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Three-dimensional charts showing clam distribution and substrate profile of two replicate field grids, A and B. Spikes in upper chart represent clam positions.
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Aquaculture has been the traditional focus of tridacnid giant clam research whereas their ecology and behaviour have received much less attention. This study was based on the observation that juvenile fluted giant clams (Tridacna squamosa), when evenly distributed in a tank, will move and aggregate over time. We observed movement in clams ranging f...
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... was higher in the live clam run (0.2087± 0.0137) than the simulations (p b 0.001). Random walk (−0.1120± 0.0229) resulted in less clumped distribution than random distribution (0.0276 ± 0.0111, p b 0.001). The field grids also had higher mean CLUMPY results compared to the tank grids. Substrate profiles of two field grids are illustrated in Fig. 6, with respective clam occur- rences represented by sharp peaks on the surface plots above them. No correlation was found between the ...
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Our study provides evidence that, in addition to diel vertical migration, zooplankton residing at >300-m depth during the day perform high-frequency, vertical migrations due to light modulation by clouds. Using a water-following framework and measurements and modeling of the twilight zone light field, we isolated the detailed phototact...
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... This is related to the decrease of the filtration rates of bivalve species based on the stress intensity . Similarly, there was a reduction in fluorescent intensities from NP-PMMA collected on the foot tissues at an exposure concentration of 25 mg/L (Fig. 4, B, iii), which could be explained based on the continuous loss of surface-adhered NPs on the foot during dragging movement (Huang et al., 2007). However, when the exposure time was extended, significant accumulations of NPs occurred on the foot tissues as well (Fig. 3, A and B, iii). ...
Plastic products have become an integral part of our life. A widespread usage, high stability, uncontrolled disposal and slow degradation of plastics in the environment led to the generation and accumulation of nanoparticles of polymers (NPs) in the marine environment. However, little is known about the aggregation, consumption and distribution of NPs from common polymers such as polyvinyl chloride (NP-PVC) and polymethyl methacrylate (NP-PMMA), inside marine animal physiologies. In the current study, two types of polymers (PVC and PMMA) × four exposure concentrations (1, 5, 15 and 25 mg/L) × four times (4, 8, 12 and 24 h) exposure studies were conducted to understand the consumption and distribution of luminescent NP-PVC (98.6 ± 17.6 nm) and NP-PMMA (111.9 ± 37.1 nm) in R. philippinarum. Under laboratory conditions, NP-PVC showed a higher aggregation rate than NP-PMMA in seawater within a period of 24 h. Aggregations of NPs increased with an increase in initial NP concentrations, leading to significant settling of nanoparticles within 24 h exposure. Such aggregation and settling of particles enhanced the consumption of NPs by bottom-feeding R. philippinarum at all exposure concentrations during 4 h exposure. More interestingly, NP-PVC and NP-PMMA were seen in high amounts in both liver and gills (22.6 % - 29.1 %) of the clams. Furthermore, NP-PVC was detected in most organs of R. philippinarum as compared to NP-PMMA. This study demonstrates that different polymers distribute and accumulate differently in the same biological model under laboratory exposure conditions based on their chemical nature.
... Lack of behavioural response towards conspecific cues 387Mytilus edulis did not show any behavioural change in response to conspecific cues, in 388 accordance with previous work on the effect of conspecific cues on M. edulis aggregation 389 patterns(Commito et al., 2016). These observations are, however, in contrast with previous 390 studies which showed that positive chemotaxis was the main driver of conspecific aggregation 391(Huang et al., 2007) and in particular in M. edulis (De Vooys, 2003). These 392 discrepancies may, however, be related to (i) potential behavioural divergence in M. edulis 393 between those living on the bottom of a concrete ditch with running seawater or on beach 394 groynes as seen in Netherlands (De Vooys, 2003) with those living on natural rocky shores 395 habitats as seen in France (present work) and/or (ii) the presence of a seasonal component in 396 the behavioural response of M. edulis to conspecific cues (De Vooys, 2003). ...
The massive contamination of the environment by plastics is an increasing global scientific and societal concern. Knowing whether and how these pollutants affect the behaviour of keystone species is essential to identify environmental risks effectively. Here, we focus on the effect of plastic leachates on the behavioural response of the common blue mussel Mytilus edulis, an ecosystem engineer responsible for the creation of biogenic structures that modify the environment and provide numerous ecosystem functions and services. Specifically, we assess the effect of virgin polypropylene beads on mussels’ chemotactic (i.e. a directional movement in response to a chemical stimulus) and chemokinetic (i.e. a non-directional change in movement properties such as speed, distance travelled or turning frequency in response to a chemical stimulus) responses to different chemical cues (i.e. conspecifics, injured conspecifics and a predator, the crab Hemigrapsus sanguineus). In the presence of predator cues, individual mussels reduced both their gross distance and speed, changes interpreted here as an avoidance behaviour. When exposed to polypropylene leachates, mussels moved less compared to control conditions, regardless of the cues tested. Additionally, in presence of crab cues with plastic leachates, mussels significantly changed the direction of movement suggesting a leachate-induced loss of their negative chemotaxis response. Taken together, our results indicate that the behavioural response of M. edulis is cue-specific and that its anti-predator behaviour as well as its mobility are impaired when exposed to microplastic leachates, potentially affecting the functioning of the ecosystem that the species supports.
