Portland State University. Department of Biology
Luis A. Ruedas
Date of Award
Master of Science (M.S.) in Biology
1 online resource (viii, 129 pages)
I recorded and analyzed the morning duet calls of eastern tarsiers (Tarsius spp.) in North Sulawesi to examine the effects of geography and geologic history on their call structure. Tarsius species exhibit interspecifically variable duet calls shown to correlate with species differentiation and distribution. They are distributed across Sulawesi, a biogeographically complex island in the Indonesian archipelago, where tectonic activity and multiple glaciations during the Pleistocene generated and modified barriers to their dispersal and gene flow.
Recordings were made at ten locations from November of 2012 through June of 2014. Two locations were categorized as mainland, while eight island locations were categorized as either shallow or deep, according to the distance and bathymetric depth separating them from the mainland. My first hypothesis was that tarsier calls on islands separated by depths of less than 130 meters would be more strongly correlated to calls found on the mainland than would the calls from islands separated by deeper water, due to dispersal and possible hybridizations during glaciations. There was a higher degree of similarity between the mainland locations and the shallow water islands than was found between the deep water islands and either shallow water islands or the mainland.
My second hypothesis was that a stepping stone pattern of colonization would be evidenced in the acoustic structure of tarsiers from the Sangihe Arc, with each island showing vocalizations more similar to its immediate neighbors than to other islands. Since tarsiers were not found to be present on two of the islands, I was unable to trace the entire arc as planned. It was found, however, that Sangihe (the largest island and the farthest north of the islands) was the most acoustically unique, as expected.
Both genetic drift and environmental factors pay a role in evolving animal communication, but I hypothesize that it is more likely the former at work in this case, as the habitats are similar, and I found no strong evidence of short term habitat adaptations or frequency partitioning. The spectral and temporal structure of the duet calls on the mainland and shallow water islands showed no clear geographical bias or patterns, suggesting that panmixia and hybridization during recurring glaciations may function in preventing subdivisions among the populations.
Kulander, Olivia Clare, "Whence and Whither: Acoustic Variability and Biogeography of Tarsiers in North Sulawesi" (2018). Dissertations and Theses. Paper 4360.
Available for download on Tuesday, March 19, 2019