Closely related bird species demonstrate flexibility between beak morphology and underlying developmental programs.

Area of Science:

• Evolutionary biology
• Developmental biology
• Comparative anatomy

Background:

• Bird beak diversity is linked to diet and avian diversification.
• Darwin's finches (Geospiza spp.) exhibit beak shape variation driven by signaling pathways regulating prenasal cartilage (pnc) and premaxillary bone (pmx) growth.
• The developmental basis for beak variation in other closely related species remained largely unexplored.

Purpose of the Study:

• To investigate the developmental mechanisms underlying beak shape variation in Caribbean bullfinches (Loxigilla spp.).
• To compare the developmental pathways of beak morphogenesis in Loxigilla species with those of Geospiza finches.
• To understand the relationship between developmental processes and morphological outcomes in avian beak evolution.

Main Methods:

• Comparative analysis of beak development in three Loxigilla species.
• Examination of signaling pathways (Bmp4, CaM, TGFβIIr, β-catenin, Dkk3, Ihh) involved in beak morphogenesis.
• Histological and molecular techniques to study tissue patterning and skeletal component development.

Main Results:

• Caribbean bullfinches (Loxigilla spp.) independently evolved novel beak shapes, distinct from Geospiza, with variation primarily due to scaling.
• Despite similar beak shapes, Loxigilla species exhibit different developmental signaling pathways.
• Loxigilla noctis development resembles Geospiza (pnc-first), while L. violacea and L. portoricensis rely predominantly on pmx expansion regulated by Ihh and Bmp4.
• Identical beak shapes can arise from different developmental programs, and similar programs can pattern different shapes.

Conclusions:

• The evolution of bird beak morphology demonstrates significant developmental plasticity.
• Convergent evolution of beak shape can occur through distinct underlying genetic and developmental mechanisms.
• Understanding these diverse developmental pathways is crucial for comprehending the evolution of avian diversity.