... The donation of amino acids from the symbionts to the host could support shell formation (Teh et al., 2021), which needs to synthesize a proteinaceous matrix for CaCO 3 deposition (Greenfield et al., 1984). The foot muscle is instrumental to lateral movement (Stasek, 1962;Huang et al., 2007), and its tip contains a concentrated population of coccoid dinoflagellates (Poo et al., 2020). Ammonia absorbed by symbionts in the foot muscle can be assimilated into amino acids, which can be shared with the host for muscle production (Teh et al., 2021). ...
Giant clams harbor dinoflagellates generally of the three genera (Symbiodinium, Cladocopium, and Durusdinium) of phototrophic Symbiodiniaceae. Coccoid dinoflagellates (alias zooxanthellae) are found mainly inside zooxanthellal tubules located in the colorful outer mantle. The symbionts need to obtain carbon, nitrogen and phosphorus from the host for growth and metabolism. The host can absorb exogenous ammonia through the ctenidium and assimilate it into glutamine. Although the host does not normally excrete ammonia, its hemolymph contains only low concentrations of ammonia, indicating that the symbionts can absorb and recycle the ammonia produced metabolically by the host. In this study, we had obtained from the outer mantle of the giant clam, Tridacna squamosa, three major ammonium transporter 2 (AMT2) sequences, one each for Symbiodinium spp. (Symb-AMT2), Cladocopium spp. (Clad-AMT2), and Durusdinium spp. (Duru-AMT2), which comprised 1341 bp, 1308 bp, and 1296 bp, respectively. The respective deduced amino acid sequences contained 447 (~ 46.5 kDa), 436 (~ 45.5 kDa), and 432 (~ 45.0 kDa) residues. Phenogramic and sequence similarity analyses confirmed that these sequences were derived from dinoflagellates. Zooxanthellae-AMT2 (Zoox-AMT2), which represented comprehensively AMT2 of Symbiodinium spp., Cladocopium spp., and Durusdinium spp. was localized at the dinoflagellates’ plasma membranes, indicating that it could partake in the absorption of ammonia from the luminal fluid of the zooxanthellal tubules. Zoox-AMT2 expression was detected in the outer mantle, inner mantle, foot muscle, hepatopancreas and ctenidium of T. squamosa, indicating that the coccoid dinoflagellates residing in all five organs had the potential of ammonia absorption. The outer mantle had the highest transcript level of Zoox-AMT2, and illumination upregulated the protein abundance of Zoox-AMT2 therein. Therefore, it can be deduced that the coccoid dinoflagellates residing in the outer mantle could augment the potential of ammonia absorption in alignment with photosynthesis as the assimilation of ammonia required an increased supply of carbon chains.
... Vicose & Chou, 1999;Huang, Todd & Guest, 2007;Ling et al., 2008;Neo et al., 2009;Sim et al., 2018). Subsequent studies on the populations of giant clams in Singapore revealed that current low densities and scattered distributions are likely to impede any natural recovery of local stocks (Guest et al., 2008;Neo & Todd, 2012a;. ...
Giant clam populations in Singapore are endangered due to historical exploitation, habitat loss, and sediment pollution.
Transplanting cultured giant clams onto reefs is a potential conservation strategy. This study examined the growth and survival of three initial size classes (50.0–60.0 mm, 60.1–70.0 mm, >70 mm) of cultured juvenile fluted giant clams, Tridacna squamosa , transplanted to three reef sites under two caging treatments (caged and uncaged).
After 145 days, there was no significant difference in clam survival within the size classes and within caging treatments across reef sites, even though environmental conditions varied greatly between sites. However, there was a significant effect of initial size class on T. squamosa survival, with higher survival with increasing size class (50.0–60.0 mm: 11.1%; 60.1–70.0 mm: 34.1%; >70.0 mm: 46.9%).
Clams in caged treatments had significantly lower survival (16.7%) than uncaged clams (43.1%), likely due to biofouling atop caged treatments reducing light availability. Growth rates in the caged treatment (2.2 ± SD 1.8 mm month ⁻¹ ) were also lower than those in the uncaged treatment (3.9 ± SD 2.2 mm month ⁻¹ ).
