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Malka Halpern - One of the best experts on this subject based on the ideXlab platform.
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quorum sensing signaling by chironomid Egg Masses microbiota affects haemagglutinin protease hap production by vibrio cholerae
Molecular Ecology, 2020Co-Authors: Rotem Sela, Brian K Hammer, Malka HalpernAbstract:Vibrio cholerae, the causative agent of cholera, is commonly isolated, along with other bacterial species, from chironomid insects (Diptera: Chironomide). Nevertheless, its prevalence in the chironomid Egg Masses' microbiota is less than 0.5%. V. cholerae secretes haemagglutinin/protease (HAP) that degrades the gelatinous matrix of chironomid Egg Masses and prevents hatching. Quorum sensing (QS) activates HAP production in response to accumulation of bacterial autoinducers (AIs). Our aim was to define the impact of chironomid microbiota on HAP production by V. cholerae. To study QS signaling, we used V. cholerae bioluminescence reporter strains (QS-proficient O1 El-Tor wild-type and QS-deficient mutants) and different bacterial species that we isolated from chironomid Egg Masses. These Egg mass isolates, as well as a synthetic AI-2, caused an enhancement in lux expression by a V. cholerae QS-deficient mutant. The addition of the Egg mass bacterial isolate supernatant to the QS-deficient mutant also enhanced HAP production and Egg mass degradation activities. Moreover, the V. cholerae wild-type strain was able to proliferate using Egg Masses as their sole carbon source, while the QS-deficient was not. The results demonstrate that members of the chironomid bacterial consortium produce external chemical cues that, like AI-2, induce expression of the hapA gene in V. cholerae. Understanding the interactions between V. cholerae and the insects' microbiota may help uncover the interactions between this pathogen and the human gut microbiota.
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Aeromonas chitinase degrades chironomid Egg Masses
Environmental Microbiology Reports, 2015Co-Authors: Sivan Laviad, Malka Halpern, Amnon Golan, Tamar Shakéd, Dalit Vaizel-ohayon, Elah PickAbstract:Summary Chironomids are freshwater insects that undergo a complete metamorphosis of four life stages. Chironomid Egg Masses can be degraded by Vibrio cholerae and some Aeromonas species. Egg mass degradation by V. cholerae requires haemagglutinin protease activity. Our aim was to identify the Egg mass degrading (EMD) factor secreted by Aeromonas dhkanesis 3K1C15. Following the hypothesis that the EMD factor of A. dhkanesis is also a protease, secreted proteases were screened, but none of them proved to have the same properties as the EMD factor. Using conventional protein purification methods, we found that the active fraction included chitinases. We further confirmed chitin as a building block of the Egg Masses. Interestingly, by supplementing bacterial growth media with chitin, we observed unexpected EMD factor activity in Aeromonas isolates that initially were not able to degrade Egg Masses. Accordingly, we concluded that although strain 3K1C15 secretes chitinases constitutively, most Aeromonas strains secrete chitinases inductively. Induction of chitinases in nature presumably occurs when bacteria are attached to the Egg mass habitat, in which chitin is abundant. Considering that chitinases are highly conserved across bacteria phyla, we assume that the role of this enzyme in the bacteria–insect interplay could be wider than is currently thought.
