Genetic comparison of water molds from embryos of amphibians Rana cascadae, Bufo boreas and Pseudacris regilla

Abstract

Water molds that cause the disease saprolegniasis have been implicated in widespread mortality of amphibian embryos. However, because of the limitations of traditional identification methods, water mold species involved in die-offs or utilized in ecological studies often remain unidentified or identified only as Saprolegnia ferax. Furthermore, water mold taxonomy requires revision, so very distinct organisms may all be called S. ferax. Recent DNA-based studies indicate that the diversity of water molds infecting amphibian embryos is significantly higher than what was previously known, but these studies rely on culture methods, which may be biased towards taxa that grow best under laboratory conditions. In this study, total embryo-associated DNA was extracted from 3 amphibian species in a pond in central Washington, USA. The internal transcribed spacer (ITS) region of DNA was amplified with primers capable of amplifying a broad array of eukaryotic microorgansisms, and was used to construct clone libraries. Individual clones were sequenced and relationships among newly recovered sequences and previously studied taxa were analyzed using phylogenetics. These methods recovered several new taxa in association with amphibian embryos. Samples grouped into 11 distinct phylotypes with ITS sequence differences ranging from 4 to 28%. The water mold communities recovered differed among Rana cascadae, Bufo boreas, and Pseudacris regilla egg masses. Furthermore, the diversity of water molds increased as egg masses aged, and members comprising this diversity changed over time.

Heterogeneous Occupancy and Density Estimates of the Pathogenic Fungus Batrachochytrium dendrobatidis in Waters of North America

“…Numerous amphibian diseases have been identified, with mass mortality events attributed to water molds ( Saprolegnia spp.) [22]–[24], Aeromonas bacterial infections [25], iridoviruses [26]–[29], alveolate infections [30], [31], and malformations caused by trematodes [32], [33]. Chytridiomycosis, the emerging infectious disease caused by the amphibian chytrid fungus, Batrachochytrium dendrobatidis ( Bd ), is implicated as a causal agent in many recent global amphibian population declines and extinctions [34]–[36].…”

Multihost saprobes are facultative pathogens of bullfrog Lithobates catesbeianus eggs

“…Strain B, probably belonging to the genus Achlya, was the next most common in the collection and also the most infectious. The genus Achlya has recently been documented infecting am phi bian eggs in the Pacific Northwest (Ault et al 2012). Strain C grouped with the genus Saprolegnia, which is a genus that has been commonly implicated in amphibian infections (Kiesecker et al 2001, Fernández-Benéitez et al 2008).…”

“…The distribution of water molds within a pond is not uniform and species differ in where they reside within the water column (Johnson et al 2002). (3) Our method of isolating water molds on cornmeal agar may have been selective for certain strains (Ault et al 2012). (4) Finally, the environment may affect the ability of water molds to be pathogenic.…”

“…Within a pond, different amphibian species can be infected by different water mold species (Ruthig 2009) and single infected amphibian eggs can be infected by multiple species of water molds (Ault et al 2012).…”

Population of origin and environment interact to determine oomycete infections in spotted salamander populations

“…Traditionally, oomycete species were distinguished by the morphology of reproductive structures when viewed with light microscopy. However, more recent molecular phylogenetic studies indicate a history of misidentifications and taxonomic confusion based on oomycete morphology (Johnson et al , Robideau et al , Ault et al , Sandoval‐Sierra et al ).…”