Biological effects of salinity gradient reversals in a southeast African estuarine lake

St Lucia Lake on the north coast of Natal, South Africa, has an area of 325 km² and is the largest estuarine complex in Africa. It consists of a 20 km tidal channel, averagingca. 400 m in width, linking the sea with the non-tidal lake which is H-shaped with a maximum length ofca. 40 km and width ofca. 20 km. Except during flood periods the depth of the lake does not exceed 2 m. The salinity gradient depends on evaporation, the configuration of the mouth and on the input of fresh water from four rivers which discharge into the northern and western areas of the lake. If fresh water input is high, the lake and much of the channel may be fresh. An intermediate stage features a normal salinity gradient while a third stage shows a reversed salinity gradient with salinities in excess of 100‰ in the upper reaches of the system. Changing salinities have marked effects on the biota. Aquatic macrophytes show cycles of appearance and disappearance depending on salinity tolerance and the presence of dormant stages. The resident benthic faunal species go through cycles of range expansion and contraction depending on prevailing salinities and recolonisation by dispersal phases. To date salinities in the southern part of the lake have approached, but not exceeded, lethal levels and this has therefore acted as a reservoir area. Catchment degradation and water abstraction are anticipated to exacerbate future salinity extremes. This has resulted in concern for the long term viability of this Ramsar site which has major southern African populations of hippopotamus and crocodile, provides breeding sites for South African Red Data water bird species and plays an important nursery role for marine fish and penaeid prawns.     

QTL mapping for two commercial traits in farmed saltwater crocodiles (Crocodylus porosus)

The recent generation of a genetic linkage map for the saltwater crocodile (Crocodylus porosus) has now made it possible to carry out the systematic searches necessary for the identification of quantitative trait loci (QTL) affecting traits of economic, as well as evolutionary, importance in crocodilians. In this study, we conducted genome‐wide scans for two commercially important traits, inventory head length (which is highly correlated with growth rate) and number of scale rows (SR, a skin quality trait), for the existence of QTL in a commercial population of saltwater crocodiles at Darwin Crocodile Farm, Northern Territory, Australia. To account for the uncommonly large difference in sex‐specific recombination rates apparent in the saltwater crocodile, a duel mapping strategy was employed. This strategy employed a sib‐pair analysis to take advantage of our full‐sib pedigree structure, together with a half‐sib analysis to account for, and take advantage of, the large difference in sex‐specific recombination frequencies. Using these approaches, two putative QTL regions were identified for SR on linkage group 1 (LG1) at 36 cM, and on LG12 at 0 cM. The QTL identified in this investigation represent the first for a crocodilian and indeed for any non‐avian member of the Class Reptilia. Mapping of QTL is an important first step towards the identification of genes and causal mutations for commercially important traits and the development of selection tools for implementation in crocodile breeding programmes for the industry.     

Cloning and sequencing of complete tau-crystallin cDNA from embryonic lens of Crocodylus palustris

τ-Crystallin is a taxon-specific structural protein found in eye lenses. We present here the cloning and sequencing of complete τ-crystallin cDNA from the embryonic lens ofCrocodylus palustris and establish it to be identical to the α-enolase gene from non-lenticular tissues. Quantitatively, the τ-crystallin was found to be the least abundant crystallin of the crocodilian embryonic lenses. Crocodile τ-crystallin cDNA was isolated by RT-PCR using primers designed from the only other reported sequence from duck and completed by 5′- and 3′-rapid amplification of cDNA ends (RACE) using crocodile gene specific primers designed in the study. The complete τ-crystallin cDNA of crocodile comprises 1305 bp long ORF and 92 and 409 bp long untranslated 5′- and 3′-ends respectively. Further, it was found to be identical to its putative counterpart enzyme α-enolase, from brain, heart and gonad, suggesting both to be the product of the same gene. The study thus provides the first report on cDNA sequence of τ-crystallin from a reptilian species and also re-confirms it to be an example of the phenomenon of gene sharing as was demonstrated earlier in the case of peking duck. Moreover, the gene lineage reconstruction analysis helps our understanding of the evolution of crocodilians and avian species.     

