Haley Puckett 1 20 15 Ecology Evolutionary Biology Beach Mice Dark colored subspecies tend to live inland where soils are dark brown while the lighter subspecies live on beaches where the sand is light brown Ancestral populations of beach mouse likely had dark fur coats indicating that light fur color is a recent evolutionary event Strong correlation between soil brightness and coat color Selection pressure initially established and currently maintains the differing coat colors Most animals that hunt beach mice are sight and sound predators so being able to blend into the substrate can provide significant advantage to help the mice avoid detection Avoiding predation allows mice a better opportunity to find a mate and pass their fur color alleles along to their offspring Predation can be a driving force that changes fur color allele frequencies Experiment light colored clay mice were frequently attacked in dark soil environments and dark colored clay mice were frequently attacked in light soil environments Light colored clay mice in light soil environments and dark colored clay mice in dark soil environments were comparatively unharmed Cell Biology Different sub species of the beach mouse have different fur colors These differences are best described by examining melanocyte cell function Melanocytes are located at the base of the hair papilla and make a pigment molecule called eumelanin Pigment is then transported from the base to the hair cortex where coloration becomes visible Eumelanin is a polymer of cross linked dihydroxyindole carboxylic acids Its many units can vary slightly in their composition Activation of the MC1R protein occurs when it successfully binds to a molecule called an melanocyte stimulating hormone MSH Alternatively if the MC1R protein binds to a different molecule an agouti stimulating peptide the biosynthetic pathway leading to eumelanin synthesis may not occur However assuming that MSH binding occurs cAMP synthesis begins cAMP a common gene regulator and that aids in the expression of enzymes necessary in the biosynthetic pathway leading to eumelanin stimulates the expression of four genes c Tyr Tryp1 Tyrp2 and p c Tyr gene responsible for an enzyme called tyrosinase that catalyzes a reaction in a biosynthetic pathway that converts the amino acid tyrosine into a molecule called dopaquinone 1 Tyrp1 and Tryp2 genes hold the blueprint for tyrosine related enzymes that catalyze reactions in a subsequent pathway that converts dopachrome into eumelanin p gene responsible for a protein that also aids in this process Eumelanosomes are then made in the golgi apparatus of the melanocyte that are then transported out of the melanocyte to the hair cortex Without the successful binding of an MSH molecule by the MC1R protein cAMP is not adequately regulated and the multistep biosynthetic pathway for eumelanin synthesis cannot take place Structural changes to the MC1R protein as a result of a genetic mutation make it essentially non functional and result in a different coat color due to changes in pigment production This is often the case in coastal populations of beach mice where coat colors are lighter than their inland neighbors Molecular Genetics Fur color in beach mice Peromyscus polionotus can be altered if the transmembrane protein MC1R has a mutation that disrupts its role in the synthesis of the eumelanin pigment A functional MC1R protein binds to an melanocyte stimulating hormone that stimulates intracellular pigment production whereas a non functional MC1R protein does not 4 nucleotides in DNA Adenine A Thymine T Guanine G and Cytosine C Nucleotides are held together by a phosphate sugar backbone and are complemented by a parallel strand of nucleotides making a DNA molecule double stranded Parallel strands are held together by hydrogen bonds between bases Adenine binds to Thymine and Cytosine binds to Guanine Discrete sections of DNA carry sequences responsible for proteins and functional RNA chains these sections are called genes When making a protein the DNA is transcribed into a single stranded piece of messenger RNA mRNA using an enzyme called RNA polymerase This mRNA is then translated through a ribosome into a long chain of amino acids This chain of amino acids folds up to make a functional protein Proteins build the organism including all measurable and observable characteristics A single nucleotide substitution in the MC1R gene results in a non functional MC1R protein This single change within the protein results in a conformation change that does not allow the MC1R protein to bind extracellular melanocyte stimulating hormone When this binding fails to occur eumelanin is not effectively produced within melanocyte cells Population Genetics Different sub species of the beach mouse Peromyscus polionotus have different fur colors best described by examining melanocyte cell function Melanocytes are located at the base of the hair papilla and make a pigment molecule called eumelanin 2 Pigment is then transported from the base to the hair cortex where coloration becomes visible 2 different alleles that can be identified for the MC1R gene that aid in eumelanin production Allele a variant of a gene which is a discrete section of DNA that codes for a polypeptide i e protein or a functional RNA molecule 2 alleles in beach mice for MC1R gene R and C R results in functional MC1R protein that stimulates eumelanin production C results in a non functional MC1R protein that does not stimulate eumelanin production MC1R gene is located on chromosome 16 in mice Each mouse possesses 2 copies of the MC1R 1 on each chromosome possible genotypes are RR CC RC RR mice are darker than the RC mice which are darker than the CC mice Different alleles of the MC1R gene are responsible for some of the coat color differences observed among beach mouse populations These alleles cannot explain all the color variation among populations It is probable that mutation in other genes and their alleles contribute to differences in coat color Question If you were a predator an owl how would your hunting be affected if the prey blended in with the habitat Hypothesis If I were a predator and my prey blended in with the habitat I think that my hunting would suffer a lot at first because I would experience extreme difficulty spotting prey As a result I would begin to suffer from starvation and I would attempt to hunt for a different kind of prey In other words I would try to alter my diet in order