Effects of the pathogenic water mold Saprolegnia ferax on survival of amphibian larvae

Abstract

Infectious diseases are a significant threat to worldwide biodiversity. Amphibian declines, a significant part of current biodiversity losses, are in many cases associated with infectious disease. Water molds are one group of pathogens affecting amphibians on a worldwide basis. Although water molds have been studied extensively for their effects on host embryos, little information is available about how they affect post-embryonic amphibians. We tested the effects of one species of water mold, Saprolegnia ferax, in a comparative study of larvae of 4 amphibian species: Pseudacris regilla (Pacific treefrog), Rana cascadae (Cascades frog), Ambystoma macrodactylum (long-toed salamander), and R. aurora (red-legged frog). S. ferax can kill amphibians at the embryonic and juvenile life history stages, depending on the amphibian species. In the present study, a 1 wk exposure to S. ferax killed P. regilla larvae and a 2 wk exposure killed R. aurora larvae. Larvae of the other host species were unaffected after 1 wk of exposure to S. ferax. Our results suggest that S. ferax can kill amphibian larvae and further suggest that evaluation of how pathogens affect amphibians at the population level requires investigation at various life stages.KEY WORDS: Water mold · Saprolegnia · Amphibian · Ambystoma macrodactylum · Pseudacris regilla · Rana aurora · Rana cascadae Resale or republication not permitted without written consent of the publisherDis Aquat Org 83: [187][188][189][190][191][192][193] 2009 multiple species of both Achlya and Saprolegnia caused mortality and sublethal effects in embryos of Rana sylvatica (wood frog) and Bufo americanus (American toad) . The effects of water molds on amphibian embryos appear to be influenced by several environmental factors, including temperature, pH, ultraviolet-B radiation, precipitation, plant cover, and oviposition behavior (Kiesecker & Blaustein 1995, Green 1999, Kiesecker et al. 2001a, Ruthig 2006, additional references in Romansic et al. 2006.In contrast to the extensive research on the effects of water molds on amphibian embryos, there is relatively little information available about how water molds affect post-embryonic amphibians. There is experimental evidence that Saprolegnia influences competitive interactions between larvae of Rana cascadae (Cascades frog) and Pseudacris regilla (Pacific treefrog), apparently by mediating densities of the competing species through differential effects on embryos (Kiesecker & Blaustein 1999). Water mold infections have been reported in amphibian larvae in nature (Bragg & Bragg 1958, Bragg 1962, Berger et al. 2001, and occur occasionally in larvae of North American species . Berger et al. (2001) reported massive mortality of Bufo marinus (cane toad) larvae associated with Aphanomyces sp. infection, and Saprolegnia has been found on dead amphibian larvae after mass mortality events (Bragg & Bragg 1958, Bragg 1962. Romansic et al. (2006) demonstrated that Saprolegnia can kill larvae of R. aurora (northern red-legged frog), and Rom...

Differences in susceptibility to Saprolegnia infections among embryonic stages of two anuran species

“…The negative effects of Saprolegnia on aquatic stages of several amphibian species have been demonstrated (Blaustein et al 1994;Kiesecker et al 2001;Fernández-Benéitez et al 2008;Sagvik et al 2008a,b;Romansic et al 2009;Ruthig 2009), and have been associated with the extinction of populations of Rana pipiens and Bufo terrestris (Bragg 1958(Bragg , 1962, increased mortality in salamander Ambystoma maculatum (Walls and Jaeger 1987), and massive deaths of B. calamita, R. temporaria (Banks and Beebee 1988;Beattie et al 1991) and B. boreas (Blaustein et al 1994) eggs.…”

“…Consequently, there is a need to investigate how Saprolegnia spp. affect amphibians at various life stages, which is important when evaluating the effects of these pathogens at the population level (Romansic et al 2009). …”

The cause of global amphibian declines: a developmental endocrinologist's perspective

“…Disease is one of the most widely reported causes of the rapid decline of amphibian populations (Berger et al, 1998;Cunningham et al, 2008;Daszak et al, 1999;Lips et al, 2008;Stuart et al, 2004). The greatest volume of evidence that specific pathogens may lead to amphibian deformity, disease or death exists for two species of fungi (Batrachochytrium dendrobatidis and Saprolegnia ferax), an iridovirus (ranavirus), and the trematode parasite (Ribeiroia) (Berger et al, 1998;Bollinger et al, 1999;Green et al, 2002;Jancovich et al, 1997;Johnson et al, 1999;Kiesecker and Blaustein, 1995a;Rohr et al, 2008c;Romansic et al, 2009). …”

Interactive effects of competition and predator cues on immune responses of leopard frogs at metamorphosis

“…One important innate immune response is the array of antimicrobial peptides (AMPs) that are released from granular glands onto the skin as part of the sympathetic stress response. Many pathogens that negatively impact amphibian populations can infect the skin, including the bacterium Aeromonas hydrophila, the chytrid fungus Bd, the water mold Saprolegnia ferax and iridoviruses (Hird et al, 1981;Romansic et al, 2009;Rollins-Smith et al, 2011). AMPs from frogs inhibit the growth of gram-negative and gram-positive bacteria and fungal pathogens including Bd (reviewed in Rollins- Smith and Conlon, 2005;Rollins-Smith et al, 2011).…”