Fluorescence in amphibians and reptiles: new cases and insights

From Firenze University Press Journal: Acta Herpetologica

Lucas M. Botelho, Projeto Dacnis, Estrada do Rio Escuro, 4754, Sertão das Cotias, Ubatuba, São Paulo, 11680–000

Suzana E. Martins, IPBio — Instituto de Pesquisas da Biodiversidade, Reserva Betary

Gregory Melocco, Departamento de Ciências Farmacêuticas (Toxicologia e Fitopatologia), Farmácia

Luís F. Toledo, Laboratório de História Natural de Anfíbios Brasileiros (LaHNAB), Departamento de Biologia Animal, Instituto de Biologia, Unicamp

Ivan Sazima, Museu de Diversidade Biológica, Instituto de Biologia, Universidade Estadual de Campinas

Edelcio Muscat, Projeto Dacnis, Estrada do Rio Escuro, Sertão das Cotias

Biofluorescence was first described in the early 16thcentury through the study of medicinal herbs by a Span-ish researcher (Lagorio et al., 2015). However, the first in situ observation was only reported in the 20th centu-ry for green-blue algae (Tswett, 1911). Cockayne (1924) published the first studies about biofluorescent animals. Since then, fluorescence has been the subject of investi-gation by numerous researchers. Among vertebrates, bio-fluorescence was primarily reported for marine species (Wucherer and Michiels, 2012; Sparks et al., 2014), while research on terrestrial tetrapods has only gained atten-tion in recent years (Prötzel et al., 2021). For amphibians and reptiles, three main types of fluorescence are known. In reptiles, bone fluorescence stands out (Prötzel et al., 2018; Sloggett, 2018; Jeng, 2019; Top et al., 2020; Pinto et al., 2021; Maria et al., 2022), along with dermal fluo-rescence (Paul and Mendyk, 2021; Prötzel et al., 2021). In amphibians, in addition to dermal (Taboada et al., 2017a, b; Deschepper et al., 2018; Chaves-Acuña et al., 2020; Whitcher, 2020) and bone fluorescence (Goutte et al., 2019; Rebouças et al., 2019; Nunes et al., 2021), ocu-lar fluorescence was reported recently (Deschepper et al., 2018; Alvarez et al., 2022).Although the evolution of biofluorescence is still barely understood (Macel et al., 2020), some hypoth-eses have been proposed to explain its function. These include prey attraction (Haddock and Dunn, 2015; Paul and Mendyk, 2021), predator avoidance (Rebouças et al., 2019), camouflage (Sparks et al., 2014), visual commu-nication (Goutte et al., 2019; Gray, 2019; Alvarez et al., 2022), visual recognition, mate choice, and sexual attrac-tion (Hausmann et al., 2003; Prötzel et al., 2018).In this study, we describe and illustrate fluorescence in four amphibian and four reptile species, and provide a list of amphibians that apparently did not display fluores-cence when observed under UV light.We used an UltraFire WF-5016 flashlight with a wavelength of 365 nm to test UV light fluorescence of sev-eral amphibians and reptiles. To maximize the chances of finding fluorescence, we caught and exposed the amphib-ians to light on all body sides, including the ocular region. When detecting the presence of UV fluorescence, we pho-tographed the animal using a Nikon D7100 digital cam-era with a 100mm Sigma macro lens, with an aperture of f/5, ISO sensitivity of 3200, and a shutter speed of 1/200. After the tests, we recorded the presence or absence of fluorescence in a field spreadsheet and released the ani-mals into the same location where we captured them. We categorized the fluorescence as dermal when detected on the surface of the animal’s skin or in soft tissues, as bone fluorescence when reflected in areas such as the skull or vertebral column, and as ocular fluorescence when the fluorescence was displayed in the animal’s eyes.Individuals of Brachycephalus nodoterga were found in March 2022 in the Núcleo Santa Virgínia of the Parque Estadual da Serra do Mar, Natividade da Serra, São Pau-lo, Brazil. The specific location was known as “trilha do campinho” (23.866667°S, 45.568611°W, 855 m a.s.l.). Natividade da Serra is in mosaic-like Atlantic Forest vegetation, consisting of primary and secondary forests in different stages, bordered by eucalyptus plantations and pastures. The