Evolutionary Trends in the Individuation and Polymorphism of Colonial Marine Invertebrates

by Venit, Edward Peter

Abstract (Summary)
All life is organized hierarchically. Lower levels, such as cells and zooids, are

nested within higher levels, such as multicellular organisms and colonial animals. The

process by which a higher-level unit forms from the coalescence of lower-level units is

known as “individuation”. Individuation is defined by the strength of functional

interdependencies among constituent lower-level units. Interdependency results from

division of labor, which is evidenced in colonial metazoans as zooid polymorphism. As

lower-level units specialize for certain tasks, they become increasing dependant on the

rest of the collective to perform other tasks. In this way, the evolution of division of

labor drives the process of individuation.

This study explores several ways in which polymorphism evolves in colonial

marine invertebrates such as cnidarians, bryozoans, and urochordates. A previous

study on the effect of environmental stability on polymorphism is revisted and

reinterpreted. A method for quantifying colonial-level individuation by measuring the

spatial arrangement of polymorphic zooids is proposed and demonstrated. Most

significantly, a comparison across all colonial marine invertebrate taxa reveals that

polymorphism only appears in those colonial taxa with moderately to strongly

compartmentalized zooids. Weakly compartmentalized and fully compartmentalized

taxa are universally monomorphic. This pattern is seen across all colonial marine

invertebrate taxa and is interpreted as a “rule” governing the evolution of higher-level

individuation in the major taxa of colonial marine invertebrates. The existence of one

rule suggests that there may be others, including rules that transcend levels of biological

hierarchy. The identification of such rules would strongly suggest that new levels in the

hierarchy of life evolve by a universal pattern that is independent of the type of

organism involved.

Bibliographical Information:

Advisor:McShea, Daniel W.; Brandon, Robert; Johnson, Sonke; Roth, V. Louise; Wray, Gregory

School:Duke University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:individuation division of labor polymorphism colony hierarchy colonial marine invertebrates


Date of Publication:05/10/2007

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