Date of Award

Summer 2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Program/Concentration

Biology

Committee Director

Alex Greenwood

Committee Director

Wayne Hynes

Committee Member

Christopher Osgood

Committee Member

Fred Dobbs

Call Number for Print

Special Collections LD4331.B46 W93 2007

Abstract

The Durham Collection and the Cambridge and Oxford University Museums provided the materials to investigate the possibility that the extinction of indigenous rats of Christmas Island was a result of disease introduced by infected ship rats (R. rattus) in 1899. The collections of H.E. Durham in 1901-1902 reveal that R. macleari was present on Christmas Island up to then and includes specimens of R. rattus together with specimens that exhibit characteristics of both R. rattus and R. macleari. Durham's notes indicate both R. rattus and R. macleari specimens were heavily infected with trypanosomes at the time of collection. In addition, documentation from a visit to the island by K.R. Hanitsch of the Raffles Museum in Singapore suggests that by 1904 R. macleari was no longer present. Thus, the invasion of the island by ship rats, the presence of a pathogenic organism and the extinction of an endemic rat species all coincide at the same time. Portions of nuclear gene sequences were analyzed from skin samples of the Durham collection to determine if R. macleari was a unique species and if hybridization occurred when ship rats were introduced to the island. Specimens were also analyzed to determine the presence of trypanosome infection.

The morphologically described R. macleari samples revealed sequences different from those of known rats, suggesting R. macleari was in fact a unique, endemic rat species that is now extinct. The molecular evidence thus far does not suggest that hybridization occurred between R. macleari and R. rattus. In addition, four of the rats showed a clear signal for rat specific trypanosomes, indicating that the pathogen was present. An independent laboratory has confirmed the results. Although the data are correlative, this is the first confirmed example of a known disease-causing agent coincident with an extinction event in an endemic species and could serve as a model for first contact followed by extinction as may have occurred to multiple species at the end of the Pleistocene era over 10,000 years ago.

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DOI

10.25777/97he-1k75

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