This article is from the source 'bbc' and was first published or seen on . It last changed over 40 days ago and won't be checked again for changes.
You can find the current article at its original source at http://www.bbc.co.uk/news/science-environment-34944735
The article has changed 3 times. There is an RSS feed of changes available.
| Version 1 | Version 2 |
|---|---|
| Tarantulas evolved blue colour 'at least eight times' | Tarantulas evolved blue colour 'at least eight times' |
| (2 months later) | |
| Tarantulas have evolved almost exactly the same shade of vibrant blue at least eight separate times. | Tarantulas have evolved almost exactly the same shade of vibrant blue at least eight separate times. |
| That is the conclusion of a study by US biologists, exploring how the colour is created in different tarantula species. | That is the conclusion of a study by US biologists, exploring how the colour is created in different tarantula species. |
| The hue is caused by tiny structures inside the animals' hairs, but those shapes vary across the family tree. | The hue is caused by tiny structures inside the animals' hairs, but those shapes vary across the family tree. |
| This suggests, the researchers say, that the striking blue is not driven by sexual selection - unlike many other bright colours in the animal kingdom. | This suggests, the researchers say, that the striking blue is not driven by sexual selection - unlike many other bright colours in the animal kingdom. |
| This argument is also supported by the fact that tarantulas have poor colour vision, and do not appear to show off their hairy blue body parts during courtship. | This argument is also supported by the fact that tarantulas have poor colour vision, and do not appear to show off their hairy blue body parts during courtship. |
| Blue branches | Blue branches |
| Nonetheless, Bor-Kai Hsiung and his colleagues found that 40 out of 53 groupings (genera) of tarantula exhibit a very vibrant blue. | Nonetheless, Bor-Kai Hsiung and his colleagues found that 40 out of 53 groupings (genera) of tarantula exhibit a very vibrant blue. |
| "We collected published data and constructed a super-tree, which combined the previous published small trees," said Mr Hsiung, a PhD student at the University of Akron in Ohio and the first author of the study, published in Science Advances. | "We collected published data and constructed a super-tree, which combined the previous published small trees," said Mr Hsiung, a PhD student at the University of Akron in Ohio and the first author of the study, published in Science Advances. |
| They then mapped blueness onto that evolutionary tree, based on a bank of tarantula snaps scoured from the internet. | They then mapped blueness onto that evolutionary tree, based on a bank of tarantula snaps scoured from the internet. |
| "If the genus has at least one species that's blue, we say that's a blue genus," Mr Hsiung explained. | "If the genus has at least one species that's blue, we say that's a blue genus," Mr Hsiung explained. |
| Given that scattering of blue species, he added, they then calculated "the lowest number of changes that can produce a distribution of blue colouring like this". | Given that scattering of blue species, he added, they then calculated "the lowest number of changes that can produce a distribution of blue colouring like this". |
| The answer? "Eight is the lowest number, so it's [evolved] at least eight times." | The answer? "Eight is the lowest number, so it's [evolved] at least eight times." |
| What is more, all these blue spiders evolved almost precisely the same shade; the wavelengths the team saw in the images all fell within a tight 20 nanometre range, clustered around 450nm - a bright, cobalt blue. | What is more, all these blue spiders evolved almost precisely the same shade; the wavelengths the team saw in the images all fell within a tight 20 nanometre range, clustered around 450nm - a bright, cobalt blue. |
| The team also purchased specimens of eight tarantula species, and took a close look at those blue hairs. | The team also purchased specimens of eight tarantula species, and took a close look at those blue hairs. |
| They used electron microscopes to zoom in on tiny shapes within the hairs and conducted simulations of how those shapes could produce a "structural colour" by reflecting - very specifically - this wavelength of blue light. | |
| Receiver unknown | Receiver unknown |
| The results, again, pointed to the colour cropping up multiple times independently: several different types of shape could be seen, even on the same branch of the family tree. | The results, again, pointed to the colour cropping up multiple times independently: several different types of shape could be seen, even on the same branch of the family tree. |
| "That's one of the reasons why it must have evolved so many times - because we don't see a very clear pattern of how these different mechanisms split," Mr Hsiung said. | "That's one of the reasons why it must have evolved so many times - because we don't see a very clear pattern of how these different mechanisms split," Mr Hsiung said. |
| "If we could see a clear split, then it might have evolved just one or two times. But it's all over the place." | "If we could see a clear split, then it might have evolved just one or two times. But it's all over the place." |
| So why did all these different species acquire the same colour? | So why did all these different species acquire the same colour? |
| Given their relatively simple eyes, it is doubtful that tarantulas can distinguish this shade of blue from any other colour. | Given their relatively simple eyes, it is doubtful that tarantulas can distinguish this shade of blue from any other colour. |
| That is one of the reasons that sexual selection seems unlikely - by contrast with some other spiders, which have remarkably good vision and put on very colourful courtship displays, such as the mesmerising peacock spider. | That is one of the reasons that sexual selection seems unlikely - by contrast with some other spiders, which have remarkably good vision and put on very colourful courtship displays, such as the mesmerising peacock spider. |
| "It evolved from multiple origins and different mechanisms produce the very same blue colour," Mr Hsiung said. "That's very strong evidence to suggest that this blue colour has a very important visual signalling function. | "It evolved from multiple origins and different mechanisms produce the very same blue colour," Mr Hsiung said. "That's very strong evidence to suggest that this blue colour has a very important visual signalling function. |
| "But if it's not for other tarantulas, then it must be to some other receivers out there." | "But if it's not for other tarantulas, then it must be to some other receivers out there." |
| It may be that this colour helps conceal the critters from their prey while they hunt at night; or perhaps it serves as a warning to stop the tarantulas themselves being eaten. | It may be that this colour helps conceal the critters from their prey while they hunt at night; or perhaps it serves as a warning to stop the tarantulas themselves being eaten. |
| "We don't know yet," Mr Hsiung said. | "We don't know yet," Mr Hsiung said. |
| Follow Jonathan on Twitter | Follow Jonathan on Twitter |