Abstract Detail

Evolutionary Developmental Biology (Evo-Devo)

Niklas, Karl [1], Cobb, Edward [2].

Evolutionary origins of multicellularity.

The traditional scenario for the evolution of multicellular plants and animals involves an evolutionary sequence starting with a unicellular organism that evolved a colonial body plan that subsequently evolved into a multicellular organism. This sequence requires two evolutionary phases: (1) an alignment-of-fitness phase in which genetic similarity among cells prevents cell-cell conflict, and (2) an export-of-fitness phase in which cells become interdependent and collaborate in a sustained effort. The first of these two phases establishes the colonial body plan; the second of these two phases establishes the multicellular body plan. An examination of molecular plant phylogenies supports the unicellular-to-colonial-to-multicellular scenario, which indirectly supports the necessity of the two phases (and thus the traditional evolutionary model for the origins of multicellularity). However, an alternative scenario for the evolution of multicellular organisms is equally viable both theoretically and empirically. This alternative scenario begins with a siphonous organism that evolves the multicellular body plan directly. This evolutionary transition does not require the alignment-of-fitness phase (because, barring mutations, all the nuclei in the siphonous organism are genetically identical and thus have no conflict of interest) nor does it require the export-of-fitness phase (because the formation of individualized cells does not interfere a priori with the somatic or reproductive missions of nuclei derived directly from a siphonous progenitor). Empirically, the transition from a siphonous to a multicellular body plan is seen in the development of siphonocladous algae, i.e., segregative cell division, which may reflect the evolutionary co-option of a wound response in a siphonous progenitor. These concepts and speculations will be discussed and illustrated as an alternative to the “standard model” for the origin of multicellular organisms.

Broader Impacts:

1 - Cornell University, Plant Biology, 412 Mann Library, ITHACA, NY, 14853-5908, USA
2 - Cornell University, Department of Plant Biology, 412 Mann Library, Ithaca, NY, 14853-5908, USA

Keywords:
body plans
Algae
siphonous body plan
segregative cell division.

Presentation Type: Oral Paper:Papers for Topics
Session: 47
Location: Jasperwood/Riverside Hilton
Date: Wednesday, July 31st, 2013
Time: 1:30 PM
Number: 47001
Abstract ID:188
Candidate for Awards:None