Our brief review attempt to fill this gap of proximate mechanisms of color pattern formation by extending the conceptual frame-work presented by Arnold (1983) into color pattern evolution ( Figure 2). Yet, we could point out that here have been no recent reviews on the proximate mechanisms underlying various color patterns in reptiles, though several important studies in this topic have been published to date. The rich diversity of reptiles, as a stem lineage of terrestrial vertebrates living in various ecosystems, provides an invaluable opportunity to study coloration by mainly focusing on functional mechanisms of adaptation for avoiding predation ( Ruxton et al., 2018) such as aposematic coloration and coral snake mimicry ( Wallace, 1867 Jackson et al., 1976 Pfennig et al., 2001), back ground matching for cryptic coloration ( Poulton, 1890 Cott, 1940 Rosenblum et al., 2004), and predator avoidance by motion dazzle coloration ( Thayer, 1909 Stevens et al., 2008 Murali et al., 2018 Kodandaramaiah et al., 2020). Basically, animal color pattern is a longstanding and important topic in evolutionary biology in general, and squamates in particular, which exhibit a wide variety of color patterns such as warning signal of venomous coral snakes and its mimicry by the distantly related non-venomous snakes ( Figure 1A), and convergent evolution of stripes and vivid blue tails by small lizards ( Figure 1B), are important target of several agents of natural selection for effective visual signals to conspecifics for reproduction, to predators for avoidance, and to sometimes prey for feeding (e.g., Cooper and Greenberg, 1992 Pianka and Vitt, 2003 Stuart-Fox et al., 2008 McKinnon and Pierotti, 2010 Kronforst et al., 2012 Allen et al., 2013 Olsson et al., 2013). Why do we study color pattern production mechanisms in squamate reptiles. Clarifying the contributions of pigment cells and genetic factors improves our general understanding of reptilian color pattern evolution. The pigment cell based color production and pattern formation during embryogenesis were reviewed for the recent studies on lizards and snakes, by focusing on different color production mechanisms in terms of epidermal and dermal pigment cell architectures, and then discuss the genetic determinants of pattern formation considering both biologically relevant theoretical models which consider pigment cell specification, migration, and architecture differentiation. In order to understand molecular and genetic mechanism of color pattern formation, not only adult phenotypes but also processes and mechanisms of color production and pattern formation during embryonic and postembryonic stages should be described.
2Laboratory of Geographical Ecology, Department of Biology, Faculty of Science, Toho University, Chiba, Japan.
1Institute of Natural and Environmental Sciences, University of Hyogo, Tamba, Japan.Takeo Kuriyama 1, Arata Murakami 2,3, Matt Brandley 4 and Masami Hasegawa 2*
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