By optimizing transplant procedures for Singapore's turbid reef conditions, T. squamosa restocking efforts could play an important role in boosting local population numbers to facilitate natural recovery.
... Tettelbach (2017) reports an increase in horizontal movement for the bivalve Mercenaria mercenaria in response to changes in animal density but also in the presence of other individuals of the same species. This suggests that a possible chemical or environmental stimulus created by the other cockle sizes (as observed in other bivalves; Nelson and Allison 1940;Balfour andSmock 1995 andHuang et al., 2007) may have increased the mobility of large cockles. ...
Eutrophication is an increasing problem worldwide and can disrupt ecosystem processes in which macrobenthic bioturbators play an essential role. This study explores how intraspecific variation in body size affects the survival, mobility and impact on sediment organic matter breakdown in enriched sediments of an infaunal bivalve. A mesocosm experiment was conducted in which monocultures and all size combinations of three body sizes (small, medium and large) of the Sydney cockle, Anadara trapezia, were exposed to natural or organically enriched sediments. Results demonstrate that larger body sizes have higher tolerance to enriched conditions and can reduce survival of smaller cockles when grown together. Also, large A. trapezia influenced sediment organic matter breakdown although a direct link to bioturbation activity was not clear. Overall, this study found that intraspecific variation in body size influences survival and performance of bioturbators in eutrophic scenarios.
... Pediveligers then continue to metamorphose into juvenile spats, where they thicken and enlarge their shells and overall body size. Juvenile giant clams remain motile using their foot for locomotion (Huang et al., 2007), and search for suitable substrata (Neo et al., 2009(Neo et al., , 2015b or conspecifics (Sim et al., 2018) before attaching themselves on the seabed with byssal threads. Despite their high fecundity, size distributions of giant clams suggest that recruitment of juvenile clams is low, implying that mortality of early pelagic or postmetamorphic stages is high (Yamaguchi, 1977). ...
... The foot is also covered in cilia that allows the giant clam larva to sense and orientate to its surroundings in search of shelter (Dumas et al., 2014;Neo et al., 2009). The pediveligers, over time, become increasingly sedentary but remain mobile as they grow into juveniles and adults (Huang et al., 2007;Suzuki, 1998). Interestingly, juvenile clams have been shown to move more at night, potentially an adaptation to avoid visual predators (Soo and Todd, 2014;Suzuki, 1998). ...
... Interestingly, juvenile clams have been shown to move more at night, potentially an adaptation to avoid visual predators (Soo and Todd, 2014;Suzuki, 1998). Juveniles were also observed to move nonrandomly and clump towards conspecifics (Huang et al., 2007), and further experiments have found that aggregative behavior have trade-offs between predator defense and conspecific competition (Sim et al., 2018). Some notable behavior in adult giant clams include self-righting (Fankboner, 1971), shadow responses (Stasek, 1965), and squirting reflexes , which can aid as antipredatory defenses. ...
The charismatic giant clam is globally endangered due to overharvesting, loss of habitats, pollution, and climate change. Some conservation measures have shown success in curbing further declines of wild populations, but it is clear that active management is required to prevent the disappearance of giant clam species as they continue to face threats linked to human behaviors.
... Populations of giant clams may not be able to adapt to changing environmental conditions as quickly as other marine invertebrates, due to their long life cycles (Lucas 1988) and limited genetic diversity (DeBoer et al. 2008;Nuryanto and Kochzius 2009;Neo et al. 2012). Juvenile clams have substantial locomotion capacity (Huang et al. 2007) but this is probably not sufficient for them to migrate away from unfavorable conditions. ...
This paper examines the responses of the fluted giant clam Tridacna squamosa pediveligers to elevated temperature and reduced light levels. In a light reduction experiment, a total of 104,000 T. squamosa pediveligers were exposed to four different levels of shading for approximately one month. The most heavily shaded treatment, at 0.4% of ambient light, had significantly lower survival than the other groups, which all received 1% or more of ambient light. In a second experiment, for approximately two weeks 13,000 T. squamosa pediveligers were divided among three treatments: one at ambient temperature averaging 29.5 °C, and two with elevated temperatures averaging 32.2 °C and 34.8 °C. The elevated temperature treatments resulted in near total mortality. The highest temperature survived by any pediveliger was 32.8 °C. Our results indicate a potential synergetic effect, with turbidity causing giant clam pediveligers to settle in shallower water―where they will likely be exposed to higher temperatures.
