Are Internal, Death-Promoting Mechanisms Ever Adaptive?
|John W Pepper1,2, Deborah E Shelton1, Armin Rashidi1 and Pierre M Durand1,3*|
|1Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, USA|
|2National Cancer Institute, Bethesda, Maryland, USA|
|3Department of Molecular Medicine and Haematology, University of the Witwatersrand, Johannesburg, South Africa|
|Corresponding Author :||Pierre M Durand
Department of Molecular Medicine and Haematology
University of the Witwatersrand, Johannesburg, South Africa
E-mail: [email protected]
|Received March 26, 2013; Accepted July 08, 2013; Published July 18, 2013|
|Citation: Pepper JW, Shelton DE, Rashidi A, Durand PM (2013) Are Internal, Death-Promoting Mechanisms Ever Adaptive? J Phylogen Evolution Biol 1:113. doi: 10.4172/2329-9002.1000113|
|Copyright: © 2013 Pepper JW, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.|
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Natural selection acts primarily on organisms, and the existence of evolved, active, internal mechanisms that cause organismal death would seem paradoxical. However, there is substantial evidence that internal death promoting mechanisms exist and are taxonomically widespread. Where these are argued to be ‘programmed organismal death’ (POD), they require evolutionary explanations. Any such explanation must draw on our understanding of fitness trade-offs and multiple levels of selection in evolution. This review includes two main categories of putative POD: senescence in multicellular-organisms, and programmed cell death in unicellular organisms. The evidence for POD as a genetically controlled phenotype is strong for semelparous and significant but more controversial for iteroparous plants and animals. In multicellular organisms the program frequently (although not always) appears to be the result of fitness trade-offs. Here the death phenotype itself is not adaptive but the fitness related program most likely is. However, in some cases of behavioral suicide, particularly in insects, there are distinct advantages to kin and group level benefits may play a role. In unicells, programmed death is ubiquitous and POD often provides benefits to others. While benefits do not equate with adaptations, they are consistent with it. Here, death may be adaptive at a level other than the individual cell. In other instances of POD in unicells the phenotype (eg autophagy) can be explained as pleiotropy. The overall picture of POD as a natural phenomenon is still emerging, and continued work on diverse lines of evidence is necessary to complete our evolutionary understanding of this apparent paradox. While some questions remain, we conclude that POD is most likely, in some circumstances at least, adaptive.