Why animals construct helical burrows: Construction vs. post-construction benefits

Area of Science:

• Paleontology
• Zoology
• Evolutionary Biology

Background:

• Helical burrowing is an extended phenotype observed across diverse animal taxa since the Cambrian explosion.
• Previous research proposed several hypotheses for helical burrowing, but a unifying explanation is lacking.

Purpose of the Study:

• To review and compile hypotheses for helical burrowing behavior in animals.
• To test the applicability of these hypotheses across a wide range of extant and extinct taxa using trace fossil evidence.

Main Methods:

• Compiled 10 hypotheses for helical burrowing, categorizing them as post-construction or construction benefits.
• Examined the fit of these hypotheses to 21 extant taxa and ichnotaxa, representing numerous species.
• Analyzed evidence for each hypothesis across taxa and environmental contexts.

Main Results:

• Antipredator and biomechanical advantage hypotheses were not rejected for any species.
• Six hypotheses, including microclimate buffer and reduced falling sediment, fit most species.
• Construction hypotheses were supported for a significant portion of taxa, suggesting benefits during burrow formation.
• Hypotheses like increased drainage and microbial farming explained behavior in a minority of taxa.

Conclusions:

• No single general explanation accounts for the evolution of helical burrowing across all animal taxa.
• The function of helical burrows as an extended phenotype likely varies, offering different advantages depending on the taxon, environment, and physicochemical controls.
• Further research is needed to test specific hypotheses for selected taxa.