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The protective role of endogenous bacterial communities in chironomid Egg Masses and larvae
The ISME Journal, 2013Co-Authors: Yigal Senderovich, Malka HalpernAbstract:Insects of the family Chironomidae , also known as chironomids, are distributed worldwide in a variety of water habitats. These insects display a wide range of tolerance toward metals and organic pollutions. Bacterial species known for their ability to degrade toxicants were identified from chironomid Egg Masses, leading to the hypothesis that bacteria may contribute to the survival of chironomids in polluted environments. To gain a better understanding of the bacterial communities that inhabit chironomids, the endogenous bacteria of Egg Masses and larvae were studied by 454-pyrosequencing. The microbial community of the Egg Masses was distinct from that of the larval stage, most likely due to the presence of one dominant bacterial Firmicutes taxon, which consisted of 28% of the total sequence reads from the larvae. This taxon may be an insect symbiont. The bacterial communities of both the Egg Masses and the larvae were found to include operational taxonomic units, which were closely related to species known as toxicant degraders. Furthermore, various bacterial species with the ability to detoxify metals were isolated from Egg Masses and larvae. Koch-like postulates were applied to demonstrate that chironomid endogenous bacterial species protect the insect from toxic heavy metals. We conclude that chironomids, which are considered pollution tolerant, are inhabited by stable endogenous bacterial communities that have a role in protecting their hosts from toxicants. This phenomenon, in which bacteria enable the continued existence of their host in hostile environments, may not be restricted only to chironomids.
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Bacterial community composition associated with chironomid Egg Masses.
Journal of Insect Science, 2012Co-Authors: Yigal Senderovich, Malka HalpernAbstract:Chironomids (Diptera: Chironomidae) are the most widely distributed and often the most abundant insect in freshwater. They undergo a complete metamorphosis of four life stages, of which the Egg, larva, and pupae are aquatic and the adult is terrestrial. Chironomid Egg Masses were found to be natural reservoirs of Vibrio cholerae and Aeromonas species. To expand the knowledge of the endogenous bacterial community associated with chironomid Egg Masses, denaturing gradient gel electrophoresis and clone analysis of 16S rRNA gene libraries were used in this study. Bacterial community composition associated with chironomid Egg Masses was found to be stable among different sampling periods. Cloned libraries of Egg Masses revealed that about 40% of the clones were related to bacteria known to degrade various toxicants. These findings were further supported when bacterial species that showed resistance to different toxic metals were isolated from Egg Masses and larval samples. Chironomids are found under a wide range of water conditions and are able to survive pollutants. However, little is known about their protective mechanisms under these conditions. Chironomid Egg Masses are inhabited by a stable endogenous bacterial community, which may potentially play a role in protecting chironomids from toxicants in polluted environments. Further study is needed to support this hypothesis.
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Culturable and VBNC Vibrio cholerae: Interactions with Chironomid Egg Masses and Their Bacterial Population
Microbial Ecology, 2007Co-Authors: Malka Halpern, Ori Landsberg, Dina Raats, Eugene RosenbergAbstract:Vibrio cholerae , the etiologic agent of cholera, is autochthonous to various aquatic environments. Recently, it was found that chironomid (nonbiting midges) Egg Masses serve as a reservoir for the cholera bacterium and that flying chironomid adults are possible windborne carriers of V. cholerae non-O1 non-O139. Chironomids are the most widely distributed insect in freshwater. Females deposit Egg Masses at the water's edge, and each Egg mass contains Eggs embedded in a gelatinous matrix. Hemagglutinin/protease, an extracellular enzyme of V. cholerae , was found to degrade chironomid Egg Masses and to prevent them from hatching. In a yearly survey, chironomid populations and the V. cholerae in their Egg Masses followed phenological succession and interaction of host–pathogen population dynamics. In this report, it is shown via FISH technique that most of the V. cholerae inhabiting the Egg mass are in the viable but nonculturable (VBNC) state. The diversity of culturable bacteria from chironomid Egg Masses collected from two freshwater habitats was determined. In addition to V. cholerae , representatives of the following genera were isolated: Acinetobacter , Aeromonas , Klebsiella , Shewanella , Pseudomonas , Paracoccus , Exiguobacterium , and unidentified bacteria. Three important human pathogens, Aeromonas veronii , A. caviae , and A. hydrophila , were isolated from chironomid Egg Masses, indicating that chironomid Egg Masses may be a natural reservoir for pathogenic Aeromonas species in addition to V. cholerae . All isolates of V. cholerae were capable of degrading chironomid Egg Masses. This may help explain their host–pathogen relationship with chironomids. In contrast, almost none of the other bacteria that were isolated from the Egg Masses possessed this ability. Studying the interaction between chironomid Egg Masses, the bacteria inhabiting them, and V. cholerae could contribute to our understanding of the nature of the V. cholerae –Egg mass interactions.
