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THE OCEAN IS NOT DEEP ENOUGH
Pressure tolerance of Mytilus edulis early life stages
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Major Question
How were deep sea environments colonized?
• High pressure environment• Noxious environment• Temperature extremes
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Le Chatelier’s Principle
Background
“If a chemical system at equilibrium experiences a change in concentration, temperature, volume or total pressure, the equilibrium will shift in order to counteract the imposed change” (Mestre et al. 2009)
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Pressure
Effects biochemical reactions and membrane functionality
• Keq = [C][D]/[A][B], G = -RTlnKeq and v = k[s]
• P sensitivity of reactions: Kp = K1e(-PV/RT) and kp = k1e-PV‡/RT
• P therefore affects both Keq and k (Kinsey 2009)
• Increased pressure will move the equilibrium to the side with lowest volume
Limits depth range of marine organisms Pressure tolerances are different for different life stages
Some life stages are more suited for deep-sea colonization
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Along with pressure also plays an important role in biochemical reactionsCan speed up or slow down metabolism
Response also varies with life stage Can counteract pressure effects
If membrane is more compressed because of pressure can be somewhat decompressed by higher temperature
Temperature
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What would limit organisms to a depth and temperature range in early ontogeny?
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Biochemical reactions during fertilization
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Program for post-fertilization changes in egg of sea urchins
Epel 1975
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Ca-Wave After Fertilization
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Biochemical pathways are sensitive pathways Could organisms, like mussels, with
sensitive biochemical pathways colonize deep-sea habitat?
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How were deep sea environments colonized by
mussels?Mestre et al. chose a shallow-
water relative of a deep-sea inhabitant
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Phylogenetic Relationship
subfamilys Mytilinae and Bathymodiolinae
Shallow water species Mytilus edulis found here
The rest are associated with one of the following:
Hydrothermal ventCold-water seepWood/bone
(Kyuno et al. 2009)
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Free-spawning marine invertebrates
Worldwide distribution
Found in intertidal zones and estuaries
Endure a wide range of temperatures and physical challenges
Mytilus edulis
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Origin of deep-sea mussels 2 Hypotheses:
Deep sea species evolved from shallow-sea species in step-wise fashion via wood/bone habitat
Direct colonization via larval transport from shallow-sea to deep-sea habitats.
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Origin of deep-sea mussels 2 Hypotheses:
Deep sea species evolved from shallow-sea species in step-wise fashion via wood/bone habitat
Direct colonization via larval migration from shallow-sea to deep-sea habitats○ Determine larval functional tolerance of
pressure and temperature
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Methods
3 ExperimentsTemperature effect on embryonic larvae and
developmentPressure effect on embryonic larvae and
development with fertilization under pressure
Pressure effect on embryonic larvae and development with fertilization at atmospheric pressure
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Staging criteria for larvae:
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Embryonic stages
D-larvae
Fertilized eggSixteen-cell
stage
Multi-cell stage
Early blastula
Two-cell stage
Four-cell stage
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Temperature effect on embryonic larvae and development
5 temperature treatments5, 10, 15, 20, and 25C, at atmospheric pressure
Incubated until all treatments had reached D-larvae stage.
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Pressure Vesselsa) Plastic vial filled with the
egg suspension and the microcentrifuge tube hald-filled with sperm suspension
b) Pressure vessel showing the plastic vials inside
Figure 1 from Mestre et al. 2009
Pressure Experiments
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Pressure effect on embryonic and larvae development with fertilization under pressure Placed sperm in separate vial which ruptured at
pressure Resulting embryos were incubated at different
temperature/pressure treatments Pressure/Temperature treatments
Temperature treatments○ 10, 15, and 20C
Pressure treatments○ 1, 100, 200, and 300 atm ○ + 400 and 500atm for 4 hour treatments
○Incubated for 4 and 24 hours
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Pressure effect on embryonic and larval development with fertilization at atmospheric pressure
Fertilization at atmospheric pressure, at 15C
Resulting embryos were incubated at 4 different pressures and 5 different temperaturesTemperature treatments
○ 5, 10, 15, 20, and 25CPressure treatments
○ 1, 100, 200, and 300 atm
Incubated for 50 hours
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Results Divided results from 3 methods into 2
categories:Temperature effects on embryonic and larval
developmentPressure effects on embryonic and larval
development
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Temperature effects on embryonic and larval development
Mytilus edulis embryos develop faster at higher temperatures
Effect in the proportion of abnormally developing embryos
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Pressure effects on embryonic and larval development with fertilization at atmospheric pressure after 50hrs
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Pressure effects with fertilization under pressure at 4 hours
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Pressure effects with fertilization under pressure at 24 hours
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Krustal-Wallis analysis of variance
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Conclusions Temperature tolerance window is from
approximately 10-20C Embryo development possible up to
500atm (~5000m)Hypothesized pressure presents no barrier to
fertilization Slower development with increasing
pressure Increase in abnormal cells with increasing
pressure due to membrane rupture
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“reasonable to hypothesize that the invasion of the deep sea by M. edulis is possible in terms of pressure tolerances in embryos and larvae
Was hypothesis correct?
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References Kyuno, Akiko; Shintaku, Mifue; Fujita, Yuko; Matsumoto,
Hiroto; Utsumi, Motoo; Watanabe, Hiromi; Fujiwara, Yoshihiro; Miyazaki, Jun-Ichi. 2009. Dispersal and Differentiation of Deep-Sea Mussels of the Genus Bathymodiolus (Mytilidae, Bathymodiolinae). Journal of Marine Biology. Vol. 2009. pp. 15.
Epel, David. 1975. The Program of and Mechanisms of Fertilization in the Echinoderm Egg. American Zoologist. 15, 3. pp. 507-522.
Mestre, Nelia C.; Thatje, Sven; Tyler, Paul A. 2009. The ocean is not deep enough: pressure tolerances during early ontogeny of the blue mussel Mytilus edulis. Proc. R. Soc. B 276, pp. 717-726.
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Discussion Questions
What other effects of pressure could cause developmental problems?
Do their results support direct colonization?Last section of discussion implies it does