The Shifting Role of Cell Division During an Evolutionary Transition to Multicellular-Level Individuality

Persistent Link:
http://hdl.handle.net/10150/311564
Title:
The Shifting Role of Cell Division During an Evolutionary Transition to Multicellular-Level Individuality
Author:
Shelton, Deborah
Issue Date:
2013
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
During the transitions from unicellularity to multicellularity, cells transitioned from functioning as wholes to functioning as parts of wholes. In the colonial freshwater green flagellates known as volvocine algae, living "intermediate form" species give ample evidence concerning how cells gradually lost autonomy and began functioning as dedicated parts. This dissertation concerns how and why the role of cell division changed in unicellular to colonial volvocine algae. We review a recent book on levels of selection and apply a proposed three-stage transition to the example of volvocine algae. We found that, in contrast to the previous description of "stage 1", the concept of group reproduction is potentially applicable to very early-branching colonial volvocine algae. This possibility indicates that the role of cell division could have shifted (to function in group reproduction) earlier than was previously thought (Appendix A). We show that, given some reasonable assumptions, cell- and colony-level fitness are equivalent in undifferentiated colonial volvocines (Appendix B). In spite of this, our models show that cell division number could evolve in response to specifically colony-level factors. Cell division number could be regulated indirectly via allocation to growth (Appendix B) or directly via regulation of the growth-to-first division transition (Appendix C). The extent to which group factors matter in the outcome of selection on cell division number is a matter of degree and is quantifiable (Appendix B). Colony cell number could be a genuine group-level adaptation, even in the simplest volvocine algae (Appendix B and C). Because a size-dependent growth trajectory is a substantial group-level cost of higher division numbers, our analysis highlights the potential importance of understanding how colony size affects cell growth (Appendix C). We also present data on cell-type allocation in Volvox (Appendix D). The Volvox colony is clearly the level of function for cell divisions and cell fate acquisition. However, this work indicates that the precision with which Volvox development attains these colony-level goals may be low compared to more complex multicellular organisms.
Type:
text; Electronic Dissertation
Keywords:
Ecology & Evolutionary Biology
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Ecology & Evolutionary Biology
Degree Grantor:
University of Arizona
Advisor:
Michod, Richard E.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleThe Shifting Role of Cell Division During an Evolutionary Transition to Multicellular-Level Individualityen_US
dc.creatorShelton, Deborahen_US
dc.contributor.authorShelton, Deborahen_US
dc.date.issued2013-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractDuring the transitions from unicellularity to multicellularity, cells transitioned from functioning as wholes to functioning as parts of wholes. In the colonial freshwater green flagellates known as volvocine algae, living "intermediate form" species give ample evidence concerning how cells gradually lost autonomy and began functioning as dedicated parts. This dissertation concerns how and why the role of cell division changed in unicellular to colonial volvocine algae. We review a recent book on levels of selection and apply a proposed three-stage transition to the example of volvocine algae. We found that, in contrast to the previous description of "stage 1", the concept of group reproduction is potentially applicable to very early-branching colonial volvocine algae. This possibility indicates that the role of cell division could have shifted (to function in group reproduction) earlier than was previously thought (Appendix A). We show that, given some reasonable assumptions, cell- and colony-level fitness are equivalent in undifferentiated colonial volvocines (Appendix B). In spite of this, our models show that cell division number could evolve in response to specifically colony-level factors. Cell division number could be regulated indirectly via allocation to growth (Appendix B) or directly via regulation of the growth-to-first division transition (Appendix C). The extent to which group factors matter in the outcome of selection on cell division number is a matter of degree and is quantifiable (Appendix B). Colony cell number could be a genuine group-level adaptation, even in the simplest volvocine algae (Appendix B and C). Because a size-dependent growth trajectory is a substantial group-level cost of higher division numbers, our analysis highlights the potential importance of understanding how colony size affects cell growth (Appendix C). We also present data on cell-type allocation in Volvox (Appendix D). The Volvox colony is clearly the level of function for cell divisions and cell fate acquisition. However, this work indicates that the precision with which Volvox development attains these colony-level goals may be low compared to more complex multicellular organisms.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectEcology & Evolutionary Biologyen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineEcology & Evolutionary Biologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorMichod, Richard E.en_US
dc.contributor.committeememberMichod, Richard E.en_US
dc.contributor.committeememberBadyaev, Alexanderen_US
dc.contributor.committeememberElliott, Daviden_US
dc.contributor.committeememberMonti-Masel, Joannaen_US
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