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Paul M. Brakefield - One of the best experts on this subject based on the ideXlab platform.

Helen R. Mcrobie - One of the best experts on this subject based on the ideXlab platform.

  • Multiple origins of Melanism in two species of North American tree squirrel (Sciurus).
    BMC evolutionary biology, 2019
    Co-Authors: Helen R. Mcrobie, Nancy D. Moncrief, Nicholas I. Mundy
    Abstract:

    While our understanding of the genetic basis of convergent evolution has improved there are still many uncertainties. Here we investigate the repeated evolution of dark colouration (Melanism) in eastern fox squirrels (Sciurus niger; hereafter “fox squirrels”) and eastern gray squirrels (S. carolinensis; hereafter “gray squirrels”). We show that convergent evolution of Melanism has arisen by independent genetic mechanisms in two populations of the fox squirrel. In a western population, Melanism is associated with a 24 bp deletion in the melanocortin-1-receptor gene (MC1RΔ24 allele), whereas in a south-eastern population, Melanism is associated with a point substitution in the agouti signalling protein gene causing a Gly121Cys mutation. The MC1R∆24 allele is also associated with Melanism in gray squirrels, and, remarkably, all the MC1R∆24 haplotypes are identical in the two species. Evolutionary analyses show that the MC1R∆24 haplotype is more closely related to other MC1R haplotypes in the fox squirrel than in the gray squirrel. Modelling supports the possibility of gene flow between the two species. The presence of the MC1R∆24 allele and Melanism in gray squirrels is likely due to introgression from fox squirrels, although we cannot completely rule out alternative hypotheses including introgression from gray squirrels to fox squirrels, or an ancestral polymorphism. Convergent Melanism in these two species of tree squirrels has evolved by at least two and probably three different evolutionary routes.

  • The genetic and molecular basis of Melanism in the grey squirrel (Sciurus carolinensis)
    2014
    Co-Authors: Helen R. Mcrobie
    Abstract:

    The grey squirrel (Sciurus carolinensis) has wildtype and melanic (dark) colour morphs. Melanism is associated with variations in the melanocortin-1 receptor (MC1R) gene in a number of species. The MC1R protein is a G-protein coupled receptor, predominantly expressed in melanocytes, where it is a key regulator of pigment production. To investigate the genetic and molecular basis of Melanism, the MC1R genes of the wildtype and melanic grey squirrel were sequenced. The wildtype (MC1R-wt) and melanic (MC1RΔ24) variants of the MC1R were then functionally characterised in a cell-based assay. The MC1R gene of the grey squirrel was found to have a 24 base pair (bp) deletion associated with Melanism. The MC1R is typically activated by its agonist, the alpha-melanocyte stimulating hormone (α-MSH), which stimulates dark pigment production by raising intracellular cAMP levels. Conversely, the MC1R is inactivated by its inverse agonist, the agouti signalling protein (ASIP), which stops dark pigment production by lowering intracellular cAMP levels. To investigate the effects that the 24 bp deletion have on receptor function, MC1R-wt and MC1RΔ24 genes were transfected into HEK293 cells. Cells expressing either MC1R-wt or MC1RΔ24 were stimulated with α-MSH or ASIP and intracellular cAMP levels were measured. Unstimulated MC1RΔ24 cells showed higher basal activity than the MC1R-wt cells. Both MC1R-wt and MC1RΔ24 cells responded to α-MSH with a concentration-dependent increase in intracellular cAMP. However, while the MC1Rwt cells responded to ASIP with a concentration-dependent decrease in intracellular cAMP, MC1RΔ24 cells responded with an increase in cAMP. Melanism in the grey squirrel is associated with a 24 bp deletion in the MC1R. Cells expressing MC1RΔ24 have higher basal levels of cAMP than MC1R-wt cells. ASIP acts as an inverse agonist to the MC1R-wt but as an agonist to the MC1RΔ24. As MC1RΔ24 cells have higher levels of cAMP, and higher levels of cAMP lead to dark pigment production, the 24 bp deletion is the likely molecular cause of Melanism in the grey squirrel.

  • melanocortin 1 receptor mc1r gene sequence variation and Melanism in the gray sciurus carolinensis fox sciurus niger and red sciurus vulgaris squirrel
    Journal of Heredity, 2014
    Co-Authors: Helen R. Mcrobie, Nancy D. Moncrief, Linda M King, Cristina Fanutti, Peter J Coussons, Alison P M Thomas
    Abstract:

    Sequence variations in the melanocortin 1 receptor (MC1R) gene are associated with Melanism in many different species of mammals, birds, and reptiles. The gray squirrel (Sciurus carolinensis), found in the British Isles, was introduced from North America in the late 19th century. Melanism in the British gray squirrel is associated with a 24-bp deletion in the MC1R. To investigate the origin of this mutation, we sequenced the MC1R of 95 individuals including 44 melanic gray squirrels from both the British Isles and North America. Melanic gray squirrels of both populations had the same 24-bp deletion associated with Melanism. Given the significant deletion associated with Melanism in the gray squirrel, we sequenced the MC1R of both wild-type and melanic fox squirrels (Sciurus niger) (9 individuals) and red squirrels (Sciurus vulgaris) (39 individuals). Unlike the gray squirrel, no association between sequence variation in the MC1R and Melanism was found in these 2 species. We conclude that the melanic gray squirrel found in the British Isles originated from one or more introductions of melanic gray squirrels from North America. We also conclude that variations in the MC1R are not associated with Melanism in the fox and red squirrels.

