Neural development in metatherian and eutherian mammals: variation and constraint

Area of Science:

• Comparative neurodevelopmental biology
• Evolutionary developmental biology

Background:

• The Finlay and Darlington model (1995) accurately predicts neurogenesis timing in eutherian mammals.
• Extending this model to metatherians can reveal conserved and divergent patterns in mammalian brain development.

Purpose of the Study:

• To extend the predictive model of neurogenesis timing to additional metatherian species.
• To assess the predictability of other neural developmental events, including axonal outgrowth and connection formation.
• To compare the timing and variability of neural development between metatherian and eutherian mammals.

Main Methods:

• Application of the Finlay and Darlington predictive model to five metatherian species.
• Analysis of the timing of neurogenesis, axonal outgrowth, and connection establishment/segregation.
• Logarithmic scaling of developmental event timing for comparative analysis.

Main Results:

• The model's predictability extends to axonal outgrowth and connection formation in metatherians.
• Developmental events show consistent predictability across early and late stages on a logarithmic scale.
• Metatherians exhibit a curvilinear relationship between event scales compared to eutherians, with later events slowed.
• Neural development timing is more variable in metatherians than in eutherians.
• Slower late developmental events in metatherians correlate with longer weaning times.

Conclusions:

• The fundamental order of mammalian neural development is conserved across eutherians and metatherians.
• Metatherians display unique temporal scaling of neural development, with a relative slowing of later events.
• Increased variability and slowed late development in metatherians are associated with their extended juvenile periods.