Variation in pollinator preference between two Ipomopsis contact sites that differ in hybridization rate

Area of Science:

• Ecology
• Evolutionary Biology
• Botany

Background:

• Pollinator behavior is crucial for reproductive isolation between plant species.
• Ethological isolation, driven by pollinator preference and constancy, can limit hybridization.
• Assessing pollinator behavior in contact zones with varying hybrid frequencies reveals isolation mechanisms.

Purpose of the Study:

• To investigate how pollinator preference and constancy differ between plant contact sites with low versus high hybrid frequencies.
• To determine the role of hawkmoths (Hyles lineata) and hummingbirds in pollinator-mediated reproductive isolation.
• To explore potential environmental factors, such as nocturnal foraging conditions, influencing pollinator behavior.

Main Methods:

• Observing pollinator visitation (hummingbirds, hawkmoths) in natural and artificial mixed-species arrays of Ipomopsis aggregata and I. tenuituba.
• Comparing pollinator preference and constancy at two contact sites: one with few hybrids and one with abundant hybrids.
• Analyzing hawkmoth foraging behavior in relation to nocturnal conditions and floral traits.

Main Results:

• Pollinator preference and constancy were significantly stronger at the site with fewer hybrids.
• Hawkmoths exhibited stronger preference and constancy for I. tenuituba at the low-hybrid site, visiting both species equally at the high-hybrid site.
• Warmer nights at the low-hybrid site may facilitate nocturnal foraging, favoring the visibility of I. tenuituba's pale corollas.

Conclusions:

• Differences in pollinator behavior between contact sites can directly and indirectly impact plant hybridization rates.
• Hawkmoth foraging behavior, potentially influenced by nocturnal conditions, plays a key role in pollinator-mediated isolation.
• Site-specific pollinator dynamics contribute to varying levels of reproductive isolation between plant species.