Jacinta Bowler
Orb weaver spiders’ webs are the stuff of legend. One night you might have a clear doorway, and the next morning you’ve got an entire intricate lattice of web ready to accidently walk into.
But scientists are zooming in on one particularly sticky part of the web – the glue – to understand how different spider species quickly change their formula.
“Discovering the sticky protein components of biological glues opens the doors to determining how material properties evolve,” said Dr Nadia Ayoub, a Washington and Lee University evolutionary biologist.
“Spider silk fibres and glues represent a fantastic model for answering such questions since they are primarily made of proteins and proteins are encoded by genes.”
A spider’s web needs to be perfectly aligned to their environment. The web has a stiff frame and radial lines to absorb the impact of any flying insects, but there’s also a glue substance covering the web which traps the creatures. This glue absorbs water from the air. If the weather is humid the glue needs to be different to an area which is dry.
To see what is going on, researchers looked at two species of orb weaver spiders – Argiope argentata — which lives in dry environments — and Argiope trifasciata, which lives in humid environments.
The researchers collected webs from the wild and also got the spiders to create webs in the lab. Both spider species had equivalent diets, and droplets of the glue were tested between wild and lab grown to ensure the lab wasn’t changing the properties.
The team found that it mostly wasn’t the genes themselves that were different between the species as both species had very similar protein components. But the differences between the two webs were stark.
A. argentata’s glue droplets were smaller than A. trifasciata’s, and they absorbed less water as humidity increased.
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The ‘cores’ of the protein also were different. A. argentata’s protein cores were smaller and absorbed less water from the atmosphere.
A. argentata thread glue droplets were also generally more closely spaced and stickier.
“Despite the dramatic differences in material properties, the two species share most of their protein components,” said one of the researchers, Dr Brent Opell of Virginia Tech.
“The sequences of these proteins are also similar between species, but the relative abundance of individual proteins differs. Modifying the ratios of proteins is likely a rapid mechanism to adjust material properties of biological glues.”
The researchers only looked at two species, so more species will need to be investigated before we can confirm this is the case for all orb weavers.
The research has been published in Frontiers in Ecology and Evolution