinal projections of Caiman crocodilus and Crocodylus niloticus were investigated by means of the orthograde axonal transport of either rhodamine β-isothiocyanate or tritiated proline. In these two species, each tracer revealed contralateral retinal projections to three hypothalamic regions (subventricular gray matter, nucleus suprachiasmaticus, and area optica hypothalami lateralis), five thalamic regions (nuclei ovalis, dorsolateralis anterior, ventrolateralis and ventrobasalis, and lateral geniculate complex, of which six subcomponents can be distinguished), six pretectal regions (nuclei posterodorsalis, lentiformis mesencephali, griseus tectalis, geniculatus pretectalis, area optica commissurae posterior and area optica pretectalis lateroventralis), six outermost layers of the optic tectum, and the nucleus opticus tegmenti. Weak ipsilateral retinal projections have been observed in two hypothalamic nuclei and in the nucleus opticus tegmenti. Comparative analysis with other data show that the contralateral retinal projections of crocodiles are considerably more reptilian than avian. Moreover, crocodiles share with birds an extremely poor contingent of ipsilateral retinal projections.
J Reperant - One of the best experts on this subject based on the ideXlab platform.
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gnrh immunoreactive centrifugal visual fibers in the nile crocodile Crocodylus niloticus
Brain Research, 2005Co-Authors: Monique Medina, J Reperant, D Miceli, Roger Ward, Lutgarde ArckensAbstract:Abstract Thin varicose centrifugal visual fibers, between 30–45 in number and displaying cGnRH-I immunoreactivity, were identified in Crocodylus niloticus . Approximately 80% of these fibers were also FMRF-amide-like immunoreactive. The cGnRH-I fibers extended from the preoptic region to the retina where they appeared to terminate in the external portion of the inner plexiform layer. The location of their neurons of origin could not be determined precisely following the intraocular injection of the retrograde axonal tracer RITC. Nevertheless, the presence of cGnRH-I-immunoreactive neurons exclusively within the complex comprising the terminal nerve and the septo-preoptic region, and of several retinopetal fibers labelled retrogradely with the axonal tracer at the septo-preoptic junction, indicates that the cGnRH-immunoreactive centrifugal visual system originates from within this complex.
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retinal projections in two crocodilian species caiman crocodilus and Crocodylus niloticus
Anatomy and Embryology, 1999Co-Authors: Y Derobert, Monique Medina, J Reperant, Roger Ward, J P Rio, M J Marchand, D MiceliAbstract:The retinal projections of Caiman crocodilus and Crocodylus niloticus were investigated by means of the orthograde axonal transport of either rhodamine β-isothiocyanate or tritiated proline. In these two species, each tracer revealed contralateral retinal projections to three hypothalamic regions (subventricular gray matter, nucleus suprachiasmaticus, and area optica hypothalami lateralis), five thalamic regions (nuclei ovalis, dorsolateralis anterior, ventrolateralis and ventrobasalis, and lateral geniculate complex, of which six subcomponents can be distinguished), six pretectal regions (nuclei posterodorsalis, lentiformis mesencephali, griseus tectalis, geniculatus pretectalis, area optica commissurae posterior and area optica pretectalis lateroventralis), six outermost layers of the optic tectum, and the nucleus opticus tegmenti. Weak ipsilateral retinal projections have been observed in two hypothalamic nuclei and in the nucleus opticus tegmenti. Comparative analysis with other data show that the contralateral retinal projections of crocodiles are considerably more reptilian than avian. Moreover, crocodiles share with birds an extremely poor contingent of ipsilateral retinal projections.