Coloration in Reptiles - Research Paper Example

Coloration in Reptiles Introduction The term coloration as is applied in biological studies refers to the visual appearance that is observed with regard to the color variations and the arrangement of colors. Reptiles, just as mammals have their skins exemplify certain similar traits to the mammals and other traits are different. Particularly, the skin of reptiles is comprised of two layers; dermis and the epidermis. The epidermis has a characterization of complete coverage of the skin by keratin, similar to mammals while the reptile dermis comprises of connective tissues. Thus, it is the skin of the reptiles that will be used to generate color variations among different species and categorizations. The production of color for the skin of reptiles is usually dependent on two sets of cells; chromatophores and melanocytes. However, the absence or presence of the cells and their distribution and density when present in each layer is the greatest determinant of coloration among reptiles. Melanocytes, which are usually present throughout in the epidermis’ basal layers, are essential during the skin renewal process of epidermal growth since they send the pseudopodia into the keratocytes that bear the melanin; thus, initiating the transfer of the said melanin into the skin. In reptiles such as crocodiles, snakes and iguanids, the keratocytes are obtained in the β-layer while, in other reptiles, they may exist in both α and β layers. On the other hand, chromatophores are usually layered upon each other in the exterior portion of the dermis to provide the pigment cells xanthophores (yellow) and erythrophores (reddish-purple) plus other fat soluble pigment cells for use in the construction of the basal membrane. In this study, the main focus shall be on the understanding of the process of coloration among reptiles taking into consideration the evolution and genetics of variations in color among reptiles. The achievement of this shall be through the scientific review of about fifteen research articles conducted in various studies with the concept of coloration as the key theme. This broader coverage is to ensure adequate and in-depth analysis of the reptilian coloration. As such, the study shall be categorized into the genetically, evolutionary and morphologically impacts on coloration. The reviews shall mainly be from scientific papers written by different scholars under different themes but, centered on coloration. Literature Review Introduction According to a study by Olsson et al. (2013), there has been a flourishing of the studies on coloration in reptiles for nearly two decades, most of which has been in relation to the genetics that underlies the color traits, the application of the colors in social interactions and the fragmentary selection of the traits among the reptiles. By profoundly considering the taxonomical bias, the study focused on case studies that had complete color evolution causal consequences from the phenotypic variations in colors to the selection. The reviews that shall be considered in this study shall be categorized according to the themes described in them and the impacts of the same, whether genetically, morphologically and evolutionary. Genetically impacts of coloration in reptiles Functionally, the coloration in reptiles results from a succession of multifaceted interactions occurring between the pigment and structural components of the skin hence, impacting on both the conditional dependence and proximate control of the color expression. Considering the color variable species, color heritability estimates and color patterns, a simple Mendelian inheritance pattern has always been observed. With this, there is always a striking difference in the reproductive tactics among color polymorphic species such as lizards, given that those differences are mostly genetically encoded (Olsson et al., 529-541). With this, the study noted that there was mostly a substantial constituent of socio-sexual signaling of the lizards based on the variations in the colors for females and males. Thus, as a genetic impact, the substantiation for hormonal effects and color expressions conditions with the parasite loads and immunocompetence tradeoffs was always variable. Subsequently, given that the lizards used in the study showed a fade in their color in response to the ageing and psychological stress they undergo, the model would be appropriately practical in finding the interactions between the indicator traits, handicaps and the immunoecology (Husak 156-160). An additional illustration would be in the case of breeding in which the female lizards would change skin color as an indication of deterring or attracting male counterparts for courtship. This behavior has been commonly noticed in the Crotaphytus collaris lizard species. The iguanian, Holbrookia maculata species have been commonly observed using coloration intensity to monitor the receptiveness of females (Olsson et al., 529-541). Thus, coloration is depicted here as an essential determinant of reproduction. In another related study by Baird (2004) on the reproductive coloration in female Crotaphytus collaris, the noted result of the coloration is the stimulation of courtship between the male and female species. Morphologically, the