Literaturdatenbank
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Britson, C. A. (1996). Behavioral defenses associated with plastral coloration in hatchling, freshwater turtles. Unpublished thesis , University of Memphis.
Added by: Admin (06 Jan 2014 18:24:08 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: anon1996 View all bibliographic details  |
Categories: General Keywords: Chrysemys picta, Emydidae, Fressfeinde - predators, Habitat - habitat, Nordamerika - North America, Schildkröten - turtles + tortoises, Trachemys scripta, Verhalten - ethology Creators: Britson Publisher: University of Memphis |
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| Abstract |
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The assumption that large fish prey on hatchling freshwater turtles is thoroughly entrenched in the literature on turtle life histories. This assumption probably stems from the repeated citation of early literature reports which speculale on possible predators of hatchlings. The largemouth bass (Micropterus salmoides) is one of the assumed predators of hatehling turtles. Contrary to this popular assumption. however, previous research has determined that hatchling painted turtles (Chrysemys picta) and red-eared sliders (Trachemys scripta) are able to avoid predation by largemouth bass through the use of escape behaviors, such as biting and clawing, within the buccal cavity and upper digestive tract of bass upon being engulfed. Yet, the same fish will readily eat dead or anesthetized hatchlings. After experience with an active hatchling, however, largemouth bass will avoid feeding on any type of hatchling (dead. anesthetized. or active). Largemouth bass appear to be associating the conspicuous plastral colors of the hatchlings with the potentially damaging (to the mouth lining and gill apparati) escape behaviors. The plastral colors are thus serving a functional role as an aposematic antipredator mechanism. Many new questions are related to the phenomena of behaviorally associated aposematic coloration in hatchling freshwater turtles. One criticism of previous experiments was that wild-caught bass were used as naive predators. If largemouth The assumption that large fish prey on hatchling freshwater turtles is thoroughly entrenched in the literature on turtle life histories. This assumption probably stems from the repeated eitation of early literature reports which speculale on possible predators of hatchlings. The largemouth bass (Micropterus salmoides) is one of the assumed predators of hatehling turtles. Contrary to this popular assumption. however. previous research has determined that hatchling painted turtles (Chrysemys picta) and red-eared sliders (Trachemys seripta) are able to avoid predation by largemouth bass through the use of escape behaviors. such as biting and clawing, within the buccal cavity and upper digestive tract of bass upon being engulfed. Yet. the same fish will readily eat dead or anesthetized hatchlings. After experience with an active hatchling. however. largemouth bass will avoid feeding on any type of hatchling (dead. anesthetized. or active). Largemouth bass appear to be associating the conspicuous plastral colors of the hatehlings with the potentially damaging (to the mouth lining and gill apparati) eseape behaviors. The plastral colors are thus serving a functional role as an aposematic antipredator mechanism. Many new questions are related to the phenomena of behaviorally associated aposematic coloration in hatchling freshwater turtles. One criticism of previous experiments was that wild-caught bass were used as naive predators. If largemouth avoidance behavior of conspicuous hatchling turtles over seasons. Results supports the hypothesis that leamed avoidance behavior is not permanent in predatory organisms if the stimulus is not continuously present. Not all species of hatchling freshwater turtles are conspicuously colored even though they are assumed prey of predatory fish, such as largemouth bass (e.g., cryptic cOlnmon snapping turtle (Chelydra ser:pentina) hatchlings). In the second experiment, the categorical feeding responses, quantitatively defined feeding behaviors, and leaming capabilities of largemouth bass to hatchling painted turtles (conspicuous) and snapping turtles (cryptic) were examined. Dead. anesthetized, and active hatchlings of both species were presented to 11 adult largemouth bass. Significantly more active snapping turtles were rejected, rather than avoided, as compared to dead or anesthetized snapping turtles. Significantly more active hatchling painted turtles were avoided, rather than rejected, as compared to allother hatchling treatments. When largemouth bass attempted to prey on active painted turtle hatchlings there were significantly more bites (repeated attacks) and spits (repeated rejections) per hatchling than when bass attempted to prey on active snapping turtle hatchlings. The intensity of the predatory response was greater when largemouth bass preyed on snapping tunles than on painted turtles. The intensity of the predatory response and the length of handling time was also greater when largemouth bass attacked active hatchlings of either species as compared to dead, or