Comparative NMR studies of diffusional water permeability of red blood cells from different species: XVIII platypus (Ornithorhynchus anatinus) and saltwater crocodile (Crocodylus porosus)

As part of a programme of comparative measurements of P _d (diffusional water permeability) the RBCs (red blood cells) from an aquatic monotreme, platypus (Ornithorhynchus anatinus), and an aquatic reptile, saltwater crocodile (Crocodylus porosus) were studied. The mean diameter of platypus RBCs was estimated by light microscopy and found to be ～6.3 μm. P _d was measured by using an Mn²⁺‐doping 1H NMR (nuclear magnetic resonance) technique. The P _d (cm/s) values were relatively low: ～2.1×10^?3 at 25°C, 2.5×10^?3 at 30°C, 3.4×10^?3 at 37°C and 4.5 at 42°C for the platypus RBCs and ～2.8×10^?3 at 25°C, 3.2×10^?3 at 30°C, 4.5×10^?3 at 37°C and 5.7×10^?3 at 42°C for the crocodile RBCs. In parallel with the low water permeability, the E _a,d (activation energy of water diffusion) was relatively high, ～35 kJ/mol. These results suggest that “conventional” WCPs (water channel proteins), or AQPs (aquaporins), are probably absent from the plasma membranes of RBCs from both the platypus and the saltwater crocodile.     

洗胃法在鳄蜥食性研究中的应用

为了研究洗胃法是否适用于鳄蜥（Shinisaurus crocodilurus）的食性研究,2006年8～9月我们在广东罗坑省级自然保护区,通过投喂食物,然后再冲洗的方法来检验洗胃法的冲洗效果。结果显示洗胃法对成体和亚成体鳄蜥的总洗出率均高于99．30％,食物个体数的洗出率均高于90．83％,投喂的12种食物都能被洗出。观察发现洗胃之后,对鳄蜥的正常生活没有影响。鳄蜥吃进的实验食物中,未洗出的食物大小与鳄蜥的体长、头宽、体重不相关;食物的洗出效率与鳄蜥的体长、头宽、体重不相关。成体、亚成体洗出和未洗出的食物大小均存在显著差异。未被洗出的食物个体在12种食物中不是随机分布的,体积大的食物比体积小的食物容易被洗出。研究表明,洗胃法适用于鳄蜥的食性研究,并且效果较好。     

Reptilian transferrins: evolution of disulphide bridges and conservation of iron-binding center

Transferrins, found in invertebrates and vertebrates, form a physiologically important family of proteins playing a major role in iron acquisition and transport, defense against microbial pathogens, growth and differentiation. These proteins are bilobal in structure and each lobe is composed of two domains divided by a cleft harboring an iron atom. Vertebrate transferrins comprise of serotransferrins, lactoferrins and ovotransferrins. In mammals serotransferrins transport iron in physiological fluids and deliver it to cells, while lactoferrins scavenge iron, limiting its availability to invading microbes. In oviparous vertebrates there is only one transferrin gene, expressed either in the liver to be delivered to physiological fluids as serotransferrin, or in the oviduct with a final localization in egg white as ovotransferrin. Being products of one gene sero- and ovotransferrin are identical at the amino-acid sequence level but with different, cell specific glycosylation patterns. Our knowledge of the mechanisms of transferrin iron binding and release is based on sequence and structural data obtained for human serotransferrin and hen and duck ovotransferrins. No sequence information about other ovotransferrins was available until our recent publication of turkey, ostrich, and red-eared turtle (TtrF) ovotransferrin mRNA sequences [Ciuraszkiewicz, J., Olczak, M., Watorek, W., 2006. Isolation, cloning and sequencing of transferrins from red-eared turtle, African ostrich and turkey. Comp. Biochem. Physiol. 143 B, 301-310]. In the present paper, ten new reptilian mRNA transferrin sequences obtained from the Nile crocodile (NtrF), bearded dragon (BtrF), Cuban brown anole (AtrF), veiled and Mediterranean chameleons (VtrF and KtrF), sand lizard (StrF), leopard gecko (LtrF), Burmese python (PtrF), African house snake (HtrF), and grass snake (GtrF) are presented and analyzed. Nile crocodile and red-eared turtle transferrins have a disulphide bridge pattern identical to known bird homologues. A partially different disulphide bridge pattern was found in the Squamata (snakes and lizards). The possibility of a unique interdomain disulphide bridge was predicted for LtrF. Differences were found in iron-binding centers from those of previously known transferrins. Substitutions were found in the iron-chelating residues of StrF and TtrF and in the synergistic anion-binding residues of NtrF. In snakes, the transferrin (PtrF, HtrF and GtrF) N-lobe "dilysine trigger" occurring in all other known transferrins was not found, which indicates a different mechanism of iron release.     

