Historic black rat invasions into Sri Lanka lead to hybridization forming two sub-lineages in the <em>Rattus rattus</em> species complex

Abstract

In this work, we used two mitochondrial (16S rRNA and cytochrome-b) and one nuclear (Rag 1) gene fragments to analyse phylogeographic history of black rats in Sri Lanka at subspecies level. Of the five subspecies recorded in Sri Lanka three (Rattus rattus kelaarti, R.r. rufescens, R. r. kandianus) are believed to have invaded Sri Lanka in prehistoric times and two (R.r. alexandrinus, R. r. rattus) in the recent past through trade ships from Europe and India. All subspecies, except R. r. kandianus, have restricted destribution with none occuring sympatrically. Rattus r. kandianus is widely destributed throughout the country. In the phylogeny, all black rats from Sri Lanka fell into the Rattus rattus complex lineage I. But, R.r. kelaarti, R.r. rufescens most of R.r. kandianus and one individual of R.r. alexandrinus formed a unique Sri Lankan sub-lineage within the lineage I. The results suggests hybridization with mitochondrial introgression of the endemic R.r. kandianus with all other subspecies separately. Introgression of R.r. alexandrinus mitochondrial DNA into a subpopulation of R.r. kandianus is responsible for placing few individuals of the latter in the widespead sub-lineage in the Lineage I with R.r. alexandrinus and R. rattus from other parts of the world. The fifth subspecies, R.r. rattus which was reported in small numbers from ports in 1930s, has most likely been replaced by R.r. alexandrinus.

Keywords

• subspecies, mitochondrial inrogression, muroid