Evolution Update

Evolution Update

The Slow Evolution of Pelican Spiders

Jerome April 5, 2015

By examining the subtle variations in the Pelican Spider’s phenotypic structural evolution over a long period of time, researchers from the University of California discovered why the process was unusually prolonged.

The Pelican Spider, or the assassin spider, has resided in Madagascar for thousands of years. Generally found in high elevated areas in Madagascar, they share a relatively close lineage to some species found in South Eastern Asia, Africa, and Australia. The evolution process of this spider has taken many years for the unconventionally slow and meticulous creation of the Pelican Spider we see today.

The peculiar shape of this spider took many years to be created on the Madagascan island. Many pelican spiders are very similar, but there are physical characteristics of the spider are noticeably nuanced. For example, the neck of the spider has adapted to be long amongst all Pelican Spiders, but some spiders have rather wide necks and others have thinner necks. Along with the variation in neck sizes, the pelican spiders had noticeably different head lengths, femur lengths, and shell composition.

These subtle differences made researches from the University of California wonder why these changes happened, and whether the changes happened recently or in the distant past. They did this by looking into the phylogenetic relationships (its evolutionary history) of the spider, looking at where they are commonly found in Madagascar, and by comparing fossils from the Eocene and Jurassic periods.

While looking into the phylogenetic information of the spider, the researchers discovered that the variations were caused in part by ancient climatic events taking place in mountainous areas in Madagascar. This idea correlates with the premise that most Pelican spiders are found in elevated areas. They were able to reach this conclusion by comparing older fossils of the spider to the current Pelican spider of today, and examining the changes in their phenotypic characteristics, thus allowing them to infer that the changes were caused by climatic changes. They also concluded that the elongation of the spider's neck was due to its diet of spider fauna. The elongation could be seen as a way of gaining another food source and eliminating potential competition when preying on other spiders.

After reaching this conclusion the researchers compared the phylogenetic information with information gathered from African Pelican spiders and other Non-Madagascan pelican spiders, and found that the Madagascan Pelican spider’s evolutionary process was slower and more diverse than its relatives found in other lands. This information provides insight as to how the species that dwell on Madagascar each have unique evolutionary pathways of varying speeds.

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