Pressure tolerance of Mytilus edulis early life stages.
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Direct Deep-sea Colonization
The ocean is not deep enoughPressure tolerance of Mytilus edulis early life stages
Major QuestionHow were deep sea environments colonized?High pressure environmentNoxious environmentTemperature extremes
Le Chateliers PrincipleBackgroundIf 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)
PressureEffects biochemical reactions and membrane functionalityKeq = [C][D]/[A][B], G = -RTlnKeq and v = k[s]P sensitivity of reactions: Kp = K1e(-PV/RT) and kp = k1e-PV/RTP therefore affects both Keq and k (Kinsey 2009)Increased pressure will move the equilibrium to the side with lowest volumeLimits depth range of marine organismsPressure tolerances are different for different life stagesSome life stages are more suited for deep-sea colonizationAlong with pressure also plays an important role in biochemical reactionsCan speed up or slow down metabolismResponse also varies with life stageCan counteract pressure effectsIf membrane is more compressed because of pressure can be somewhat decompressed by higher temperature
Temperature What would limit organisms to a depth and temperature range in early ontogeny?Biochemical reactions during fertilization
Program for post-fertilization changes in egg of sea urchins
Epel 1975Ca-Wave After Fertilization
Biochemical pathways are sensitive pathwaysCould organisms, like mussels, with sensitive biochemical pathways colonize deep-sea habitat?
How were deep sea environments colonized by mussels?Mestre et al. chose a shallow-water relative of a deep-sea inhabitant
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)Free-spawning marine invertebrates
Found in intertidal zones and estuaries
Endure a wide range of temperatures and physical challenges
Origin of deep-sea mussels2 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.Origin of deep-sea mussels2 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 habitatsDetermine larval functional tolerance of pressure and temperatureMethods3 ExperimentsTemperature effect on embryonic larvae and developmentPressure effect on embryonic larvae and development with fertilization under pressurePressure effect on embryonic larvae and development with fertilization at atmospheric pressure
Staging criteria for larvae:Embryonic stages
D-larvaeFertilized eggSixteen-cell stageMulti-cell stageEarly blastulaTwo-cell stageFour-cell stageTemperature 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.
Purpose was to examine temperature effects on larval development, in order to isolate temp. effect from pressure effects20Pressure VesselsPlastic vial filled with the egg suspension and the microcentrifuge tube hald-filled with sperm suspensionPressure vessel showing the plastic vials inside
Figure 1 from Mestre et al. 2009Pressure ExperimentsPressure effect on embryonic and larvae development with fertilization under pressure
Placed sperm in separate vial which ruptured at pressureResulting embryos were incubated at different temperature/pressure treatmentsPressure/Temperature treatmentsTemperature treatments10, 15, and 20CPressure treatments1, 100, 200, and 300 atm + 400 and 500atm for 4 hour treatmentsIncubated for 4 and 24 hoursPressure effect on embryonic and larval development with fertilization at atmospheric pressureFertilization at atmospheric pressure, at 15CResulting embryos were incubated at 4 different pressures and 5 different temperaturesTemperature treatments5, 10, 15, 20, and 25CPressure treatments1, 100, 200, and 300 atmIncubated for 50 hoursResultsDivided results from 3 methods into 2 categories:Temperature effects on embryonic and larval developmentPressure effects on embryonic and larval developmentTemperature effects on embryonic and larval development
Mytilus edulis embryos develop faster at higher temperaturesEffect in the proportion of abnormally developing embryos
Pressure effects on embryonic and larval development with fertilization at atmospheric pressure after 50hrs
Pressure effects with fertilization under pressure at 4 hours
Pressure effects with fertilization under pressure at 24 hours
Krustal-Wallis analysis of varianceConclusionsTemperature tolerance window is from approximately 10-20CEmbryo development possible up to 500atm (~5000m)Hypothesized pressure presents no barrier to fertilizationSlower development with increasing pressureIncrease in abnormal cells with increasing pressure due to membrane rupture
reasonable to hypothesize that the invasion of the deep sea by M. edulis is possible in terms of pressure tolerances in embryos and larvaeWas hypothesis correct?ReferencesKyuno, 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. Discussion QuestionsWhat other effects of pressure could cause developmental problems?Do their results support direct colonization?Last section of discussion implies it does