Journal Articles - UP - MSI
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- Genetic variation in Symbiodinium isolates from giant clams based on random-amplified-polymorphic DNA (RAPD) patternsBaillie, B. K.; Belda-Baillie, C. A.; Silvestre, V.; Sison, M.; Gomez, A. V.; Gomez, E. D.; Monje, V. (Springer, 2000-06-16)We have compared the random-amplified-polymorphic DNA (RAPD) patterns of Symbiodinium isolates from seven species of giant clams to investigate the large genetic variation that we previously reported for this group of dinoflagellate symbionts using allozyme analysis. Comparisons of 163 RAPD characters by unweighted pair-group arithmetic-average cluster analysis (UPGMA) corroborate our previous findings that giant clams associate with a large number of genetically distinguishable algal symbionts, and that the isolates from a single Tridacna gigas individual form a group of closely related algae. However, the overall topology of the UPGMA tree constructed from RAPD data differs from that of the previous allozyme data, indicating that the combined data we have collected to date are insufficient to accurately infer phylogenetic affiliations between the isolates studied. Comparisons of our data set with those published for strains of Gymnodinium catenatum, a toxic dinoflagellate with a sexual life stage, shows that our isolates are even more diverse. Algal isolates from giant clams have a level of RAPD variation comparable to organisms that are able to undergo sexual recombination. This study demonstrates the sensitivity of the RAPD technique in detecting genetic diversity in this group of algae, and highlights the need for more comparative data for the major clades of Symbiodinium.
- Characterization of the hidden break in giant clam 28S ribosomal RNATan, Keana; Conaco, Cecilia (Oxford University Press, 2021-09)The molluscan 28S ribosomal RNA (rRNA) naturally cleaves into two fragments of similar size as 18S rRNA. This phenomenon, known as the hidden break, has been described in many other protostome species. Here, we characterize the 28S rRNA hidden break region in seven giant clam species, Tridacna gigas, T. derasa, T. maxima, T. noae, T. crocea, Hippopus hippopus and H. porcellanus. We confirm that the break consistently occurs in giant clams and is observed in all tissues and developmental stages. The region of the giant clam 28S rRNA break is located at a position homologous to the well-characterized 28S rRNA break in insects. High AU content and a stem–loop secondary structure in the region may contribute to fragmentation of the 28S rRNA molecule. An awareness of the existence of the hidden break in molluscs, such as the giant clams, which are emerging systems for understanding how environmental change affects life in the ocean, will facilitate progress of RNA sequencing-based analyses that currently rely on standard RNA profiles as a measure of sample integrity.The authors would like to thank Dr Ronnie Estrellada of the Semirara Marine Laboratory and Hatchery for generously providing giant clam samples, the Bolinao Marine Laboratory for providing access to the Silaqui Island Giant Clam Ocean Nursery and Niño Dan Posadas for sharing sponge RNA. This work was supported by a grant to C.C. from the Philippine Council for Agriculture, Aquaculture and Natural Resources Research and Development of the Department of Science and Technology (grant no. QMSR-MRRD-MEC-314-1545).
- Diversity of dinoflagellate symbionts (zooxanthellae) in a host individualCarlos, A. A.; Baillie, B. K.; Maruyama, T. (Inter-Research Science Center, 2000)Zooxanthellae are phototrophic dinoflagellates that exist in symbiosis with a variety of marine invertebrates. The traditional view of zooxanthella-invertebrate symbioses suggests that individual hosts harbor taxonomically homogeneous symbiont populations. To assess the diversity of the zooxanthella assemblage inhabiting an individual host, zooxanthellae from 6 species of clam (Tridacna gigas, T. squamosa, T. crocea, Hippopus hippopus, H. porcellanus and Corculum cardissa) and 1 species of sea anemone (Aiptasia sp.) were studied using temperature-gradient gel electrophoresis (TGGE), coupled with polymerase chain reaction (PCR) using zooxanthella-specific primers that were designed to target hypervariable regions of the small subunit ribosomal RNA (ssrRNA) gene. Results revealed that 1 clam may harbor 2 or more genotypically distinct zooxanthellae, with 1 or more dominant taxa occurring at a time. The clams studied associated with at least 4 zooxanthellar taxa. Nucleotide sequencing of the TGGE bands and phylogenetic reconstruction revealed that the zooxanthellar taxa in clams were Symbiodinium spp.; 1 was identical to previously cultured clam symbiont isolates, 1 appeared identical to a previously studied unculturable clam symbiont, and the other 2 clams represented novel strains of Symbiodinium. Individual Aiptasia sp. harbored only 1 zooxanthellar taxon, which had a ssrRNA sequence identical to that of S. pulchrorum, previously isolated from Aiptasia pulchella. This study has shown that individual tridacnid and cardiid clams can harbor heterogeneous zooxanthellae.
