The evolution of beak size and shape in Darwin’s Finches The role of Developmental Genes and Environmental Conditions Lindsey Williams Elisabet Minter Corita Fields

Smithsonian: Osteology Hall

Examples of Beak Morphology Smithsonian: Osteology Hall

Beak Components Frontonasal mass Maxillary prominences Lateral nasal prominences Mandibular prominences

Beak Morphology Beak length, width, and depth – Environmental Parental Diet Food Availability – Developmental Genes BMP4 and Calmodulin

Parental Diet Food Availability – Small beaked finches prefer small seeds – Large beaked finches prefer large seeds but have the ability to consume small seeds Environmental Influence

During drought of 1977 – soft seeds less abundant – Tribulus seeds more abundant Large, difficult to open Larger beaked finches were more fit than their smaller beaked counterparts Larger beaks survived due to their ability to open Tribulus seeds easier.

Genetic Influence Bone morphogenic protein 4 (BMP4) Calmodulin (CaM)

BMP4 Expression Examined BMP4 Expression in distal beak mesenchyme of finches Figure. A. Beak morphologies. B. Stage 26 BMP4 expression C. Stage 29 BMP4 expression

Result – Enhanced cell proliferation – larger beaks due to significant increases in width, and depth Conclusion – Darwin’s finches exhibit different beak morphologies in part due to the expression of BMP4 BMP4 Expression

Calmodulin Expression Embryonic Stage – Injected CaM via a RCAS virus into embryo at stage 24 – Collected specimens at day 10 Result and Conclusion Figure. A shows the wild type specimen without additional presence of calmodulin. B shows the RCAS:CaM infected specimen.

Calmodulin Expression Examined expression and calmodulin in the skull of embryonic finches Conclusion Figure. A. and B. Morphologies from a monophyletic group. C. Skeletal morphological differences. D. CaM expression in distal – ventral domain in the mesenchyme of the upper beak.

BMP4 and CaM Expression

Conclusion and Further Research Beak morphology is influenced by both developmental genes and environmental factors, not just one Expression of CaM and BMP4 in other anatomical structures in both birds and mammals What protein is expressed that increases beak length once CaM is expressed?

Bibliography Abbott, Ian, L. K. Abbott, and P. R. Grant. "Seed Selection and Handling Ability of Four Species of Darwin's Finches." The Condor 7.3 (1975): Abzhanov, Arhat, Winston P. Kuo, Christine Hartmann, B. Rosemary Grant, Peter R. Grant, and Clifford J. Tabin. "The Calmodulin Pathway and Evolution of Elongated Beak Morphology in Darwin's Finches." Nature (2006): Print. Abzhanov, Arhat, Meredith Protas, B. Rosemary Grant, Peter R. Grant and Clifford J. Tabin. “Bmp4 and Morphological Variation of Beaks in Darwin's Finches.” Science (2004): Freeman, Scott, and Jon C. Herron. Evolutionary Analysis. 4th ed. Upper Saddle River, NJ: Pearson Prentice Hall, Print Grant, Rosemary B. and Peter R. Grant. “High Survival of Darwin's Finch Hybrids: Effects of Beak Morphology and Diets.” Ecology (1996): Herrel, A., J. Podos, S. K. Huber, and A. P. Hendry. "Bite Performance and Morphology in a Population of Darwin's Finches: Implications for the Evolution of Beak Shape." Functional Ecology 19.1 (2005): Snodgrass, Robert E. "The Relation of the Food to the Size and Shape of the Bill in the Galapagos Genus Geospiza." The Auk 19.4 (1902): JSTOR. Web. 19 Apr Wu, Ping, Ting-Xin Jiang, Sanong Suksaweang, Randall Bruce Widelitz, and Cheng-Ming Chuong. "Molecular Shaping of the Beak." Science (2004):

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