Resource-dependent temporal changes in antipredator behavior of common toad (Bufo bufo) tadpoles
Inducible behavioral defenses against predators, and how environmental factors mediate such responses, have been the focus of behavioral ecological research for decades. However, results often remained contradictory, perhaps because the ontogenetic context was ignored. Here, we investigated how antipredator behavioral responses of common toad (Bufo bufo) tadpoles are affected by food limitation and how the mediated responses changed during larval development. We raised tadpoles in the presence or absence of chemical cues indicating predation risk, combined with low or high food levels, and repeatedly monitored tadpole activity and visibility. We found that the presence of cues indicating predation risk and resource availability interactively affected visibility, but not relative activity, and this interactive effect changed with time over the larval period. Visibility of tadpoles decreased with time but to a greater extent when tadpoles were exposed to cues indicating predation risk compared to control groups, and this difference was more expressed when food was limited. Activity of tadpoles also decreased during larval development but to a greater extent in case of tadpoles raised in resource-limited environment compared to the other treatments. Also, activity of tadpoles was higher when food was scarce; however, the magnitude of this effect was not influenced by the predator-cue treatment. Thus, in addition to describing the trajectories of ontogenetic changes in tadpole behavior, our study also demonstrated that responses to environmental factors, such as predation threat and food availability, vary with age.
Antipredator behavior is a common phenomenon in nature, and its expression is known to be influenced by the amount of available resources. How such defensive responses change with age, however, has been studied barely. By repeatedly observing common toad (Bufo bufo) tadpoles exposed to predators and/or food limitation, we found that tadpoles’ activity and visibility decreased with age and did so to a greater extent when tadpoles were exposed to chemical cues indicating predation risk compared to control groups. Our study demonstrated how responses to environmental factors, such as predation threat and food availability, vary with age in an important amphibian model species. These results draw attention to the importance of considering age when studying behavioral responses to environmental change and provide a possible explanation for some inconsistencies in the relevant literature.
KeywordsToad Behavioral plasticity Feeding activity Developmental changes Trade-off
We thank Josh Van Buskirk for the suggestions during the planning phase and Dániel Koska for the outstanding assistance in implementing the experiments. We are grateful also to Balázs Vági, János Ujszegi, Virág Wizl, Zoltán Gál, and Zsanett Mikó for the help in animal collection and husbandry. We also would like to thank the Referees for their valuable comments which helped to improve earlier versions of this paper.
Financial support was provided by the “Lendület” program of the Hungarian Academy of Sciences (MTA, LP2012-24/2012), the MTA postdoctoral research program (SZ-029/2013), a Sparkling Science project of the Bundesministerium für Wissenschaft und Forschung, Austria (SPA 04/171), and an FP7 Marie Curie Career Integration Grant (PCIG13-GA-2013-631722).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures involving animals in this study were approved by the Közép-Duna-Völgyi KTVF (KTVF 10350-2/2012) and the Ethical Commission of the MTA ATK NÖVI. All applicable international, national, and institutional guidelines for the care and use of animals were followed.
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