Identifying fungal-host associations in an amphibian host system

Host-associated microbes can interact with macro-organisms in a number of ways that affect host health. Few studies of host-associated microbiomes, however, focus on fungi. In addition, it is difficult to discern whether a fungal organism found in or on an ectotherm host is associating with it in a durable, symbiotic interaction versus a transient one, and to what extent the habitat and host share microbes. We seek to identify these host-microbe interactions on an amphibian, the Colorado boreal toad (Anaxyrus boreas boreas). We sequenced the ITS1 region of the fungal community on the skin of wild toads (n = 124) from four sites in the Colorado Rocky Mountains, across its physiologically dynamic developmental life stages. We also sampled the common habitats used by boreal toads: water from their natal wetland and aquatic pond sediment. We then examined diversity patterns within different life stages, between host and habitat, and identified fungal taxa that could be putatively host-associated with toads by using an indicator species analysis on toad versus environmental samples. Host and habitat were strikingly similar, with the exception of toad eggs. Post-hatching toad life stages were distinct in their various fungal diversity measures. We identified eight fungal taxa that were significantly associated with eggs, but no other fungal taxa were associated with other toad life stages compared with their environmental habitat. This suggests that although pre- and post-metamorphic toad life stages differ from each other, the habitat and host fungal communities are so similar that identifying obligate host symbionts is difficult with the techniques used here. This approach does, however, leverage sequence data from host and habitat samples to predict which microbial taxa are host-associated versus transient microbes, thereby condensing a large set of sequence data into a smaller list of potential targets for further consideration.

Unpalatable, yet unprotected: trout reduce survival and development rate of rare toad tadpoles despite chemical defense

Unpalatable prey species often have toxins that protect from direct consumption. However, negative effects of prey manipulation by predators are rarely considered and may understate impacts to unpalatable species. When both prey and predator are species of concern, stronger understanding of the predator–prey relationship is warranted. We explored direct and indirect effects of greenback cutthroat trout (Oncorhynchus clarkii stomias) on boreal toad (Anaxyrus boreas boreas) tadpole survival, growth, and development, as well as postmetamorphosis survival and growth. We found exposure to O. clarkii stomias delayed metamorphosis by 1–2.5 days and reduced tadpole survival by up to 25%, even though only a single tadpole was consumed. Tadpoles from captive-bred eggs had lower survival, growth, and greater loss in body condition after metamorphosis compared with tadpoles from wild eggs. We found that O. clarkii stomias do not innately avoid A. boreas boreas but instead strike tadpoles to determine prey palatability and repeated gustation likely reduced survival. Our results shed light on unresolved issues with A. boreas boreas captive breeding and demonstrate the nonconsumptive negative impacts of predators.

Scale and landscape perception: the case of refuge use by Boreal Toads (Anaxyrus boreas boreas)

Refugia likely represent a critical resource necessary for the persistence of populations of Boreal Toads ( Anaxyrus boreas boreas (Baird and Girard, 1852)) in a given area. However, the features that define suitable refuge microsites and the extent to which the habitat surrounding refugia is exploited remains unclear. We sought to describe refuge characteristics in the context of their surroundings and to determine whether local-scale movement behaviour associated with refuge use might provide a novel perspective of landscape-level habitat selection. A pilot study suggested that refugia were selected primarily for physical structure in the form of coarse woody debris, but this was not the case. Instead, refugia provided favourable microclimates with elevated relative humidity compared with the surrounding habitat. Boreal Toads tended to forage at night within 15 m from refugia. This distance was used to calculate activity centres across toad summer home ranges. Activity centres prioritized the importance of treeless habitat overall and wetland habitat for females when compared with 50% core home ranges. This approach could be used to pinpoint critical habitat at the landscape scale, which may be of particular importance for conserving populations currently in decline.