Chew, Shit Fun

Suspended animation has long fascinated scientists because of its great application potentials in fields ranging from medicine to space travel. Animals become inactive during suspended animation, with absolutely no intake of food and water, and hence producing minimal or no urine and faecal materials, for an extended period. They enter into a state of torpor, possibly slowing down the biological time in relation to the clock time. If suspended animation can be achieved in humans, surgeons would have more time to operate on patients during critical moments when the blood circulation stops, and the dream of long distance space travel can be realized. In nature, suspended animation is expressed in some adult animals undergoing hibernation or aestivation. ‘Aestivation’ is a loose term that signifies little more than an animal undergoing a state of torpor to survive arid conditions (except for aquatic aestivators like certain sponges and sea cucumbers) at high temperature, in many cases during summer. The term has been used to describe the listless state of endotherms, like ground squirrels and cactus mouse at the height of summer heat, and ectotherms, like amphibians and African lungfishes that make cocoons to encase themselves for weeks to more than a year during the hot dry season.

Giant clams are photosymbiotic molluscs, hosting Symbiodiniaceae dinoflagellates. Serving as an alternative model organism for ecophysiological studies within reef environments, giant clams differ from corals due to their anatomical complexity, with extracellular symbionts present in multiple organs. We aimed to determine if clams, under thermal stress, exhibit symbiont shuffling both at the organism level and across individual organs. Therefore, the fluted giant clam, Tridacna squamosa, was exposed to control and heat-stress temperatures of 26 and 30 ºC, respectively, for 45 days. Subsequently, the degree of bleaching was assessed through quantification of symbiont cells and chlorophyll-a loss via fluorometric detection and photometric analysis. The relative composition of Symbiodiniaceae ITS2 rDNA profiles across ten different organs was determined using metabarcoding by next-generation sequencing. Findings show that the outer mantle of heat-stressed clams lost approximately 30% of its symbionts and 45% of the chlorophyll-a content. Extensive shuffling took place at the organism level, with the downregulation of thermally-sensitive Durusdinium phylotype D4/D5, and upregulation of thermally-tolerant, homologous and generalist phylotypes belonging to Symbiodinium and Cladocopium genera. At the organ level, shuffling took place only in the outer mantle, the only organ directly exposed to light. The other organs did not undergo compositional changes in symbiont phylotypes and may potentially serve as symbiont reservoirs. These results illuminate the complexities of symbiont shuffling within an anatomically intricate organism, offering perspectives for other photosymbiotic reef organisms. Additionally, this study advances the knowledge regarding bleaching in giant clams, a relevant resource that has experienced substantial population declines.

In order to refine teaching styles and methods of assessing students' learning, it is important to realise the perceptions different schools hold about teaching and learning. Thus, this study was undertaken to compare students in the Bachelor of Science with Diploma in Education (Secondary) programme (PGDE) on their perceptions of the desirable characteristics of a "good" lecturer, their preferences of teaching methods and student assessment, their motives for taking the course and their learning styles employed. The results indicate that both groups of students were genuinely interested in the courses they enrolled in. Although there was a high degree of unanimity among students in their conception of a "good" lecturer and their preferred learning styles, the PGDE students preferred lecturers who were more expressive. In addition, the PGDE students were more independent in their learning than the BSC students. The findings of the present study may serve to kindle some genuine ideas among lecturers on how to improve the quality of teaching and learning in the University.

Nitrogen-deficient symbiotic dinoflagellates (zooxanthellae) living inside the fluted giant clam, Tridacna squamosa, need to obtain nitrogen from the host. Glutamine synthetase 1 (GS1) is a cytosolic enzyme that assimilates ammonia into glutamine. We determined the transcript levels of zooxanthellal GS1 (Zoox-GS1), which represented comprehensively GS1 transcripts of Symbiodinium, Cladocopium and Durusdinium, in five organs of T. squamosa. The outer mantle had significantly higher transcript level of Zoox-GS1 than the inner mantle, foot muscle, hepatopancreas and ctenidium, but the transcript ratios of Zoox-GS1 to zooxanthellal form II ribulose-1,5-bisphosphate carboxylase/oxygenase (Zoox-rbcII), which represented the potential of ammonia assimilation relative to the phototrophic potential, were comparable among these five organs. Based on transcript ratios of Zoox-GS1 to zooxanthellal Urease (Zoox-URE), the outer mantle had the highest potential of urea degradation relative to ammonia assimilation among the five organs, probably because urea degradation could furnish CO2 and NH3 for photosynthesis and amino acid synthesis, respectively, in the symbionts therein. The protein abundance of Zoox-GS1 was upregulated in the outer mantle and the inner mantle during illumination. Zoox-GS1 could catalyze light-enhanced glutamine formation using ammonia absorbed from the host or ammonia released through urea degradation in the cytoplasm. The glutamine produced could be used to synthesize other nitrogenous compounds, including amino acids in the cytoplasm or in the plastid of the dinoflagellates. Some of the amino acids synthesized by the symbionts in the inner mantle and foot muscle could be donated to the host to support shell organic matrix formation and muscle production, respectively.