study sought to establish the hypothesis that the natural color makings on the females led to longer courtship periods by male reptiles and involved more displays by males around such females. This is as opposed to the artificial markings that the researcher made on experimental lizards. This behavior suggested that the females’ coloration development functioned to stimulate the courtship given that the females were receptive. The results from the study’s experiment also suggested likewise and not that the courtship frequency difference signaled rejection. Bowen (2003), in studying about the ontogenetic coloration changes that result on a northern water snake specie, Nerodia sipedon sipedon notes the possession of a striking dorsal pattern in the coloration of the young snake (juvenile), as opposed to the adults that had a uniform dorsal coloration. Based on past researches, which had hypothesized the color shift as resulting from the darkening ground color, Bowen sought to establish more of these hypotheses for the reason that none of the past studies had been quantitatively tested. The results from the test analysis indicated a darkening of the dorsal ground with an increase in snake length. However, the coloration of the ventral patterns and dorsal blotches did not change. Thus, this impact can be said to genetically entail a relative constant ventral snake pattern with changing benefits and costs as a result of the dorsal coloration. Evolutionary impacts of coloration in reptiles Certain times, the reptiles’ coloration abilities are dependent on evolutionary factors that exist in their habitat. In doing this, it is recommended that the conditions promoting maintenance and evolution of various populations be determined together with their variants. This is because a study of the evolutionary impacts often takes into consideration the color polymorphism consequences. Forsman & Viktor (2008) in a study to determine the association of coloration with the breadth of the niche and status of conservation, consider the population predictions as containing ‘ecomorphs’ already having gene complexes that are co-adapted. These are noted to utilize more diverse resources, as well as displaying higher rates of colonization success, range expansions, and population persistence. While these take place, the normal reptile population is considered as less vulnerable to contraction ranges and extinction as compared to the monomorphic populations (Forsman & Viktor 160-168). Accordingly, the study by Forsman and Viktor, (160-168) which was based on pairwise comparative analysis recognizes that the color patterns of the species that were variable possessed larger ranges; hence, could be attributed to the utilization of a greater habitat diversity types. Consequently, the results for the association is as indicated above due to the fact that the variable coloration was less represented among those species whose habitat appeared as currently threatened. Evolutionarily, coloration may be said to have had an impact in the reptiles here through the co-occurrence of multiple variants of colors that could promote ecological success. The results in the study above are aggregated by a different study by Rosenblum et al., (1794-1808). This study sought to determine the adaptive color variation in reptiles and the evolution of the MCIR gene, taking into consideration the consequences of numerous pigmentation phenotypes. This offered a prospect for scholars to study the ecologically important traits of the reptiles based on variations in the molecular basis. Considering the molecular sequence of a complete melanocortin – 1 receptor (Mc1r), the study focused on the diverse phylogenetically squamate species. Their blanched forms were associated with dissimilar colored substrates and thermal environments hence, leading to the result that the high level silent site heterozygosity was due to the high rates of mutation. Therefore, there association between the Mc1r polymorphism and the color differences is considered strong. Finally, the provision of nuclear gene comparative data among reptiles indicates that the utilization of the gene approach results in an in-depth understanding evolution. Works Cited Baird, Troy. Reproductive Coloration in Female Collared Lizards, Crotophytus Collaris, Stimulates Courtship by Males. Herpetologica. 60.3 (2004): 337-348. Web. 13 Feb. 2014. Bowen, Kenneth. Ontogenetic Changes in the Coloration of the Northern Watersnake, Nerodia sipedon sipedon. Journal of Herpetology. 37.4 (2003): 729-731. Web. 13 Feb. 2014 Forsman, Anders, and Viktor Berg. Associations of Variable Coloration with Niche Breadth and Conservation Status among Australian Reptiles. Ecology 89.5 (2008): 1201-1207. Web. 13 Feb. 2014. Husak, J. F., J. K. McCoy, S. F. Fox, and T. A. Baird. 2004. Is coloration of juvenile male collared lizards (Crotaphytus collaris) female mimicry? An experimental test. Journal of Herpetology 38:156-160. Olsson, M, D Stuart-Fox and C Ballen. Genetics and evolution of colour patterns in reptiles. Elsevier: PubMed. 24.6-7 (2013): 529-541. Rosenblum Erica, Hopi Hoekstra, Michael Nachman, and J. Hey. Adaptive Reptile Color Variation and the Evolution of the MC1R Gene. Evolution. 58.8 (2004): 1794-1808. Web. 13 Feb. 2014. Read More