Demonstration of subsurface passive acoustic monitoring (SPAM) to survey for and estimate populations of imperiled underwater-calling frogs

The management and recovery of threatened and endangered amphibians on Department of Defense (DoD) lands relies on an understanding of their distribution and abundance. Fortunately, most anuran species can be surveyed acoustically using vocalizations during the breeding season. This work demonstrated the use of subsurface passive acoustic monitoring (SPAM) to survey for rare underwater-calling, at-risk anuran species on DoD installations. We evaluated the performance of SPAM relative to traditional passive acoustic monitoring (PAM) (microphone) and human manual calling survey (MCS) methods. Results showed that SPAM outperformed PAM and MCS in validation experiments where calls were generated underwater; SPAM was less successful than PAM and MCS in the field demonstration. Most leopard frog calls were apparently produced in air despite previous reports of extensive underwater-calling behavior. This project highlights how acoustic information can help address a data gap in the ecology of at-risk species, which can help refine future survey methodology and management efforts. Ultimately, the utility of SPAM for underwater-calling species will depend on the focal species, the landscape where it occurs, and technological considerations available to the surveyor. SPAM is more expensive than traditional methods but, in some situations, may be the only way to effectively detect species.

Comparative Genomics Analysis between frog Virus 3-like Ranavirus from the First Canadian Reptile Mortality Event and Similar Viruses from Amphibians

Ranaviruses are emerging pathogens that threaten the biodiversity of wild and captive cold-blooded vertebrates. Reports of ranavirus-induced mortality events are increasing and ranavirus disease is reportable to the World Organization for Animal Health. Previous studies have suggested interclass transmission of ranaviruses and Frog virus 3 (FV3)-like viruses are of particular interest. This study presents the whole-genome assembly of a 106 kb FV3-like genome obtained from the liver tissue of a reptile (wild Chelydra serpentina, common snapping turtle) that died of ranavirus disease in Canada. The FV3-like ON turtle/2018 strain shares the highest genome-wide nucleotide identity (99.71%) with the wild-type FV3 virus detected in the USA from a Northern leopard frog and an FV3-like strain identified from a wood frog in 2017 in Alberta, Canada. The novel genome contains all 26 Iridoviridae core genes, 11 FV3-like genes, and 9 unique truncations, three of which are core Iridoviridae ORFs. Additionally, the two most closely related FV3-like strains from amphibians, were compared to a non-FV3-like amphibian infecting and a fish infecting ranavirus species that showed similar codon usage patterns. G/C-ending codons were the preferred codons for all five strains. Investigation of putative recombination events identified four potential recombination events in the FV3-like ON turtle/2018 genome consistent with this FV3-like reptile infecting strain originating from an amphibian infecting FV3-like ranavirus. Altogether, this study provides insights into the genome structure and the differences in the novel FV3-like genome compared to other ranavirus genomes.

Brain plasticity in response to short-term exposure to corticosterone in larval amphibians

Exposure to stressors and elevation of glucocorticoid hormones such as corticosterone (CORT) has widespread effects on vertebrate brain development. Previous studies have shown that exposure to environmental stressors alters larval amphibian brain morphology and behavior, yet the effects of CORT on amphibian neural development are still unknown. We exposed prometamorphic Northern Leopard Frog (Lithobates pipiens (Schreber, 1782)) tadpoles for 7 days to a concentration of exogenous CORT (45.56 g/L ) that produced physiologically-relevant increases in plasma CORT. This brief exposure to CORT, relatively late in development, resulted in a significantly larger diencephalon width (relative to body mass) when compared to controls. Although we were unable to detect changes in behavior or body morphology, our results indicate that brain shape is modulated by exposure to CORT. More studies are needed to better understand what accounts for the CORT-induced change in brain shape as well as the functional consequences of these changes.

