Search for: All records

Here, we investigated whether Cuban treefrogs tadpolesOsteopilus septentrionaliscan gain protection from Bd through exposure to a prophylaxis treatment composed of killed zoospores or soluble Bd metabolites. We used a 2 × 2 factorial design, crossing the presence or absence of killed zoospores with the presence or absence of Bd metabolites. All hosts were subsequently exposed to live Bd to evaluate susceptibility.

Exposure to killed zoospores did not induce a protective response. However, tadpoles exposed to Bd metabolites had significantly lower Bd intensity and prevalence than tadpoles that were not exposed to metabolites.

The metabolites Bd produce pose no risk of Bd infection and therefore make an epidemiologically safe prophylaxis treatment, protecting tadpoles against Bd. This work provides a promising potential for protecting amphibians in the wild as a disease management strategy for controlling Bd‐associated declines.

Here we experimentally created >100 natural wetland communities to quantify the relative effects of fertilizer, six insecticides (chlorpyrifos, terbufos, malathion, λ‐cyhalothrin, permethrin and esfenvalerate), and six herbicides (acetochlor, alachlor, metolachlor, atrazine, propazine and simazine) on two snail genera responsible for 90% of global schistosomiasis cases.

We identified four of six insecticides (terbufos, permethrin, chlorpyrifos and esfenvalerate) as high risk for increasing snail biomass by reducing snail predators. Hence, malathion and λ‐cyhalothrin might be useful for improving food production without increasing schistosomiasis. This top‐down effect of insecticides on predators was so strong that the effects of herbicides on schistosomiasis risk were masked in the presence of predators because there were so few snails. In the absence of snail predators, herbicide effects on snails were generally negative by reducing submerged vegetationHydrilla verticillata. The exception was that atrazine and acetochlor significantly increased the biomass of infected snails and total snails respectively.

Like insecticides, fertilizer had strong positive effects on snail populations. Fertilizer increased both snail habitat (submerged vegetation) and snail food (periphyton), but of these two pathways, the increases in snail habitat resulted in greater snail population growth. Total snail biomass was positively associated with both infected snail biomass and parasite production and thus human infection risk.

Synthesis and applications. Our findings suggest that fertilizers and insecticides generally have consistently higher chances of increasing human schistosomiasis than herbicides in natural communities. Furthermore, our results highlight the need to identify other low risk insecticides, which might help reduce crop pests without increasing snails and thus risk of schistosomiasis.

Here, we compare the effects of a nematodeAplectana hamatospiculathat is native to Cuba but appears to be introduced to Florida on the native Floridian treefrog,Hyla femoralis, and on the Cuban treefrog (CTF),Osteopilus septentrionalis. We were particularly interested in CTFs because their introduction to Florida has led to reported declines of native treefrogs.

In the laboratory, infection withA. hamatospiculacaused a greater loss in body mass ofH. femoralisthan CTFs despiteH. femoralisshedding fewer total worms in their faeces than CTFs. Field collections of CTFs,H. femoralis, and another native Floridian treefrog,H.squirella(Squirrel treefrog) from Tampa, FL also showed that CTFs shed more larval worms in their faeces than both native frogs when controlling for body size. Hence, the non‐native CTF is a supershedder of this non‐native parasite that is spilling over to less tolerant native treefrogs.

Any conservation intervention to reduce the effects of CTFs on native treefrogs would benefit from knowing the traits that contribute to the invasive host being a supershedder of this parasite. Hence, we conducted necropsies on 330 CTFs to determine how host sex and body size affect the abundance ofA. hamatospicula, and two other common parasites in this species (acuariid nematodes and trematode metacercariae).

There was a significant linear increase inA. hamatospiculaand encysted acuariids with CTF body size, but there was no detectable relationship between host body size and the intensity of metacercariae. Female CTFs were bigger, lived longer and, on average, had moreA. hamatospiculathan male CTFs.

Synthesis and applications. These results of the study suggest that there is parasite spillover from the invasive Cuban treefrog (CTF) to native treefrogs in Florida. Additionally, at least some of the adverse effects of CTFs on native treefrogs could be caused by the introduction and amplification of this introduced parasite, and female and larger CTFs seem to be amplifying these infections more than males and smaller CTFs, respectively, suggesting that management could benefit from targeting these individuals.

The present study primarily tests how environmental context influences the relative contributions of pathogen survival and per capita transmission on host infection prevalence using the amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) as a model system. Secondarily, we evaluate how environmental context influences the decomposition of Bd because previous studies have shown that dead Bd and its metabolites can illicit acquired resistance in hosts. We conducted Bd survival and infection experiments and then fit models to discern how Bd mortality, decomposition and per capita transmission rates vary among water sources [e.g. artificial spring water (ASW) or water from three ponds].

We found that infection prevalence differed among water sources, which was driven by differences in mortality rates of Bd, rather than differences in per capita transmission rates. Bd mortality rates varied among pond water treatments and were lower in ASW compared to pond water.

These results suggest that variation in Bd infection dynamics could be a function of environmental factors in waterbodies that result in differences in exposure of hosts to live Bd. In contrast to the persistence of live Bd, we found that the rates of decomposition of dead Bd did not vary among water sources, which may suggest that exposure of hosts to dead Bd or its metabolites might not commonly vary among nearby sites. Ultimately, a mechanistic understanding of the environmental dependence of free‐living pathogens could lead to a deeper understanding of the patterns of outbreak heterogeneity, which could inform surveillance and management strategies.

Here, we investigated whether four taxonomically distinct amphibians, Cuban tree frogsOsteopilus septentrionalis, southern toadsAnaxyrus(Bufo)terrestris, greenhouse frogsEleutherodactylus planirostrisand pine woods tree frogsHyla femoralis, exhibited any innate or learned avoidance of Bd on a moist substrate and, if so, what cues they used to identify the fungus.

Cuban tree frogs, pine woods tree frogs and greenhouse frogs did not appear to exhibit detectable innate or learned avoidance of Bd. However, southern toads learned to avoid Bd after only one exposure. Southern toads avoided any treatment containing Bd metabolites but did not avoid treatments that lacked Bd metabolites even when dead zoospores were present.

Bd metabolites appeared to be the cues that amphibians use to avoid Bd. These metabolites may have a distinct smell or may cause discomfort, which would be consistent with a classical or Pavlovian conditioning response.

Synthesis and applications. Not all species of amphibians respond the same way to Bd exposure; some can learn to avoid Bd and the metabolites it produces, while others do not. These findings have important implications for both management practices and policy, and should be considered when developing disease models and conservation plans for amphibians.