Behavioral responses to variations in the microenvironments of motile spores of the Antarctic epiphyte E. antarctica and the motile epiphytic diatom, Navicula sp. were investigated.
Most macroalgal species along the Western Antarctic Peninsula are chemically defended against predation and are also mostly devoid of free living filamentous algal epiphytes. However, one endo/epiphyte, Elachista antarctica, is found growing exclusively out of the palatable rhodophyte Palmaria decipiens. Choice and no choice feeding assays with tissues of epiphyte and host were conducted in three different trials with four amphipods commonly found on P. decipiens to test whether meso-grazers prefer the host over the epiphyte. Three of four fed on the epiphyte at faster rates than its host and one consumed both species. Aggressive grazing of the epiphyte indicated that differences in palatability do not explain the exclusive epiphyte-host interaction.
It was suspected that spore chemoresponses to chemicals associated with defended macrophytes are responsible for this exclusive epiphyte-host selection. First, phototactic movements of E. antarctica spores were quantified in order to control for this response during the chemosensory assays. Spores exhibited positive phototactic attraction toward higher irradiances.
Settlement, germination, and swimming behaviors of the epiphyte’s motile spores were quantified in the presence of crude extracts of host P. decipiens and other sympatric rhodophytes. Host P. decipiens was the only alga tested that did not inhibit spore settlement. Spores were chemotactically attracted to hydrophilic and lipophilic extracts of host P. decipiens. These results indicate that chemosensory behaviors of the epiphyte’s spores to metabolites associated with these chemically defended macrophytes can explain this exclusive epiphyte-host interaction.
The epiphytic diatom Navicula sp. which was found in association with a seagrass biofilm was isolated. Gliding movements were recorded at five irradiances and in the presence of nutrient rich media to test for phototactic and chemotactic stimulated gliding, respectively. There was no significant effect on directional of travel or speed across all assays. Chemotactic response of rate of change of direction varied across trials. Although very motile, this diatom did not exhibit gliding migrations that were chemotactically or phototactically sensitive.
Keywords: chemotaxis, diatom, palatability, phototaxis, spore
|Advisor:||Amsler, Charles D.|
|Commitee:||McClintock, James B., Sullivan, Michael J., Thacker, Robert W., Van Zandt, Peter A.|
|School:||The University of Alabama at Birmingham|
|School Location:||United States -- Alabama|
|Source:||DAI-B 73/04, Dissertation Abstracts International|
|Subjects:||Ecology, Evolution and Development, Macroecology|
|Keywords:||Bacillariophyceae, Chemotaxis, Diatom, Heterokonts, Palatability, Phaeophyceae, Phototaxis, Spore|
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