̽��ֱ�� of Cambridge - Australian National ̽��ֱ��

Cuckoos evolve to look like their hosts - and form new species in the process

jg533 — Thu, 30 May 2024 18:05:07 +0000

̽��ֱ��theory of coevolution says that when closely interacting species drive evolutionary changes in each other this can lead to speciation - the evolution of new species. But until now, real-world evidence for this has been scarce.

Now a team of researchers has found evidence that coevolution is linked to speciation by studying the evolutionary arms race between cuckoos and the host birds they exploit.

Bronze-cuckoos lay their eggs in the nests of small songbirds. Soon after the cuckoo chick hatches, it pushes the host’s eggs out of the nest. ̽��ֱ��host not only loses all its own eggs, but spends several weeks rearing the cuckoo, which takes up valuable time when it could be breeding itself.

Each species of bronze-cuckoo closely matches the appearance of their host’s chicks, fooling the host parents into accepting the cuckoo.

̽��ֱ��study shows how these interactions can cause new species to arise when a cuckoo species exploits several different hosts. If chicks of each host species have a distinct appearance, and hosts reject odd-looking nestlings, then the cuckoo species diverges into separate genetic lineages, each mimicking the chicks of its favoured host. These new lineages are the first sign of new species emerging.

̽��ֱ��study is published today in the journal Science.

“This exciting new finding could potentially apply to any pairs of species that are in battle with each other. Just as we’ve seen with the cuckoo, the coevolutionary arms race could cause new species to emerge - and increase biodiversity on our planet,” said Professor Kilner in the ̽��ֱ�� of Cambridge’s Department of Zoology, a co-author of the report.

̽��ֱ��striking differences between the chicks of different bronze-cuckoo lineages correspond to subtle differences in the plumage and calls of the adults, which help males and females that specialise on the same host to recognise and pair with each other.

“Cuckoos are very costly to their hosts, so hosts have evolved the ability to recognise and eject cuckoo chicks from their nests,’’ said Professor Naomi Langmore at the Australian National ̽��ֱ��, Canberra, lead author of the study.

She added: “Only the cuckoos that most resemble the host’s own chicks have any chance of escaping detection, so over many generations the cuckoo chicks have evolved to mimic the host chicks.”

̽��ֱ��study revealed that coevolution is most likely to drive speciation when the cuckoos are very costly to their hosts, leading to a ‘coevolutionary arms race’ between host defences and cuckoo counter-adaptations.

A broad scale analysis across all cuckoo species found that those lineages that are most costly to their hosts have higher speciation rates than less costly cuckoo species and their non-parasitic relatives.

“This finding is significant in evolutionary biology, showing that coevolution between interacting species increases biodiversity by driving speciation,” said Dr Clare Holleley at the Australian National Wildlife Collection within CSIRO, Canberra, senior author of the report.

̽��ֱ��study was made possible by the team’s breakthrough in extracting DNA from eggshells in historical collections, and sequencing it for genetic studies.

̽��ֱ��researchers were then able to combine two decades of behavioural fieldwork with DNA analysis of specimens of eggs and birds held in museums and collections.

̽��ֱ��study involved an international team of researchers at the ̽��ֱ�� of Cambridge, Australian National ̽��ֱ��, CSIRO (Australia’s national science agency), and the ̽��ֱ�� of Melbourne. It was funded by the Australian Research Council.

Reference: Langmore, N E et al: ‘Coevolution with hosts underpins speciation in brood-parasitic cuckoos.’ Science, May 2024. DOI: 10.1126/science.adj3210

Adapted from a press release by the Australian National ̽��ֱ��.

Two decades of cuckoo research have helped scientists to explain how battles between species can cause new species to arise

This exciting new finding could potentially apply to any pairs of species that are in battle with each other...the coevolutionary arms race could cause new species to emerge - and increase biodiversity on our planet

Rebecca Kilner

Mark Lethlean

Male wren (left) brings food to a cuckoo fledgling (right)

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Ancient stars at the centre of the Milky Way contain ‘fingerprints’ from the very early Universe

sc604 — Wed, 11 Nov 2015 18:00:00 +0000

An international team of astronomers, led researchers from the ̽��ֱ�� of Cambridge and the Australian National ̽��ֱ��, have identified some of the oldest stars in our galaxy, which could contain vital clues about the early Universe, including an indication of how the first stars died.

