Iheringia Disgusting or delicious ? Predatory behavior of the hylid frog Phyllodytes luteolus on sympatric ants

The phytotelm-dwelling frogs from the genus Phyllodytes Wagler, 1830 have been characterized as specialist frogs regarding their diet strategy which is mainly composed by colonial insects. Herein, we used two species of ants (Camponotus sp. and Gnamptogenys sp.) with distinct defensive mechanisms to test the predatory behavior of Phyllodytes luteolus Wied, 1824. The experiment was conducted with frogs inhabiting a patch of 20 bromeliads (Aechmea cf. blanchetiana). Ants were off ered randomly to the frogs until we obtained ten observations of predation of each ant species. We observed and recorded the time that P. luteolus needed to keep each ant species inside its mouth before it could ingest it. Predatory behavior was highly distinct. While Camponotus were caught and swallowed within six seconds and without apparent discomfort, individuals of P. luteolus had more diffi culty in swallowing Gnamptogenys individuals, the time of manipulation ranging from 57 to 177 seconds. The mean values of time of predation observed in each treatment was highly signifi cant (p<0.001). We conclude that diff erences found in the time of manipulation are highly correlated with defense mechanisms of each species of ants.

The Yellow Heart-tongued Frog Phyllodytes luteolus Wied, 1824 is distributed along the Atlantic Forest of Brazil, from the state of Paraíba to the north of the state of Rio de Janeiro (Vrcibradic et al., 2006;Haddad et al., 2013).Individuals are commonly found inside bromeliads thriving in open areas, in axils usually containing at least 100 ml of water (Teixeira et al., 1997).Reproduction also takes place in bromeliad axils where each female may lay up to three eggs and where tadpoles develop feeding on debris (Peixoto, 1995;Giaretta, 1996).Although its diet is diversifi ed, P. luteolus has been considered a specialist regarding its foraging strategy once its diet is mainly composed by colonial insects (Ferreira et al., 2012).Feeding on ants and termites seems to be the common share for several bromeligenous and bromelicolous frog species as e.g.Thoropa miliaris (Spix, 1824) and Scinax arduous Peixoto, 2002(Pertel et al., 2010).However, Motta-Tavares et al. (2016) argued that it is not possible to assume diet strategy of species if no studies evaluate whether frogs select prey items or if they consume them according to prey availability inside bromeliads.Moreover, ants possess a very large arsenal of defense strategies involving chemical defenses as formic acid (Falótico et al., 2007), stinging (Haddad Jr & Larsson, 2015) and biting (Peeters & Ito, 2015).As amphibians from several species have been reported to sequester alkaloids from dietary arthropods as ants and mites (Hantak et al., 2013) they should be able to deal with these defense strategies to overwhelm their prey.In order to aid to elucidate this dilemma we set up an experiment offering two sympatric species of ants with distinct defense mechanisms (chemical and stinging) to specimen of P. luteolus inside bromeliad axils.We wanted to find out if there would be differences on the time of prey processing in relation to the defense mechanism of the ant.As no previous behavioral information on how bromeliad frogs deal with ants exist we hypothesize that both species possess attributes that may delay or accelerate their ingestion.On one hand frogs may try to swallow ants with a sting rapidly, thus neutralizing the risk of being stung.On the other hand they may delay the ingestion in order to avoid being stung while the ant is still alive inside their stomach.

MATERIALS AND METHODS
To carry out the experiment we used individuals of Phyllodytes luteolus as predators and two species of ants of similar size -Camponotus sp. and Gnamptogenys sp.as target species.Both ants occur in syntopy with the frogs and were chosen based on previous ad libitum observations performed by MS which revealed that P. luteolus were able to prey on them.Individuals of P. luteolus used in the experiment inhabited a patch of 20 bromeliads (Aechmea cf.blanchetiana), which were cultivated by MS since 2010 in the municipality of Ilhéus, state of Bahia, Brazil (14°54'44.3"S,39°01'27.8"W).This population of P. luteolus comprised around 80 individuals.The experiment was conducted on October 1 st 2014 between 22:00h and 24:00h until we obtained ten observations of predation of each ant species.Ants, which had been previously collected in activity during the same night at the study site, were gently placed manually inside bromeliad axils containing a randomly chosen frog.For each ant offered we observed and recorded the manipulation time in the mouth that P. luteolus needed to ingest each one.To compare the time of predation between each treatment (prey models) we performed a t-test (p<0.05).

RESULTS
Predatory behavior was highly distinct between both ant species.While Camponotus sp. were caught and swallowed in up to six seconds (mean = 2.4 ± 2.27; n = 10) and without apparent distress, those individuals of Phyllodytes luteolus that tried to feed on Gnamptogenys sp.showed more difficulty in swallowing them.Frogs manipulated individuals of Gnamptogenys sp. with their mouth, keeping the abdomen of the prey outside for 57 to 177 seconds (mean = 108.3± 48.52; n = 10), in order to avoid injuries due to the ant's sting (Fig. 1).The mean values observed among the time of predation in each treatment were highly significant (p<0.001).We also noted that for Gnamptogenys sp., amphibians opened their mouth several times until they finally managed to swallow their prey.

DISCUSSION
Defensive tactics in prey forced predators to coevolve simultaneously generating a predator-prey arms race (Brodie & Brodie, 1999a,b;Geffeney et al., 2002).Results provided by our experiment demonstrated that Camponotus sp. and Gnamptogenys sp. can be consumed by Phyllodytes luteolus, but with distinct behaviors for each ant species.As both ant species are similar in size this result can be explained due to the distinct defense mechanisms against predators of those ant species.While Camponotus sp. can use its well-developed jaws as a defense mechanism Gnamptogenys sp.injects formic acid through its stinger located at the final portion of its abdomen.Although P. luteolus showed ability to withstand the discomfort caused by the defense mechanisms of both ants, the pain caused by Gnamptogenys stinging seemed to be much more uncomfortable than the bites inflicted by Camponotus sp.(authors pers.obs.).We conclude that individuals of P. luteolus are adapted to eat both targeted species of ants.Future studies using simultaneously both ant species to test prey preferences would be useful to determine the capacity of prey selection in P. luteolus.

Fig. 1 .
Fig.1.Phyllodytes luteolus Wied, 1824 manipulating its prey, an ant of the genus Gnamptogenys.Note that the frog has kept the abdominal region of the ant outside of the mouth in order to prevent injuries caused by its sting.