Invasive predatory crayfish do not trigger inducible defences in tadpoles

Area of Science:

• Ecology
• Evolutionary Biology
• Conservation Biology

Background:

• Invasive species pose significant threats to global biodiversity, often overwhelming native species' defense mechanisms.
• Indigenous species possess defenses against native predators, but these are frequently ineffective against invasive species.
• Understanding the mechanisms behind defense failures against invasive species is crucial for conservation efforts.

Purpose of the Study:

• To investigate whether Iberian green frog tadpoles can detect and respond to chemical cues from an invasive predator (red swamp crayfish).
• To determine if tadpoles exhibit inducible defenses against native predators (dragonfly nymphs) and if these defenses are activated against invasive predators.
• To assess the potential for local adaptation in predator cue recognition following prolonged exposure to an invasive species.

Main Methods:

• Tadpoles were exposed to chemical cues from both native dragonfly nymphs and invasive red swamp crayfish.
• Behavioral (activity levels) and morphological (tail depth, pigmentation) defensive responses were measured.
• Tadpole survival rates were compared when facing native vs. invasive predators.
• Local adaptation was tested by comparing tadpole responses from populations with and without historical crayfish exposure.

Main Results:

• Tadpoles exhibited reduced activity and developed defensive morphology (increased tail depth and pigmentation) in response to native dragonfly nymph cues.
• These defensive responses were not activated when tadpoles were exposed to cues from invasive red swamp crayfish.
• Despite increased survival benefits of induced defenses against both predator types, cue recognition failure prevented activation against crayfish.
• Tadpoles from both crayfish-exposed and crayfish-free ponds failed to show inducible defenses against crayfish, indicating insufficient evolutionary adaptation over 30 years.

Conclusions:

• Iberian green frog tadpoles possess functional inducible defenses against native predators but fail to recognize cues from the invasive red swamp crayfish.
• This failure in cue recognition by tadpoles represents a significant vulnerability to invasive species, despite the potential survival benefits of induced defenses.
• Approximately 30 years (10-15 generations) of contact with invasive crayfish have not been sufficient for the evolution of predator cue recognition in this amphibian population.