Testing the neutral hypothesis of phenotypic evolution
Wei-Chin Hoa, Yoshikazu Ohyab, and Jianzhi Zhanga,1
Author Affiliations
Edited by Wen-Hsiung Li, Academia Sinica, Taipei, Taiwan, and approved October 6, 2017 (received for review June 29, 2017)
Source/Fonte: Amazon Books
Significance
Despite the universal recognition that adaptation by Darwinian selection can shape phenotypic variations within and between species, it remains unknown whether most phenotypic variations observed have adaptive values, in part because addressing this question requires examining a large, random set of traits while past studies were biased toward traits that are likely adaptive. Here, we study 210 yeast morphological traits chosen purely on the basis of experimental feasibility and expression levels of all yeast genes with reliable measurements. We find that morphological variations, but not expression variations, are largely adaptive, suggesting that different classes of phenotypic traits are subject to adaptive evolution to varying extents.
Abstract
Although evolution by natural selection is widely regarded as the most important principle of biology, it is unknown whether phenotypic variations within and between species are mostly adaptive or neutral due to the lack of relevant studies of large, unbiased samples of phenotypic traits. Here, we examine 210 yeast morphological traits chosen because of experimental feasibility irrespective of their potential adaptive values. Our analysis is based on the premise that, under neutrality, the rate of phenotypic evolution measured in the unit of mutational size declines as the trait becomes more important to fitness, analogous to the neutral paradigm that functional genes evolve more slowly than functionless pseudogenes. However, we find faster evolution of more important morphological traits within and between species, rejecting the neutral hypothesis. By contrast, an analysis of 3,466 gene expression traits fails to refute neutrality. Thus, at least in yeast, morphological evolution appears largely adaptive, but the same may not apply to other classes of phenotypes. Our neutrality test is applicable to other species, especially genetic model organisms, for which estimations of mutational size and trait importance are relatively straightforward.
adaptation gene expression morphology neutrality yeast
Footnotes
1To whom correspondence should be addressed. Email: jianzhi@umich.edu.
Author contributions: W.-C.H. and J.Z. designed research; W.-C.H. and Y.O. performed research; Y.O. contributed new reagents/analytic tools; W.-C.H. analyzed data; and W.-C.H. and J.Z. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1710351114/-/DCSupplemental.
Published under the PNAS license.
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