DISCUSSION
Polychromatism has been recorded in several anuran species and may serve distinct functions such as disruptive camouflage, aposematism, sexual identification, and others (Hoffman and Blouin 2000; Wells 2007). Although in the present study we observed multiple coloration patterns in individuals from the same locality, no studies have been conducted to assess the evolutionary mechanisms that have selected for these characteristics in the different populations of A. hoogmoedi . The diurnal activity displayed by species within this genus, coupled with their specific habitat in stream environments characterized by background noise, likely played a role in the evolution of visual communication signals (Heyer et al., 1990; Hödl & Amézquita, 2001).
Geographic isolation can generate phenotypic diversity in certain amphibian species (Rudh et al., 2007). However, this does not seem to be the case in A. hoogmoedi , as populations in close proximity exhibit distinct color patterns. Color variation among individuals in different populations has been described as a consequence of genetic drift associated with geographic features in Adelphobates galactonotus (Rojas et al., 2020). Furthermore, for some species dorsal coloration in males may play a role in female mate preferences (Maan & Cummings, 2008), although differences in coloration may not be sex-related for others (Ávila-Pires et al., 2010). The use of visual displays in Atelopus is described in the literature, both for the defense of territory and for aggression between individuals (Crump 1988, Lindquist and Hetherington 1996, 1998). Examining how the various color patterns of A. hoogmoedi may influence sexual selection or reproductive territory defense can provide insights into the selective pressures acting on this trait.
In certain polychromatic anuran species, color variation can lead to varying predation rates (Noonan & Comeault, 2009; Chouteau & Angers, 2011; Hegna et al., 2013; Amézquita et al., 2013; Willink et al., 2014). This can be attributed to the search image and prior predator experience exposed to different color patterns. In terms of parsimony, it would be expected that a monomorphic color pattern within a species facilitates easier learning of the signal by predators (Rojas et al., 2015). This phenomenon is observed in Mullerian mimicry organisms (Chatelain et al., 2023). Polychromatism has been extensively studied in the context of predator-prey relationships, particularly when the models are geographically isolated, such as on islands (Hegna et al., 2013) or separated by rivers that act as a geographic barrier (Rojas et al., 2015; Jeckel et al., 2019). Populations exhibiting distinct color patterns that are geographically isolated may arise as a response to different predators in each locality. However, in the case of A. hoogmoedi which is distributed within a continuous forest landscape, the explanations may not be as straightforward.
Hence, the advantage of the polychromatic pattern in Atelopus hoogmoedi remains a mystery, prompting the need for further research encompassing genetic, behavioral, sexual and environmental selection. This characteristic provides an excellent opportunity to elucidate how evolutionary mechanisms such as selection, drift, or geographic isolation may operate to select for these patterns. Despite A. hoogmoedi being widely distributed in the Eastern Amazon and being one of the few species within the genus Atelopus that does not show strong evidence of population reduction (Valencia & Fonte, 2022), there are still significant gaps in our understanding of the species’ biology and even its taxonomic delimitation (Silva et al., 2020).
We strongly encourage further investigations to elucidate the factors influencing color variation in this species. Scientific research on the biodiversity of the Amazon Rainforest has recently faced significant challenges due to funding cuts in the scientific budget implemented by the previous Brazilian government (Angelo, 2019; Fernandes et al., 2017; Escobar, 2019). Additionally, the increase in losses of natural areas in the last years (Peres et al., 2023) highlights the need to accelerate studies in the region before the loss of basic information. This jeopardizes the study and understanding of Neotropical biodiversity, particularly concerning a highly endangered group of vertebrates such as the anurans of the genus Atelopus . Therefore, it is imperative to allocate investments toward integrative research on the evolution and ecology of this genus of anurans.