Sink or swim: a test of tadpole behavioral responses to predator cues and potential alarm pheromones from skin secretions

Abstract

Chemical signaling is a vital mode of communication for most organisms, including larval amphibians. However, few studies have determined the identity or source of chemical compounds signaling amphibian defensive behaviors, in particular, whether alarm pheromones can be actively secreted from tadpoles signaling danger to conspecifics. Here we exposed tadpoles of the common toad Bufo bufo and common frog Rana temporaria to known cues signaling predation risk and to potential alarm pheromones. In both species, an immediate reduction in swimming activity extending over an hour was caused by chemical cues from the predator Aeshna cyanea (dragonfly larvae) that had been feeding on conspecific tadpoles. However, B. bufo tadpoles did not detectably alter their behavior upon exposure to potential alarm pheromones, neither to their own skin secretions, nor to the abundant predator-defense peptide bradykinin. Thus, chemicals signaling active predation had a stronger effect than general alarm secretions of other common toad tadpoles. This species may invest in a defensive strategy alternative to communication by alarm pheromones, given that Bufonidae are toxic to some predators and not known to produce defensive skin peptides. Comparative behavioral physiology of amphibian alarm responses may elucidate functional trade-offs in pheromone production and the evolution of chemical communication.

A matter of proportion? Associational effects in larval anuran communities under fish predation

“…However, the effects were reduced in the presence of carp, indicating that fish mitigated interspecific competition between tadpoles (see also Bardsley and Beebee 1998) through thinning and, presumably, behavioural changes induced in the competitively superior R. temporaria tadpoles. In cages with fish, metamorph mass of R. temporaria was lower, presumably because its tadpoles reduce their activity in the presence of predators (Laurila et al 1997; Laurila 2000a; Lardner 2000; Maag et al 2012), leading to reduced food intake (Lardner 2000; Relyea 2007). In B. bufo , a species whose tadpoles reduce their activity only slightly in the presence of predators (Laurila et al 1997; Maag et al 2012), metamorph mass was unaffected by fish.…”

“…In cages with fish, metamorph mass of R. temporaria was lower, presumably because its tadpoles reduce their activity in the presence of predators (Laurila et al 1997; Laurila 2000a; Lardner 2000; Maag et al 2012), leading to reduced food intake (Lardner 2000; Relyea 2007). In B. bufo , a species whose tadpoles reduce their activity only slightly in the presence of predators (Laurila et al 1997; Maag et al 2012), metamorph mass was unaffected by fish. Predators can also induce changes in the timing of metamorphosis in anurans, but the magnitude and direction of the effect are variable (Relyea 2007; Wells 2007).…”

Toxin depletion has no effect on antipredator responses in common toad (Bufo bufo) tadpoles

“…To manipulate the degree of investment into toxin production, we applied in vivo hormonal stimulation to deplete toxin stores present in the skin of tadpoles. Sensu Maag, Gehrer & Woodhams (), we placed tadpoles in the norepinephrine treatment group into a 3‐mL, 100 μM norepinephrine‐bitartrate (CAS 3414‐63‐9; Sigma‐Aldrich) solution for 15 min. To wash off norepinephrine from the skin, we subsequently transferred individuals into a bin filled with 700 mL of RSW for 1 min and finally placed them back into their rearing containers.…”

“…To wash off norepinephrine from the skin, we subsequently transferred individuals into a bin filled with 700 mL of RSW for 1 min and finally placed them back into their rearing containers. Similar methods have been successfully used in both in vitro (Benson & Hadley, 1969;Castillo & Orce, 1997) and in vivo (Dockray, 1975;Rollins-Smith, 2005;Quagliata et al, 2008;Giuliani & Rinaldi, 2010) studies on anurans, and also specifically on B. bufo tadpoles for inducing skin peptide release (Maag et al, 2012). In the treatment group receiving only handling, we placed tadpoles into 3 mL of RSW and otherwise handled them the same way as described above.…”

Differential oviposition and offspring success of gray treefrogs in the presence of an invasive fish

“…, Maag et al. , Gazzola et al. ] which could deter oviposition), or potential physical contact between the mosquitofish and the ovipositing females (females are harassed to leave by nips or other contact by the free‐ranging mosquitofish).…”