The evolutionary and developmental basis of parallel reduction in mammalian zeugopod elements

Area of Science:

• Evolutionary biology
• Developmental biology
• Comparative anatomy

Background:

• Parallel evolution, where similar traits evolve independently in different lineages, offers insights into the interplay between development and evolutionary processes.
• The reduction of zeugopod elements (ulna and fibula) is a recurrent theme in mammalian evolution, linked to locomotor specialization.

Purpose of the Study:

• To investigate the role of developmental mechanisms in the repeated reduction of mammalian zeugopod elements.
• To determine if the same developmental pathways underlie parallel evolutionary trends in limb reduction across different mammalian species.

Main Methods:

• A morphometric study combining variation analysis and phylogenetics was conducted on mammalian limbs.
• Developmental basis of limb reduction was examined in specific cases: bat (Carollia perspicillata) ulna and fibula, and mouse (Mus musculus) fibula.

Main Results:

• An evolutionary trend of width reduction in the posterior zeugopod elements (ulna and fibula) was identified in mammals.
• Reduced element width, the most common reduction pattern, was achieved through a conserved developmental process (slower growth rate) in both bat and mouse limbs.
• Developmental mechanisms for other reduction characteristics, such as element fusion, were found to be non-conserved and taxon-specific.

Conclusions:

• The parallel reduction in width of mammalian posterior zeugopod elements likely occurred through the repeated evolution of the same developmental mechanism.
• While width reduction appears developmentally conserved, other aspects of limb reduction, like element fusion, evolve via diverse developmental pathways.