Gplates helps track spidery footsteps around the world
Examples of reconstructed dispersal of golden orbweaver spiders using AuScope enabled Gplates. Image: Turk et al. (left) and Chris Hamilton (right)
Before the pandemic crept in, we hoped to bring you this story of Slovenia based biologists using NCRIS enabled GPlates (earth modelling) software to help explain how golden orbweaver spiders migrated around the world over the last 130 million years. But it’s an intricate web we weave, you see, and only now can we wrap this up and honour the research led by contributor herein, Eva Turk.
Through Eva’s eyes
Our research, published in Wiley in early 2020, set out to determine the geographical origin of the golden orbweaver spiders - in other words, to uncover where the common ancestor of the family evolved. It also aimed to reconstruct the pattern of the spiders’ subsequent spread across the (sub)tropics. To do that, our team of biologists from Slovenia undertook a holistic biogeographical reconstruction that incorporates plate tectonics and tested two hypotheses: the ‘Out of Africa’ hypothesis, predicting these spiders originated in Africa, and the ‘Out of Burma’ hypothesis, predicting they originated in Australasia or Indomalaya.
First, we looked at the wide geographic distribution that golden orbweavers have in the world today,
and broke it down into seven constituent biogeographical areas.
Present-day distribution of the golden orbweavers and the seven biogeographical areas used in this study. Image: Turk et al. (2020)
We then needed to look back through time and space at how the plate tectonic regime altered over the last 130 million years. I came across GPlates during my literature review, and reached out to Dr Sabin Zahirovic from Sydney University who is both a GPlates power user and contributor to development of the software through the Earthbyte research group.
“Dr Zahirovic readily supplied me with an appropriate reconstruction model. I found the software’s user interface to be completely intuitive and featuring a number of useful functions.”
Giving the data (hairy) legs
After receiving support from Sabin to get started with GPlates, Eva managed to export the position of landmasses at specific points in time — every 10 million years — in a variety of formats. GPlates allowed her to fine-tune the analysis in an innovative way, by using past physical distances among landmasses, modeled by GPlates, as a proxy for the spiders’ dispersal probabilities. The software also allowed her to prepare figures for publication.
Eva and her team’s impressive visualisation comprising Earth’s tectonic regime over the last 130 million years juxtaposed with the ancestral (phylogenetic) tree of the spiders with reconstructed ancestral biogeographical regions. Turk et al. (2020)
A novel way to map evolutionary relationships
As a result of this study Eva and her colleagues were able to interpret the spiders’ evolutionary history and diversification (phylogeny) from ecological, biological and evolutionary perspectives. Eva explains:
“GPlates has enabled us to conduct original evolutionary tests to establish patterns in spider dispersal, while accounting for their biological specifics.”
Golden Orbweavers build large, strong and impressive webs with a golden sheen, making them a perfect candidate for the ‘spider’ in Mary Howitt’s 1829 poem, Spider and the Fly in which the spider proclaims to its prey “Tis the prettiest little parlour that ever you did spy.” Pictured: The Joro spider (Trichonephila clavata), distributed from the Himalayas to Japan. Image: Kuang-Ping Yu
Scuttle from down under
So what of the ‘Out of Burma’ and ‘Out of Africa’ hypotheses? Based on rigorous models in this study, Eva and her colleagues find support for the ‘Out of Burma’ hypothesis and suggest that the ‘Out of Africa’ hypothesis is far less plausible. Though there is great existing diversity of golden orbweaver species across Africa, model reconstructions suggest this eight legged family dispersed out of Indomalaya and Australasia.
Use of GPlates allowed the researchers to assess relatively specific dispersal probabilities, which in turn allowed them to visualise global movements of golden orbweavers. In reflecting on this study, they believe:
“Our novel use of a geological model in this biological research is the main contribution of our study, and we believe it will become common practice in biogeographical research. As all things in nature are profoundly interrelated, combining expertise from different fields of science is absolutely necessary for credible results.”
STOEY IN A NUTSHELL
Slovenia based biologists have used NCRIS enabled GPlates (earth modelling) software, and support from AuScope’s Simulation, Analysis and Modelling Program team, to help explain how golden orbweaver spiders migrated around the world over the last 130 million years.
AUTHORS
Eva Turk, Philomena Manifold
and Jo Condon