Which neurotransmitter is associated with sleep mood and appetite?

The serotonin neurotransmitter system.

Explanation:

The serotonin neurotransmitter system is involved with the regulation of sleep cycles, attention or mood and appetite in the brain of healthy adults. Serotonin is a chemical substance released by neurons for communication. A disturbance in the concentration of serotonin has been linked with depression.

because they are eaten by the frog and the frog getseaten by the snake and the snake by the eagle

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).