Yechezkel Kashi - One of the best experts on this subject based on the ideXlab platform.
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vibrio cholerae hemagglutinin protease degrades chironomid Egg Masses
Applied and Environmental Microbiology, 2003Co-Authors: Malka Halpern, Hanan Gancz, Meir Broza, Yechezkel KashiAbstract:Cholera is a severe diarrheal disease caused by specific serogroups of Vibrio cholerae that are pathogenic to humans. The disease does not persist in a chronic state in humans or animals. The pathogen is naturally present as a free-living organism in the environment. Recently, it was suggested that Egg Masses of the nonbiting midge Chironomus sp. (Diptera) harbor and serve as a nutritive source for V. cholerae, thereby providing a natural reservoir for the organism. Here we report that V. cholerae O9, O1, and O139 supernatants lysed the gelatinous matrix of the chironomid Egg mass and inhibited Eggs from hatching. The extracellular factor responsible for the degradation of chironomid Egg Masses (Egg mass degrading factor) was purified from V. cholerae O9 and O139 and was identified as the major secreted hemagglutinin/protease (HA/P) of V. cholerae. The substrate in the Egg mass was characterized as a glycoprotein. These findings show that HA/P plays an important role in the interaction of V. cholerae and chironomid Egg Masses.
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Vibrio cholerae Hemagglutinin/Protease Degrades Chironomid Egg Masses
Applied and Environmental Microbiology, 2003Co-Authors: Malka Halpern, Hanan Gancz, Meir Broza, Yechezkel KashiAbstract:Cholera is a severe diarrheal disease caused by specific serogroups of Vibrio cholerae that are pathogenic to humans. The disease does not persist in a chronic state in humans or animals. The pathogen is naturally present as a free-living organism in the environment. Recently, it was suggested that Egg Masses of the nonbiting midge Chironomus sp. (Diptera) harbor and serve as a nutritive source for V. cholerae, thereby providing a natural reservoir for the organism. Here we report that V. cholerae O9, O1, and O139 supernatants lysed the gelatinous matrix of the chironomid Egg mass and inhibited Eggs from hatching. The extracellular factor responsible for the degradation of chironomid Egg Masses (Egg mass degrading factor) was purified from V. cholerae O9 and O139 and was identified as the major secreted hemagglutinin/protease (HA/P) of V. cholerae. The substrate in the Egg mass was characterized as a glycoprotein. These findings show that HA/P plays an important role in the interaction of V. cholerae and chironomid Egg Masses.
H. Arthur Woods - One of the best experts on this subject based on the ideXlab platform.
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Temperature–oxygen interactions in Antarctic nudibranch Egg Masses
Journal of Experimental Biology, 2008Co-Authors: H. Arthur Woods, Amy L. MoranAbstract:The Southern Ocean is one of the coldest, most stable marine environments on Earth and represents a unique environment for investigating metabolic consequences of low temperature. Here we test predictions of a new diffusion-reaction model of O(2) distributions in Egg Masses, using Egg Masses of the Antarctic nudibranch mollusk, Tritonia challengeriana. When warmed from -1.5 degrees to +1.5 degrees C, embryos of T. challengeriana showed large increases in O(2) consumption (Q(10) values of 9.6-30.0). Oxygen electrode measurements in intact Masses showed, however, that O(2) levels were high throughout and virtually unaffected by temperature. The model suggested that both effects stemmed from very low metabolic densities in Egg Masses. Detailed morphological measurements of Egg Masses of T. challengeriana and a temperate congener, T. diomedea, revealed large differences in structure that may be related to O(2) availability. Egg Masses of T. challengeriana were approximately twice as thick. However, the most dramatic effects were observed in embryos: embryos of T. challengeriana were >32 times larger (by volume) than embryos of T. diomedea. Antarctic embryos also were contained singly in large Egg capsules ( approximately 500 mum diameter). Consequently, Antarctic embryos occurred at much lower densities, with very low metabolic densities.
