Ants look back on an evolutionary story of success. The photo shows workers of the Asian weaver ant.
© Lukas Schrader
One of creationism’s favourite assertions is that evolution cannot produce “new genetic information” without an intelligent designer. What usually goes missing is a clear definition of information, an explanation of why known genetic mechanisms cannot generate novelty, or any evidence of the supposed designer doing anything. Meanwhile, evolutionary biologists continue to investigate the natural processes by which genomes change and organisms acquire new capabilities. A new study of ants provides another example of how productive that scientific approach can be.
As reported in Science Advances, an international team led by Dr Lukas Schrader has investigated the contribution of transposable elements, commonly called “jumping genes”, to ant evolution. These mobile DNA sequences can move or copy themselves within genomes. Their activity can be disruptive, but it can also supply material for evolutionary innovation. The research links their activity to the expansion of gene families, including those encoding the odour receptors so important to ants’ chemical communication.
The researchers compared genomes from 163 ant species, representing twelve of the sixteen living subfamilies. They identified independent bursts of transposable-element activity in the ancestors of major ant groups, preceding their rapid diversification following the Cretaceous–Palaeogene, or K–Pg, mass extinction approximately 66 million years ago. The findings support a connection between changes within genomes and the evolutionary opportunities created by a profoundly altered world.
The evolutionary significance is straightforward. A mass extinction changes the conditions under which survivors live: ecological relationships are disrupted, resources become available in different ways, and opportunities arise as ecosystems recover. A genetic variant that previously offered little advantage may become useful under these new conditions. Natural selection can then favour organisms carrying it. Neither the mutation nor the environmental upheaval needs to anticipate the outcome.
Nor does genetic novelty require a complete, finished gene to appear from nowhere. Duplication supplies additional copies of existing sequences, which can subsequently diverge; changes to the regulation and arrangement of DNA can also alter what an organism does. Calling the starting material “existing information” does nothing to prevent its descendants from acquiring new functions. The relevant questions concern what changed, how it changed, and what consequences followed—not whether creationists are willing to call the result “information”.
Here, the specific finding is an association between mobile DNA, expanding gene families and subsequent diversification. It should not be inflated into a claim that every extra receptor acquired a demonstrated new function, or that the asteroid impact directly produced particular beneficial mutations. Nevertheless, the study supplies evidence for a natural route connecting genomic change with evolutionary diversification, precisely where the creationist argument substitutes an assertion of impossibility.
For young-Earth creationists, there is the additional inconvenience of the timescale. This diversification followed an extinction event some 66 million years ago—thousands of times further into the past than their entire supposed history of the Universe allows. Ant evolution was already unfolding in a world unimaginably ancient by biblical standards. What emerges is a history of genetic change, environmental catastrophe and opportunities exploited by surviving lineages, without foresight or a predetermined destination.
How jumping genes generate evolutionary novelty A genome is not a fixed instruction book. DNA sequences can be copied, rearranged, altered and recruited for different functions. Among the contributors to this continual change are transposable elements, popularly known as “jumping genes”.The paper in Science Advances was accompanied by a University of Münster news release:
What actually jumps?
Transposable elements are stretches of DNA capable of moving or producing copies that insert elsewhere in a genome. Many DNA transposons use a mechanism resembling “cut and paste”, while retrotransposons spread through “copy and paste”: their DNA is transcribed into RNA, which is then copied back into DNA and inserted at another location. Many ancient copies eventually lose their ability to move, leaving traces of earlier activity.
How can this produce something new?
Several routes connect mobile DNA with genetic novelty:
Why are extra gene copies useful?
- Changing gene regulation. An insertion can affect when, where or how strongly a nearby gene is expressed. Transposable elements can also supply regulatory sequences that become incorporated into the host’s gene-control systems.
- Facilitating duplication and rearrangement. Repeated copies at different locations can promote recombination between the wrong positions, sometimes duplicating, deleting or rearranging neighbouring DNA. Some mobile elements can also carry gene fragments to new locations.
- Supplying material for new functions. Sequences originating in transposable elements can become parts of genes or acquire useful regulatory roles. Evolution can recruit material whose original activity served the element’s own propagation.
Gene duplication creates additional genetic material on which evolution can act. One copy may preserve an ancestral function while another accumulates changes. Sometimes the copies divide the original gene’s roles between them; occasionally, one acquires a new function. Many duplicates are eventually lost or disabled, so duplication provides an opportunity, not a guarantee of improvement.
A new gene therefore need not appear fully formed from an entirely unrelated sequence. Copying, modification and changes in regulation can generate novelty through a succession of inherited steps.
Why does this matter to ants?
Ants depend heavily on chemical signals to locate food, recognise nestmates and coordinate colony activities. Odour receptors help them detect these signals, making the evolution of receptor repertoires particularly relevant to their ecology.
The new study associates transposable elements with expansions of odour-receptor and other gene families. It also identifies bursts of mobile-element activity preceding the diversification of major ant lineages after the K–Pg extinction. These findings support a contribution to evolutionary innovation; they do not establish that every additional receptor acquired a new function or that every insertion was beneficial.
