Adaptation in a plant-hummingbird association

Area of Science:

• Ecology
• Evolutionary Biology
• Ornithology
• Botany

Background:

• Sexual dimorphism in the Caribbean purple-throated carib hummingbird (Eulampis jugularis) is linked to floral dimorphism in its primary food sources, Heliconia caribaea and Heliconia bihai.
• This hummingbird species is the exclusive pollinator for these two Heliconia plant species.

Purpose of the Study:

• To investigate the coadaptation between hummingbird bill morphology and Heliconia floral traits.
• To understand how feeding preferences drive the evolution of sexual dimorphism in both the hummingbird and its food plants.

Main Methods:

• Comparative analysis of bill morphology in male and female hummingbirds.
• Examination of floral morphology and color morphs in Heliconia caribaea and Heliconia bihai across different islands (St. Lucia and Dominica).
• Assessment of nectar rewards in relation to floral morphs and hummingbird feeding preferences.

Main Results:

• Male hummingbirds possess short, straight bills that match the flowers of H. caribaea.
• Female hummingbirds have long, curved bills that correspond to the flowers of H. bihai.
• On St. Lucia, H. bihai evolved a second color morph to accommodate male hummingbird bills; on Dominica, H. caribaea evolved a second color morph for female hummingbird bills.

Conclusions:

• Feeding preferences of hummingbirds, driven by their bill morphology and energy needs, have led to the coevolution of floral traits in Heliconia species.
• This study supports the hypothesis that reciprocal selective pressures between pollinators and plants drive adaptive evolutionary changes.