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Oxygen profiles in Egg Masses predicted from a diffusion-reaction model.
Journal of Experimental Biology, 2008Co-Authors: H. Arthur Woods, Amy L. MoranAbstract:We developed a novel diffusion-reaction model to describe spatial and temporal changes in oxygen concentrations in gelatinous Egg Masses containing live, respiring embryos. We used the model in two ways. First, we constructed artificial Egg Masses of known metabolic density using embryos of the Antarctic sea urchin Sterechnius neumayeri, measured radial oxygen profiles at two temperatures, and compared our measurements to simulated radial oxygen profiles generated by the model. We parameterized the model by measuring the radius of the artificial Masses, metabolic densities (=embryo metabolic rate x embryo density) and oxygen diffusion coefficients at both ambient (-1.5 degrees C) or slightly warmer (+1.5-2 degrees C) temperatures. Simulated and measured radial oxygen profiles were similar, indicating that the model captured the major biological features determining oxygen distributions. Second, we used the model to analyze sources of error in step-change experiments for determining oxygen diffusion coefficients (D), and to determine the suitability of simpler, analytical equations for estimating D. Our analysis indicated that embryo metabolism can lead to large (several-fold) overestimates of D if the analytical equation is fitted to step-down-traces of central oxygen concentration (i.e. external oxygen concentration stepped from some high value to zero). However, good estimates of D were obtained from step-up-traces. We used these findings to estimate D in Egg Masses of three species of nudibranch molluscs: two Antarctic species (Tritonia challengeriana and Tritoniella belli; -1.5 and +2 degrees C) and one temperate Pacific species (Tritonia diomedea; 12 and 22 degrees C). D for all three species was approximately 8 x 10(-6) cm(2) s(-1), and there was no detectable effect of temperature on estimated D. For the Antarctic species, D in Egg Masses was 70-90% of its value in seawater of similar temperature.
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Temperature-oxygen interactions in Antarctic nudibranch Egg Masses.
The Journal of experimental biology, 2008Co-Authors: H. Arthur Woods, Amy L. MoranAbstract:The Southern Ocean is one of the coldest, most stable marine environments on Earth and represents a unique environment for investigating metabolic consequences of low temperature. Here we test predictions of a new diffusion-reaction model of O(2) distributions in Egg Masses, using Egg Masses of the Antarctic nudibranch mollusk, Tritonia challengeriana. When warmed from -1.5 degrees to +1.5 degrees C, embryos of T. challengeriana showed large increases in O(2) consumption (Q(10) values of 9.6-30.0). Oxygen electrode measurements in intact Masses showed, however, that O(2) levels were high throughout and virtually unaffected by temperature. The model suggested that both effects stemmed from very low metabolic densities in Egg Masses. Detailed morphological measurements of Egg Masses of T. challengeriana and a temperate congener, T. diomedea, revealed large differences in structure that may be related to O(2) availability. Egg Masses of T. challengeriana were approximately twice as thick. However, the most dramatic effects were observed in embryos: embryos of T. challengeriana were >32 times larger (by volume) than embryos of T. diomedea. Antarctic embryos also were contained singly in large Egg capsules ( approximately 500 mum diameter). Consequently, Antarctic embryos occurred at much lower densities, with very low metabolic densities.
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Oxygen in Egg Masses: interactive effects of temperature, age, and Egg-mass morphology on oxygen supply to embryos.
