Mutational heterogeneity: A key ingredient of bet‐hedging and evolutionary divergence?

Abstract

Here, we propose that the heterogeneity of mutational types in populations underpins alternative pathways of evolutionary adaptation. Point mutations, deletions, insertions, transpositions and duplications cause different biological effects and provide distinct adaptive possibilities. Experimental evidence for this notion comes from the mutational origins of adaptive radiations in large, clonal bacterial populations. Independent sympatric lineages with different phenotypes arise from distinct genetic events including gene duplication, different insertion sequence movements and several independent point mutations. The breadth of the mutational spectrum in the ancestral population should be viewed as a form of bet-hedging, reducing the risk of evolutionary dead ends and complementing the phenotypic and epigenetic heterogeneities that improve the survival capabilities of a population. Different mutational events arise from distinct cellular processes and are subject to separate environmental impacts, so the availability of any particular type of mutation may constrain or promote adaptive pathways in populations.

The Identification of Intrinsic Chloramphenicol and Tetracycline Resistance Genes in Members of the Bacillus cereus Group (sensu lato)

“…One possibility is that they are transcribed from non-vegetative Sigma factor promoters induced, for example, in response to specific stresses, quorum sensing pheromones or differentiation processes, and that are not encountered under the MIC test conditions. Another is that their expression has been down regulated over evolutionary time by single base-pair mutations that, as a bet-hedging strategy (Ferenci and Maharjan, 2015), are able to revert at a high frequency and subsequently selected under appropriate conditions. This might account for the resistance phenotypes of B. toyonensis BCT-7112 T .…”

Antibiotic resistance in Enterobacteriaceae: mechanisms and clinical implications

“…There may be great differences between MIC and MBC, which vary with organism, drug, and growth conditions as different populations arise among the progeny of a single organism to suit changed conditions. 74 75 Acquired antibiotic resistance thus results from normal adaptive capacities that are a balance of compromises or evolutionary tradeoffs, [76][77][78] and that do not necessarily require acquisition of new genetic material.…”

Irregularities in genetic variation and mutation rates with environmental stresses

“…It is almost impossible to predict whether, say, an increase in transpositions rather than BPSs or indels increases or decreases the possibility of beneficial mutations. As discussed in detail elsewhere, new mutations may need to be of particular types to impart a benefit (Ferenci and Maharjan, ). For example, gains of new protein functions through substitutions (e.g.…”

“…A further fundamental question is whether the individual mixes of mutations seen in different environments have direct benefits in adapting to these environments; is it significant that phosphate limitation generates a different mix of mutations to carbon limitation (Maharjan and Ferenci, )? This leads to the core unresolved question (Ferenci and Maharjan, ; Agashe, ) of how environments and mutations affect evolutionary pathways in natural habitats.…”