A pathogenic skin fungus and sloughing exacerbate cutaneous water loss in amphibians

Abstract

() is a pathogenic fungus that causes the cutaneous, infectious disease chytridiomycosis and has been implicated in population declines of numerous anuran species worldwide. Proximate cause of death by chytridiomycosis is asystolic cardiac arrest as a consequence of severe disruption to electrolyte balance. Animals heavily infected with also experience a disruption to their skin sloughing regime, indicating that core functions of the skin, such as water retention, may be severely impacted. This study examined how skin sloughing, body size and infection interact to influence water loss rates in five Australian frog species: ,, , and Rates of water loss more than doubled during sloughing in During active periods across all species, water loss rates were on average 232% higher in infected frogs than in uninfected frogs. This indicates that dehydration stress may be a significant factor contributing to the morbidity of severely infected anurans, a symptom that is then exacerbated by an increased rate of sloughing. When taking size into account, smaller and/or juvenile anurans may be more at risk from dehydration due to infection, as they lose a greater amount of water and slough more frequently than adults. This may in part explain the higher mortality rates typical for small and juvenile frogs infected with Understanding how affects the core functions of the skin, including rates of water loss, can improve our predictions of disease outcome in amphibians.

Fungal disease and temperature alter skin microbiome structure in an experimental salamander system

“…The abundance of putatively anti‐Bd bacterial OTUs increased with Bd load, but this did not reduce salamander mortality. Anti‐Bd bacteria may gain a competitive advantage by acting as opportunistic colonists or responding to changes in host physiology caused by Bd infection (Russo, Ohmer, Cramp, & Franklin, ). For instance, the amphibian host may respond to Bd by producing antimicrobial peptides (AMPs), which can interact and change microbial communities (Kueng et al, ; Myers et al, ).…”

Phylogenetic investigation of skin sloughing rates in frogs: relationships with skin characteristics and disease-driven declines

“…Sloughing usually occurred before the daily activity period began in all species, which may be adaptive in that frogs would usually slough in day or night refuges (depending on whether they are nocturnal or diurnal), and then commence the active period. Frogs typically select refuges that reduce the rates of cutaneous water loss [68,69], and frogs demonstrate high rates of evaporative water loss during sloughing [70]. Thus, sloughing within a refuge could allow frogs to potentially avoid thermal or hydric extremes during the sloughing period, or reduce the risk of predation.…”

An emerging fungal pathogen is associated with increased resting metabolic rate and total evaporative water loss rate in a winter‐active snake

“…Mycotic skin infections may also carry hydric consequences for the host via their effects on cutaneous water exchange (McGuire et al, ; Russo et al, ). We documented an increase in total EWL in SFD‐positive snakes, which may be attributable to increases in cutaneous and/or respiratory water loss rates.…”

“…Perhaps less appreciated are the sublethal effects of fungal infection. Given that these fungal pathogens preferentially invade the skin of their host, the physiological consequences of infection may extend beyond energetic costs of immune system activation to disturbances in water and ion balance (Cryan et al, ; McGuire, Mayberry, & Willis, ; Peterson et al, ; Russo, Ohmer, Cramp, & Franklin, ; Verant et al, ; Voyles et al, ). Thus, the physiological costs and resultant life‐history trade‐offs imposed by certain fungal diseases may be more pronounced than those observed for other pathogens.…”