Reptiles use pterin and carotenoid pigments to produce yellow, orange, and red colors. These conspicuous colors serve a diversity of signaling functions, but their molecular basis remains unresolved. Here, we show that the genomes of sympatric color morphs of the European common wall lizard (Podarcis muralis), which differ in orange and yellow pigmentation and in their ecology and behavior, are virtually undifferentiated. Genetic differences are restricted to two small regulatory regions near genes associated with pterin [sepiapterin reductase(SPR)] and carotenoid [beta-carotene oxygenase 2(BCO2)] metabolism, demonstrating that a core gene in the housekeeping pathway of pterin biosynthesis has been coopted for bright coloration in reptiles and indicating that these loci exert pleiotropic effects on other aspects of physiology. Pigmentation differences are explained by extremely divergent alleles, and haplotype analysis revealed abundant transspecific allele sharing with other lacertids exhibiting color polymorphisms. The evolution of these conspicuous color ornaments is the result of ancient genetic variation and cross-species hybridization.

Reptiles use pterin and carotenoid pigments to produce yellow, orange, and red colors.These conspicuous colors serve a diversity of signaling functions, but their molecular basis remains unresolved. Here, we show that the genomes of sympatric color morphs of the European common wall lizard, which differ in orange and yellow pigmentation and in their ecology and behavior, are virtually undifferentiated. Genetic differences are restricted to two small regulatory regions, near genes associated with pterin (SPR) and carotenoid metabolism (BCO2), demonstrating that a core gene in the housekeeping pathway of pterin biosynthesis has been co-opted for bright coloration in reptiles and indicating that these loci exert pleiotropic effects on other aspects of physiology. Pigmentation differences are explained by extremely divergent alleles and haplotype analysis revealed abundant trans-specific allele sharing with other lacertids exhibiting color polymorphisms. The evolution of these conspicuous color ornaments is the result of ancient genetic variation and cross-species hybridization.To investigate the genetic and evolutionary bases of the vivid colors displayed by reptiles, and to test hypothesis about how and why color polymorphisms and correlated trait variation persist within populations, we studied the European common wall lizard (Podarcis muralis) (Fig. 1A)a polymorphic lizard in which the ventral scales of males and females exhibits one of three distinct colors (orange, yellow, and white) or a mosaic pattern combining two colors (orange-yellow and orange-white) (12,13). Each of these five color morphs can be found throughout most of the broad geographic distribution of the species (Fig. 1B), and are shared by intraspecific sub-lineages thought to have diverged up to 2.5 million years ago (14). While the white morph is typically the most common (>50%), the relative frequency of morphs is highly variable even at small regional scales and the yellow or orange morphs may occasionally prevail (15,16) (SI Appendix, Fig. S1). The widespread distribution and persistence of color variation is thought to be due to balancing selection and the product of an interplay between natural and sexual selection (17). Previous work has shown that morphs mate assortatively with respect to ventral color (~75% of pairs) and differ in additional traits, including morphology, behavior, physiology, immunology, and reproduction (12,(18)(19)(20)(21)(22). The mode of inheritance of the color morphs is unknown. RESULTS Carotenoid and pterin pigments underlie pigmentation differencesWe began by determining the biochemical and cellular basis of pigmentation differences among morphs. Using electron microscopy (TEM), we found that the ventral skin of all morphs contained the same set of dermal pigment cells arranged as three superimposed 6 layers (xantophores, iridophores, and melanophores; Fig. 1C). The iridophore layer was thinner in orange individuals compared to yellow and white, but the most noticeable difference among morphs was observed in the...

Animal body coloration is a complex trait resulting from the interplay of multiple mechanisms. While many studies address the functions of animal coloration, the mechanisms of colour production still remain unknown in most taxa. Here we compare reflectance spectra, cellular, ultra- and nano-structure of colour-producing elements, and pigment types in two freshwater turtles with contrasting courtship behaviour, Trachemys scripta and Pseudemys concinna . The two species differ in the distribution of pigment cell-types and in pigment diversity. We found xanthophores, melanocytes, abundant iridophores and dermal collagen fibres in stripes of both species. The yellow chin and forelimb stripes of both P. concinna and T. scripta contain xanthophores and iridophores, but the post-orbital regions of the two species differ in cell-type distribution. The yellow post-orbital region of P. concinna contains both xanthophores and iridophores, while T. scripta has only xanthophores in the yellow-red postorbital/zygomatic regions. Moreover, in both species, the xanthophores colouring the yellow-red skin contain carotenoids, pterins and riboflavin, but T. scripta has a higher diversity of pigments than P. concinna . Trachemys s. elegans is sexually dichromatic. Differences in the distribution of pigment cell types across body regions in the two species may be related to visual signalling but do not match predictions based on courtship position. Our results demonstrate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs (i.e. vertical layering/stacking of different pigment cell types and interplay of carotenoids and pterins), but also employ novel mechanisms (i.e. nano-organization of dermal collagen) shared with mammals.