Journal of Experimental Biology, 2007Co-Authors: Amy L. Moran, H. Arthur WoodsAbstract:SUMMARY Embryos of many marine invertebrates are encased in gelatinous Masses for part or all of development. Because gel and intervening embryos retard oxygen flux, such a life-history mode profoundly affects partial pressures of metabolic gases surrounding embryos. However, little is known about relationships between Egg-mass structure and the opportunities and constraints imposed on structure by metabolic gas transport. We examined the effects of four factors (temperature, embryo age, embryo density and Egg-mass size) on the metabolism of Egg Masses using both natural Egg Masses of a nudibranch and artificial Egg Masses made from sand dollar embryos and low-melting point agarose. Both temperature and embryo age strongly affected metabolic rates of nudibranch embryos. For embryos of a given age (stage), rates of oxygen consumption roughly doubled between 12 and 21°C; from early cleavage to the veliger stage, consumption rose two- to fourfold, depending on temperature. Oxygen profiles in Egg Masses showed that advanced embryonic age, and to a lesser extent high temperature, both led to steeper oxygen gradients into Egg Masses. Egg Masses containing advanced embryos at 21°C had very low central oxygen levels. Small-diameter artificial Masses (2 mm diameter) had virtually no internal oxygen gradients regardless of embryo density or temperature, while medium (4 mm) and large diameter (10 mm) artificial Masses had oxygen profiles that depended strongly and interactively on embryo density and temperature. Together, our data on natural and artificial Egg Masses suggest that (i) multiple factors have strong effects on metabolic rate; (ii) rates of oxygen transport are relatively invariant with temperature in simple, artificial systems but may vary more strongly with temperature in natural Egg Masses; and (iii) the four factors – temperature, embryo age, embryo density and Egg-mass size – interact in important ways bearing on Egg mass design. A simple mathematical model is developed to provide a quantitative means of estimating primary and interactive effects of the different factors. We also show that in T. diomedea the gel itself is the main barrier to oxygen transport into Egg Masses, and that the metabolic activity of embryos increases substantially when embryos are artificially released from the capsules that contain them within the gel mass.
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Photosynthesis Drives Oxygen Levels in Macrophyte- Associated Gastropod Egg Masses
The Biological Bulletin, 2007Co-Authors: H. Arthur Woods, Robert D. PodolskyAbstract:Many aquatic animals deposit fertilized Eggs in adherent clutches or gelatinous Masses. Egg aggregation carries certain risks, including the potential for inadequate oxygen supply to embryos. Physical and biological condi- tions alter such risks. We examined the effects of light levels and associated photosynthetic organisms on the dis- tribution of oxygen inside gelatinous Egg Masses of four temperate gastropod species. Egg Masses of two species, the opisthobranchs Melanochlamys diomedea and Haminoea callidegenita, contained significant populations of diatoms but generally were not associated with macrophytes. Egg Masses of the other two species, the opisthobranch Hamin- oea vesicula and the prosobranch Lacuna sp., occurred commonly on subtidal macrophytes and appeared not to contain significant populations of diatoms. In the laboratory, we used microelectrodes to measure oxygen levels inside Masses exposed to alternating dark and light conditions; light level had an enormous influence on oxygen profiles in Egg Masses of all four species. Masses of H. vesicula and Lacuna sp., when experimentally separated from their mac- rophytes, showed only slight increases in oxygen upon light exposure, indicating that the main source of oxygen in situ was the macrophyte rather than associated microalgae. Our findings indicate that photosynthesis by macrophytes can drive large changes in internal oxygen profiles.
Kreiter Serge - One of the best experts on this subject based on the ideXlab platform.
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Mites associated with Egg Masses of the viburnum leaf beetle Pyrrhalta viburni (Paykull) on Viburnum tinus L.
