The Evolution of Endemic Birds in Hawaii

What was the reason for Hawaii’s evolutionary vigor? What was so special about the islands such that evolution was so creative? The theory of evolution started with Darwin’s elevation about the finches on the Galapagos Islands. The normal flinches had originated from the mainlands into the islands, these birds tried out a variety of lifestyles until they evolved into separate species. Each species had its own unique beak that allowed it to live a special lifestyle. Hawaii’s evolution was similar and more prolific. The first birds that reached Hawaii’s islands came from East Asia where they evolved into at least 140 species. Among the originators was the Hawaiian honeycreepers, an equivalent of Darwin’s finches that evolved into at least 56 species. The species differ in color, shapes of beaks and the size as well. Swiss Army Knife is also often compared to the multicolored akiapolaau in regard to the similarities in their beaks (Wylie, 2015). 

Materials and Methods 

The study focused in revealing and acquiring knowledge in the size and modes of morphological diversification of skulls in avian evolution and particularly adaptive radiations on oceanic islands. It was done by quantitatively studying and comparing the shapes of skulls in both Hawaiian honeycreepers and Darwin’s finches shared group taxa and respective relatives. Cranial skeletons necessary for the research were borrowed from history museums. 14 species of Darwin’s finches were sampled to give 101 individuals; 50 individuals of 10 Coerebinae species that were related to the finches; 30 species of Hawaiian honeycreepers produced 100 individuals; 68 related individuals of the honeycreepers form families Estrildidae and Ploceidae. XRA-002 micro CT scanner was used to take high-resolution three-dimensional images of the heads of the specimens. Landmarks were strategically placed on the digital images of the right side of each skull, and in special cases on the left side. The coordinates of the landmarks were identified and compared among the individuals. 

Results 

The cranial subdivision in the groups was used to evaluate the shape of the whole skull as RV coefficients by use of a PLS analysis. 

Discussion 

A covariation is regarded as a land bird radiation that is clearly evident in other lineages of birds. The cranium and the shapes of the upper beak showed a solid covariation as revealed in the PLS analysis. Additionally, as indicated in the table, the Hawaiian honeycreepers and Darwin’s finches are less strongly coupled with the whole shape of the skull (Tokita et al., 2017). The results suggested that the high disparity levels in the skull morphology, identified in Hawaiian honeycreepers was related to the changes in the integration of individual skull elements and modularity. This meant that more evolutionary flexibility was allowed and hence the exploration of morphospace 

Conclusion 

The analysis was done to prove the cranial diversity in the Darwin’s finches and Hawaiian honeycreepers of which showed a phenotypic evolutionary diversity. The extreme variation of the skull shapes in Hawaiian honeycreepers is associated with the birds’ specialty in feeding on nectar and insects. On the other hand, a big degree of overlap in the parts of morphospace showed a widespread convergence that represented a taxon with different diets. From the study, there was an indication of the presence of common structural and biochemical requirements for feeding otherwise different food sources. 

References 

Tokita, M., Yano, W., James, H. F., & Abzhanov, A. (2017). Cranial shape evolution in adaptive radiations of birds: comparative morphometrics of Darwin's finches and Hawaiian honeycreepers.  Philosophical transactions of the Royal Society of London. Series B, Biological sciences ,  372 (1713), 20150481. 

Wylie, R. (2015). Hawaii: The islands where evolution ran riot. BBC Earth . Retrieved from http://www.bbc.com/earth/story/20150625-islands-where-evolution-ran-riot .