SELECTION ON BILL CHARACTERS IN A POPULATION OF DARWIN'S FINCHES: GEOSPIZA CONIROSTRIS ON ISLA GENOVESA, GALÁPAGOS

Area of Science:

• Evolutionary biology
• Quantitative genetics
• Ornithology

Background:

• Darwin's finches exhibit significant variation in bill morphology, crucial for their adaptation.
• Understanding selection on correlated traits is key to explaining evolutionary trajectories.

Purpose of the Study:

• To measure selection on correlated quantitative traits in Darwin's finches.
• To identify targets and directions of selection on bill dimensions across life stages.

Main Methods:

• Utilized Lande and Arnold's (1983) technique for measuring selection.
• Analyzed selection on three bill dimensions in Geospiza conirostris on Isla Genovesa.
• Differentiated selection pressures from male-male competition and female choice.

Main Results:

• Disruptive selection on bill dimensions observed during dry conditions due to differential survival.
• Selection favored increased bill length for female longevity and breeding success.
• Males experienced selection for increased bill depth and length due to territorial competition.

Conclusions:

• Bill evolution is constrained by correlated selection across sexes, traits, and life stages.
• Strong directional selection at one stage can drive evolutionary response if traits are heritable.
• Findings support frequent natural selection acting on Galápagos finch populations.