Batrachochytrium dendrobatidis exposure effects on foraging efficiencies and body size in anuran tadpoles

Abstract

Chytridiomycosis, the amphibian disease caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), is fatal to adults of many species. Bd is largely sublethal to amphibian larvae; however, it is known to reduce larval (i.e. tadpole) growth rates, with possible long-term effects on population dynamics and fitness. We conducted an experiment to test how Bd altered southern leopard frog Lithobates sphenocephalus tadpole mouthpart damage, percentage of food ingested, and subsequent body size. We examined our results using path analyses. We hypothesized that Bd would increase mouthpart damage, causing less food to be ingested, and ultimately reduce body size. In our model, both Bd exposure and increased mouthpart damage significantly reduced food ingested and subsequent body size. However, our study provides evidence against the long-standing hypothesis of mouthpart damage as a pathway for Bd-induced reductions in larval group. Here we provide evidence for reduced foraging efficiency (percentage of food ingested) as a mechanism for Bd-induced reductions in body size. This work highlights the importance of studying the sublethal effects of Bd on larval amphibians. KEY WORDS: Chytrid fungus · Feeding · Larvae · Life history traits · Path analysisResale or republication not permitted without written consent of the publisher © Inter-Research 2015 · www.int-res.com Dis Aquat Org 112: [237][238][239][240][241][242] 2015 al. (2013) showed that Bd exposure reduced tadpole size, and mouthpart damage reduced the size of tadpole guts relative to body size. In other words, studies have shown that Bd causes mouthpart damage, damage reduces foraging efficiency, and reduced efficiency reduces growth. So it can be inferred that Bd-induced mouthpart damage potentially reduces growth. However, this pathway has never been proven. While previous studies have provided evidence for possible pathways by which Bd-induced reductions in tadpole growth may occur, a direct pathway from Bd-induced mouthpart damage to reduced growth has yet to be confirmed.Much work has focused on the direct, lethal effects of Bd on host populations. While such research is imperative to our understanding of the disease, the sublethal effects of Bd, especially on larval amphibians, could have lasting carry-over effects that negatively alter natural populations. To address the sublethal impact(s) of Bd on tadpoles and identify a pathway whereby Bd reduces growth and development, we tested the hypothesis that Bd would cause mouthpart damage, food intake, and subsequent growth. We conducted a laboratory study using southern leopard frog Lithobates sphenocephalus tadpoles. Using path analyses, we tested how Bd, mouthpart damage, and percentage of food in the gut (hereafter gut content), directly or indirectly influenced body size (growth measure). We predicted that Bd would increase mouthpart damage, in turn reducing gut content and subsequent body size. Also, independent of Bd exposure, we predicted that increased mouthpart damage would negati...

Effects of nutrient supplementation on host‐pathogen dynamics of the amphibian chytrid fungus: a community approach

“…However, by metamorphosis, the effects of Bd on development were evident, with Bd‐exposed tadpoles metamorphosing sooner than unexposed individuals, even though mass was not affected by Bd exposure. Although qPCR analysis detected infections in only approximately half of the tadpoles exposed to Bd, previous studies have shown that exposure can incur costs, even in the absence of detectable infections (Rohr et al ., ), and that Bd exposure may be a better predictor of effects than Bd load (Hanlon et al ., ). In response to Bd infection, larval amphibians generally delay metamorphosis (Parris & Baud, ; Parris & Cornelius, ).…”

Amphibian chytridiomycosis: a review with focus on fungus-host interactions

“…In anuran larvae, clinical signs of chytridiomycosis due to B. dendrobatidis are generally limited to depigmentation of the mouthparts, without morbidity and mortality [ 3 , 59 ]. However, B. dendrobatidis may cause sub-lethal effects, including lethargy or poor swimming abilities, leading to low foraging efficiencies which is reflected in reduction in body size [ 60 ]. In metamorphosed amphibians clinical signs are variable and range from sudden death without obvious disease to significant skin disorder but infection may nonetheless elapse asymptomatically.…”

Disease recovery in bats affected by white-nose syndrome

“…hair follicles, glands), or glandular products of the skin (Meteyer et al, 2009;Rosenblum et al, 2010;Martel et al, 2013). These pathogens cause physiological disruption by permeating the skin, which can lead to mortality (Voyles et al, 2009;Cryan et al, 2010;Martel et al, 2013;Warnecke et al, 2013;Verant et al, 2014), but for hosts that do not suffer mortality, there are often latent challenges associated with skin damage, including structural changes to locomotor and sensory organs (Parris and Beaudoin, 2004;Reichard and Kunz, 2009;Venesky et al, 2009;Chatfield et al, 2013;Hanlon et al, 2015), which can influence survival and reproduction after primary pathology has subsided.…”