Steneosaurus edwardsi (Thalattosuchia: Teleosauridae), the largest known crocodylomorph of the Middle Jurassic

Teleosaurids were a clade of marine crocodylomorphs that were globally distributed during the Jurassic Period. They evolved a wide range of body sizes, from small (～2–3 m) to very large (> 9 m). Until now, the largest known Middle Jurassic teleosaurid was ‘Steneosaurus’ obtusidens, from the Oxford Clay Formation of the UK. Here, we re‐examine a very large Oxford Clay specimen (ilium, ischium, and femur) that had been tentatively attributed to ‘S.’ obtusidens. Based on comparative anatomical study with the ‘S.’ obtusidens holotype and referred specimens of Steneosaurus edwardsi and Steneosaurus leedsi, we conclude that this very large individual actually pertains to S. edwardsi. Based on comparisons with the Machimosaurus mosae neotype (which has a complete femur and skeleton), we estimate a total length in excess of 7 m for this large S. edwardsi individual, making it the largest known Middle Jurassic teleosaurid. Therefore, along with the closely related genus Machimosaurus, this clade of large‐bodied Middle–Late Jurassic teleosaurids were the largest species during the first 100 million years of crocodylomorph evolution. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●● , ●●–●●.     

广东罗坑自然保护区鳄蜥夏季生境特征

2005年6—8月,在广东省罗坑自然保护区对36处鳄蜥的生境特征进行了研究。采用样线调查法,在保护区内鳄蜥分布区随机选取了30条溪沟进行调查,对每处有鳄蜥分布的生境测量了15个相关的生态因子。通过主成分分析发现,回水塘长度和宽度、水源距离、水流速度、栖枝高度、栖枝直径、干扰距离、植被类型、植被盖度等9个生态因子对鳄蜥的生境选择有显著影响,而回水塘底质组成、回水塘水深、栖枝枯活状况、栖枝角度、溪沟类型和溪沟坡向6个生态因子的影响不显著。鳄蜥偏好的生境可归结为回水塘长度、宽度中等(均为1.0—2.0m),有位于水源正上方的栖枝,水流速度缓慢,栖枝高度0.5—1.0m、栖枝直径≤1.00cm,干扰距离>500m,植被类型为常绿阔叶林、植被盖度>60%的生境。建议提高当地居民的保护意识,重点保护水源林和溪沟两侧的植被。     

Natal origin and dispersal of problem saltwater crocodiles in the Darwin Harbor,Australia

Management programs that successfully recovered wild saltwater crocodile (Crocodylus porosus) populations in the Northern Territory of Australia did so with an expanding commitment to maintaining public safety. One aspect of the program is the ongoing removal of resident and immigrant crocodiles within Darwin Harbor (since 1979), the main urban center. We determined the likely sources of crocodiles caught as problem animals between 2015–2017 by comparing recently developed methods for population assignment. Depending on the assignment model used, we estimated that between 30% and 50% of crocodiles in Darwin Harbor originated from the Adelaide and Mary rivers, and the Kakadu region east of Darwin, and between 20% and 30% of crocodiles originated from the Finniss, Reynolds, and Daly rivers southwest of Darwin. Saltwater crocodiles occur at particularly high densities in these catchments. The remainder came from a mixture of different sources across the Northern Territory. The most common animals captured were immature (150–180 cm) males that have traveled 100–200 km. We did not identify any relationships between the distance from the inferred origin to Darwin Harbor and the size and sex of the crocodiles, or the year of capture. The targeted removal of crocodiles from specific sites such as Darwin Harbor, near where most people live, improves public safety in the highest risk areas, without compromising abundant source populations in most areas.