Flying primates? Megabats have the advanced pathway from eye to midbrain

Area of Science:

• Neuroscience
• Evolutionary Biology
• Comparative Anatomy

Background:

• The pattern of connections between the retina and midbrain (retinotectal pathway) is crucial for visual processing.
• Understanding these connections across diverse species provides insights into evolutionary relationships and adaptations.
• Bats, with their unique adaptations for flight, offer a valuable model for studying neural evolution.

Purpose of the Study:

• To determine the pattern of retinotectal connections in two major bat subdivisions: megachiropteran (fruit bats) and microchiropteran bats.
• To compare these patterns with those found in other vertebrates, particularly primates.
• To infer the evolutionary history of visual pathways and potentially the evolution of flight in mammals.

Main Methods:

• Electrophysiological methods were used to record neural activity.
• Neuroanatomical techniques were employed to trace neural pathways.
• These methods were applied to Pteropus spp. (megabats) and Macroderma gigas (microchiropteran bat).

Main Results:

• Megachiropteran fruit bats (Pteropus spp.) exhibit an advanced retinotectal pathway with vertical hemidecussation, similar to primates.
• Microchiropteran bat Macroderma gigas displays the ancestral (symplesiomorphous) pattern of retinotectal connections, common to most vertebrates.
• These findings establish a link between primates and megachiropteran bats based on visual pathway organization.

Conclusions:

• The study reveals distinct evolutionary trajectories for retinotectal pathways within Chiroptera (bats).
• The advanced pathway in megabats, shared with primates, suggests convergent evolution or a shared ancestral trait.
• These findings support the hypothesis that flight may have evolved independently twice in mammals.