Evidence for complex life cycle constraints on salamander body form diversification

Area of Science:

• Evolutionary Biology
• Developmental Biology
• Comparative Anatomy

Background:

• Metazoans exhibit diverse life cycles, influencing phenotypic evolution.
• Life cycle complexity can correlate with trait diversification but also impose constraints.
• Few studies have linked life cycle evolution to macroevolutionary patterns of trait diversification.

Purpose of the Study:

• To investigate the impact of life cycle complexity on trait diversification rates in salamanders.
• To determine if life cycle complexity explains variations in vertebral number and body form.
• To compare diversification rates across aquatic-only, biphasic, and direct-developing salamander lineages.

Main Methods:

• Comparative analysis of trait evolution across salamander lineages with different life cycle complexities.
• Phylogenetic methods to infer rates of diversification in vertebral column and body form.
• Statistical modeling to assess the influence of life cycle type versus larval ecology on trait evolution.

Main Results:

• Salamanders with simple, aquatic-only (paedomorphic) life cycles showed significantly higher rates of vertebral column and body form diversification than those with complex, aquatic-terrestrial (biphasic) life cycles.
• Life cycle complexity was a stronger predictor of vertebral number and adult body form variation than larval ecology.
• Direct-developing (terrestrial-only) lineages exhibited higher adult body form evolution rates than biphasic lineages, but lower than aquatic-only lineages.

Conclusions:

• Transitions in life cycle complexity can drive substantial shifts in phenotypic evolution.
• Stage-dependent constraints associated with different life cycle strategies significantly influence trait diversification.
• Understanding life cycle evolution is crucial for explaining macroevolutionary patterns in morphology.