Feeding habits of Lithobates megapoda (Anura: Ranidae), a threatened leopard frog used for human consumption, in Lake Chapala, Mexico

The Big-footed Leopard Frog (Lithobates megapoda) is a threatened and endemic species from western Mexico. This species has aquatic habits and it is distinguished by its large size, particularly by the length of its legs, reason for which it is captured for human consumption. Also, knowledge about its natural history is scarce and incomplete. In this study, we analyzed the composition of the diet of L. megapoda on the shore of Lake Chapala, the largest lake in Mexico. A total of 69 adult individuals were collected lifeless in fishing nets, during the rainy season (June-October), of which 48 had stomach contents. A total of 96 prey items were identified, which correspond to 13 prey categories. Fish constituted the most dominant prey category in the diet in terms of number, volume, frequency of occurrence, and relative importance. No significant differences were found in the consumption by prey type (aquatic or terrestrial). However, the aquatic preys had a greater relative importance and were more voluminous than the terrestrial ones. The diversity of prey categories, in terms of prey volume, indicates males may have a higher dietary diversity than females, but we not evaluated possible bias. In addition, a significant effect was found in the interaction of size (SVL) of frogs with the average of prey volume. Females (that are larger than males) consumed prey within a wide volume range and, the larger they are, more voluminous are prey. In this way it is possible that intraspecific competition for trophic resources in the environment is reduced. This study helps us understand the trophic ecology of L. megapoda, a frog species that plays an important role in the food web where it lives, as a predator feeding on aquatic and terrestrial organisms.

Assessing the Impact of Algae Management Strategies on Anurans and Aquatic Communities

Residential areas are increasing on the landscape but their ability to provide suitable habitat is often based on management for recreational use and aesthetics. Amphibians rely on both aquatic and terrestrial habitat making them susceptible to changes in land-cover and land-use. As anthropogenic land-use change increases, it is imperative to assess how pond management practices impact aquatic communities. We assessed the impact of Aquashade (a common non-toxic pond dye) and copper sulfate (a toxic algaecide) on American toad (Anaxyrus americanus), northern leopard frog (Lithobates pipiens), and Cope’s gray treefrog (Hyla chrysoscelis) metamorphosis in outdoor mesocosm experiments. We also evaluated the relative impact of tadpole grazing and chemical treatment on phytoplankton and periphyton abundance. We found no significant effects of pond management treatment on anuran metamorphosis, suggesting that addition of Aquashade and copper sulfate does not significantly impact anurans under these experimental conditions. However, while we found no differences in phytoplankton and periphyton abundance due to pond management treatment, presence of tadpoles significantly decreased phytoplankton and periphyton abundance over time. This result suggests that the creation of suitable pond habitat for anuran tadpoles may be an efficient and ecologically beneficial form of pond management treatment to maintain water quality.

The distribution and effects of microbeads on host-parasite interactions of Ontario wetland fauna: tadpoles, snails and trematodes

Plastic microbeads pose an environmental problem as they easily enter into waterbodies, take a long time to break down, and their ingestion can have negative effects on aquatic organisms. I found that microbead consumption had a significant negative effect on the growth of northern leopard frog (Lithobates pipiens) tadpoles, as well as their susceptibility to trematode parasite (Echinostoma trivolvis) infection, but minimal effects on leukocyte profiles and infection tolerance. Freshwater snails (Stagnicola elodes) given microbead diets exhibited a non-monotonic response in their production of trematode (Haematolechus parviplexus) infectious stages, with those in the highest microbead treatment tending to exhibit greater growth and shorter longevity. I also found that algae (Chlorella pyrenoidosa) and microbeads created density-dependent aggregations that could be a potential ingestion pathway for herbivorous fauna. Lastly, I found many particles in Ontario wetlands and ponds that may be used for controlled pesticide release, thus potentially posing a threat.

The distribution and effects of microbeads on host-parasite interactions of Ontario wetland fauna: tadpoles, snails and trematodes

Plastic microbeads pose an environmental problem as they easily enter into waterbodies, take a long time to break down, and their ingestion can have negative effects on aquatic organisms. I found that microbead consumption had a significant negative effect on the growth of northern leopard frog (Lithobates pipiens) tadpoles, as well as their susceptibility to trematode parasite (Echinostoma trivolvis) infection, but minimal effects on leukocyte profiles and infection tolerance. Freshwater snails (Stagnicola elodes) given microbead diets exhibited a non-monotonic response in their production of trematode (Haematolechus parviplexus) infectious stages, with those in the highest microbead treatment tending to exhibit greater growth and shorter longevity. I also found that algae (Chlorella pyrenoidosa) and microbeads created density-dependent aggregations that could be a potential ingestion pathway for herbivorous fauna. Lastly, I found many particles in Ontario wetlands and ponds that may be used for controlled pesticide release, thus potentially posing a threat.