PLASTICITY OF HATCHING IN GREEN FROGS (RANA CLAMITANS) TO BOTH EGG AND TADPOLE PREDATORS ANNIKA L. ANDERSON AND WILLIAM D. BROWN 1 Department of Biology, State University of New York at Fredonia, Fredonia, New York 14063, USA ABSTRACT: We examined whether embryos of the green frog (Rana clamitans) would adaptively alter hatching times in the presence of both egg predators (the crayfish Procambarus nigrocinctus) and tadpole predators (the dragon nymph Anax junius). Under laboratory conditions, we exposed eggs with developing embryos to four experimental treatments that varied in the type of caged predator: egg predator only, tadpole predator only, both predators together, or no predator. As predicted, the presence of an egg predator caused a significant reduction in time to hatching. However, contrary to our prediction, eggs also hatched sooner in the presence of a tadpole predator. Moreover, there was no significant interaction between the effects of the two predators and thus no evidence that R. clamitans embryos can distinguish between predator types. We also found significantly lower hatching success in the presence of an egg predator, despite the fact that the predator did not have direct contact with the eggs. These results suggest adaptive early and delayed hatching do not co-occur in this species with this particular predator regime. Key words: Green frogs; Hatching; Life history; Niche shift; Predation; Rana RISK of mortality can be modified through a change in the timing of ontogenetic niche shifts (life-history events such as egg hatching and metamorphosis) that drastically alter an individual’s environment, diet, and predator regime (e.g., Chivers et al., 1996, 1999; Dodson and Harvell, 1988; Rowe and Ludwig, 1991; Sih, 1986; Warkentin, 1995; Werner, 1986). Earlier life stages, such as eggs and larvae, are often more vulnerable to stage- specific risks, including predators, especially in species lacking parental care (Kiesecker and Blaustein, 1997; Touchon et al., 2006; Werner and Gilliam, 1984). Growth and mortality rates are considered the most important fitness components in pre-repro- ductive amphibians, and they vary between habitats and with individual size (Warkentin, 1995; Werner and Gilliam, 1984). The timing of niche shifts can be critical to survival and may evolve either to a fixed point, or to a plastic response (Dodson, 1989; Harvell, 1990; Schalk et al., 2002; Warkentin, 1995). If predation risk varies with time or location, plasticity in the timing of hatching allows embryos to use immediate, localized cues to reduce mortality risk (Blaustein, 1997; Sih and Moore, 1993; Vonesh, 2005; Warken- tin, 1995). Based on niche-shift models, a relatively safe egg environment combined with high mortality of hatchlings will favor a delay in hatching (Moore et al., 1996; Sih and Moore, 1993), while increased egg mortality will favor earlier hatching (e.g., Kusch and Chivers, 2004; Vonesh, 2005; see Orizaola and Bran ˜ a, 2004 for review). There is evidence from a variety of species that predator-induced plasticitiy in hatching time exists (Sih and Moore, 1993; Warkentin, 1995). For example, embryos of the stream- side salamander Ambystoma barbouri delayed hatching when exposed to larval predators (Moore et al., 1996; Sih and Moore, 1993), embryos of the red-eyed treefrog Agalychnis callidryas hatched sooner in the presence of egg-eating snakes and wasps (Warkentin, 1995, 2000), and the embryos of the Pacific treefrog Pseudacris regilla and the cascade frog Rana cascadae hatched sooner in the presence of egg-eating leeches (Chivers et al., 2001). Similar predator-induced hatching plasticity has also been demonstrated in arachnids and fish, and may occur in crusta- ceans (Blaustein, 1997; Johnson et al., 2003; Jones et al., 2003; Laurila et al., 2002; Li, 2002; Schalk et al., 2002; Vonesh, 2005; Wedekind, 2002). If early hatching is to be an efficient defense against egg mortality, it must be employed in time for the embryos to escape. If predator cues are only available upon direct 1 CORRESPONDENCE: e-mail, William.Brown@fredonia. edu Herpetologica, 65(2), 2009, 207–213 E 2009 by The Herpetologists’ League, Inc. 207