Scientists discover why tarantulas come in vivid blues and greens

Date:
September 24, 2020
Source:
Yale-NUS College
Summary:
Researchers find support for new hypotheses: that tarantulas'
vibrant blue colors may be used to communicate between potential
mates, while green coloration confers the ability to conceal among
foliage. Their research also suggests that tarantulas are not as
color-blind as previously believed, and that these arachnids may
be able to perceive the bright blue tones on their bodies.



FULL STORY ==========================================================================
Why are some tarantulas so vividly coloured? Scientists have puzzled
over why these large, hairy spiders, active primarily during the evening
and at night- time, would sport such vibrant blue and green colouration
-- especially as they were long thought to be unable to differentiate
between colours, let alone possess true colour vision.


==========================================================================
In a recent study, researchers from Yale-NUS College and Carnegie Mellon University (CMU) find support for new hypotheses: that these vibrant blue colours may be used to communicate between potential mates, while green colouration confers the ability to conceal among foliage. Their research
also suggests that tarantulas are not as colour-blind as previously
believed, and that these arachnids may be able to perceive the bright
blue tones on their bodies. The study was published in Proceedings of
the Royal Society B on 23 September, and is featured on the front cover
of the current (30 September 2020) issue.

The research was jointly led by Dr Saoirse Foley from CMU, and Dr Vinod
Kumar Saranathan, in collaboration with Dr William Piel, both from the
Division of Science at Yale-NUS College. To understand the evolutionary
basis of tarantula colouration, they surveyed the bodily expression of
various opsins (light- sensitive proteins usually found in animal eyes)
in tarantulas. They found, contrary to current assumptions, that most tarantulas have nearly an entire complement of opsins that are normally expressed in day-active spiders with good colour vision, such as the
Peacock Spider.

These findings suggest that tarantulas, long thought to be colour-blind,
can perceive the bright blue colours of other tarantulas. Using
comparative phylogenetic analyses, the team reconstructed the colours of
110 million-year- old tarantula ancestors and found that they were most
likely blue. They further found that blue colouration does not correlate
with the ability to urticate or stridulate -- both common defence
mechanisms -- suggesting that it did not evolve as a means of deterring predators, but might instead be a means of attracting potential mates.

The team also found that the evolution of green colouration appears to
depend on whether the species in question is arboreal (tree-dwelling), suggesting that this colour likely functions in camouflage.

"While the precise function of blueness remains unclear, our results
suggest that tarantulas may be able to see these blue displays, so mate
choice is a likely potential explanation. We have set an impetus for
future projects to include a behavioural element to fully explore these hypotheses, and it is very exciting to consider how further studies will
build upon our results," said Dr Foley.

The team's survey of the presence of blue and green colouration across tarantulas turned up more interesting results. They found that the
blue colouration has been lost more frequently than it is gained across tarantulas.

The losses are mainly in species living in the Americas and Oceania,
while many of the gains are in the Old World (European, Asian, and
African) species. They also found that green colouration has evolved
only a few times, but never lost.

"Our finding that blueness was lost multiple times in the New World,
while regained in the Old, is very intriguing. This leaves several
fascinating avenues for future research, when considering how the
ecological pressures in the New and the Old Worlds vary," said Dr
Saranathan. "For instance, one hypothesis would be differences in the
light environments of the habitats between the New and the Old World,
which can affect how these colours might be perceived, if indeed they
can be, as our results suggest."

========================================================================== Story Source: Materials provided by Yale-NUS_College. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Saoirse Foley, Vinodkumar Saranathan, William H. Piel. The
evolution of
coloration and opsins in tarantulas. Proceedings of the Royal
Society B: Biological Sciences, 2020; 287 (1935): 20201688 DOI:
10.1098/ rspb.2020.1688 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200924101925.htm

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