Corpus callosum size in delphinid cetaceans

Area of Science:

• Neuroscience
• Comparative Anatomy
• Zoology

Background:

• The corpus callosum facilitates interhemispheric communication in mammals.
• Understanding its size relative to brain mass provides insights into cognitive evolution.
• Dolphins (family Delphinidae) represent a diverse group of cetaceans with varying brain sizes.

Purpose of the Study:

• To quantify the midsagittal surface area of the corpus callosum in 13 Delphinidae species.
• To compare the corpus callosum size relative to brain mass across these species.
• To investigate potential sex differences in corpus callosum size in bottlenose dolphins (Tursiops truncatus).

Main Methods:

• Computer-assisted morphometry was used to measure the midsagittal surface area of the corpus callosum.
• Measurements were taken from 57 brains of juvenile and adult delphinids.
• Statistical analysis compared callosal area to brain mass, including sex-based comparisons in Tursiops truncatus.

Main Results:

• Absolute callosal areas ranged from 104 to 829 mm² across the studied species.
• Dolphins exhibited a smaller corpus callosum relative to brain mass (0.08-0.31 mm²/g) compared to other mammals.
• Larger-brained odontocetes showed a decreased corpus callosum to brain mass ratio, suggesting non-proportional increases in brain size.
• No significant sex differences in the corpus callosum to brain mass ratio were found in Tursiops truncatus.

Conclusions:

• Dolphin corpus callosum size does not scale proportionally with brain mass, particularly in larger-brained species.
• This suggests that increased brain size in dolphins may not necessitate a corresponding increase in interhemispheric white matter linkage.
• The study found no evidence of sex-based differences in the relative size of the corpus callosum in bottlenose dolphins.