Geometric Morphometric And Antipredator Response Study Of Different Color Strains Of The Golden Apple Snail Pomacea Canaliculata (Caenogastropoda: Ampullariidae)

The predator affects the prey by direct killing or nonlethal actions. The presence of merely the predator could be at large the factor impacting on the prey populaiton by inducing the changes covering those in in life history, behavior, and phenotypic traits. In aquatic environments, the medium reduces the capacity of prey to detect the predator of the prey that have to rely more on chemical cue to escape from the risk. In Pomacea canaliculata, the juveniles can recoginize and be sitmulated by the wound companion before they crawl out of water to avoid risk.The relationships among coloration type, sex, and shell morphology of the parent Golden Apple Snail are examined using geometric morphometric methods. All snails used are laboratory-reared F5 or F6 snails and are sexually matured. The snails are landmarked upon their pictures from three aspects, i.e. right aperture view, aperture view and apical view. After standard procedure dealing with landmarks, Shape differentiations of the shells of two colorations and from both sexes were then studied using the principal component analysis, the canonical variable analysis and the thin-plate spline graphical technique. The principal component analysis suggested that between two shell-coloration strains the shell shape variation was of significance which was more representative in the landmark data obtained from the right-aperture view than from the other two views, while the variation representing sexual dimorphism within each shell-coloration strain seemed more remarkable than that between coloration strains. The canonical variable analysis results were showed by the Procrustes distance and the Mahalanobis distance. The Mahalanobis distances among all tested groups were significantly different, and the Procrustes distances among groups except that respectively between dark brown and yellow females, and between dark brown and yellow males, both in apical view, were significantly different. As revealed by the relative contribution of each landmark for relative warps, it suggests the shell morphological changes may occur on the upper part of aperture. The study supports the idea that Golden Apple Snails has two morphotypes corresponding to two coloration strains and its sexual dimorphism is also displayed in shell shape.In the second part of the work, seventy egg-mass, respectively spawned by different coloration strains of GAS snails (Black ♀×Black ♂, three parent pairs; Yellow ♀× Yellow ♂, nine pairs; Black ♀×Yellow ♀, seven pairs; Yellow ×Black ♂, four pairs), where every parental snail is homozygous at the coloration locus. The hatchlings were tested, using the predator cue produced from the homozygous yellow strain and from the homozygous black strain with the same age of the tested hatchlings, at their 3rd,5th,7th,9th and 11th day after they hatched, in order to detect the possible antipredator response of the hatchlings. The result shows:1, the antipredator response fluctuated with the age; 2, the chemical cue works on the hatchling of the same or different strain; 3, the heterozygous strain holds advantage over the homozygous strain in a highest antipredator response rate, while among four genetypic strains the yellow strain shows weakest response to the cues; and 4, different cue results in different response:yellow strain is more sensible to the homozygous black hatchling cue than to the yellow hatchling cue; while homozygous black strain is more sensible to response to the yellow strain cue than to the homozygous black cue. It is suggested that the prey may regulate its antipredator strategy based on the predator’s status, its physiological state and possiblely the environmental conditions, the consistency of which may make the hatchling insist on a stable strategy in antipredator responsing.