Grant, Peter, Rosemary Grant, and Kenneth Petren. “The Allopatric Phase of Speciation: The Sharp-Beaked Ground Finch (Geospiza difficilis) on the Galapagos Islands.” Biological Journal of the Linnaean Society 69.3(2000): 287-317. Print.
Speciation can be defined as a prolonged course of differentiation that ultimately causes the absolute termination of the genetic switch between two populations originating from a common antecedent. Speciation takes place in two transitional stages that entail the creation of a pair of allopatric or parapatric populations. Grant, Grant and Petren (288) sought to understand the mechanism and cause of differentiation. They also cited that little information was available to enable the forecasting of those two fates during speciation. The authors studied disparities in physical attributes and the vocalization of Geospiza difficilis and used the dissimilarities to figure out the course of differentiation in allopatry as the initial phase of speciation. The authors used microsatellite DNA variation, morphological measurement and sonograms made from tape-recordings in the field to examine phylogenetic relationships of G. difficilis. Microsatellite data were amalgamated at 16 loci and used to develop a phylogenetic relationship at the species level. The authors carried out univariate and multivariate testing on structural data to exemplify and relate the alignment of structural segregation amongst groups of G. difficilis. The authors realized that the morphology of the finches’ beaks changed with respect to time and availability of different foods. Natural and sexual selection led to changes in vocal traits, which were independent of the size of the beaks. The authors concluded that physical attributes, vocalization and genetic qualities did not change consistently among the six populations of finches. They recommended that G. difficilis should be renamed as a new species G. acutirostris based on the principles of phylogenetic species.
Podos Jeffrey and Nowicki Stephen. “Beaks, Adaptation, and Vocal Evolution in Darwin’s Finches.” Bioscience 54.6. (2004): 500-510. Print.
Experimental studies show that beaks change by natural selection due to alterations in native environmental conditions. Additionally, recent studies reveal that beaks serve a practical function in the production of songs in songbirds. Podos and Stephen (501) aimed at demonstrating how studies on the connection between beaks and song provide fresh insights into the interaction of morphological acclimatization and the advancement of communication signs. The authors performed a detailed literature analysis of written material, literature and experiments on beak, sound production and the squeak of the finch. In their analysis, the authors examined and compared various vocal mechanisms in birds and vertebrates (505). They explored Darwin’s finch songs especially their structural features such as annotation and syllabus. Ultimately, they correlated literature on diversity and functions of beaks with song production. The authors used the available data to formulate the premise that the differences in the beaks of Darwin’s finches had an impact on their eating and singing conduct (507). The authors concluded that Darwin’s finches showed an advanced level of diversity in beak morphology hence making them the most suitable candidates for identifying interconnected development between beaks and song. Additionally, Darwin’s finches produced shrill songs hence making the assessment of vocal performance feasible. However, the authors recommended that additional functional data was necessary and proposed that other songbird clusters with specialized beak structures needed to be investigated. The authors also recommended that additional studies were necessary to determine the effect of vocal features in compelling evolutionary changes in female preferences.
Tebbich, Sabine, Fessl Birgit and Blomquist Donald. “Exploration and Ecology in Darwin’s Finches.” Evolution Ecology 23.1(2009): 591-605. Print.
Exploratory behavior enables animals to gather information regarding the status and inconsistency of essential reserves such as food, shelter and mates. In this study, Tebbich, Birgit and Donald (593) aimed at unravelling the influence of the ecology in the evolution of exploratory behavior. The authors found that Darwinian finches were the ideal candidates for their study because they were confined to the islands. In addition, these birds exhibited advanced levels of exploration. Field experiments on three islands were used to investigate the intrinsic exploratory behavior of thirteen Darwinian finches from January to March 2000. The information gathered was merged with published data on several environmental factors. The authors performed a comparative analysis of inter-specific variations in exploration to the predominant environmental conditions. Phylogenetically autonomous contrasts were used to scrutinize the association between exploration and ecosystem. Linear regression analyses assessed the association of investigation and ecology. The authors realized that investigative behavior in Darwin’s finches compared with several factors of their ecosystem. The findings of the study corroborated the theoretical assumptions that a significant positive correlation existed between explorations and diet diversity (breadth). The authors had also predicted that there was a remarkable positive correlation between exploration and the amount of concealed food in the diet (Tebbich, Birgit and Donald 594), which turned out to be true. The authors recommended that the constancy of resources was a vital factor that needed to be considered when investigating the association between concealed food and investigative behavior.