Evolution of adaptive phenotypic traits without positive Darwinian selection

Abstract

Recent evidence suggests the frequent occurrence of a simple non-Darwinian (but non-Lamarckian) model for the evolution of adaptive phenotypic traits, here entitled the plasticity-relaxation-mutation (PRM) mechanism. This mechanism involves ancestral phenotypic plasticity followed by specialization in one alternative environment and thus the permanent expression of one alternative phenotype. Once this specialization occurs, purifying selection on the molecular basis of other phenotypes is relaxed. Finally, mutations that permanently eliminate the pathways leading to alternative phenotypes can be fixed by genetic drift. Although the generality of the PRM mechanism is at present unknown, I discuss evidence for its widespread occurrence, including the prevalence of exaptations in evolution, evidence that phenotypic plasticity has preceded adaptation in a number of taxa and evidence that adaptive traits have resulted from loss of alternative developmental pathways. The PRM mechanism can easily explain cases of explosive adaptive radiation, as well as recently reported cases of apparent adaptive evolution over ecological time.

Evolutionary Ecology of the Marine Roseobacter Clade

“…This coincidence of Roseobacter genome innovation with the radiation of red plastid phytoplankton is consistent with adaptive evolution, but the underlying population genetic mechanism of genome change is not clear and will be difficult, if not impossible, to test for such an ancient event. Genome changes may have been dominated by exaptations (69,70), in which case changes occurred by chance prior to roseobacters encountering the environment in which they proved useful. Alternatively, genome evolution may have been dominated by positive selection, as has been suggested for other marine bacterioplankton clades (71), in which case environmental change was followed by LGT events, which were then selectively favored.…”

Complex patterns of global spread in invasive insects: eco-evolutionary and management consequences

“…In fact, phenotypic plasticity itself -once considered an impediment to adaptive evolution -can mask cryptic diversity and promote the emergence of novel traits, ultimately leading to an increase in heritable genetic variation and to population and/or species divergence or local adaptation (Hughes et al 2008;Pfennig et al 2010;Hughes 2012). Additionally, theoretical models demonstrate that genetic bottlenecks have the capacity to increase additive genetic variation in affected populations -either by "converting" epistatic into additive variation via the fixation of some alleles due to drift (Goodnight 1988) or by increasing the frequency of rare recessive alleles at loci where dominance effects occur (Robertson 1952;Willis and Orr 1993).…”

Whole-genome sequencing identifies a recurrent functional synonymous mutation in melanoma

“…S2) each to have identical synonymous mutations in three and four additional cases, respectively. The frequency of these recurrent alterations in the validation sample is significantly elevated (P < 1 × 10 −7 and P < 1 × 10 −11 ), suggesting that they have either undergone relaxation of purifying selection (16) or been under selection during tumor development. Because BCL2L12 has previously been linked to tumorigenesis (17), we screened the BCL2L12 cytosine to thymine change at position 51 (F17F) in another 87 melanoma samples.…”

“…This study, thus, shows that synonymous mutations may be selected in cancer and play a role in tumorigenesis. Importantly, the selection mechanism may possibly be through the relaxation of purifying selection and/or the plasticity-relaxation-mutation mechanism as well as some other alternatives (16,(27)(28)(29)(30)(31) rather than positive selection. The data presented here cannot unambiguously select one specific mechanism.…”