ECOL330 4/8/2019. Structure of Adult Beak. Where does the beak come from? A developmental perspective. What determines beak shape?

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1 Beak Evolution in Birds Structure of Adult Beak Evolution of Animal Form & Function Dr Alex Badyaev Office hours: T 11 12, by apt BSW 416 Lecture Instructor: Sarah Britton ECOL330 A developmental perspective What determines beak shape? Beak polymorphism (small, large, mega) in the black bellied seedcracker Coexistance, random breeding Functional differences A single locus controls beak size in small versus large morphs: IGF1 (insulin like growth factor 1) Frontal nasal mass Lateral nasal prominence (x2) Maxillary process (x2) Mandibular process (x2) What determines beak shape? Polygenic control of bill length in great tits COL4A5 associated with longer beaks, higher mating success, and feeder use Two bony elements in beak that give it shape: 1. Prenasal cartilage shapes the beak early in development 2. Premaxillary bone shapes the beak later in development 1

2 Developmental Studies of Darwin s Finches 1. Prenasal cartilage Expression of bone morphogenic protein 4 (BMP4) regulates depth/width Expression of calmodulin (CaM) regulates length Developmental Studies of Darwin s Finches 2. Premaxillary bone Expression of B catenin, Dkk3, TGFBIIr regulate depth and length How do researchers experimentally test for developmental role of genes? How do researchers experimentally test for developmental role of genes? Overexpression of BMP4 using RCAS (replication competent AVSLvector) system Wider and deeper upper beaks Higher cell proliferation What is a quck? Transplanting mesenchymal neural crest cells 1. Duck host with quail donor = duck with quaillike bill (quck) 2. Quail host with duck donor = quail with ducklike bill (duail) Abzhanov et al. 2004, Science Schneider and Helms 2003, Science House finch beak evolution House finch beak evolution DAB brown color Anti mouse antibody (goat) Anti B catenin antibody (mouse) B catenin protein with antigen 2

3 House finch beak evolution Constrained songbird beak shape variation can be explained by scaling and shear transformations Expression of Expression of fgf8 TgfB2 at stage 31 at stage 35 Fritz et al Role of mechanical forces in beak development Qualitative versus quantitative shape changes Mechanical interactions among beak prominences in development Modularity of developmental programs A historical perspective A historical perspective = Aves = Neornithes Louchart and Viriot

4 A historical perspective Ichthyornis dispar Late 1800s Keratin beak where teeth are Precision pincer like appendage Why replace teeth with a beak? 1. Weight conservation Zhongjianornis yangi Zhou and Li, 2010 Why replace teeth with a beak? 2. Ecological (dietary) factors Juvenile Why replace teeth with a beak? 3. Selection for faster incubation Adult Zanno et al Tooth loss within an individual (ontogenetic change) as diet shifts from omnivorous to herbivorous Wang et al Oviraptosaur with toothless beak Yang and Sander, 2018 Adaptations to tooth loss Gizzard food processing Diversification of the rhampotheca adds stability to beak Kinesis and precision of beak (beak replaces manipulation of hands) Did beaks allow persistence through KT boundary? Beak size is related to bite force in Darwin s finches 4

5 Hummingbird bill size corresponds to flower shape in a highland tropical rainforest (niche partitioning) Crossbill beaks and conifer seeds Wolf et al Benkman et al Rhynchokinesis in probing birds Ability to independently move distal tip of bill Tactile perception in beaks Larger and more numerous afferent nervous cells Help to sense prey in tactile foragers (ducks, probing shorebirds) Estrella and Masero, 2007 Schneidera et al., 2014 not just for eating! The beak and song not just for eating! The beak and song 5

6 not just for eating! The beak and thermoregulation not just for eating! The beak and thermoregulation Thermoregulation vascularized beaks allows for rapid change in surface temperature Greenberg et al What else has a beak? Keratin Chitin Flurapotine 6