Feeding and thermal selection of Chinese green tree viper, Trimeresurus s. stejnegeri

Autor:	Tein-Shun Tsai, 蔡添順
Rok vydání:	2005
Druh dokumentu:	學位論文 ; thesis
Popis:	93 The Chinese green tree vipers (Trimeresurus s. stejnegeri) are nocturnal and ambush prey in arboreal habitats. They feed mainly on amphibians in field, but rodents, shrews, lizards, geckos, and birds were also consumed. Several topics about this species have been studied, but no studies have focused on the behavior and physiology of feeding. In this dissertation, all subjects were associated with the feeding of this snake, and the relations of these subjects to arboreality, nocturnality, and ambush-feeding habitat were concerned. In Chapter 1, I found Trimeresurus s. stejnegeri held on the prey after capturing it, which should be adapted to the less aggressive prey (i.e., frog), lower prey size, and avoidance the inconvenience for tracing the released prey from a twig. I fed the snake with frog (Rana limnocharis) and mouse (Mus musculus) in the laboratory (22 ± 1 oC), under three sensory deprivation conditions (intact cues, visual cue blocked, visual and infrared thermal cues blocked). The feeding behavior was recorded by videotape-recording method or naked eyes. The snake withdrawal and pulled up the prey from the ground following catching it. The prey was hanged and the body tilted, like a lever with the snake-biting site as the fulcrum. Mostly, the snake gradually moved its jaw to the upper end of the prey body and ingested it. That is, the capturing site, which should be decided before attacking the prey, determined the ingestion direction The snake ingested mouse mainly from head, as in other snakes; but the pattern was not dominant in feeding frog. More proportion of frogs was stroked on the posterior end than that of mice. The ratio of prey ingested from anterior to posterior side was 55 : 19 and 29 : 22 for mouse and frog, respectively, under intact sensory condition. When the visual and infrared cues were blocked, the ingested direction ratio, 14 : 4 and 14 : 9 for mouse and frog respectively, did not shift significantly from above. The snakes spent more time feeding on frogs than on mice. On feeding mice, the spending time to launch successful strikes (T1) was lowest at intact cues groups and significantly increased when the visual and/or thermal cues were blocked. On feeding frogs, however, T1 did not differ significantly among the sensory deprivation conditions. Visual and thermosensory cues seem to be less important on feeding frogs (but not on feeding mice) for T. s. stejnegeri. Besides, on feeding frogs but not mice, the time from capturing prey to start moving the jaws (T2) was significantly longer when ingesting prey from the anterior end. On feeding mice but not frogs, the time from moving the jaws to start flicking the tongue following the ingestion (T3) was longer when feeding prey from the posterior end. The feeding time (T2, T3) decreased when the sensory cues were blocked. In Chapter 2 and 3, I measured the temperature selection of adult males and females in a linear thigmothermal gradient and checked the degree of instrumental interferences. I conducted three experiments to study the possible effect of thermocouples, the influence of seclusion, and the presence of water on the temperature-selecting behavior of the snake. Thermocouples might change a snake’s preferred temperature (Tp) by causing it to lift its prehensile tail from the gradient floor or affecting its movement. With the videotape-recording method, the snake presented postprandial thermopily only when seclusion sites and water were provided in the gradient. In the absence of seclusion sites and water, the fasting and postprandial body temperature (Tb) of males was 23.0 ± 1.2 oC and 24.7 ± 1.2 oC, respectively. With seclusion sites and water, the fasting and postprandial Tb of males was 22.5 ± 1.0 oC (the set point Tset = 20.3 ~ 24.3 oC) and 27.8 ± 0.6 oC (Tset = 26.5 ~ 28.8 oC), respectively. The fasting and postprandial Tb of non-reproductive females (N = 16) was 21.2 ± 1.4 oC (Tset = 20.6 ~ 23.8 oC) and 24.8 ± 1.5 oC (Tset = 25.0 ~ 26.3 oC), respectively. Preferred temperature of females was higher after feeding or during pregnancy. Preferred temperature of pregnant snakes (N = 5) was 27.4 ± 2.0 oC. In Chapter 4, I investigated the combined effect of meal size (below 30%) and temperature (15~35 oC) on the aerobic metabolism, digestive efficiency, and digestive rate in this study. As other sit-and-wait foraging species, the snake had lower resting metabolic rate (0.033 ± 0.002 ml O2/g/hr at 25 oC). But it showed less difference at 20 and 25 oC (Q10 = 1.58). Respiratory quotient significantly increased at the anterior part of digestion period except at 15 oC. Specific dynamic action (SDA), peak VO2 and scope of peak VO2 increased with meal size, while temperature had little effect on SDA and SDA coefficient. Similar with other crotalids, the SDA coefficient was lower (15.8 ± 0.6%) in this study. With regression analysis, I found SDA in T. s. stejnegeri responded latterly and less sharply than other sit-and-wait feeding snakes. The metabolizable energy coefficient (= 0.66~0.89) was lowest at 15 oC and tended to peak at the postprandial Tset of the snake. In addition, I investigated the digestive rate from three aspects, included gut passage time (gut movement), gastric digesting time (Tbone; chemical digestion), and the timing of SDA (digestive metabolism). The final defecation time (PTe) and Tbone, but not the first defecation time, increased with food ration. PTe was less than two weeks at above 25 oC, but was larger than one month at 15 oC. The time to peak VO2, Tbone, and duration of SDA represented about 20%, 50%, and 80% of total digestion process (PTe), respectively. In Chapter 5, I tested whether temperature selection makes maximal net energy gain in Chinese green tree viper. I used multiple linear regressions, which expressing the effects of snake mass, mouse mass as well as temperature on digestion-associated variables, to simulate the monthly maximal net energy gain (Enet) under certain feeding frequencies and activity levels. With the energy budget model, I found some dominant trends. Enet peaked at lower temperature when snakes had less food ration. At high feeding frequency, selecting high body temperature, which closes to the postprandial Tp of the snake, could get higher Enet. When feeding frequencies lower down, Enet could be negative at 10% meal size, and the superiority or necessity to select high postprandial temperature disappear because of broad range of B80 at 20 ~ 30% meal size. Owing to the potential low feeding frequency in wild, T. s. stejnegeri may not get relative maximal Enet by postprandial behaviors. I have suggested potential reasons about why the snake selects high postprandial temperatures still under less energetic benefits. In conclusion, many innovated ideas and investigations have been mentioned in this dissertation. Several characters (nocturnality, arboreal habitats and ambush-feeding behavior) of Chinese green tree vipers may have important influences on the results. Whether these attributes occurred in wild as well as in other arboreal and/or ambush-feeding snakes is worth to study in future researches.
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Externí odkaz:	http://ndltd.ncl.edu.tw/handle/29234018245527934176 Zobrazit plný text záznamu