Idea of ice age 'species pump' in the Philippines boosted by new way of drawing evolutionary trees
Does the Philippines’ astonishing biodiversity result in part from rising and falling seas during the ice ages?
Scientists have long thought the unique geography of the Philippines — coupled with seesawing ocean levels — could have created a “species pump” that triggered massive diversification by isolating, then reconnecting, groups of species again and again on islands. They call the idea the “Pleistocene aggregate island complex (PAIC) model” of diversification.
But hard evidence, connecting bursts of speciation to the precise times that global sea levels rose and fell, has been scant until now.
A groundbreaking Bayesian method and new statistical analyses of genomic data from geckos in the Philippines shows that during the ice ages, the timing of gecko diversification gives strong statistical support for the first time to the PAIC model, or “species pump.” The investigation, with roots at the University of Kansas, was just published in the Proceedings of the National Academy of Sciences.
“The Philippines is an isolated archipelago, currently including more than 7,100 islands, but this number was dramatically reduced, possibly to as few as six or seven giant islands, during the Pleistocene,” said co-author Rafe Brown, curator-in-charge of the herpetology division of the Biodiversity Institute and Natural History Museum at KU. “The aggregate landmasses were composed of many of today’s smaller islands, which became connected together by dry land as sea levels fell, and all that water was tied up in glaciers. It’s been hypothesized that this kind of fragmentation and fusion of land, which happened as sea levels repeatedly fluctuated over the last 4 million years, sets the stage for a special evolutionary process, which may have triggered simultaneous clusters or bursts of speciation in unrelated organisms present at the time. In this case, we tested this prediction in two different genera of lizards, each with species found only in the Philippines.”
For decades, the Philippines has been a hotbed of fieldwork by biologists with KU’s Biodiversity Institute, where the authors analyzed genetic samples of Philippine geckos as well as other animals. However, even with today’s technology and scientists’ ability to characterize variation from across the genome, the development of powerful statistical approaches capable of handling genome-scale data is still catching up — particularly in challenging cases, like the task of estimating past times that species formed, using genetic data collected from populations surviving today. More