Acarologia, 2019Co-Authors: Desurmont, Gaylord A., Kerdellant Elven, Pfingstl Tobias, Auger Phillipe, Tixier Marie-stéphane, Kreiter SergeAbstract:International audienceThe viburnum leaf beetle Pyrrhalta viburni (Coleoptera: Chrysomelidae) is a specialist Viburnum leaf-feeder that is native to Eurasia and invasive in North America. Eggs of P. viburni are laid in round cavities excavated by the ovipositing female beetle and covered with a protective secretion. We document in this paper the mite fauna associated with P. viburni Egg Masses on Viburnum tinus in southern France. We then report the results of experiments investigating the seasonal patterns of mite infestation and the effects of the most common mite found within Egg Masses, Trichoribates trimaculatus (Oribatida: Ceratozetidae), on P. viburni Egg survivorship. A diverse mite fauna of 18 species was found on V. tinus twigs, often living within P. viburni Egg Masses, including predaceous, phytophagous, and detritivorous species. Mite abundance and diversity were higher on Viburnum twigs containing at least one intact Egg mass and were positively correlated with the number of intact Egg Masses per twig. Detritivorous mites were more abundant on twigs nine months after oviposition than one and four months after oviposition. Finally, we found no evidence that T. trimaculatus impacts P. viburni Egg survivorship and overwintering success. These findings show that P. viburni Egg Masses and their associated cavities form a microhabitat favorable for the establishment of several mite species. It seems likely that these associations are cases of commensalism where mites benefit from the presence of food and shelter in these protected cavities, with no direct negative impact on P. viburni Eggs
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Mites associated with Egg Masses of the viburnum leaf beetle Pyrrhalta viburni Paykull) on Viburnum tinus L.
2019Co-Authors: Desurmont, Gaylord A., Kerdellant Elven, Pfingstl Tobias, Tixier Marie-stéphane, Auger Philippe, Kreiter SergeAbstract:The viburnum leaf beetle Pyrrhalta viburni (Coleoptera: Cluysomelidae) is a specialist Viburnum leaf-feeder that is native to Eurasia and invasive in North America. Eggs of P. viburni arc laid in round cavities excavated by the ovipositing female beetle and covered with a protective secretion. We document in this paper the mite fauna associated with P vihurni Egg Masses on Viburnum tinus in southern France. We then report the results of experiments investigating the seasonal patterns of mite infestation and the effects of the most common mite found within Egg Masses, Trichoribates trimaculatus (Oribatida: Ceratozetidae), on P vihurni Egg survivorship. A diverse mite fauna of 18 species was found on V. tinus twigs, often living within P. vihurni Egg Masses, including predaceous, phytophagous, and detritivorous species. Mite abundance and diversity were higher on Viburnum twigs containing at least one intact Egg mass and were positively correlated with the number of intact Egg Masses per twig. Detritivorous mites were more abundant on twigs nine months after oviposition than one and four months after oviposition. Finally, we found no evidence that T. trimaculatus impacts P. viburni Egg survivorship and overwintering success. These findings show that P. viburni Egg Masses and their associated cavities form a microhabitat favorable for the establishment of several mite species. It seems likely that these associations are cases of commensalism where mites benefit from the presence of food and shelter in these protected cavities, with no direct negative impact on P. viburni Eggs
Amy L. Moran - One of the best experts on this subject based on the ideXlab platform.
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Temperature–oxygen interactions in Antarctic nudibranch Egg Masses
Journal of Experimental Biology, 2008Co-Authors: H. Arthur Woods, Amy L. MoranAbstract:The Southern Ocean is one of the coldest, most stable marine environments on Earth and represents a unique environment for investigating metabolic consequences of low temperature. Here we test predictions of a new diffusion-reaction model of O(2) distributions in Egg Masses, using Egg Masses of the Antarctic nudibranch mollusk, Tritonia challengeriana. When warmed from -1.5 degrees to +1.5 degrees C, embryos of T. challengeriana showed large increases in O(2) consumption (Q(10) values of 9.6-30.0). Oxygen electrode measurements in intact Masses showed, however, that O(2) levels were high throughout and virtually unaffected by temperature. The model suggested that both effects stemmed from very low metabolic densities in Egg Masses. Detailed morphological measurements of Egg Masses of T. challengeriana and a temperate congener, T. diomedea, revealed large differences in structure that may be related to O(2) availability. Egg Masses of T. challengeriana were approximately twice as thick. However, the most dramatic effects were observed in embryos: embryos of T. challengeriana were >32 times larger (by volume) than embryos of T. diomedea. Antarctic embryos also were contained singly in large Egg capsules ( approximately 500 mum diameter). Consequently, Antarctic embryos occurred at much lower densities, with very low metabolic densities.
