From the point of view of the type of molecule that is obtained after the degradation of the hydrocarbon skeleton, amino acids can be classified as: glucogenic and ketogenic. The main difference between glucogenic amino acids and ketogenic amino acids is that glucogenic amino acids can be converted to pyruvate or other glucose precursors, while ketogenic amino acids can be converted to acetyl CoA and acetoacetylCoA.
Explanation:
Glucogenic amino acids are amino acids that break down to pyruvate, alpha-ketoglutarate, succinyl Co-A, fumarate, and oxaloacetate and are so named because the synthesis of glucose from these molecules is feasible. Both pyruvate and the Krebs cycle intermediates noted above can be converted to phosphoenolpyruvate and subsequently glucose through gluconeogenesis.Ketogenic amino acids are the amino acids that generate acetyl-CoA or acetacetyl-CoA and are called by this name because they can cause ketone bodies. Since mammals lack the proper enzyme system, these compounds can never be used as precursors for glucose biosynthesis. Of the twenty universal amino acids, fourteen are purely glucogenic and two are purely ketogenic (leucine and lysine). The remaining four (isoleucine, phenylalanine, tryptophan and tyrosine) are glucogenic and ketogenic simultaneously since a part of the hydrocarbon skeleton originates precursors for the biosynthesis of glucose (pyruvate or Krebs cycle intermediates) and the other part acetyl-CoA or acetacetyl -CoA.
In this question, there are no options given to choose from. So i would answer this question based on my knowledge. The most likely cause of the observed variation is adaptation and evolution. The birds of that island adapted to the food source and then they evolved as per the requirement of the place and food source.
