Neuromeric Organization of the Microbat Brain: Conserved and Distinct Regional Features

Area of Science:

• Comparative neuroanatomy
• Evolutionary biology
• Mammalian brain evolution

Background:

• Bats (Microchiroptera) and rodents (Muridae) diverged ~85 million years ago.
• Understanding brain regional variations aids in studying mammalian evolution.
• The study uses two microbat species, Myotis myotis and Tadarida brasiliensis, as representatives of bat evolution.

Purpose of the Study:

• To investigate if the evolutionary divergence between bats and rodents resulted in significant regional brain variations.
• To compare brain structures between two microbat species and rodents using the prosomeric framework.
• To identify specific brain regions that show divergence due to evolutionary history.

Main Methods:

• Comparative analysis of brain derivatives from neuromeric partitions.
• Utilized the prosomeric framework for brain region identification.
• Examined tyrosine hydroxylase (TH)-positive processes and tracts in specific brain areas.

Main Results:

• Conserved fundamental neuromeric organization across bats and rodents.
• Bats exhibit smaller corpus callosum, isocortex, optic chiasm, and cerebellum compared to rodents.
• Tyrosine hydroxylase (TH) expression patterns in the basal plate were similar, but medial habenula (MHb) showed differential TH expression between bat species.

Conclusions:

• The 85-million-year evolutionary split between bats and rodents has caused notable regional brain anatomical differences.
• Despite regional variations, the basic modular brain plan remains conserved.
• Differential TH expression in the medial habenula (MHb) highlights specific evolutionary adaptations within bats.