Distance-dependent switching of anti-predator behavior of frogs from immobility to fleeing

To avoid predation, many animals are required to appropriately switch between immobility for crypsis and fleeing for escape. We conducted two staged-encounter experiments using a frog and a snake to examine factors that affect the occurrence of immobility and fleeing, and to evaluate the efficiency of them. The first experiment demonstrated that frogs initially exhibit immobility, when snakes are moving at a long distance, and then switch from immobility to fleeing at a shorter distance even when snakes have not detected them. The second experiment demonstrated that snakes at 400–800 mm distance detect only fleeing frogs, whereas snakes at 100 mm or closer detect both immobile and fleeing frogs. Thus, the ability of snakes to detect motionless frogs depends on the distance, and the distance-dependent switching can be considered an adaptive strategy of the frog. However, a previous model predicts that cryptic prey should flee immediately on seeing a predator or not flee until being detected by the predator. To explain this discordance, we propose two factors: engagement of intensive searching mode by predator at short distance and effects of sudden fleeing at close distance. We suggest incorporating them in future theory for better understanding of anti-predator strategy

A miniaturized threshold-triggered acceleration data-logger for recording burst movements of aquatic animals

Although animal-borne accelerometers are effective tools for quantifying the kinematics of animal behaviors, quantifying burst movements of small and agile aquatic animals remains challenging. To capture the details of burst movements, accelerometers need to sample at a very high frequency, which will inevitably shorten the recording duration or increase the device size. To overcome this problem, we developed a high-frequency acceleration data-logger that can be triggered by a manually-defined acceleration threshold, thus allowing the selective measurement of burst movements. We conducted experiments under laboratory and field conditions to examine the performance of the logger. The laboratory experiment using red seabream (Pagrus major) showed that the new logger could measure the kinematics of their escape behaviors. The field experiment using free-swimming yellowtail kingfish (Seriola lalandi) showed that the loggers trigger correctly. We suggest that this new logger can be applied to measure the burst movements of various small and agile animals.</jats:p

Multiple preferred escape trajectories are explained by a geometric model incorporating prey\u27s turn and predator attack endpoint

The escape trajectory (ET) of prey - measured as the angle relative to the predator\u27s approach path - plays a major role in avoiding predation. Previous geometric models predict a single ET; however, many species show highly variable ETs with multiple preferred directions. Although such a high ET variability may confer unpredictability to avoid predation, the reasons why animals prefer specific multiple ETs remain unclear. Here, we constructed a novel geometric model that incorporates the time required for prey to turn and the predator\u27s position at the end of its attack. The optimal ET was determined by maximizing the time difference of arrival at the edge of the safety zone between the prey and predator. By fitting the model to the experimental data of fish Pagrus major, we show that the model can clearly explain the observed multiple preferred ETs. By changing the parameters of the same model within a realistic range, we were able to produce various patterns of ETs empirically observed in other species (e.g., insects and frogs): a single preferred ET and multiple preferred ETs at small (20-50°) and large (150-180°) angles from the predator. Our results open new avenues of investigation for understanding how animals choose their ETs from behavioral and neurosensory perspectives

ヘビに対するカエルの捕食回避戦略: 逃走と不動の適応的な使い分けについて

京都大学0048新制・課程博士博士(理学)甲第18827号理博第4085号新制||理||1587(附属図書館)31778京都大学大学院理学研究科生物科学専攻(主査)准教授 森 哲, 教授 沼田 英治, 教授 高橋 淑子学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA

A game of patience between predator and prey: waiting for opponent’s action determines successful capture or escape

When predator and prey animals face each other, preemptive actions by both sides are considered to mediate successful capture or escape. However, in spite of the general presumption, some animals, such as predatory snakes and their frog prey, occasionally remain motionless or move slowly for a while before striking or escaping, respectively. To clarify the possible advantages of this behaviour, we examined interactions between Japanese Four-lined Ratsnakes (Elaphe quadrivirgata (H. Boie, 1826)) and Black-spotted Pond Frogs (Pelophylax nigromaculatus (Hallowell, 1861)), focusing especially on kinematic features of strike behaviour of snakes and flight behaviour of frogs in close quarters. Staged encounter experiments and field observations revealed that counteractions against an opponent’s preemptive actions are effective for both snakes and frogs until a certain distance because they are hardly able to change their trajectories once they initiate strike or escape behaviours. Snakes and frogs also appropriately switched their behaviour from waiting for the opponent’s action to taking preemptive action at this threshold distance. These results suggested the occurrence of a game of patience between snakes and frogs in which they wait for the opponent’s action to achieve effective countermeasures. Our study provides new insights for predicting optimal decision-making by predators and prey and will contribute to a better understanding of their strategies.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author