... Having reached a new (micro)environment, the settlement might fail due to (i) the presence of predators [39], (ii) ending up in an unsuitable habitat [40] or (iii) the loss of facilitative interactions with other species (figure 1c) [41]. Though often ignored, dispersing organisms can also cope with the costs of habitat optimization, either by looking for supporting habitats [42] or by constructing their niches [43]. Yet, on the one hand, metastatic cells seem to be constrained by only two of these factors [29]: the loss of immunosuppression [44] and the loss of supporting interactions [45]. ...
Despite significant progress in oncology, metastasis remains the leading cause of mortality of cancer patients. Understanding the foundations of this phenomenon could help contain or even prevent it. As suggested by many ecologists and cancer biologists, metastasis could be considered through the lens of biological dispersal: the movement of cancer cells from their birth site (the primary tumour) to other habitats where they resume proliferation (metastatic sites). However, whether this model can consistently be applied to the emergence and dynamics of metastasis remains unclear. Here, we provide a broad review of various aspects of the evolution of dispersal in ecosystems. We investigate whether similar ecological and evolutionary principles can be applied to metastasis, and how these processes may shape the spatio-temporal dynamics of disseminating cancer cells. We further discuss complementary hypotheses and propose experimental approaches to test the relevance of the evolutionary ecology of dispersal in studying metastasis.
... Having reached a new (micro)environment, the settlement might fail due to (i) the presence of predators [39], (ii) ending up in an unsuitable habitat [40] or (iii) the loss of facilitative interactions with other species (figure 1c) [41]. Though often ignored, dispersing organisms can also cope with the costs of habitat optimization, either by looking for supporting habitats [42] or by constructing their niches [43]. Yet, on the one hand, metastatic cells seem to be constrained by only two of these factors [29]: the loss of immunosuppression [44] and the loss of supporting interactions [45]. ...
Selfish 'meiotic drive' alleles are transmitted to more than 50% of offspring, allowing them to rapidly invade populations even if they reduce the fitness of individuals carrying them. Theory predicts that drivers should either fix or go extinct, yet some drivers defy these predictions by persisting at low, stable frequencies for decades. One possible explanation for this discrepancy is that drivers are especially costly when homozygous, although empirical tests of this idea are rare and equivocal. Here, we measure the fitness of female Drosophila pseudoobscura carrying zero, one or two copies of the X-linked driver sex ratio (SR). SR had strong negative effects on female offspring production and the probability of reproductive failure, and these effects were largely similar across four genetic backgrounds. SR was especially costly when homozygous. We used our fitness measurements to parametrize a population genetic model, and found that the female fitness costs observed here can explain the puzzlingly low allele frequency of SR in nature. We also use the model to show how spatial variation in female mating behaviour, fitness costs of SR and the reduced siring success of SR males can jointly explain the north-south cline in SR frequencies across North America.
... Neo et al. [41] reported that the settlement competency period in T. squamosa is 14 days, and until then, the larvae actively swim and are able to alter the depth distribution and settlement location. Chemosensory abilities in giant clam larvae could be coupled with their locomotory behavior [42]. If such sensory behavior could control access to preferable zooxanthella sources, a higher rate of symbiosis stage in certain zooxanthellal source may occur but should be addressed in the future. ...
Unlike most bivalve shellfishes, giant clams (tridacnines) harbor symbiotic microalgae (zooxanthellae) in their fleshy bodies. Zooxanthellae are not maternally inherited by tridacnine offspring, hence, the larvae must acquire zooxanthellae from external sources, although such algal populations or sources in the environment are currently unknown. It is well known that giant clams expel fecal pellets that contain viable zooxanthellae cells, but whether these cells are infectious or just an expelled overpopulation from the giant clams has not been investigated. In this study, we observed the ultrastructural and photosynthetic competencies of zooxanthellae in the fecal pellets of Tridacna crocea and further tested the ability of these cells to infect T. squamosa juveniles. The ultrastructure of the zooxanthellae cells showed that the cells were intact and had not undergone digestion. Additionally, these zooxanthellae cells showed a maximum quantum yield of photosystem II (Fv/Fm) as high as those retained in the mantle of the giant clam. Under the assumption that feces might provide symbionts to the larvae of other giant clams, fecal pellets from Tridacna squamosa and T. crocea were given to artificially hatched 1-day-old T. squamosa larvae. On the 9th day, 15-34% of the larvae provided with the fecal pellets took up zooxanthellae in their stomach, and on the 14th day, zooxanthellae cells reached the larval margin, indicating the establishment of symbiosis. The rate reaching this stage was highest, ca. 5.3%, in the larvae given whole (nonhomogenized) pellets from T. crocea. The composition of zooxanthellae genera contained in the larvae were similar to those in the fecal pellets, although the abundance ratios were significantly different. This study is the first to demonstrate the potential of giant clam fecal pellets as symbiont vectors to giant clam larvae. These results also demonstrate the possibility that fecal pellets are a source of zooxanthellae in coral reefs.