These stars, which have been at the very centre of the Milky Way for billions of years, contain extremely low amounts of metal: one of the stars is the most metal-poor star yet discovered in the centre of our galaxy. These stars also contain chemical fingerprints which indicate that the very first stars may have died in spectacular deaths known as hypernovae, which were ten times more energetic than a regular supernova. ̽��ֱ��findings, reported today (11 November) in the journal Nature, could aid in understanding just how much the Universe has changed over the past 13.7 billion years.

For decades, astronomers have been trying to determine what the Universe was like soon after the Big Bang – understanding how the first stars and galaxies formed is crucial to this goal. While some astronomers are looking outward to galaxies billions of light years away to untangle this mystery, others are looking inward to the centre of our galaxy.

If you’ve ever looked up at the night sky from a dark place you might see the centre of the Milky Way. There are billions of stars in our galaxy, and astronomers are interested in picking out the oldest stars and finding out about their chemical composition and movements.

Soon after the Big Bang, the Universe was entirely made up of only hydrogen, helium and small amounts of lithium. All of the other elements, like the oxygen we breathe or the sodium in our toothpaste, have been made inside stars or when they die as supernovae. This has led astronomers to search for extremely metal-poor stars: stars with lots of hydrogen, but very little of any other element.

It had been thought that the very first stars formed in the centre of the galaxy, where the effects of gravity are strongest. But after decades of searches, astronomers found that most stars in the centre of our galaxy have a similar metal content of those much closer to us. While the stars at the centre of the galaxy are about seven billion years older than the Sun, they’re still not old enough to understand what the conditions were like in the early Universe.

Using telescopes in Australia and Chile, astronomers may have landed on a winning strategy to find the oldest stars in the galaxy. Stars with a low metal content look slightly bluer than other stars: a key difference that can be used to sift through the millions of stars at the centre of the Milky Way.

Using images taken with the ANU SkyMapper telescope in Australia, the team selected 14,000 promising stars to look at in more detail, with a spectrograph on a bigger telescope. A spectrograph breaks up the light of the star, much like a prism, allowing astronomers to make detailed measurements.

Their best 23 candidates were all very metal-poor, leading the researchers to a larger telescope in the Atacama desert in Chile. From this data the team identified nine stars with a metal content less than one-thousandth of the amount seen in the Sun, including one with one-ten-thousandth the amount – now the record breaker for the most metal-poor star in the centre of the galaxy.

“If you could compress all the iron in the Sun to the size of your fist, some of these stars would contain just a tiny pebble by comparison,” said Dr Andrew Casey of Cambridge’s Institute of Astronomy, one of the study’s co-authors. “They’re very, very different kinds of stars.”

However, knowing that these stars have low amounts of metal wasn’t enough to be certain that they formed very early in the Universe. They could be stars that formed much later in other parts of the galaxy that weren’t as dense, and they are just now passing through the centre. To separate those possibilities, researchers measured distances and used precise measurements of the stars’ movement in the sky to predict how the stars were moving, and where they had been in the past.

They found that while some stars were just passing through, seven of the stars had spent their entire lives in the very centre of our galaxy. Computer simulations suggest that stars like this must have formed in the very early Universe.

“There are so many stars in the centre of our Galaxy – finding these rare stars is really like looking for a needle in a haystack,” said Casey. “But if we select these stars in the right way, it’s like burning down the farm and sweeping up the needles with a magnet.”

When the very first stars in the galaxy died, they left a chemical signature on the generation of stars reported on in this latest study. This chemical fingerprint suggests the very first stars may have died in spectacular deaths known as hypernovae, an explosion ten times more energetic than a regular supernova. This would make it one of the most energetic things in the Universe, and very different from the kinds of stellar explosions we see today.

“This work confirms that there are ancient stars in the centre of our Galaxy. ̽��ֱ��chemical signature imprinted on those stars tells us about an epoch in the Universe that’s otherwise completely inaccessible,” said Casey. “ ̽��ֱ��Universe was probably very different early on, but to know by how much, we’ve really just got to find more of these stars: more needles in bigger haystacks.”

Reference:
L.M. Howes et. al. ‘Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way.’ Nature (2015). DOI: 10.1038/nature15747

Astronomers have discovered some of the oldest stars in the galaxy, whose chemical composition and movements could tell us what the Universe was like soon after the Big Bang.

Finding these rare stars is really like looking for a needle in a haystack. But if we select these stars in the right way, it’s like burning down the farm and sweeping up the needles with a magnet

Andrew Casey

ESO

An artist's impression of a hypernova, an explosive death of a star roughly ten times more energetic than a normal supernova.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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