Morph‐specific differences in disease prevalence and pathogen‐induced mortality in a terrestrial polymorphic salamander

Abstract

Polymorphic species provide an excellent system to study population divergence because different phenotypes often face diverse selection pressures within their shared environment. Previous studies have demonstrated that different color morphs of Plethodon cinereus (striped and unstriped), which vary in their degree of melanin-based coloration, vary temporally in their seasonal activity and differ in metrics associated with stress physiology. Despite the known association between melanin-based coloration and disease resistance among vertebrates, few studies have examined this relationship in amphibians. In a laboratory experiment, we exposed juvenile and adult P. cinereus to the pathogenic chytrid fungus [Batrachochytrium dendrobatidis (Bd)] and tested the hypothesis that the different color morphs would differ in their response to Bd. If the degree of melanization is positively associated with immune traits in this species, we predicted that unstriped salamanders would be more resistant to Bd and would exhibit higher survival rates compared to striped salamanders. Our results suggest that unstriped salamanders have a higher prevalence of infection when they do not behaviorally avoid Bd. Unstriped salamanders also exhibited higher rates of Bd-induced mortality compared to striped salamanders. These results conflict with our initial predictions and with general findings suggesting that individuals with higher levels of melanin production are more resistant to disease. Behavioral traits of the unstriped morph, including responses to predators and interactions with territorial opponents, may contribute to increased levels of stress and reduced resistance to infection. Future studies that directly manipulate glucocorticoid levels and/or temperature are needed to better understand the differences in Bd resistance in this species.

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

“…After that, 50 mL of Bd inoculum (1.3 × 10 7 zoospores/mL) was added to the Physalaemus Bd + aquarium (previously containing 950 mL of dechlorinated water), and 250 mL of the same Bd inoculum to the Xenopus Bd + aquarium (previously containing 4,750 mL of dechlorinated water), to reach a final concentration of 6.5 ×10 5 zoospores /mL in each inoculated aquarium. This concentration is consistent with the inoculum load used by other researches investigating chytrid infection in laboratory conditions ( Savage & Zamudio, 2011 ; Gervasi et al, 2013 ; Salla et al, 2015 ; Venesky et al., 2015 ; Bovo et al, 2016 ). Both species remained under the same conditions for one week, monitored and fed daily, with no water change.…”

“…Host defenses against pathogens can usually be defined into two types: those that limit pathogen infection intensity by preventing or reducing infection; and those that decrease the fitness consequences of the infection ( Venesky et al, 2015 ). In addition, alterations of physiological parameters may lead to the increased susceptibility to various environmental stressors ( Formicki, Zamachowski & Stawarz, 2003 ).…”

Evolutionary response to global change: Climate and land use interact to shape color polymorphism in a woodland salamander

“…For example, predation pressure may vary between striped and unstriped morphs due to differences in coloration (Lotter & Scott, ), behavior (Moreno, ; Venesky & Anthony, ; Otaibi, Johnson, & Cosentino, In press) or local frequency (i.e., frequency‐dependent selection; Fitzpatrick, Shook, & Izally, ). Striped and unstriped individuals also vary in diet (Anthony et al., ), territorial behavior (Reiter, Anthony, & Hickerson, ), and disease resistance (Venesky et al., ). There are a host of evolutionary mechanisms that can maintain color polymorphism in animals (McLean & Stuart‐Fox, ), and thermal selection imposed by climate and land use likely operate with other spatially variable selection pressures to affect color polymorphism.…”

Colour polymorphism inSalamandra salamandra(Amphibia: Urodela), revealed by a lack of genetic and environmental differentiation between distinct phenotypes

“…), the chytrid Batrachochytrium dendrobatidis (Venesky et al. ) and possibly climate (Fisher‐Reid et al. ) play significant roles in maintaining different phenotypes.…”

“…; Venesky et al. ). As all other polymorphic salamander species have proven to be plethodontids (García‐París et al.…”