Rodeo™ Herbicide Negatively Affects Blanchard's Cricket Frogs (Acris blanchardi) Survival and Alters the Skin-Associated Bacterial Community

Abstract

Disease-associated mortality is a leading cause of amphibian declines and extinctions worldwide. Understanding the influence of land-management practices, like herbicide use, on amphibian immune defense traits could guide changes to improve conservation outcomes. Amphibians are partially protected from pathogens by two skin-associated immune defense traits: bacterial communities inhabiting their skin, and antimicrobial peptides secreted by the skin. Utilizing the Blanchard's Cricket Frog (Acris blanchardi), a declining North American amphibian species, as our model, we manipulated Rodeoe aquatic herbicide concentration and the life stage at which Rodeo exposure occurred. We assessed juvenile survival, time to metamorphosis, juvenile mass, and skinassociated immune defense traits. We found a 37% decrease in survival of larvae exposed to 2.5 mg a.e. L-1 (acid equivalent) compared to controls despite that this commercial herbicide formulation does not contain an added surfactant. Surviving larvae exposed to 2.5 mg a.e. L-1 Rodeo had structurally different larval skin bacterial communities compared to controls. Larval Rodeo exposure did not carry over to postmetamorphic traits (juvenile mass, juvenile skin bacterial community, juvenile natural peptide secretions). Rodeo treatments did not affect time to metamorphosis or juvenile survival. Rodeo concentration had marginally significant effects on juvenile mass and the juvenile skin bacterial community. This study suggests glyphosate-based herbicide use may indirectly contribute to disease-related amphibian declines by altering the skin bacterial community that can provide pathogen resistance. Improving our knowledge of the influence of herbicide use on amphibians across life stages provides an opportunity for changes to application strategies to protect amphibian health or at minimum, lessen negative effects of the practice.

Conservation biology needs a microbial renaissance: a call for the consideration of host-associated microbiota in wildlife management practices

“…Documenting the threats to host-associated microbial communities. a land-use change -habitat fragmentation is associated with reductions in diversity and altered community composition of the mammalian gut [18,19] and amphibian skin microbiomes [20] -urbanization decreases bacterial richness and alters the community composition and functional profile of the bird gut microbiome [21] -amphibians living in agricultural habitats have distinct gut microbial community composition from those living in natural habitats [22] contamination -heavy metal exposure decreases diversity and alters the community composition of the fish gut microbiome [23] -exposure to polychlorinated biphenyls alters the community composition of the larval amphibian gut microbiome, which persists in the adult life stage [24] -pesticide and herbicide use are, respectively, linked to compositional changes in the gut microbiome of insects [25] and the skin microbiome of larval and adult amphibians [26] climate change -increased temperature results in losses of diversity and alterations to the community composition of reptile [27] and amphibian [28] gut microbiomes -warming ocean temperature alters the assemblage of the microbial communities associated with marine sponges [29] -ocean acidification reduces diversity and alters the community composition of coral associated microbes [30] infectious disease -parasite infection can decrease diversity of the bird gut microbiome [31], and alter community composition of the mammalian [32 -34] and amphibian [35] gut microbiomes -viral infections alter the community composition of the bird gut microbiome [36] and amphibian skin microbiome [37] -cutaneous fungal infection alters skin microbial communities of amphibians [38], the degree of which increases with pathogen load [39] captivity -gut microbial communities of fish [40], reptiles [41], birds [42] and mammals [43 -47], and skin microbial communities of amphibians [48,49] and reptiles [50], are distinct between captive individuals and their wild conspecifics -mammalian gut microbial communities [47] and amphibian skin microbial communities…”

Typha (Cattail) Invasion in North American Wetlands: Biology, Regional Problems, Impacts, Ecosystem Services, and Management

“…While cutting followed by flooding or cutting below water is highly effective at killing Typha (Weller 1975;Sale and Wetzel 1983;Jordan and Whigham 1988;Ball 1990), this approach results in high levels of mortality to native emergent species as well (Lishawa et al 2017). Amphibians and other gillbreathing organisms are also at risk from aggressive and high frequency nature of Typha control, particularly during early spring and summer when larvae are present and metamorphosing, although there is still considerable uncertainty regarding these impacts (Krynak et al 2017).…”

Amphibian conservation in Scotland: A review of threats and opportunities

“…In Scotland, Bird et al (2018) surveyed 19 peri-urban ponds for heavy metal pollutants, salt, and chlorophyll (as an indicator of plant nutrient levels): frog breeding occurred successfully over a wide range of pollutant concentrations, but high levels of aluminium were shown to be detrimental to development. We know of no Scottish study that has reported the effects of agrichemicals, as demonstrated elsewhere, such as: alteration of tadpole brain development by exposure to sublethal concentrations of the pesticide chlorpyrifos (Woodley, Mattes, Yates, & Relyea, 2015); reduced tadpole survival and damage to the cutaneous bacterial community by the herbicide glyphosate (Krynak, Burke, & Benard, 2017); and feminization of male gonadal development by the herbicide atrazine (Orton & Tyler, 2015). The great crested newt population at Gartcosh in North Lanarkshire may illustrate how seriously (or not) Scotland takes its duties over protected species.…”