Hatching plasticity in two temperate anurans: responses to a pathogen and predation cues

Abstract

Water molds are widespread in aquatic environments and are important causes of mortality in amphibian and fish eggs. We tested the ability of two species of North American anurans with different breeding phenologies ( Rana sylvatica LeConte, 1825 and Bufo americanus Holbrook, 1836) to alter their hatching timing in response to three indicators of environmental risk: infection with a water mold, exposure to simulated egg predation cues, or exposure to simulated larval predation cues. When infected with water mold (Saprolegniaceae), B. americanus eggs hatched, on average, 44% earlier than the controls and R. sylvatica eggs hatched 19% earlier than the controls. In addition, B. americanus but not R. sylvatica eggs hatched significantly earlier than the controls when exposed to simulated egg and larval predation cues. Bufo americanus embryos hatched before developing muscular response, suggesting that hatching occurs through enzymatic egg capsule degradation combined with ciliary movement, not through behavior. Bufo americanus breeds later than R. sylvatica and responded to infection and simulated predation cues more strongly. This may reflect a history of stronger selection by pathogens and predators that accumulate in ponds as the breeding season progresses. To our knowledge, these are the first examples of induced hatching of amphibians in response to aquatic pathogens.

Forecasting phenology under global warming

“…Here, it appears that spatial variability was probably driven not by latitude, but rather by other site-specific factors such as precipitation, soils, biotic interactions, human development, etc. (de Beurs & Henebry 2003;Touchon et al 2006;Franks et al 2007). Later spring phenologies in some locations may also be explained in part by species' inability to meet chilling requirements under warmer conditions, thereby delaying flower or leaf production (e.g.…”

Water molds of the genera Saprolegnia and Leptolegnia are pathogenic to the North American frogs Rana catesbeiana and Pseudacris crucifer, respectively

“…Water mold treatments consisted of eggs in water containing a piece of cornmeal agar with the water mold Saprolegnia growing on it. Control treatments consisted of eggs in water containing a sterile piece of agar rating the R. catesbeiana eggs I disrupted their protective jelly layer and likely made them more susceptible to infection (Gomez-Mestre et al 2006). A potential way to test the impact of separating R. catesbeiana eggs on their susceptibility to pathogenic water molds would be to include an additional control with a known saprophytic water mold and compare the mortality of the eggs exposed to the saprophytic and pathogenic strains.…”

“…Parents may lay their eggs in locations where they are less likely to become infected (Ruthig 2006(Ruthig , 2008. The eggs also contain their own defense mechanisms that protect them (Sagvik et al 2008a,b), including the jelly surrounding the eggs (Gomez-Mestre et al 2006) and phenotypic plasticity in hatching time of eggs exposed to water molds (Touchon et al 2006). These defenses can break down as the abiotic environment changes (Kiesecker et al 2001a, Ruthig 2006, Touchon et al 2006, leaving amphibian populations vulnerable to global climate change.…”

“…To date, the eggs of Hyla regilla (Kiesecker & Blaustein 1995), R. clamitans (Karraker & Ruthig 2009) and Ambystoma maculatum (Gomez-Mestre et al 2006, Karraker & Ruthig 2009) have been found to be resistant to infection when exposed to water molds in controlled experiments.…”

“EYE OF NEWT AND TOE OF FROG”: HERPETOLOGY IN 21STCENTURY SCIENCE

“…(See Gomez et al, 2006;Touchon et al, 2006;Vonesh and Warkentin, 2006;Warkentin, 1995Warkentin, , 1999aWarkentin, ,b, 2000aWarkentin, ,b, 2005Warkentin et al, 2001Warkentin et al, , 2005Warkentin et al, , 2006aWarkentin et al, ,b, 2007. 2.…”