Peter W. De Jong - One of the best experts on this subject based on the ideXlab platform.

Nancy D. Moncrief - One of the best experts on this subject based on the ideXlab platform.

  • Multiple origins of Melanism in two species of North American tree squirrel (Sciurus).
    BMC evolutionary biology, 2019
    Co-Authors: Helen R. Mcrobie, Nancy D. Moncrief, Nicholas I. Mundy
    Abstract:

    While our understanding of the genetic basis of convergent evolution has improved there are still many uncertainties. Here we investigate the repeated evolution of dark colouration (Melanism) in eastern fox squirrels (Sciurus niger; hereafter “fox squirrels”) and eastern gray squirrels (S. carolinensis; hereafter “gray squirrels”). We show that convergent evolution of Melanism has arisen by independent genetic mechanisms in two populations of the fox squirrel. In a western population, Melanism is associated with a 24 bp deletion in the melanocortin-1-receptor gene (MC1RΔ24 allele), whereas in a south-eastern population, Melanism is associated with a point substitution in the agouti signalling protein gene causing a Gly121Cys mutation. The MC1R∆24 allele is also associated with Melanism in gray squirrels, and, remarkably, all the MC1R∆24 haplotypes are identical in the two species. Evolutionary analyses show that the MC1R∆24 haplotype is more closely related to other MC1R haplotypes in the fox squirrel than in the gray squirrel. Modelling supports the possibility of gene flow between the two species. The presence of the MC1R∆24 allele and Melanism in gray squirrels is likely due to introgression from fox squirrels, although we cannot completely rule out alternative hypotheses including introgression from gray squirrels to fox squirrels, or an ancestral polymorphism. Convergent Melanism in these two species of tree squirrels has evolved by at least two and probably three different evolutionary routes.

  • melanocortin 1 receptor mc1r gene sequence variation and Melanism in the gray sciurus carolinensis fox sciurus niger and red sciurus vulgaris squirrel
    Journal of Heredity, 2014
    Co-Authors: Helen R. Mcrobie, Nancy D. Moncrief, Linda M King, Cristina Fanutti, Peter J Coussons, Alison P M Thomas
    Abstract:

    Sequence variations in the melanocortin 1 receptor (MC1R) gene are associated with Melanism in many different species of mammals, birds, and reptiles. The gray squirrel (Sciurus carolinensis), found in the British Isles, was introduced from North America in the late 19th century. Melanism in the British gray squirrel is associated with a 24-bp deletion in the MC1R. To investigate the origin of this mutation, we sequenced the MC1R of 95 individuals including 44 melanic gray squirrels from both the British Isles and North America. Melanic gray squirrels of both populations had the same 24-bp deletion associated with Melanism. Given the significant deletion associated with Melanism in the gray squirrel, we sequenced the MC1R of both wild-type and melanic fox squirrels (Sciurus niger) (9 individuals) and red squirrels (Sciurus vulgaris) (39 individuals). Unlike the gray squirrel, no association between sequence variation in the MC1R and Melanism was found in these 2 species. We conclude that the melanic gray squirrel found in the British Isles originated from one or more introductions of melanic gray squirrels from North America. We also conclude that variations in the MC1R are not associated with Melanism in the fox and red squirrels.

Alison P M Thomas - One of the best experts on this subject based on the ideXlab platform.

  • melanocortin 1 receptor mc1r gene sequence variation and Melanism in the gray sciurus carolinensis fox sciurus niger and red sciurus vulgaris squirrel
    Journal of Heredity, 2014
    Co-Authors: Helen R. Mcrobie, Nancy D. Moncrief, Linda M King, Cristina Fanutti, Peter J Coussons, Alison P M Thomas
    Abstract:

    Sequence variations in the melanocortin 1 receptor (MC1R) gene are associated with Melanism in many different species of mammals, birds, and reptiles. The gray squirrel (Sciurus carolinensis), found in the British Isles, was introduced from North America in the late 19th century. Melanism in the British gray squirrel is associated with a 24-bp deletion in the MC1R. To investigate the origin of this mutation, we sequenced the MC1R of 95 individuals including 44 melanic gray squirrels from both the British Isles and North America. Melanic gray squirrels of both populations had the same 24-bp deletion associated with Melanism. Given the significant deletion associated with Melanism in the gray squirrel, we sequenced the MC1R of both wild-type and melanic fox squirrels (Sciurus niger) (9 individuals) and red squirrels (Sciurus vulgaris) (39 individuals). Unlike the gray squirrel, no association between sequence variation in the MC1R and Melanism was found in these 2 species. We conclude that the melanic gray squirrel found in the British Isles originated from one or more introductions of melanic gray squirrels from North America. We also conclude that variations in the MC1R are not associated with Melanism in the fox and red squirrels.