New Evidence Concerning the Extinction of The Endemic Murid Rattus macleari From Christmas Island, Indian Ocean.

Abstract

Recently rediscovered material from the collections and archives of the Oxford University Museum throws new light on the disappearance of the endemic rat Rattus macleari from Christmas Island (Indian Ocean), thought to have gone extinct between 1898 and 1908 as a result of diseases introduced by infected individuals of R. rattus. A collection of rats made by H.E. Durham in 1901-1902 reveals that R. macleari was present on Christmas Island at this time, although in lesser numbers than had been the case when the species was described in 1887. Also present in the collection are specimens of R. rattus, together with a number of rats which exhibit a mixture of characters from both R. rattus and R. macleari. Durham's notes on blood parasites in the Christmas Island rats reveal that in 1901-1902 both R. rattus and some specimens of R. macleari were heavily infested with trypanosomes. Notes deposited in the University Museum archives by Hanitsch (1923) show that R. macleari was no longer present on Christmas Island after 1904. As a result of the authors' observations on the Durham collection and the Hanitsch manuscript, it is proposed that the extinction of R. macleari occurred between 1901 and 1904. During this period, there is evidence for extensive interspecific hybridisation between R. macleari and R. rattus. The selective pressure for such hybridisation may have been parasitisation, resulting from the introduction of trypanosome-infected individuals of R. rattus in a cargo of hay in 1899.