Pterin-based pigmentation in animals

Abstract

Pterins are one of the major sources of bright coloration in animals. They are produced endogenously, participate in vital physiological processes and serve a variety of signalling functions. Despite their ubiquity in nature, pterin-based pigmentation has received little attention when compared to other major pigment classes. Here, we summarize major aspects relating to pterin pigmentation in animals, from its long history of research to recent genomic studies on the molecular mechanisms underlying its evolution. We argue that pterins have intermediate characteristics (endogenously produced, typically bright) between two well-studied pigment types, melanins (endogenously produced, typically cryptic) and carotenoids (dietary uptake, typically bright), providing unique opportunities to address general questions about the biology of coloration, from the mechanisms that determine how different types of pigmentation evolve to discussions on honest signalling hypotheses. Crucial gaps persist in our knowledge on the molecular basis underlying the production and deposition of pterins. We thus highlight the need for functional studies on systems amenable for laboratory manipulation, but also on systems that exhibit natural variation in pterin pigmentation. The wealth of potential model species, coupled with recent technological and analytical advances, make this a promising time to advance research on pterin-based pigmentation in animals.

Introduction history and natural selection jointly shape evolution of a signaling trait during biological invasion

“…Moreover, biochemical investigations of dewlap pigment composition in several Anolis species have found that pterin pigments are important sources of coloration, although carotenoids were detected as well (Ortiz, 1962;Macedonia et al, 2000, Steffen & McGraw, 2007, 2009. In contrast to carotenoids, pterins are produced endogenously (reviewed in Andrade & Carneiro, 2021). Even so, identifying genes involved in pterin synthesis has been challenging because of the complexity of underlying biochemical pathways.…”

Knockdowns of red Malphigian tubules reveal pigmentation roles in the milkweed bug

“…Ommochromes are tryptophan metabolites used as visual pigments in the eyes of arthropods and have repeatedly been co‐opted to form body pigmentation (Futahashi & Osanai‐Futahashi, 2021; Orteu & Jiggins, 2020; Reed et al, 2008). Pterins are guanosine triphosphate (GTP) metabolites commonly used to create yellow, orange, and red pigmentation in insects (Andrade & Carneiro, 2021; Futahashi & Osanai‐Futahashi, 2021). They were first described as the pigments in butterfly wings (Hopkins, 1895; Wijnen et al, 2007), but are also common across the tree of life as biosynthetic precursors (Andrade & Carneiro, 2021; Ayling et al, 2012; Feirer & Fuqua, 2017).…”

“…Pterins are guanosine triphosphate (GTP) metabolites commonly used to create yellow, orange, and red pigmentation in insects (Andrade & Carneiro, 2021; Futahashi & Osanai‐Futahashi, 2021). They were first described as the pigments in butterfly wings (Hopkins, 1895; Wijnen et al, 2007), but are also common across the tree of life as biosynthetic precursors (Andrade & Carneiro, 2021; Ayling et al, 2012; Feirer & Fuqua, 2017). Studies in water striders and butterflies suggest that pterin pathway components have repeatedly been co‐opted from eyes to wing and body tissues to drive the evolution of aposematic red (Vargas‐Lowman et al, 2019; Wee & Monteiro, 2017).…”

Environmental conditions and male quality traits simultaneously explain variation of multiple colour signals in male lizards

“…For example, while carotenoid‐based colours are physiologically costly to produce (reviewed in Svensson & Wong, 2011), melanin‐based colour signals are thought to be associated mainly with social costs (reviewed in Roulin, 2016). However, the costs associated with pterin‐based and structural colour signals, if any, remain largely unknown (Andrade & Carneiro, 2021; Kemp et al, 2012), although social costs are potential candidates (e.g. Kawamoto et al, 2021).…”