In class today, we discussed the article "Evo-Devo and Brain Scaling: Candidate Developmental Mechanisms for Variation and Constancy in Vertebrate Brain Evolution" by Christine J. Charvet, Georg F. Striedter, and Barbara L. Finlay (2011). One of the most interesting concepts was how the delay in neurogenesis can impact development and the function of an animal.
Specifically, neurogenesis in the retina and the isocortex was explored amongst various animals. When looking at the retina, the nocturnal owl monkey and the diurnal capuchin monkey was compared. During development, the highest amount of neurogenesis is delayed in the owl monkey in comparison to the capuchin monkey. This is significant due to the time when rods and cones are developed. Early in development, cones are the focus, while later development consists of rod creation. Therefore, the neurogenesis in the owl monkey is delayed which results in larger amount of rod production. Rods are specialized for light and cones are specialized for color. The owl monkey, with a higher concentration of rods, is better able to see in the dark and be nocturnal.
Next, the paper discussed the differences in isocortex development among primates and rodents. The isocortex is made up of six layers (I-VI), which all grow during different times (i.e. layer VI develops before layer I). The neurogenesis of the isocortex is delayed in primates in comparison to rats. Therefore, the later layers (II-III) are disproportionately enlarged relative to the other layers in the primates due to a delay in neurogenesis.
It is interesting how the onset or offset of neurogenesis can have such significant impacts on the development and function of certain parts of organisms.