Specific Aims
Color polymorphism is an opportunity for researchers to study how the balance between natural selection and genetic drift shapes the evolution of appearance and form. This paper intends to identify the specific mechanisms of color polymorphism and processes involved in non-primitive color variation in animals whether as a mechanism acting between populations, or within them. Interestingly enough, recent discoveries in research show comprehensive approaches are necessary to not only discover the origin of color polymorphism, but what makes it evolve, allows it to persist, and leads to speciation. The cat family, Felidae, is ideal for investigating melanistic coat coloration because it is common in at least 13 of 37 species. The actual role of the polymorphism in field predators is unknown as there is a lack of availability of genomic tools for natural populations. It is also very difficult to determine its genetic basis because the mutations are relatively common cats, but are not alike. A theory to be tested is that the coloration may have differing functions per the cat’s environment. For example, in nocturnal big cats, such as jaguars and panthers, it may be advantageous to have black fur to camouflage them from their prey and potential predators or even as a survival mechanism, preventing their susceptibility to infections. One of the genes of interest to be investigated in this paper is ASIP which affects domestic felines and in wild cats, MC1R. This is a gene that codes proteins for dark pigmentation not only in Felidae, but also in humans. MC1R codes for seven-helix protein transmembrane receptors which produce pigmentation and overall, result in melanism. Researchers believe that the black fur on felines are an example of overactive MC1R genes. This experiment will look at whether the species has to ability to adapt to a change of habitat and how this influences its color polymorphism, if at all. It is expected that felines in new environments with a higher expressivity of melanism will produce more offspring than those with less color polymorphism. As a result of these predictions, it is anticipated that the new patterns of colorism in the species will create new selective pressures within the population in terms of sexual selections. These outcomes will allow progression in the understanding of color polymorphism and eventually extend to understanding the behaviors that increase fitness.
Background
Research has relied heavily on genetics as the basis of color polymorphism. A traditional model system for linking phenotype and genotype is pigmentation because it provides (1) a plethora of candidate genes from studies in genetics, (2) an understanding of the role of these genes in pathways and networks from developmental biology and (3) ecologically relevant pigmentation phenotypes from studies in evolutionary biology (Hoekstra, 2006). Research identifying the pigmentation genes responsible for phenotypic adaptation and the developmental mechanisms by which genotypes encode phenotypic traits is necessary to truly understand the processes responsible for generating both genetic and organismal diversity (Gary et. al, 2007). Two gene mutations that have been extensively studied because of their consistent nature of melanism are MC1R and ASIP. MC1R mutations, dominantly inherited and ASIP mutations, recessively inherited, still have an unknown pattern of melanism in vertebrae. Mapping of these genes have provided a more comprehensive method for the identification of genetic regions underlying pigmentation variation and, when combined with candidate pigmentation genes, provide an extremely powerful approach to make links between genes, phenotype and fitness (Schneider et. al, 2015). Researchers mapped, cloned and sequenced homologs of the two genes (ASIP [agouti] and MC1R) to investigate their role in melanistic coat coloration in cats. Their investigation was based on the adaptive significance, genetic basis, and evolutionary history of melanistic variants and they found three independent deletions associated with dark coloration in three different species (Eizrik et. al, 2003). Further research on the coding region of the Agouti Signaling Protein (ASIP) was conducted in multiple leopard and Asian golden cat individuals, and identified distinct mutations strongly associated with melanism in each of them. The results revealed two additional cases of species-specific mutations implicated in melanism in the Felidae, and indicated that ASIP mutations may play an important role in naturally-occurring coloration polymorphism. In felids, both genes were found to be implicated, with MC1R variants underlying melanistic phenotypes in two different wild cat species (Panthera onca and Puma jaguarondi), and a mutation in ASIP inducing black color in domestic cats. It was found that two novel mutations associated with melanism are caused by loss of ASIP function. Another perspective researchers took on exploring the genetic influences of color polymorphism, they looked at parametric patterns, or lack thereof, of melanism. The five dimensions conceptualized in the study were: (i) patterned versus plain, (ii) pattern irregularity, (iii) pattern complexity, (iv) pattern element size and (v) the anisotropy (directionality) of pattern elements. Probability of patterning and probability of complex patterning were the fraction of all comparison patterns for each species classified by all observers as patterned and complexly patterned, respectively (Allen et. al, 2010).
Another factor believed to influence color polymorphism in Felidae is habitat adaptations. Researchers have assessed the potential differences in habitat association between melanistic and non-melanistic leopards because there is no distribution model focused on spatial patterns of phenotypic variation in the species. The results obtained for the two sample sets (melanistic and non-melanistic) were strikingly different, while the non-melanistic records presented a spatial distribution that approached randomness within the sampled polygon. It was concluded that the melanistic records strongly deviated from the expected pattern (Silva et. al, 2017). Further exploration into polymorphism as adaptive was because it theorized that it is a protective mechanism at multiple levels: (1) the consequences of prey polymorphism for foraging predators, (2) the consequences of predation for prey individuals that vary in color pattern, and (3) the consequences of predation for populations of prey that vary in the level of polymorphism they exhibit. (Karpestram et. al, 2016). Additional research on habitual adaptations on color polymorphism was conducted based on various biogeographic zones in India. Given the recent evolutionary history of the species, broad distribution, and relatively similar ecologies, it is expected that leopard cats and jungle cats would have similar patterns of genetic variation across the Indian subcontinent. While the jungle cat, as predicted, illustrated high variation and significant but relatively low structure, the leopard cat is deeply structured into two populations. Further results resolved ambiguity surrounding leopard cat distribution in India by showing that the North and South Indian populations are not connected. With this prior knowledge, the results support earlier inferences of possible absence of leopard cats from Central India and further show the limits of distribution for this species within India with the Himalayan and the North-East Indian populations being more similar to each other than either of them is to the Western Ghats one. In comparison to this, a comparative study and similar regions of DNA for leopard cat showed a contrasting pattern with strong phylogenetic separation between populations and significant population structuring (Allen et. al, 2010).
Research Questions
The purpose of this study is to understand the role of color polymorphism on the survival and reproductive successes of the feline species. To identify the specific mechanisms of color polymorphism and the processes involved in non-primitive color variation in animals I propose the specific question in study: if color polymorphism in Felidae is an adaptation, how does it increases their fitness? I hypothesize that color polymorphism is a result of genetic mutations in ASIP – agouti signaling peptide, and MC1R – genes providing instructions for the production of melanin genes that increase the overall fitness of populations in Felidae. Support of my hypothesis is further explored in the predicted results section.
Research Approach
I. This study will be completed at the University of Tampa, Tampa, Florida.
II. As it is an extension of work completed by the Royal Society of London, the Felidae populations studied have previously been established as a group composed of 55 jungle cats and 40 leopard cats. The necessary permissions will be obtained from members of the Indian government, law enforcement and their WOW organization. The population is present in the North and South populations India.
III. ASIP and MCR1 coding regions of each feline involved will be sequenced as follows:
a. patterned versus plain
b. pattern irregularity
c. pattern complexity
d. pattern element size and
e. the anisotropy (directionality) of pattern elements
IV. The genes sequenced will be mapped on reaction diffusion models to determine the parametric patterns of genes.
Potential Results and Broader Impacts
The purpose of this study is to understand the role of color polymorphism on the survival and reproductive successes of the feline species. This study identifies the specific mechanisms of color polymorphism and the processes involved in non-primitive color variation in Felidae. The expectations of this study are that color polymorphism in felines are influenced by the ASIP and MCR1 genes. When looking at the non-primitive color variation, it is expected…