Characterization of the Skin Microbiota of the Cane Toad Rhinella cf. marina in Puerto Rico and Costa Rica

Abstract

Rhinella marina is a toad native to South America that has been introduced in the Antilles, likely carrying high loads of microorganisms, potentially impacting local community diversity. The amphibian skin is involved in pathogen defense and its microbiota has been relatively well studied, however, research focusing on the cane toad microbiota is lacking. We hypothesize that the skin microbial communities will differ between toads inhabiting different geographical regions in Central America and the Caribbean. To test our hypothesis, we compared the microbiota of three populations of R. cf. marina toads, two from Costa Rican (native) and one Puerto Rican (exotic) locations. In Costa Rica, we collected 11 toads, 7 in Sarapiquí and 4 from Turrialba while in Puerto Rico, 10 animals were collected in Santa Ana. Separate swab samples were collected from the dorsal and ventral sites resulting in 42 samples. We found significant differences in the structure of the microbial communities between Puerto Rico and Costa Rica. We detected as much as 35 different phyla; however, communities were dominated by Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. Alpha diversity and richness were significantly higher in toads from Puerto Rico and betadiversity revealed significant differences between the microbiota samples from the two countries. At the genus level, we found in Santa Ana, Puerto Rico, a high dominance of Kokuria , Niabella , and Rhodobacteraceae, while in Costa Rica we found Halomonas and Pseudomonas in Sarapiquí, and Acinetobacter and Citrobacter in Turrialba. This is the first report of Niabella associated with the amphibian skin. The core microbiome represented 128 Operational Taxonomic Units (OTUs) mainly from five genera shared among all samples, which may represent the symbiotic Rhinella ’s skin. These results provide insights into the habitat-induced microbial changes facing this amphibian species. The differences in the microbial diversity in Puerto Rican toads compared to those in Costa Rica provide additional evidence of the geographically induced patterns in the amphibian skin microbiome, and highlight the importance of discussing the microbial tradeoffs in the colonization of new ecosystems.

Assessment of Bacterial Communities Associated With the Skin of Costa Rican Amphibians at La Selva Biological Station

“…Additionally, in our study, in every species with more than 4 amphibians sampled, the most abundant OTU was not the same in all of them. Both observations suggest that there are intraspecific variations in amphibian bacterial communities, these variations are possibly associated with environmental factors, presence of Bd or internal population variations of amphibian species, as has been reported by other studies ( Muletz et al, 2017 ; Abarca et al, 2018 ; Rebollar et al, 2018 ).…”

“…More recently, it has been suggested that environmental factors may also play an important role in the variation of the amphibian bacterial microbiota ( Muletz et al, 2017 ; Bird et al, 2018 ; Varela et al, 2018 ). It has also been reported that bacterial communities can vary according to geography ( Abarca et al, 2018 ; Rebollar et al, 2018 ), ecomorphs ( Bletz et al, 2017a ) and ontogeny ( Longo et al, 2015 ).…”

The impact of multiple climatic and geographic factors on the chemical defences of Asian toads (Bufo gargarizans Cantor)

“…Additionally, the synthesis of these compounds may involve different biosynthesis pathways, which may be selectively accessed in different environmental conditions. Some studies have indicated that bufogenins may also be transformed by certain microorganisms 33,34 , and the correlations between different chemical components may result from biotransformation of the toad skin microbiome in different habits.…”

“…As the mixed defensive toxins were obtained from different adult toads at each geographical site, this regular pattern of chemical defence phenotypic plasticity induced by geographical factors was not related to the gender, age, or size of the individual toads. Although predators and competitors in different regions may have certain effects on the variation in defensive toxin production 8,12,34 , the density and type of these species in different regions vary greatly 7,34,35 . Accordingly, we conclude that this regular variation in geographical environment was not mainly induced by the presence of these species.…”

Detection and comparative analysis of cutaneous bacterial communities of farmed and wild Rana dybowskii (Amphibia: Anura)

“…Bacillus is often used as a probiotic on farms to prevent disease; therefore, the high abundance of Firmicutes in the farmed group may depend on human factors. Bacteroidetes and Firmicutes are predominant bacteria on the skin of many amphibians (Abarca et al 2017;Bates et al 2018). The relative abundances of the phyla Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria in the two groups were significantly different, both of which belonged to the phylumlevel in LDA.…”