How important is temperature for strike success of ectotherms? Thermal effects on predator–prey interactions of free‐ranging pit vipers (Gloydius blomhoffii)

Abstract

Among various environmental factors, temperature has been considered a main determinant of outcomes of predator–prey interactions involving ectotherms. Although numerous studies have aimed to examine temperature effects on those interactions, few studies have been conducted under fully natural conditions. In this study, we examined the degree to which temperature affects the outcomes of encounters between a Japanese pit viper (Mamushi, Gloydius blomhoffii) and its prey under natural conditions. We continuously recorded ambushing behaviors and body temperatures of these snakes in the field using videography. We found that, over the range of temperatures at which Mamushi hunted, (1) temperature has only limited effects on whether Mamushis initiate a strike at prey and whether strikes successfully hit the prey; (2) prey reactions to strikes, such as whether they dodge the strike or the latency from strike initiation to dodge, are not affected by temperature; and (3) factors such as distance to prey and prey dodging movements are greater determinants than temperature on the outcomes of encounters between free‐ranging Mamushi and their prey. Our results suggest that temperature effects on the outcomes of free‐ranging snake–prey interactions may be smaller than hitherto considered.

Cold kiss still hot: limited temperature effects on envenomation performance in predatory strikes of a Japanese pit viper ( Gloydius blomhoffii )

“…40°C) carcass of a Japanese field mouse (Apodemus speciosus) to the tip of a thin rod (2 m long), slowly directing it towards the snake's head from a distance of approximately 15 cm while keeping its position as close to the ground as possible (less than ca 5 cm above the ground). This rodent species is the primary prey of Mamushi in the study population [15]. We used the carcasses to examine the envenomation performance without the effect of prey retaliation and with a large sample size.…”

“…First, we measured strike distance. In the field recordings, to estimate the distance between the prey carcass and the snake from video frames, we followed the methods used in previous studies [15,27]. Briefly, we used Image J software (https://imagej.net/ij/) to determine the distance in images from videos, with snake head length-which had been measured before the surgery on each radio-tagged snake-as a size scale in each image.…”

“…Second, viperid snakes hunt across a wide range of temperatures, including sub-optimal temperatures for ectotherms [15,16]. In hunting, viperid snakes remain in a typical ambush-coiled posture, and when a prey animal comes within range, they elicit a rapid strike and envenomate the prey to immobilize it [17].…”

“…However, viperids forage across a wide range of temperature conditions [15,16,20], so they may have evolved efficient envenomation characteristics adapted to sub-optimal Tb. Recent studies on geographic variation in snake venoms suggest that temperature significantly affects venom composition and toxicity [21,22].…”

“…Here, we used videography and enzyme-linked immunosorbent assay (ELISA) to record predatory strikes and quantify injected venom mass towards prey in a medium-sized pit viper, Mamushi (Gloydius blomhoffii), which is widely distributed on the main islands of Japan [23] and strikes prey when its Tb ranges between 13.4°C and 25.8°C under natural conditions [15]. A growing body of literature emphasizes the importance of field studies of the behaviour of free-ranging animals under natural conditions, to ensure ecological relevance [20,2425].…”