The stinging catfish, Heteropneustes fossilis, can tolerate high concentrations of environmental ammonia. Previously, it was regarded as ureogenic, having a functional ornithine-urea cycle (OUC) that could be up-regulated during ammonia-loading. However, contradictory results indicated that increased urea synthesis and switching to ureotelism could not explain its high ammonia tolerance. Hence, we re-examined the effects of exposure to 30 mmol l–1 NH4Cl on its ammonia and urea excretion rates, and its tissue ammonia and urea concentrations. Our results confirmed that H. fossilis did not increase urea excretion or accumulation during 6 days of ammonia exposure, and lacked detectable carbamoyl phosphate synthetase I or III activity in its liver. However, we discovered that it could actively excrete ammonia during exposure to 8 mmol l–1 NH4Cl. As active ammonia excretion is known to involve Na+/K+-ATPase (Nka) indirectly in several ammonia-tolerant fishes, we also cloned various nkaα-subunit isoforms from the gills of H. fossilis, and determined the effects of ammonia exposure on their branchial transcripts levels and protein abundances. Results obtained revealed the presence of five nkaα-subunit isoforms, with nkaα1b having the highest transcript level. Exposure to 30 mmol l–1 NH4Cl led to significant increases in the transcript levels of nkaα1b (on day 6) and nkaα1c1 (on day 1 and 3) as compared with the control. In addition, the protein abundances of Nkaα1c1, Nkaα1c2, and total NKAα increased significantly on day 6. Therefore, the high environmental ammonia tolerance of H. fossilis is attributable partly to its ability to actively excrete ammonia with the aid of Nka.

Giant clams are animal-dinoflagellate associations found in Indo-Pacific reef ecosystems. The clam host obtains organic nutrients from phototrophic dinoflagellates of genera Symbiodinium, Cladocopium, and Durusdinium, which reside extracellularly as symbionts (alias zooxanthellae) in the luminal fluid of zooxanthellal tubules located mainly in the colourful outer mantle. The host also needs to supply the symbionts with inorganic carbon for photosynthesis. Symbiont photosynthesis can be impeded by inhibitors of vacuolar H⁺-ATPase (VHA) because the host possesses a carbon concentration mechanism consisting of VHA to facilitate the supply of CO₂(aq) to the symbionts. Here, we report that VHA was also expressed in dinoflagellates residing in the outer mantle of the fluted giant clam, Tridacna squamosa. Three complete cDNA coding sequences of VHA subunit B (VHA-B), one for each genus of dinoflagellate, had been obtained, and each sequence comprised 1482 bp, encoding a protein of 493 amino acids (~55 kDa). As these three sequences were highly similar, we could only design real-time PCR primers to quantify comprehensively zooxanthellae-VHA-B (Zoox-VHA-B) that represented VHA-B of all three genera of dinoflagellates. The outer mantle had the highest transcript level of Zoox-VHA-B among the three organs studied, and illumination led to a significant increase in the protein abundance of Zoox-VHA-B therein. Zoox-VHA-B was immunolocalized to intracellular vesicles, which could apparently align and fuse with the plasma membrane, in the symbiotic dinoflagellates. Overall, these results indicate that photosynthesizing symbionts could increase the capacity of H⁺ secretion through VHA-containing vesicles to promote the dehydration of luminal HCO3− and the absorption of CO₂(aq) during illumination.

Giant clams represent symbiotic associations between a host clam and its extracellular zooxanthellae. They are able to grow in nutrient-deficient tropical marine environments and conduct light-enhanced shell formation (calcification) with the aid of photosynthates donated by the symbiotic zooxanthellae. In light, there is a high demand for inorganic carbon (Ci) to support photosynthesis in the symbionts and light-enhanced calcification in the host. In this study, we cloned and characterized a host Carbonic Anhydrase 4 homolog (CA4-like) from the whitish inner mantle of the giant clam Tridacna squamosa. The full cDNA coding sequence of CA4-like consisted of 1,002 bp, encoding for 334 amino acids of 38.5 kDa. The host CA4-like was phenogramically distinct from algal CAs. The transcript level of CA4-like in the inner mantle was ~3-fold higher than those in the colorful outer mantle and the ctenidium. In the inner mantle, CA4-like was immunolocalized in the apical membrane of the seawater-facing epithelial cells, but absent from the shell-facing epithelium. Hence, CA4-like was positioned to catalyze the conversion of HCO3 − to CO2 in the ambient seawater which would facilitate CO2 uptake. The absorbed CO2 could be converted back to HCO3 − by the cytoplasmic CA2-like. As the protein abundance of CA4-like increased in the inner mantle after 6 or 12 h of light exposure, there could be an augmentation of the total CA4-like activity to increase Ci uptake in light. It is plausible that the absorbed Ci was allocated preferentially for shell formation due to the close proximity of the seawater-facing epithelium to the shell-facing epithelium in the inner mantle that contains only few zooxanthellae.