In the Light of Evolution Volume I: Adaptation and Complex Design (2007) / Chapter Skim
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Pages 129-144
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From page 129... ...
We have modeled this hypothesis and have tested our models in two ways. We have studied the origin of the genetic basis for reproductive altruism (somatic cells specialized at vegetative functions)
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From page 130... ...
Being wholes, evolutionary individuals may be thought to be irreducibly complex, but this has not been the case during evolutionary history; a series of stages, each advantageous in itself, may be shown to exist allowing evolution to get from one kind of individual to another. The evolutionary concepts we use to understand evolutionary transitions in individuality involve fitness and its reorganization, fitness tradeoffs (especially the cost of reproduction to survival)
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From page 131... ...
Where two cell types are present (D–F) , the smaller cells are somatic cells and the larger cells are reproductive cells.
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From page 132... ...
The volvocine green algae, which by some estimates are between 38 and 70 million years old, present a nearly continuous array of differentiated stable forms representing each of the stages given above. There have been at least three independent origins of individuality based on specializa tion of reproductive and vegetative functions in this group (herron and Michod, in prep.)
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From page 133... ...
hence, the opportunity for conflict should be low in these groups. nevertheless, the opportunity for conflict can increase with the number of cell divisions and can depend on the type of development (e.g., rapid cell divisions, as in some volvocine algae, might not allow enough time for DnA repair)
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From page 134... ...
in the multicellular green alga V carteri, reproductive altruism is a property of the small flagellated somatic cells.
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From page 135... ...
Which cells express regA and differentiate into somatic cells is determined early in development through a series of asymmetric cell divisions. The asymmetric divisions ensure that some cells (i.e., the germ-line precursors)
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From page 136... ...
COST OF REPRODUCTION having considered how an altruistic gene might originate (by cooption of a life-history gene in a unicellular ancestor) , we now ask why this happens, that is, what are the selective forces favoring soma and reproductive altruism.
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From page 137... ...
she showed that the soma-to-reproductivecell ratio increases with colony size and that the investment in somatic tissue increases twice as fast with colony size as does the investment in germ tissue. however, no direct evidence was given as to why a higher investment in somatic cells is needed for motility as colony size increases.
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From page 138... ...
This bonus can be obtained only by groups. Alternatively, the bonus of specialization in soma may be viewed as the initial cost of somatic cells dedifferentiating into reproductive cells.
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From page 139... ...
The regA mutant indicates that flagellar force declines if somatic cells are to dedifferentiate and start reproducing. in addition, during development, as reproductive cells increase in size, motility does not change for small species, but declines for the larger species (solari, 2005; solari et al., 2006b)
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From page 140... ...
. COVARIANCE EFFECT Tradeoffs among the contributions of cells to the fitness components of the group leads to the ‘‘covariance effect,'' whereby the fitness of the group, W, is greater than the average fitness of its members, w, by the magnitude of the covariance among fitness components (Michod, 2006; Michod et al., 2006)
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From page 141... ...
Cell i specializes in reproductive effort, bi, with less effort put into vegetative functions, vi. Cell j does the reverse.
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From page 142... ...
how does a gene become altruistic? The hypothesis we have tested in the volvocine algae is that life-history genes in unicells may be coopted for reproductive altruism in the group.
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From page 143... ...
Cristian solari led the hydrodynamic work on motility. yannick viosatt had a principal role in the development of the covariance effect.
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