anesthetized hatchlings. Neither preferential nor avoidance learning of hatchling turtle prey by largemouth bass occurred in this experiment. Thus, painted turtle and snapping turtle hatchlings are not equally susceptible to predation by largemouth basso These results are consistent with the theory that the aposematic form of a noxious (chemieaI. morphological or behavioral) prey item will have a higher survival rate than a cryptic. noxious prey. The distinctive morphological feature of a1l turtles is the shell. The possibility that largemouth bass also use this visual cue in the recognition and learned avoidance of hatchling turtles was also examined in the second experiment. The effects of hatchling color and shape on the categorical feeding responses. quantitatively defined behaviors. and learning capabilities of largemouth bass to (1) aposematic and "cryptic" red-eared sliders and (2) cryptic and "aposematic" common snapping turtle (Chelydra sementina) hatchlings were examined. "Cryptic" red-eared sliders and "aposematic" snapping turtles were prepared by painting the plastrons with non-toxic acrylic paint. A color chip system was used to match painted colors with colors from living turtles. In the experiment with the red-eared slider hatchlings. significantly more dead, aposematic hatchlings were eaten. rather than avoided or rejected. as compared to all "cryptic" hatchling treatments. Additionally, significantly more active aposematic hatchlings were rejected rather than avoided as compared to allother red-eared slider hatchlings. Negative, or avoidance. learning by largemouth bass of hatchling red-eared sliders (aposematic and "cryptic") did occur over time in this experiment. Significantly more dead or anesthetized cryptic snapping turtles, as compared to active cryptic snapping turtles. were avoided rather than rejected. Neither preferential nor avoidance leaming of hatchling snapping turtle prey by largemouth bass occurred over time in this experiment. Largemouth bass may not use color (and pattern) alone as a foraging cue in leaming to avoid hatchling turtle prey. Thus. the characteristic morphology (i.e .• the shell) may be secondarily important to color in the leamed avoidance of hatchling tunle prey. In conjunction with the assumption that large fish prey on hatchling turtles, many researchers have presumed that hatchling turtles are consistently found in shoreline vegetation because hatchlings use this area as a refugia from predators. The third experiment examined the possibility that hatchlings use this area to increase their feeding success. Two turtle species. painted tunles and snapping turtles, were tested in this experiment Hatchlings of the painted turtle are conspicuously colored while the snapping turtle is cryptic. A three factor experimental design was used for each species to determine if there were differences in the number of unsuccessful attacks. number of successful attacks. position of each attacks. and the length of feeding activities under experimental conditions. Feeding behavior in hatchling painted turtles was significantly affected primarily by two factors: water depth and foodtype. More unsuccessful attacks (i.e .• wasted energy) occurred in the sloped and deep water treatments than in the shallow water treatment The number of successful attacks, however. was significantly higher for tadpole prey, as compared to mealworms or foodsticks, irrespective of water depth. The number of unsuccessful attacks made by snapping turtle hatchlings was significantly higher for tadpole prey than for mealworms or foodsticks. The number of successful attacks, however, was significantly affected by both water depth and foodtype. While snapping turtle were equally successful in capturing tadpoles at a11 water depths, there was a parallel increase in the number of suecessful attaeks on mealworm and foodstick prey with increasing water depth. Water depth and foodtype significantly influenee the overall pattern of feeding behavior and suecess in hatchling turtles. These factors do not act alone on the feeding behavior of hatchlings and interact to produce a pattern that is consistent with the known shift in dietary preference (from camivory to omnivory) as hatchlings increase in size. The role of social conditions on feeding behavior is problematic and it is unclear if hatchlings react to conspecifics in a social context, or rather they view other turtles as merely a difference in the structural complexity of the feeding environment. This experiment has demonstrated that the use of shoreline waters by hatchling turtles is related to feeding behavior and capture success. The experiments described herein demonstrate that the defenses associated with plastral coloration in hatehling, freshwater turtles can affeet many aspeets of the survival of hatchlings. The phenomena of turtle coloration has not been completely examined, however, and furtber research is needed to examine two important issues. The first is the contrasting coloration of the hatchling plastron versus that of the carapace, and the second is the gradual loss of the aposematic colors and patterns over time in hatchling turtles.
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