La Sapienza - Università di Roma

logo de La Sapienza per la stampa

Beyond Darwinian Selection: Environmental Stress

18-12-2017

A research group at the Sapienza Department of Biology and Biotechnology has reinterpreted one of the most important hypotheses on the heritability of anomalous morphological characters, acquired as a result of environmental stress. The study, funded by the Istituto Pasteur Italia - Fondazione Cenci Bolognetti and Epigenomics Flagship Project EpiGen, has been published on the Genetics magazine.

Despite the general agreement on Darwin’s Theory of Natural Selection, the scientific community has never completely abandoned the hypothesis of apparent inheritance of acquired characters caused by environmental factors.

The Sapienza Research Group analysed this phenomenon through experiments conducted on Drosophila melanogaster fruit flies. The results of the study, selected for the F1000Prime, have been published on the Genetics magazine.

In the 1940s, Conrad Waddington had submitted fruit flies to thermal shocks during their metamorphosis stage. Following this treatment, during the adult phase, the fruit flies exhibited abnormal morphological characters and, after repeated stress cycles at each generation, these characteristics became inheritable (i.e., they were transmitted to the following generations even in the absence of stress). Waddington hypothesized that the anomalous characters were not acquired as a result of environmental stress, but were caused by pre-existing genetic variability: they were cryptic characteristics that were already present in their genome. However, the Sapienza team has formulated a new explanation.

Using new molecular technologies based on DNA sequencing, Sapienza researchers demonstrated that these abnormalities arise from ex-novo changes in the genome caused by stress. In fact, heat stress can cause damage to the DNA and loss of genes, as well as the movement of transposable elements (i.e. particular gene sequences that have the ability to jump from one side of the genome to another, causing mutations). Therefore, the inheritance of abnormal characters caused by shock is not due to a cryptic variation present in the genome, but to a mechanism of mutagenesis.

"This model,” explains Sapienza Researcher Laura Fanti, “has important evolutionary implications. Environmental changes can induce non-hereditary adaptive modifications in organisms - through so-called epigenetic mechanisms – as well as mutations in their germ cells with a consequent increase in genetic variability."

In fact, phenotypic variations, which appear as a consequence of environmental stress (undergone during a critical phase of development) can be "incorporated" into the genetic heritage of biological organisms by induction and selection of corresponding gene variants, so that these variants continue to be produced even in the absence of any external stimuli. Reinterpreting the stabilization of adaptive characters by means of natural selection means proposing a new mechanism of evolution, within a Darwinian framework.

"The understanding of the evolutionary mechanisms that have led to the appearance of all life forms on the planet,” concludes Laura Fanti, “is important because it offers us the opportunity to understand current changes and predict future ones, allowing us to make appropriate choices to preserve the environment and our health."

References:

Canalization by Selection of de Novo Induced Mutations - Laura Fanti, Lucia Piacentini, Ugo Cappucci, Assunta M. Casale and Sergio Pimpinelli – Genetics, August 1, 2017 vol. 206 n.4 1995-2006; https://doi.org/10.1534/genetics.117.201079