Cardiac adaptations of bullfrog tadpoles in response to chytrid infection

Abstract

The chytrid fungus Batrachochytrium dendrobatidis (Bd) can result in heart failure in Bd-susceptible species. Since Bd infection generally does not cause mortality in North American bullfrogs, the aim of this work was to verify whether this species presents any cardiac adaptation that could improve the tolerance to the fungus. Thus, we analyzed tadpoles' activity level, relative ventricular mass, ventricle morphology, in loco heart frequency, and in vitro cardiac function. The results indicate that infected animals present an increase in both ventricular relative mass and in myofibrils' incidence, which accompanied the increase in myocytes' diameter. Such morphological alterations enabled an increase in the in vitro twitch force that, in vivo, would result in elevation of the cardiac stroke volume. This response requires much less energy expenditure than an elevation in heart frequency, but still enables the heart to pump a higher volume of blood per minute (i.e., an increase in cardiac output). As a consequence, the energy saved in the regulation of the cardiac function of Bd-infected tadpoles can be employed in other homeostatic adjustments to avoid the lethal effect of the fungus. Whether other species present this ability, and to what extent, remains uncertain, but such possible interspecific variability might explain different mortality rates among different species of Bd-infected amphibians.

Effects of invasive larval bullfrogs (Rana catesbeiana) on disease transmission, growth and survival in the larvae of native amphibians

“…A leading hypothesis is that American bullfrogs (Rana catesbeiana) may serve as an asymptomatic carrier or reservoir for Bd (Daszak et al 2004;Hanselmann et al 2004;Garner et al 2006;Salla et al 2015;Yap et al 2018;Urbina et al 2018). American bullfrogs have the ability to mount an immune response to Bd (Davis et al 2010) and can take 2-3 years to complete their aquatic larval stage.…”

Physiological responses of Brazilian amphibians to an enzootic infection of the chytrid fungus Batrachochytrium dendrobatidis

“…Clinical infections of Bd often impair amphibians from maintaining adequate homeostasis and directly impact host physiological and functional responses (Voyles et al 2009, Salla et al 2015. Specifically, Bd infection causes hyperkeratosis (skin thickening) and impairs host ability to absorb and regulate body fluids, leading to electrolyte imbalance and cardiac arrest in infected hosts (Voyles et al 2011).…”

“…Skin permeability is critically important in regulating water transport and exchange of electrolytes and respiratory gases in amphibians (Wells 2007, Hillman et al 2009, Voyles et al 2011. when hosts do not show gross pathological changes in the superficial epidermis; Voyles et al 2011), the potential impairments in physiological function remain, for the most part, unmeasured (but see also Salla et al 2015). when hosts do not show gross pathological changes in the superficial epidermis; Voyles et al 2011), the potential impairments in physiological function remain, for the most part, unmeasured (but see also Salla et al 2015).…”

Novel findings on the impact of chytridiomycosis on the cardiac function of anurans: sensitive vs. tolerant species

“…Understanding the physiological interactions between amphibian hosts and this pathogen is crucial to conserve global biodiversity ( James et al, 2015 ). Although there have been previous investigations into chytridiomycosis pathophysiology (e.g., Voyles, Rosenblum & Berger, 2011 ; Voyles et al, 2012 ; Salla et al, 2015 ; Bovo et al, 2016 ), the mechanistic process underlying this pathogenesis remain unresolved.…”

“…However, electrolyte-dependent and toxin-based mechanisms are not mutually exclusive for this disease. To date, there is not sufficient evidence to determine which is the critical process by which Bd infection alters the cardiac performance of amphibians in a species-specific manner ( Salla et al, 2015 ).…”