- Phosphate acquisition in the giant clam-zooxanthellae symbiosisBelda, C. A.; Yellowlees, D. (Springer, 1995-12)The effect of phosphate on the giant clam Tridacna gigas and on its symbiotic dinoflagellate Symbiodinium sp. was compared with that on cultured Symbiodinium sp. originally isolated from the same clarn species. Incubation of whole clams in elevated phosphate (10 μM) reduced their capacity for phosphate uptake, but the uptake capacity of the clam's zooxanthellae population was not influenced. In addition, there was no change in the zooxanthellae density and the N:P ratio, of these algae. On the other hand, cultured zooxanthellae were influenced by the phosphate regimen of their culture medium. Compared with controls (0 μM P), addition of 10 μM phosphate to the culture medium caused an increase of 100% in cell density and decreases of 50% in the N:P ratio, and 80% in the phosphate-uptake capacity of the zooxanthellae. Zooxanthellae freshly isolated from the clams exhibited properties similar to those of zooxanthellae cultured in the absence of phosphate. These results demonstrate that the zooxanthellae population of T. gigas have limited access to the inorganic phosphate in sea water and the phosphate reserves within the animal host.
- Variation in epibiont communities among restocked giant clam species (Cardiidae: Tridacninae) and across different habitat typesde Guzman, Ian Joseph A.; Cabaitan, Patrick C.; Hoeksema, Bert W.; Sayco, Sherry Lyn G.; Conaco, Cecilia (Springer, 2023-07-07)Giant clam shells provide a solid substrate for various species of epibionts. Yet, it is not well known how epibiont communities vary among populations of different giant clam species and in giant clams restocked in different habitat types. Here, we examined differences in the epibiont communities of three species of giant clams with different shell morphology (Tridacna gigas, Tridacna derasa, and Hippopus hippopus), and characterized the epibiont communities on T. gigas from three different habitat types (sandy reef flat, seagrass bed, and coral reef). Tridacna gigas had higher species richness, abundance, and cover of epibionts compared to the other two species. Tridacna gigas in coral reef habitat also displayed higher species richness and cover of sessile epibionts, while the same species in the sandy reef flat had higher species richness and abundance of mobile epibionts. Epibiont communities were more variable across habitat types than among different giant clam species restocked in a similar area. Differences in abundance of Trochus sp., Pyramidella sp., and crustose coralline algae contributed to the variability in epibiont communities among the giant clam species and across habitats. A few taxa were observed only on specific giant clam species and sites. For instance, Diadema sp. and Echinometra sp. were found only on T. gigas, and Diadema sp. was present only in the sandy reef flat. Both the complexity of the giant clam shells and habitat type contribute to differences in associated epibiont communities. This further emphasizes the ecological importance of giant clams as habitats for other invertebrates.The authors acknowledge Jun Castrence and the staff of Bolinao Marine Laboratory for assistance with field work. We also acknowledge the assistance of Edwin Dumalagan with coral and algae identification, Timothy Quimpo for his assistance and advice on statistical analysis, and Elizabeth Gomez for her assistance in generating the map of study sites. Lastly, we would like to thank members of the Coral Reef Ecology Laboratory (CoRE) for their helpful comments and suggestions on the study. This study was supported by a grant from the Philippine Council for Agriculture, Aquatic, and Natural Resources Research and Development of the Department of Science and Technology to PCC and CC (QMSR-MRRD-MEC-314-1542) and a Department of Science and Technology ASTHRDP Scholarship and University of the Philippines Marine Science Institute Thesis Writing Grant 2020 to ID. We thank the reviewers for the suggestions that helped improve our paper.
