Morphological Study Of Eye Among Hynobiid Species

Eye, as one of the most important components in visual system, could objectively transduce imaginative signal into biological impulse can be recognized by central nerous system. The biological impulse based on the received information will guide the movements and behavior responses. Retina locates at the dorsal part of eye balls in vertebrates, in a way retina can be regarded as “eye” because it can undertake the whole task to translate light to nervous signal. There are diversity adaptive behaviors in the animals because they live in significantly different environments, active pattern and evolutionary status. Thus, the proportions of visual capacity in the total sensory system are differ from among animals. Therefore, morphological researches concerned on eyes among different animals will provide a perspective to understand the adaptive evolution. In this study, hynobiid salamanders and some other amphibians and reptiles were chosen as experimental materials to research the morphological features of eye in hynobiid salamanders, and the morphological features and evolution of retinal among different species. These selected animals have a primitive status in the phylogeny, which usually exhibit a relatively lower dispersal capacity, solely habitat and high reliance on the habitat, moreover, just a few reports focused on the eye-morphology were available. Therefore, this study not only can understand the morphological variacne, the adaptive evolution of retina, yet can provide data for the other reaches associated with morphological comparison.Three hynobiid salamanders(Hynobius leechii, Onychodactylus zhangyapingi, Pachyhynobius shangchengensis, these salamanders live in different habitat and own variable habit) were sampled to take a comparison on morphological traits of eye. The collected data were checked by SPSS software to produce a honest result. The results indicate:(1) P. shangchengensis with relative bigger SVL exhibits relative smaller eyes, conversely, O. zhangyapingi with relative smaller SVL exhibits relative bigger eyes. This result partially conforms to the Haller ruler.(2) Aquatic salamander, P. shangchengensis, with relative smaller eye shows a adaptation to the lower light intensity in water, terrestrial salamanders, O. zhangyapingi and H. leechii, with the relative bigger eye show an adaptation to the more complex light intensity on land.(3) O. zhangyapingi, which belongs to crepuscular activity pattern, has relative bigger eye than P. shangchengensis and H. leechii, both belong to nocturnal. These results show that the relative size of eye is related to the activity pattern and habit, and show an adaptation to the light condition.For understanding the retinal change form the phylogeny within Hynobiidae. Seven species from Hynobiidae were objected: Salamandrella keyserlingii, Pachyhynobius shangchengensis, Hynobius leechii, Liua shihi, Onychodactylus zhangyapingi, Hynobius maoershanensis and Batrachuperus pinchonii,these species could represent the six typical genus in Hynobiidae. The published complete mitochondrial genome were used to construct a robust phylogenetic tree which also was perform ancestral character reconstruction of major retinal morphology. The result of ancestral character reconstruction showed: RRCL, ROCL, RIPL happened a profound change from the terrestrial species to aquatic species. The comparison between morphological tree based on retinal character and phylogenetic tree based on complete mitochondrial genome showed the retinal morphology exist a strong relationship with individual living habit.For further take a comparison on the retinal morphological features and evolution, the paraffin sections of the retina of Liua shihi, Batrachuperus pinchonii, H. maoershanensis, O. zhangyapingi, Cynops orientalis, Pelophylax nigromaculatus, P. plancyi, Takydromus septentrionalis, Lycodon rufozonatus were experimented. The results indicated:(1) The cell size and basic arranged structure of retina are basically similar among all studied animals.(2) Different active patterns contribute to the difference in the structure arrangement of retina. The thickness and cell density of outer cell layer and inner plexiform layer are highest in typical diurnal animal(T. septentrionalis) and lowest in the typical nocturnal animal(L. rufozonatus), and the hynobiid salamanders and other amphibians, which belong to crepuscular, have middle values.(3) The cells of retina in the reptiles are smaller but more intense density when contrast with amphibians, this reflect that the retinal of reptiles are more developed, and were verified by the behavioral data that reptiles usually have a relative bigger range of motion than amphibians. So, the eyes of reptiles have evolutional change which makes them better adapt to the terrestrial life. Meanwhile, the ratio between outer cell layer number and ganglion cell layer number looks like an insufficient considaration as charactertics of the rhythm model among animals.