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The ocean is not deep enough

Pressure tolerance of Mytilus edulis early life stages. The ocean is not deep enough. Major Question. How were deep sea environments colonized? High pressure environment Noxious environment Temperature extremes. Background. Le Chatelier’s Principle.

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The ocean is not deep enough

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  1. Pressure tolerance of Mytilusedulis early life stages The ocean is not deep enough

  2. Major Question How were deep sea environments colonized? • High pressure environment • Noxious environment • Temperature extremes

  3. Background Le Chatelier’s Principle • “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)

  4. Pressure • Effects biochemical reactions and membrane functionality • Keq = [C][D]/[A][B], G = -RTlnKeq and v = k[s] • P sensitivity of reactions: Kp = K1e(-PV/RT) and kp = k1e-PV‡/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

  5. Temperature • Along with pressure also plays an important role in biochemical reactions • Can 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

  6. What would limit organisms to a depth and temperature range in early ontogeny?

  7. Biochemical reactions during fertilization

  8. Program for post-fertilization changes in egg of sea urchins Epel 1975

  9. Ca-Wave After Fertilization

  10. Biochemical pathways are sensitive pathways • Could organisms, like mussels, with sensitive biochemical pathways colonize deep-sea habitat?

  11. How were deep sea environments colonized by mussels? Mestre et al. chose a shallow-water relative of a deep-sea inhabitant

  12. subfamilysMytilinae and Bathymodiolinae Phylogenetic Relationship Shallow water species Mytilusedulis found here The rest are associated with one of the following: Hydrothermal vent Cold-water seep Wood/bone (Kyuno et al. 2009)

  13. Free-spawning marine invertebrates Worldwide distribution Found in intertidal zones and estuariesEndure a wide range of temperatures and physical challenges Mytilusedulis

  14. 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.

  15. 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

  16. Methods • 3 Experiments • Temperature effect on embryonic larvae and development • Pressure effect on embryonic larvae and development with fertilization under pressure • Pressure effect on embryonic larvae and development with fertilization at atmospheric pressure

  17. Staging criteria for larvae:

  18. Embryonic stages Sixteen-cell stage Fertilized egg Two-cell stage Multi-cell stage D-larvae Early blastula Four-cell stage

  19. Temperature effect on embryonic larvae and development • 5 temperature treatments • 5, 10, 15, 20, and 25C, at atmospheric pressure • Incubated until all treatments had reached D-larvae stage.

  20. Pressure Experiments Pressure Vessels Plastic vial filled with the egg suspension and the microcentrifuge tube hald-filled with sperm suspension Pressure vessel showing the plastic vials inside Figure 1 from Mestre et al. 2009

  21. 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 20C • Pressure treatments • 1, 100, 200, and 300 atm • + 400 and 500atm for 4 hour treatments • Incubated for 4 and 24 hours

  22. Pressure effect on embryonic and larval development with fertilization at atmospheric pressure • Fertilization at atmospheric pressure, at 15C • Resulting embryos were incubated at 4 different pressures and 5 different temperatures • Temperature treatments • 5, 10, 15, 20, and 25C • Pressure treatments • 1, 100, 200, and 300 atm • Incubated for 50 hours

  23. Results • Divided results from 3 methods into 2 categories: • Temperature effects on embryonic and larval development • Pressure effects on embryonic and larval development

  24. Temperature effects on embryonic and larval development • Mytilusedulis embryos develop faster at higher temperatures • Effect in the proportion of abnormally developing embryos

  25. Pressure effects on embryonic and larval development with fertilization at atmospheric pressure after 50hrs

  26. Pressure effects with fertilization under pressure at 4 hours

  27. Pressure effects with fertilization under pressure at 24 hours

  28. Krustal-Wallis analysis of variance

  29. Conclusions • Temperature tolerance window is from approximately 10-20C • 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

  30. Was hypothesis correct? “reasonable to hypothesize that the invasion of the deep sea by M. edulis is possible in terms of pressure tolerances in embryos and larvae

  31. 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 Mytilusedulis. Proc. R. Soc. B 276, pp. 717-726.

  32. Discussion Questions • What other effects of pressure could cause developmental problems? • Do their results support direct colonization? • Last section of discussion implies it does

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