The evolution of beak size and shape in

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

Smithsonian: Osteology Hall Examples of Beak Morphology

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 • BMP 4 and Calmodulin

Environmental Influence • 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 (BMP 4) • Calmodulin (Ca. M)

BMP 4 Expression • Examined BMP 4 Expression in distal beak mesenchyme of finches Figure. A. Beak morphologies. B. Stage 26 BMP 4 expression C. Stage 29 BMP 4 expression

BMP 4 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 BMP 4

Calmodulin Expression • Embryonic Stage – Injected Ca. M 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: Ca. M 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. Ca. M expression in distal – ventral domain in the mesenchyme of the upper beak.

BMP 4 and Ca. M Expression

Conclusion and Further Research • Beak morphology is influenced by both developmental genes and environmental factors, not just one • Expression of Ca. M and BMP 4 in other anatomical structures in both birds and mammals • What protein is expressed that increases beak length once Ca. M is expressed?

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