When catastrophe changes what is useful
The K–Pg mass extinction, approximately 66 million years ago, profoundly disrupted ecosystems. During recovery, changing habitats, resources and interactions among species created ecological opportunities for surviving lineages.
Under changed conditions, an inherited variant that previously offered little advantage may increase survival or reproductive success. Natural selection can then increase its frequency. Both existing variation and newly arising mutations can contribute to adaptation.
The environment changes which variants succeed; it does not need to specify the mutations that organisms require. The proposed connection in ants is that genomic variation helped surviving lineages exploit ecological opportunities, without foresight or a predetermined outcome.
Are jumping genes always helpful?
No. Insertions can disrupt genes, interfere with their regulation or destabilise chromosomes. Others have little detectable effect. Transposable elements can spread because they replicate effectively, even when they provide no benefit to their host. Their occasional recruitment into useful functions does not make every copy purposeful or advantageous.
Glossary
- Transposable element
- A DNA sequence capable of changing position or generating copies elsewhere in a genome.
- Gene duplication
- The production of an additional copy of a gene.
- Gene regulation
- Control of when, where and how much a gene is expressed.
- Natural selection
- Differences in survival and reproduction associated with heritable variation, which can change the frequencies of variants over generations.
- Adaptive radiation
- The diversification of an ancestral lineage into species adapted to different ecological roles.
“Jumping genes” helped ants in their evolutionary triumph after the extinction of the dinosaurs
Researchers led by a biologist from the University of Münster assume that mobile DNA elements enable increased speciation
About 66 million years ago, the asteroid that ended the age of the dinosaurs paved the way for a spectacular expansion of new animal species. During this period, ants rose to ecological dominance. Today, they form the largest family of social insects with more than 15,000 species worldwide. New research now published in “Science Advances” shows that ants benefited from so-called transposable elements in their DNA, which are often referred to as “jumping genes”. The study was conducted by an international research team led by Dr Lukas Schrader from the Institute for Evolution and Biodiversity (IEB) at the University of Münster.
Ants look back on an evolutionary story of success. The photo shows workers of the Asian weaver ant.© Lukas Schrader
Jumping genes are DNA sequences that can move and replicate within a genome. For a long time, they were regarded as “genomic parasites” that, similar to viruses, multiply in the genome without benefiting their host and, in the worst case, can even cause diseases. However, they are now increasingly recognised as engines of evolutionary innovation. The new study shows that those ant lineages carrying the most transposable elements in their genomes are also the most species-rich today. Even more striking, the researchers identified independent bursts of transposable element activity in the ancestors of the largest ant groups in the early Palaeogene (about 66 million years ago), shortly before these lineages diversified into the thousands of species living today.The asteroid impact had dramatic consequences for the environment. We have now found the genomic mechanism that connects these ecological upheavals to the subsequent rapid diversification of the ants: transposable elements.
Lukas Schrader, first author
Institute for Evolution and Biodiversity
University of Münster
Münster, Germany.
Comparable patterns have been identified in other animal groups, with studies showing bursts of jumping gene activity during more recent phases of increased speciation, for example in primates and bats.
The team of the new study also linked transposable elements to the expansion of important gene families involved in chemical communication. Odorant receptors, which are essential for the social life of ants, played a particular role in this process – ants navigate, recognise nestmates and coordinate colonies almost exclusively by smell. Their ability to recognise and interpret chemical signals may have been enhanced by the restless activity of their own genomes.
For the current study, the team analysed and compared the genomes of 163 ant species from twelve of the 16 ant subfamilies living today, reconstructing the evolutionary history and activity of transposable elements over the past 100 million years.
Publication:
The difficulty for creationism is that genomes contain evidence of the very processes its advocates insist cannot produce evolutionary novelty. DNA is copied, rearranged and modified, and some of the resulting variation becomes useful. This study links mobile genetic elements with expanding gene families and the diversification of ants, adding to our understanding of how natural processes supply material for evolution. Invoking a designer contributes no mechanism, no testable prediction and no explanation of the observed patterns.
The relationship with the K–Pg extinction also illustrates why evolution needs no foresight. The catastrophe did not occur in order to help ants diversify, nor did their genomes anticipate the opportunities that would follow. Environmental upheaval changed the conditions under which inherited variations were advantageous. Through differential survival and reproduction, natural selection could favour variants that helped their carriers exploit the altered world. There was no requirement for a plan—just genetic variation, ecological opportunity and consequences accumulated over generations.
Nor does the occasional usefulness of transposable elements turn them into evidence of intelligent engineering. These same processes can disrupt genes, produce harmful changes or leave copies with no useful role. Evolution can recruit a beneficial consequence of an otherwise selfish genetic element without that element having arisen for the host’s benefit. This mixture of damage, redundancy and occasional innovation is entirely consistent with an unplanned evolutionary history.
For young-Earth creationists, the chronology presents an additional, fundamental problem. The diversification discussed here followed events approximately 66 million years ago, vastly predating their supposed Creation Week. The evidence concerns both how life changes and the immense time over which those changes have occurred. Neither problem disappears by repeating that new genetic information requires a designer.
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