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Oxygen profiles in Egg Masses predicted from a diffusion-reaction model.
Journal of Experimental Biology, 2008Co-Authors: H. Arthur Woods, Amy L. MoranAbstract:We developed a novel diffusion-reaction model to describe spatial and temporal changes in oxygen concentrations in gelatinous Egg Masses containing live, respiring embryos. We used the model in two ways. First, we constructed artificial Egg Masses of known metabolic density using embryos of the Antarctic sea urchin Sterechnius neumayeri, measured radial oxygen profiles at two temperatures, and compared our measurements to simulated radial oxygen profiles generated by the model. We parameterized the model by measuring the radius of the artificial Masses, metabolic densities (=embryo metabolic rate x embryo density) and oxygen diffusion coefficients at both ambient (-1.5 degrees C) or slightly warmer (+1.5-2 degrees C) temperatures. Simulated and measured radial oxygen profiles were similar, indicating that the model captured the major biological features determining oxygen distributions. Second, we used the model to analyze sources of error in step-change experiments for determining oxygen diffusion coefficients (D), and to determine the suitability of simpler, analytical equations for estimating D. Our analysis indicated that embryo metabolism can lead to large (several-fold) overestimates of D if the analytical equation is fitted to step-down-traces of central oxygen concentration (i.e. external oxygen concentration stepped from some high value to zero). However, good estimates of D were obtained from step-up-traces. We used these findings to estimate D in Egg Masses of three species of nudibranch molluscs: two Antarctic species (Tritonia challengeriana and Tritoniella belli; -1.5 and +2 degrees C) and one temperate Pacific species (Tritonia diomedea; 12 and 22 degrees C). D for all three species was approximately 8 x 10(-6) cm(2) s(-1), and there was no detectable effect of temperature on estimated D. For the Antarctic species, D in Egg Masses was 70-90% of its value in seawater of similar temperature.
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Temperature-oxygen interactions in Antarctic nudibranch Egg Masses.
The Journal of experimental biology, 2008Co-Authors: H. Arthur Woods, Amy L. MoranAbstract:The Southern Ocean is one of the coldest, most stable marine environments on Earth and represents a unique environment for investigating metabolic consequences of low temperature. Here we test predictions of a new diffusion-reaction model of O(2) distributions in Egg Masses, using Egg Masses of the Antarctic nudibranch mollusk, Tritonia challengeriana. When warmed from -1.5 degrees to +1.5 degrees C, embryos of T. challengeriana showed large increases in O(2) consumption (Q(10) values of 9.6-30.0). Oxygen electrode measurements in intact Masses showed, however, that O(2) levels were high throughout and virtually unaffected by temperature. The model suggested that both effects stemmed from very low metabolic densities in Egg Masses. Detailed morphological measurements of Egg Masses of T. challengeriana and a temperate congener, T. diomedea, revealed large differences in structure that may be related to O(2) availability. Egg Masses of T. challengeriana were approximately twice as thick. However, the most dramatic effects were observed in embryos: embryos of T. challengeriana were >32 times larger (by volume) than embryos of T. diomedea. Antarctic embryos also were contained singly in large Egg capsules ( approximately 500 mum diameter). Consequently, Antarctic embryos occurred at much lower densities, with very low metabolic densities.
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Oxygen in Egg Masses: interactive effects of temperature, age, and Egg-mass morphology on oxygen supply to embryos.
