Invading nonnative frogs use different microhabitats and change physiology along an elevation gradient

Area of Science:

• Ecology
• Invasive Species Biology
• Physiology

Background:

• The coqui frog (Eleutherus coqui) is an invasive species in Hawai'i, first introduced in the 1980s.
• Concerns exist regarding their potential negative impacts on native species in higher elevation ecosystems.
• It remains unclear if coqui frogs exhibit behavioral or physiological adaptations for invading higher altitudes.

Purpose of the Study:

• To investigate the current distribution of coqui frogs in Hawai'i, focusing on high-elevation areas.
• To determine if elevation influences coqui frog microhabitat selection (substrate, height from ground).
• To assess physiological metrics (plasma osmolality, oxidative status, glucose, free glycerol, triglycerides) in relation to elevation and sex.

Main Methods:

• Field surveys to map coqui frog distribution across elevations.
• Microhabitat assessments including substrate type and height above ground.
• Collection and analysis of physiological samples (blood plasma) for various biomarkers.

Main Results:

• Coqui frog occupancy along roads increased from 31% to 50%, with high-elevation presence rising from 1% to 16% over 14 years.
• High-elevation frogs utilized different substrates and were found closer to the forest floor, potentially due to warmer microclimates.
• Blood glucose and triglyceride levels increased with elevation, suggesting acclimation to colder temperatures and energetic demands.
• Female frogs exhibited higher plasma osmolality, dROMs, free glycerol, and triglycerides compared to males.

Conclusions:

• Coqui frog distribution and occupancy in Hawai'i have significantly expanded, including into higher elevations.
• Elevation-specific microhabitat use and physiological adjustments (e.g., elevated glucose, triglycerides) appear to facilitate coqui frog adaptation to cooler, high-elevation environments.
• These findings suggest that coqui frogs possess the capacity to further invade and impact native ecosystems at higher altitudes.