From forest to city: urbanization modulates relative abundance of anti-predator coloration

Abstract

Increased urbanization has resulted in community changes including alteration of predator communities. Little is known, however, about how such changes affect morphological anti-predator traits. Given the importance of coloration in predator avoidance, this trait in particular is expected to be susceptible to novel selective environments in urban areas. Here, we investigate the coloration pattern of a Neotropical anuran species, the túngara frog (Engystomops pustulosus), along an urbanization gradient. Túngara frogs have two distinct color patterns (unstriped and striped) which we found to occur at different frequencies along an urbanization gradient. Striped individuals increased in frequency with urbanization. To assess the strength of selection imposed by predators on the two color morphs, we deployed clay models of túngara frogs in forest and semi-urban populations. In addition, we examined microhabitat selection by individuals of the different morphs. We found higher predation rates associated with urbanization than forested areas. In particular, frogs from forested habitats had lower number of attacks by avian predators. Contrary to our predictions, however, predation rates were similar for both color morphs independent of urbanization. Also, coloration of the frogs did not affect their microhabitat preference. Overall, túngara frogs are more likely to have a striped coloration pattern in semi-urban areas where predation by birds is higher than in the forest. Our findings suggest that factors other than predation pressure shape the coloration pattern of urban frogs and emphasize the complex nature of effects that anthropogenic changes in habitat and predator communities may have on prey morphology.

United colours of the city: A review about urbanisation impact on animal colours

“…(2019) pointed out that, independently of mortality rates due to conspicuousness (see also Anderson et al . 2019), animals may be selective agents of the environments. Therefore, conspicuous species can have increased mortality in urban areas or, simply, conspicuous species can avoid urban areas.…”

“…Moreover, Anderson et al . (2019) found a higher frequency of black striped forms of the tungara frog ( Engystomops pustulosus ) in urban areas than in forest areas.…”

Genomic Analyses Reveal Association of ASIP with a Recurrently evolving Adaptive Color Pattern in Frogs

“…Phenotypes shared across such highly divergent lineages can result from ancestral alleles conserved over millions of years of evolution, or have evolved independently multiple times, perhaps driven by similar selective forces. While predator-mediated selection is a widely assumed mechanism for the evolution and maintenance of most color patterns in anurans ( Hoffman and Blouin 2000 ), the link between the anuran vertebral stripe and survival is only empirically supported in a few species ( Stewart 1974 ; Woolbright and Stewart 2008 ; McElroy 2016 ; but see Anderson et al 2019 ). To gain a better understanding of the evolutionary history of the vertebral stripe in anurans, a broad-scale comparative analysis is necessary.…”

Coloring inside the lines: genomic architecture and evolution of a widespread color pattern in frogs

“…Phenotypes shared across highly divergent lineages can result from ancestral alleles conserved over millions of years of evolution, or have evolved independently multiple times, perhaps driven by similar selective forces. While predator-mediated selection is a widely assumed mechanism for the evolution and maintenance of most color patterns in anurans 17 , the link between the anuran vertebral stripe and survival is only empirically supported in a few species 13,18,19 (but see 20 ). In order to understand the evolutionary history of the vertebral stripe in anurans, a broad-scale comparative analysis is necessary.…”