Journal of Experimental Biology, 2007Co-Authors: Amy L. Moran, H. Arthur WoodsAbstract:SUMMARY Embryos of many marine invertebrates are encased in gelatinous Masses for part or all of development. Because gel and intervening embryos retard oxygen flux, such a life-history mode profoundly affects partial pressures of metabolic gases surrounding embryos. However, little is known about relationships between Egg-mass structure and the opportunities and constraints imposed on structure by metabolic gas transport. We examined the effects of four factors (temperature, embryo age, embryo density and Egg-mass size) on the metabolism of Egg Masses using both natural Egg Masses of a nudibranch and artificial Egg Masses made from sand dollar embryos and low-melting point agarose. Both temperature and embryo age strongly affected metabolic rates of nudibranch embryos. For embryos of a given age (stage), rates of oxygen consumption roughly doubled between 12 and 21°C; from early cleavage to the veliger stage, consumption rose two- to fourfold, depending on temperature. Oxygen profiles in Egg Masses showed that advanced embryonic age, and to a lesser extent high temperature, both led to steeper oxygen gradients into Egg Masses. Egg Masses containing advanced embryos at 21°C had very low central oxygen levels. Small-diameter artificial Masses (2 mm diameter) had virtually no internal oxygen gradients regardless of embryo density or temperature, while medium (4 mm) and large diameter (10 mm) artificial Masses had oxygen profiles that depended strongly and interactively on embryo density and temperature. Together, our data on natural and artificial Egg Masses suggest that (i) multiple factors have strong effects on metabolic rate; (ii) rates of oxygen transport are relatively invariant with temperature in simple, artificial systems but may vary more strongly with temperature in natural Egg Masses; and (iii) the four factors – temperature, embryo age, embryo density and Egg-mass size – interact in important ways bearing on Egg mass design. A simple mathematical model is developed to provide a quantitative means of estimating primary and interactive effects of the different factors. We also show that in T. diomedea the gel itself is the main barrier to oxygen transport into Egg Masses, and that the metabolic activity of embryos increases substantially when embryos are artificially released from the capsules that contain them within the gel mass.
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Oxygen in Egg Masses: interactive effects of temperature, age, and Egg-mass morphology on oxygen supply to embryos.
The Journal of experimental biology, 2007Co-Authors: Amy L. Moran, H. Arthur WoodsAbstract:Embryos of many marine invertebrates are encased in gelatinous Masses for part or all of development. Because gel and intervening embryos retard oxygen flux, such a life-history mode profoundly affects partial pressures of metabolic gases surrounding embryos. However, little is known about relationships between Egg-mass structure and the opportunities and constraints imposed on structure by metabolic gas transport. We examined the effects of four factors (temperature, embryo age, embryo density and Egg-mass size) on the metabolism of Egg Masses using both natural Egg Masses of a nudibranch and artificial Egg Masses made from sand dollar embryos and low-melting point agarose. Both temperature and embryo age strongly affected metabolic rates of nudibranch embryos. For embryos of a given age (stage), rates of oxygen consumption roughly doubled between 12 and 21 degrees C; from early cleavage to the veliger stage, consumption rose two- to fourfold, depending on temperature. Oxygen profiles in Egg Masses showed that advanced embryonic age, and to a lesser extent high temperature, both led to steeper oxygen gradients into Egg Masses. Egg Masses containing advanced embryos at 21 degrees C had very low central oxygen levels. Small-diameter artificial Masses (2 mm diameter) had virtually no internal oxygen gradients regardless of embryo density or temperature, while medium (4 mm) and large diameter (10 mm) artificial Masses had oxygen profiles that depended strongly and interactively on embryo density and temperature. Together, our data on natural and artificial Egg Masses suggest that (i) multiple factors have strong effects on metabolic rate; (ii) rates of oxygen transport are relatively invariant with temperature in simple, artificial systems but may vary more strongly with temperature in natural Egg Masses; and (iii) the four factors--temperature, embryo age, embryo density and Egg-mass size--interact in important ways bearing on Egg mass design. A simple mathematical model is developed to provide a quantitative means of estimating primary and interactive effects of the different factors. We also show that in T. diomedea the gel itself is the main barrier to oxygen transport into Egg Masses, and that the metabolic activity of embryos increases substantially when embryos are artificially released from the capsules that contain them within the gel mass.