Jaw muscle development as evidence for embryonic repatterning in direct-developing frogs

Area of Science:

• Developmental biology
• Evolutionary biology
• Amphibian anatomy

Background:

• Anuran amphibians typically undergo metamorphosis with distinct larval and adult muscle forms.
• The direct-developing frog Eleutherodactylus coqui (E. coqui) presents an atypical developmental pathway.
• Understanding E. coqui's development offers insights into evolutionary modifications of life cycles.

Purpose of the Study:

• To investigate the novel jaw muscle development in the direct-developing frog E. coqui.
• To compare E. coqui's embryonic muscle development with that of metamorphosing anurans.
• To explore the role of embryonic "repatterning" in the evolution of complex traits.

Main Methods:

• Comparative analysis of embryonic muscle development in E. coqui versus metamorphosing anurans.
• Histological examination of jaw muscle primordia and myofiber development.
• Observation of developmental timing from embryonic stages to pre-hatching.

Main Results:

• E. coqui lacks larval-specific jaw muscle features and distinct larval myofibers.
• Embryonic muscle primordia in E. coqui adopt an abbreviated, mid-metamorphic form.
• Muscle remodeling occurs early, establishing adult morphology before hatching, bypassing larval stages.
• The study identified a lack of typical larval-to-adult myofiber turnover.

Conclusions:

• E. coqui exhibits a highly modified mode of jaw muscle development, reflecting evolutionary changes in cranial patterning.
• Embryonic "repatterning" in E. coqui demonstrates developmental mechanisms underlying integrated evolution.
• These mechanisms may facilitate the dissociation of embryonic, larval, and adult features in direct-developing species.