rainy season in this area occurs from October to March, while the drier season spans April to September. We searched opportunistically for other amphibians and reptiles from May to June 2023, during routine monitoring in the area of the NGO Projeto Dac-nis (23.462947°S, 45.132943°W; 15–500 m a.s.l.). Projeto Dacnis encompasses a private reserve spanning 136 ha within the Atlantic Forest in Ubatuba, São Paulo, Brazil. The area is a swampy forest in low-lying areas and patch-es of primary and secondary dry forest on steep terrain. The climate is humid with rainfall incidence throughout the year. Finally, we also tested one individual of Boker-mannohyla alvarengai in August 2023 in Monumento Natural Estadual Várzea do Lajeado e Serra do Raio, Ser-ro, Minas Gerais, Brazil. The location is close to Caminho dos Escravos, in the district of São Gonçalo do Rio das Pedras (18.43019°S, 43.464654°W, 1165 m a.s.l.). The Serro region is predominantly covered by high-altitude savannah vegetation, with rocky and sandy fields and humid floodplains. There is also Atlantic Forest, with sec-ondary forests, and areas deforested for agricultural use. The climate is characterized by two well-defined seasons, cold and dry winter, between April and September, and hot and humid summer, between October and March.In total we tested 122 individuals of 25 amphib-ian and four reptile species (Table 1). Among the tested amphibians, five species displayed fluorescence: Brachy-cephalus nodoterga had dermal bones fluorescence on the dorsum (Fig. 1A–B); Scinax argyreornatus displayed dermal fluorescence on the dorsum, inguinal region, jaw, and upper part of the head (Fig. 1C–F); Bokermannohyla alvarengai presented dermal fluorescence on the entire dorsum, but in the blue spectrum (Fig. S1); Hylodes phyl-lodes and H. asper showed fluorescence only on their eyes (Fig. S2). Among reptiles, all four tested species dis-played fluorescence. The lizard Enyalius perditus had flu-orescence on the skull, with more evident reflections in males, both on the back and the lateral side of the head (Fig. 2A–F). A juvenile Hemidactylus mabouia gecko dis-played fluorescence in both the skull and the vertebral column (Fig. 2G–I). The adult, photographed from a dis-tance, showed fluorescence only on the upper part of the head and jaw. Bothrops jararaca and B. jararacussu dis-played fluorescence only on the tail tip of juveniles (Fig. S3). From the three B. jararaca individuals (total length 28, 43, and 62 cm), the largest individual showed fluores-cence only at a small portion of the tail tip.Bone fluorescence in Brachycephalus nodotergashowed a distinct pattern from B. ephippium, B. pitan-ga and B. rotenbergae (Goutte et al., 2019; Nunes et al. 2021). This difference is due to the amount and distribu-tion of dorsal ossified plates in these species (Goutte et al., 2019; Nunes et al. 2021). UV light fluorescence in a species of the genus Scinax and Bokermannohyla is here reported for the first time, despite fluorescence being recorded in other genera and species of hylid treefrogs (Taboada et al., 2017 a, b; Deschepper et al., 2018; Chaves-Acuña et al., 2020; Whitcher, 2020). Fluorescence in frogs could be related to intraspecific communication as a visual signal that complements acoustic signalling (Goutte et al., 2019; Gray, 2019) and can contribute to achromatic vision and the detection of other individuals in low-light environments (Lamb and Davis, 2020). Flu-orescence in frogs of the genus Hylodes is also reported for the first time here. Furthermore, ocular fluorescence is reported only for four other anuran species in the genera Boana (Hylidae) and Rana (Ranidae) (Deschepper et al., 2018; Alvarez et al., 2022). Deschepper et al. (2018) suggest that fluorescent eyes are related to intraspecific recognition, whereas for Alvarez et al. (2022) this fluorescence type may be related to interspecific communication among sympatric species, thus avoiding predatory con-flicts or disputes for food and territory.

DOI: https://doi.org/10.36253/a_h-14922

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