| dc.contributor.author | Rot-Nikcevic, Irena. | en_US |
| dc.date.accessioned | 2014-10-21T12:37:03Z | |
| dc.date.available | 2004 | |
| dc.date.issued | 2004 | en_US |
| dc.identifier.other | AAINQ94055 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/54671 | |
| dc.description | Anuran larvae show the ability to time their metamorphosis in response to environmental changes. Sensory modalities that allow tadpoles to assess the features of their environment, and subsequently mediate their developmental response, are not well understood. I analyzed whether visual and tactile features of conspecifics influence developmental response in anuran larvae. I exposed tadpoles of Rana, Bufo and Xenopus genera to enhanced tactile and visual cues by putting clay model tadpoles in the rearing water. Tadpoles that experienced both enhanced visual and tactile stimuli developed the fastest, and metamorphosed at the smallest body size. They showed the highest whole-body amount of stress hormone corticosterone. Developmental rate and hormone levels were the lowest in the control groups without any enhancement. This implies that tadpoles rely on both vision and mechanoreception for habitat assessment. They experience enhanced stimuli as stressful ones, and probably mediate environmental changes into developmental response via corticosterone. | en_US |
| dc.description | The use of vision was further examined in Rana and Bufo tadpoles. The aim was to determine whether larval anurans use images of other tadpoles as visual cues in assessing conspecifics density. Both real, and increased density simulated with mirrors, decreased tadpole growth and development, and increased activity. Thus, images of conspecifics are used as visual cues in tadpole's habitat assessment, and they induce phenotypic shifts in tadpoles' development and behaviour. Such ability to dissociate growth and developmental rates allows tadpoles adaptive response to habitat changes. | en_US |
| dc.description | I examined the extent to which dissociation is possible in my study of rare giant Xenopus laevis larvae. These giants lack thyroid glands and arrest their development at an early hindlimb bud stage. They continue to grow, developing into grossly deformed giants. They have excessive axial muscle mass, hypertrophied fat bodies, partially solidified lungs, and are negatively buoyant. Nevertheless, their gonads are mature, containing eggs and sperm. Gonadal development decoupled from metamorphosis brings giant Xenopus larvae closest of any anurans to being neotenic. However, under thyroid hormone treatment giants show some metamorphic changes, but all die at the stage when tail starts resorbing. I suggest that disproportionate growth in giant larvae precludes their complete metamorphosis. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2004. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Anatomy. | en_US |
| dc.subject | Biology, Animal Physiology. | en_US |
| dc.title | Environment assessment by tadpoles and factors affecting anuran metamorphosis. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
