New Species, Born in Conflict?

Heraclitus, as pictured in Raphael’s School of Athens (Wikimedia commons, public domain)

The ancient and mysterious Greek philosopher Heraclitus once purportedly said that war is the father of all things. Now, a recent article in Trends in Ecology and Evolution presents a new perspective on the phrase.

The genome, that collection of genes representing the hereditary information of an organism might seem like quite a peaceful place. But, make no mistake, sometimes it’s a battlefield where genes succumb to conflict among themselves. This phenomenon is known as intragenomic conflict and more and more research shows that it’s not that rare, leading Egbert Leigh to describe the genome as a ‘parliament of genes’.

In the article, it is proposed that such intragenomic conflict could lead to the birth of new species, a process they term conflictual speciation (CS). In the words of the authors:

…CS by intragenomic conflict involves divergence between populations due to antagonistic interactions between opposing elements within a genome. Such interactions are expected to lead to genetic divergence, between populations, in pairs or larger sets of antagonistically-interacting loci.

In other words, conflict among genes can lead to genetic differences in populations, potentially resulting in the origination of new species. However, the authors are careful enough to mention that intragenomic conflict can, but need not, lead to speciation. Suppressing elements can arise, or if these are not (yet) in place, the battle might result in a unanimous winner.

However, the researchers stress that recent work suggests that intragenomic conflict often seems to be associated with reproductive isolation and list some mechanisms that could potentially cause CS through intragenomic conflict:

• Drive, or the phenomenon that some genes try their best to end up in more than half of the offspring.

• Transposons, or ‘jumping genes’. Genetic elements that, as the name implies, copy or cut and paste themselves into new places in the genome, even when detrimental to the rest of the ‘parliament’.

• Imprinting, or the event where genes are expressed differently depending on which parent they come from, with potential conflict between mum’s and dad’s genes.

• Cytonuclear conflict, or the struggle between genes in the nucleus and those elsewhere in the cell (such as the genes in the mitochondria).

• Chromosomal conflict, or the clash between autosomal (= non-sex) chromosomes, X, and Y chromosomes.

All these phenomena are known, and the authors propose that, given the right circumstances, they can all contribute to the rise of new species.

The Origin of it all… (Wikimedia Commons, public domain)

The hypothesis of conflictual speciation is mostly based on fairly recent observations and findings and needs further support. Some ideas for further research from the authors:

• More theoretical modeling to figure out the conditions that can promote CS.

• Studying populations at different points in the speciation process in order to find out whether intragenomic conflicts cause or follow reproductive isolation (perhaps both possible?).

• Incorporating molecular and genetic analyses in field, lab and comparative studies.

So, can new species be forged in the fire of gene battles? Perhaps. The possibility shouldn’t be discarded, as the authors note in their conclusion:

…, the study of CS and its mechanisms interfaces closely with several fields of applied importance, including human fertility, the somatic evolution of cancer, and  improvement of major crop plants. Most generally, a comprehensive understanding of how conflictual as well as extrinsic ecological selection contribute to speciation should provide new insights into the origins of diversity at all levels, from cells to the major lineages of life.

Old Heraclitus would have liked it.

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Crespi, B., & Nosil, P. (2013). Conflictual speciation: species formation via genomic conflict Trends in Ecology & Evolution, 28 (1), 48-57 DOI: 10.1016/j.tree.2012.08.015