Density-dependent selection closes an eco-evolutionary feedback loop in the stick insect Timema cristinae

Area of Science:

• Ecology and Evolutionary Biology
• Behavioral Ecology
• Population Genetics

Background:

• Empirical evidence for eco-evolutionary feedbacks remains scarce.
• Avian predators are hypothesized to impose density-dependent selection (DDS) on prey populations.
• Timema cristinae stick insects exhibit distinct cryptic and conspicuous morphs.

Purpose of the Study:

• To experimentally test if avian predators impose DDS on T. cristinae.
• To investigate the role of predator satiation in driving DDS.
• To explore the implications of eco-evolutionary feedbacks for speciation.

Main Methods:

• Field experiment involving transplantation of T. cristinae to natural habitats.
• Manipulation of insect density (low vs. high) and morph ratio (50:50 cryptic:conspicuous).
• Quantification of morph frequency changes and assessment of predator effects.

Main Results:

• Negative DDS was supported: conspicuous morphs decreased by 73% in low density vs. 50% in high density.
• Predator satiation was identified as the likely mechanism driving DDS.
• No significant impact of T. cristinae density on other arthropod communities was observed.

Conclusions:

• Eco-evolutionary feedback loops, mediated by DDS, are supported in the T. cristinae system.
• Predator-prey interactions can drive adaptive divergence and potentially speciation.
• Density-dependent selection by predators is a crucial factor in evolutionary dynamics.