Tiny molecules drove the evolution of the vertebrates

Blogging on Peer-Reviewed ResearchThe spinal column that runs down your back is an identity badge that signifies your membership among the vertebrates – animals with backbones. Vertebrates have arguably the most complex bodies and genomes of any animal group and certainly, our lineage has come a long way from its last common ancestor.

TigerThe closest evolutionary cousins of the vertebrates are simple aquatic creatures such as the jawless lancelets and the sac-like, immobile sea squirts. How did these simple body plans diversify into the vast array of sophisticated forms wielded by today’s fish, amphibians, reptiles and mammals?

Gene number

Many scientists have suggested that the answer lies in the number of our genes. At three different points, the vertebrate genome (its full suite of genes) experienced a massive jump in size as huge chunks of genes – possibly the entire lot – were duplicated. The first of these coincided with the origins of the group itself and the second happened alongside the rise of the first jawed fish, setting them and their descendants aside from more ancient jawless forms like the lampreys.

So far, there seems to be a tidy connection between gene number and complexity, but the third round of duplication is a bit of a stumbling block. It happened at some point during the evolution of the bony fishes and while this group proceeded to radiate into a multitude of different shapes, their basic body plan stayed essentially the same. No big jump in complexity there.

Indeed, as the full genome sequences of more and more species are revealed, it’s becoming clear that the basic genetic toolkit that controls the development of animal bodies is remarkably consistent across the kingdom. Even the genome of a sea anemone, one of the simplest and most ancient animals on Earth, is strikingly similar to that of vertebrates.

In this light, it’s looking increasingly unlikely that the advent of new genes can account for the large rise in vertebrate complexity. Now, Alysha Heimberg and colleagues from Dartmouth College have proposed a new theory, centred around tiny molecules called microRNAs.

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Is a virus responsible for the disappearing bees?

A group of scientists have found that a virus – IAPV – may be responsible for Colony Collapse Disorder, the mysterious condition that’s emptying the hives of European and American beekeepers.

A bee sits on a readout of its own genetic material.In 2006, American and European beekeepers started noticing a strange and worrying trend – their bees were disappearing. Their hives, usually abuzz with activity, were emptying.

Like honeycombed Mary Celestes, there was no trace of the workers or their corpses either in or around the ghost hives, which still contained larvae and plentiful stores of food. It seemed that entire colonies of bees had apparently chosen not to be.

The cause of the aptly named ‘Colony Collapse Disorder’, or CCD, has been hotly debated over the last year. Fingers were pointed at a myriad of suspects including vampiric mites, pesticides, electromagnetic radiation, GM crops, climate change and poor beekeeping practices. And as usual, some people denied that there was a problem at all.

But a large team of US scientists led by Diana Cox-Foster and Ian Lipkin have used modern genomics to reveal the main villain in this entomological whodunnit – a virus called Israeli Acute Paralysis Virus or IAPV.

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An entire bacterial genome discovered inside that of a fruit fly

Bacteria have the ability to transfer genes to one another. Now, scientists have found that one species, Wolbachia, has managed to transfer its entire genome into that of a fruit fly. These extreme gene transfers could be more common than we thought, and they have important consequences for genome-sequencing projects.

Wolbachia in yellow infecting insect cells in red.A humble species of fruit fly is the genetic equivalent of a Russian doll – peer inside its DNA and you will see the entire genome of a species of bacteria hidden within.

The bacteria in question is Wolbachia, the most successful parasite on earth and infects about 20% of the world’s species of insects. It’s a poster child for selfishness. To further its own dynasty, it has evolved a series of remarkable techniques for ensuring that it gets passed on from host to host. Sometimes it gives infected individuals the ability to reproduce asexually; at other times, it does away with an entire gender.

Now, Julie Dunning-Hotopp from the J. Craig Venter Institute and Michael Clark from the University of Rochester have found an even more drastic strategy used by Wolbachia to preserve its own immortality – inserting its entire genome wholesale into that of another living thing. Continue reading

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