Digit reduction, body size, and paedomorphosis in salamanders

Area of Science:

• Evolutionary Biology
• Developmental Biology
• Vertebrate Morphology

Background:

• Digit loss is a common evolutionary trend in tetrapods, observed across numerous major clades.
• Developmental constraints, where developmental processes influence evolutionary trajectories, are exemplified by digit loss patterns in amphibians.
• The specific drivers of digit loss in salamanders, despite its prevalence, remain incompletely understood.

Purpose of the Study:

• To investigate the evolutionary factors driving digit loss in salamanders.
• To test the hypotheses that digit loss is associated with paedomorphosis and/or reduced body size.
• To explore the interplay between developmental changes (paedomorphosis) and morphological evolution (digit loss, body size).

Main Methods:

• Combined morphometric data with phylogenetic information from 98 salamander species.
• Analyzed correlations between digit reduction, paedomorphosis, and body size across the sampled species.
• Utilized statistical approaches to assess the significance of these associations.

Main Results:

• Digit loss in salamanders is significantly associated with both paedomorphosis and reduced body size.
• A contradictory finding reveals that paedomorphosis is also significantly associated with increased body size in salamanders.
• Extreme digit reduction occurs in smaller species within paedomorphic lineages, which tend to have larger average body sizes.

Conclusions:

• The evolutionary consequences of body size changes on morphology are context-dependent.
• Paedomorphosis in salamanders is linked to increased body size, challenging the traditional assumption of reduced size.
• Understanding these complex relationships is crucial for deciphering the evolution of vertebrate limb reduction.