1 Introduction
Ecological morphology also known as ecomorphology is a comparative discipline with its central focus on the study of the interaction between morphological and ecological diversity of organisms both in the present and over evolutionary time (Kotrschal and Motta, 1991). The morphological adaptations and ecological characteristics are closely correlated because the interspecific morphological differences result from the distinct selective pressures that they suffer (Beaumord and Petrere Jr, 1994). Interactions between ecology and morphology can be studied at multiple levels; among taxonomic unites or life history intervals and between their phenotypic characteristics and their use of ecological resources in a particular environment (Norton et al., 1995). Skin as a phenotypic characteristic is a boundary between animals and their environment, serving multiple roles such as acting in protection, contributing to locomotion, maintaining moisture of the body, altering the characteristics of the skin, helping in camouflage, capturing prey, as well as contributing to physiological regulation, sensory detection, respiration, and coloration (Abo-Eleneen and Allam, 2011; Vitt and Caldwell, 2013). Snake’s scales are essentially made of folds of epidermis and dermis; however, the scales themselves are essentially originated from the epidermis. The number of scales neither increases nor reduces as the snake matures over time, but the scales grow larger and may undergo changing in shape as the snake exuviates (Swadźba and Rupik, 2010; Abo-Eleneen and Allam, 2011). Most of the body surface in reptiles is covered by these keratinized epidermal scales. Two keratin types contribute to the formation of scales; the ß-keratin covering entirely the scale’s surface, and α-keratin constructing the interscalar space or suture. This distribution of keratin produces a durable and protective scale surface with junctures between the scales that allow flexibility and expansion of the skin (Vitt and Caldwell, 2013). Generally called “Oberhautchen”, The ß-layer of scale is in direct contact with the environment. The oberhautchen exhibits a particular micro-structure in several squamate reptile groups and often is divided into cell-like parts that may bear complex three-dimensional features. The overall arrangement of these cells and their surface features are called microornamentation (Ruibal, 1968; Stewart and Daniel, 1973; Arnold, 2002). Scale shape, extent, and microornamentation can serve as important charactersistics for taxonomic and systematic investigations (Leydig, 1873; Picado, 1931; Price, 1982). Microornamantation variability may be arises from adaptation pressures directly acting upon scales, and could play important taxonomic role in discriminating generic and specific, but not family categories (Rocha-Barbosa and Moraes e Silva, 2009; Crowe-Riddell et al., 2016). Several studies have surveyed the association of scale microornamentation and systematics and ecological variation. According to these studies, since the ultrastructural features of scales might be relatively free from direct adaptational pressures, they could well be more reliable indicators of interspecific relationships (Burstein et al., 1974). Price (1982) reported that microornamentation patterns reflect the phylogenetic relationships, rather than environmental or habitat impacts and that there was no evidence for a correlation between microornamentation and habitats or environment. Nevertheless, microstructures have been used as tools in ontogenetic and/or evolutionary studies of squamates (Harvey and Gutberlet Jr, 1995). Gower (2003) and Pough et al. (2003) have found strong correlation between scale microornamentation and ecology, emphasizing that certain kinds of micro-ornamentation are associated with certain habitats.
Solar radiation consist of a wide range of wavelengths and affect all creatures on Earth. Sunlight primarily are divided into visual, ultraviolet and infrared wavelenghts that absorbed or reflected by animate and inanimate surfaces. In animals the skin is in direct contact with the environment and play an important role in absorbing or reflecting visible and invisible light. Many invertbrates and vertbrates have the ability to perceive UV light and also possess UV-reflective structures on their body surface (Shi and Yokoyama, 2003; Modarressie et al., 2013). The roles of UV in vision are manifold from animal communication, guiding navigation and orientation behavior, to detecting food and potential predators (Modarressie et al., 2013).
P. persicus and P. fieldi inhabit sandy and rocky terrains with moderate vegetation of bushes and grasses. They are nocturnal in habits, retreats during the day into crevices among rocks or burrows in comparatively hard soil near roots of bushes. Their diet consists of deserticolous lizards, mice, and arthropods (Khan, 2011). The immediate habitat of the P. urarachnoides contains hill and high grounds mostly composed of gypsum. It prefers deep cracks and holes in the gypsum substrates to benefit moisture and coolness in the warm months of summer (Fathinia et al., 2009). Its main diet in adulthood is migratory passerines (Fathinia et al., 2015). E. macmahonii is morphologically adapted to live in fine loose sand of shifting dunes. Its habitat is without any mentionable vegetation, except for very sparse growth of stunted bushes and grasses (Khan, 2011). E. carinatus recorded from sandy and rocky alluvial habitats, with sparse xerophytic to moderately dense grass and scrub vegetation. In mountainous habitats it lives under rock blocks, while in sub-mountainous regions inhabits hedges and other scrubby vegetation, noticeably avoiding marshy areas and very dense vegetation (Khan, 2011).Cerastes gasperettii as a nocturnal true desert snake prefer sandy soil regions with high temperature and some vegetation as shelters (Sadoon and Paray., 2016).Eirenis rafsanjanicus inhabits mountain areas with substrates compose of clay soil covering with numerous pebbles, and annual and perennial plants (Akbarpour et al., 2020). Lythorhynchus maynardiinhabits sandy terrains covered by bushes. The vegetation is dominated by Tamarix sp. and a syntopic snake species is Echis carinatus.
The present study is aimed to: 1) compare microstructure variation in scale surface using SEM, 2) discover variation in light reflection of scales among snake species in two families and five genera occupying both the same and different microhabitats, and 3) explore the taxonomic-ecomorphological association in the concerned species.