- Status of giant clam resources of the PhilippinesJuinio, Marie Antoinette R.; Meñez, Lambert Anthony B.; Villanoy, Cesar L.; Gomez, Edgardo D. (Oxford University Press (OUP), 1989-11-01)Field surveys were conducted to determine distribution and abundance of giant dam resources in the Philippines. All seven known species of giant clams were recorded with Tridacna crocea, T. maxima and T. squamosa occurring the most frequently. The larger species T. derasa, T. gigas, Hippopus hippopus and H. porcellanus were relatively rare. The reduction of giant dam stocks in the Philippines is due to the uncontrolled exploitation of this resource which is primarily gathered for shellcraft and as supplementary diet in coastal villages.
- Passive greenhouse heating, recirculation, and nutrient addition for nursery phase Tridacna gigas: Growth boost during winter monthsBraley, Richard D.; Sutton, David; Mingoa, S. Suzanne M.; Southgate, Paul C. (Elsevier, 1992-11)The impetus for this study was winter-related mortality of juvenile Tridacna gigas along Australia's Great Barrier Reef. Heating nursery tank water by passive solar heating in a greenhouse and the addition of dissolved inorganic nitrogen (DIN) was assessed for effect on the growth and survival of cultured juvenile clams. Two age classes of T. gigas were used, with means of 1.2 cm and 17.0 cm shell length. Treatments consisted of nutrient-spikes of 20 μ M and 40 μ M ammonium chloride daily or on alternate days, plus s spike of 2.3 μ M phosphate once per week vs. controls without nutrient addition. Three rearing systems were used: (1) recirculating water enclosed in a greenhouse; (2) flow-through water enclosed in a greenhouse; (3) flow-through water with ambient conditions. In the older clams growth in weight was best in system 2, while growth in shell length (SL) was best in system 1, and DIN treatments significantly increased growth compared with controls. In the younger clams, growth in SL was best in system 1. DIN treatments produced significantly greater growth than controls, but there was no difference between 20-μ M and 40-μ M treatments. Survival was 100% for larger clams but for smaller clams mean survival was highest overall in system 1, while 20-μ M DIN treatments within systems produced the best overall survival. The highest levels of DIN in the nursery tanks were found in the 40-μ M DIN treatments, particularly in system 1. The wet tissue weight/shell length ratio for 40-μ M DIN treatments was highest in system 1 and decreased in systems 2 and 3, while controls were similar. Dry shell weight/shell length was highest in the 40-μ M DIN treatment over the control in system 1 only. The zooxanthellae index (no. of algal cells/g clam) was significantly higher in the 40-μ M DIN treatment than in the control in all three systems. Biochemical analysis of whole animals showed higher carbohydrate content in system 2 and in treatments receiving 20 μ M DIN. Tissue protein content did not differ significantly between systems but increased with increasing nutrient concentration. Lipid content was highest in system 1 and decreased with increasing nutrient concentration. Tissue water content of clams at the 20-μ M DIN level was lower than clams in other treatments, indicating superior condition. The combination of passive solar heating, recirculated water, and nutrient addition for the giant clam land nursery phase opens possibilities for culture of this tropical bivalve in subtropical zones or in the tropics distant from the ocean.
- Fishing mortality rates of giant clams (Family Tridacnidae) from the Sulu Archipelago and Southern Palawan, PhilippinesVillanoy, Cesar L.; Juinio, Antoinette R.; Meñez, Lambert Anthony (Springer, 1988-05)Average size frequency distributions of Tridacna squamosa, T. gigas, Hippopus hippopus and H. porcellanus harvested from the Sulu Archipelago and Southern Palawan areas from 1978–1985 were derived from export records and a warehouse inventory of giant clam shells. Average species mortality rates (Z) were estimated and were used to approximate average fishing mortality rates (F) over the period 1978–1985. Crude estimates of exploitation rates (F/Z) indicate that populations of these species are already overexploited. These findings have serious implications in view of the fact that the Sulu Archipelago and Southern Palawan are thought to be the last strongholds of giant clams in Philippine waters.