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Pleistocene Ecosystem

Good Essays

During the Pleistocene many barriers to fish dispersal and recolonization already existed in the western United States. The Rocky Mountain Range was formed before the Miocene and the Sierras elevated in the Pliocene, both formidable North-South barriers (Smith 1981). Along with these significant geographic barriers, the western U.S. has historically had much smaller and more climatically unpredictable basins compared to the east. These basins held lower populations of fish which increased the probabilities of extinction and the lack of stability often interrupted speciation (Smith 1981). Despite these factors, there is still some diversity that arose out of these basins largely due to the lacustrine environment that was in place during …show more content…

2; Echelle 2008). The three species diverged from one another in the last one million years, with C. diabolis falling out most recently some 0.5 MYA. The speciation is believed to be allopatric, but there is still some uncertainty regarding C. diabolis (Duvernell & Turner 1998). The reason for this uncertainty is that the cavern that C. diabolis currently inhabits, Devil’s Hole, only opened to the surface around 60,000 years ago (Martin et al. 2016). It is possible that there was some degree of sympatric speciation happening before a colonization event occurred or, because mtDNA was used to determine divergence times, C. nevadensis could have been polymorphic for mtDNA before the cavern opened and was subsequently colonized (Echelle 2008). So how did the allopatric speciation of the Death Valley pupfish occur? Was it the result of dispersal or vicariance? When we examine figure 2 closely, we see that although the Pleistocene lakes in the Death Valley region were extensive, they still might not have connected all of the waterways. In addition, this map shows a summary of the lakes, that is to say that all of them did not exist at the same time (Knott et al. 2008). Limited connectivity of waterways as well as the late colonization and subsequent speciation of C. diabolis are potentially evidence against the hypothesis for speciation through vicariance. On the other hand, pupfish are notoriously very poor dispersers.

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