The Pleistocene Period

The Pleistocene period was a time when ecological changes emerged. During this period glacier formations began to arise and have been accredited with playing a role in the divergence of different species. For different species of avian there has been controversy between their origins and speciation events. Studies have been conducted for this controversy to try and find which theory to accept for the songbirds. Even though a majority of studies have accepted Late Pleistocene events role in the speciation of songbirds, few studies go against this theory and hypothesize a much farther speciation of songbirds in reference with today.
In the Klicka and Zink paper, they rejected the widely accepted Late Pleistocene Origins Model when it came to
In their study, they increased the sample size, sequenced mtDNA, categorized them phylogeographically, and calculated a net sequence divergence (Avise and Walker). To correct the divergence within one species, Avise and Walker took samples from different populations within a species and compared their divergence. Out of the phylogeographic group in category one, they found a “strong geographic orientation” and that “a total of 28 pairs of intraspecific phylogroups show evidence of separation dates that fall within the Pleistocene” (Avise and Walker). There was also a variety of different data types (RFLP, cty b, etc.) from different sources taken into account. A big difference between Avise and Walker from the other study was that a net sequence was taken to correct within species divergence and the bias found in gene trees. Getting rid of the outliers in the data and using the same molecular clock calculations as Klicka and Zink, Avise and Walker obtained a graph that had a vast majority of the songbird species within the Pleistocene period. Correlation between the sequence divergence and the time in this data set accepted the theory that Pleistocene events did have a major effect on the speciation of the
The lower the sequence divergence between species, the more recently they have split. Pleistocene origin in songbirds is a theory I have come to accept because the small number of DNA sequence difference showed a more recent speciation time. The Pleistocene is a more recent event in reference with today than the Pliocene. There is much divergence just within a species that to use one individual from a species would not be sufficient to represent the species as a whole. Many samples, such as populations within a species should have their divergence calculated for more reliable data. Correcting within species divergence can give more reliable data to accept. Environmental events can attribute to the variance between species. For an event as major as the glacier cycle, this could have played a role in the geographic isolation between different species of songbirds. This barrier limits the amount of cross breeding between species if there are physical barriers. This makes individuals within the same geographical region to have access to the same resources which can play a role in the development of an individual and ultimately the divergence of a species from