21Animal body coloration is a complex trait resulting from the interplay of multiple colour-producing mechanisms. 22Increasing knowledge of the functional role of animal coloration stresses the need to study the proximate causes of 23 colour production. Here we present a description of colour and colour producing mechanisms in two non-avian 24 archelosaurs, the freshwater turtles Trachemys scripta and Pseudemys concinna. We compare reflectance spectra; 25 cellular, ultra-, and nano-structure of colour-producing elements; and carotenoid/pteridine derivatives contents in 26 the two species. In addition to xanthophores and melanocytes, we found abundant iridophores which may play a 27 role in integumental colour production. We also found abundant dermal collagen fibres that may serve as 28 thermoprotection but possibly also play role in colour production. The colour of yellow-red skin patches results from 29 an interplay between carotenoids and pteridine derivatives. The two species differ in the distribution of pigment cell 30 types along the dorsoventral head axis, as well as in the diversity of pigments involved in colour production, which 31 may be related to visual signalling. Our results indicate that archelosaurs share some colour production mechanisms 32 with amphibians and lepidosaurs, but also employ novel mechanisms based on the nano-organization of the 33 extracellular protein matrix that they share with mammals. 34 35 *Jindřich Brejcha 2 36 65 Turtles are an early-diverging clade of Archelosauria, the evolutionary lineage of tetrapods leading to 66 crocodiles and birds [22]. Although many turtles have a uniform dull colour, conspicuous striped and spotted 67 patterns are common in all major lineages of turtles (for a comprehensive collection of photographs see [23-26]).68 These conspicuous colour patterns may be present in the hard-horny skin of shells, and/or in the soft skin of the 69 head, limbs or tail. The dark areas of the skin of turtles may have a threefold origin consisting either of dermal, 70 epidermal, or both epidermal and dermal melanocytes. Colourful bright regions are thought to be the result of the 71 presence of xanthophores in the dermis [27] and their interplay with dermal melanophores [28]. Iridophores have 72 never been shown to play role in coloration of turtles [27,29]. 73Pigment-bearing xanthophores were first described in the dermis of the Chinese softshell turtle (Pelodiscus 74 sinensis) [29]. Xanthophores have also been found sporadically in the dermis of the spiny softshell turtle Apalone 75 spinifera, the Murray river turtle (Emydura macquarii) and in the painted turtle (Chrysemys picta) [27]. Such scarcity 76 3 of carotenoid/pteridine derivatives-containing cells is in contrast with chemical analyses of the yellow and red 77 regions of the integument of the red-eared slider (Trachemys scripta elegans) and C. picta [30,31]. Two major 78 classes of carotenoids have been described in the integument of these turtles: short wavelength absorbing 79 apocarotenoids and longer wave...

The northern pike, Esox lucius, is one of the largest temperate freshwater apex predators with a characteristic morphology: an elongated body with pelvic, dorsal, and anal fins located at the rear as a functional feature to sprint predation. However, the typical pike character is its head, which is characterized by a long, flattened snout, a well‐armed mouth with numerous teeth, and large eyes characteristic of shallow water visual predators. Although the northern pike is becoming increasingly popular as a model system for ecology and evolutionary research, a detailed staging table has not yet been reported. In this study, we report the first comprehensive staging table for the northern pike, spanning from the one‐cell stage to the freely‐swimming juvenile stage. In addition to classical embryological descriptions, we use a DAPI staining to distinguish individual cells and embryonic structures during the early development. This dataset, in combination with the genomic and transcriptomic resources already available, serves as a foundation for in‐depth mechanistic studies dealing with development using this species.

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