Genetic distinction between contiguous urban and rural multimammate mice in Tanzania despite gene flow

Abstract

Journal of evolutionary biology, 2016; 29 (10):1952-1967Special conditions are required for genetic differentiation to arise at a localgeographical scale in the face of gene flow. The Natal multimammatemouse, Mastomys natalensis, is the most widely distributed and abundantrodent in sub-Saharan Africa. A notorious agricultural pest and a naturalhost for many zoonotic diseases, it can live in close proximity to humansand appears to compete with other rodents for the synanthropic niche. Wesurveyed its population genetic structure across a 180-km transect in centralTanzania along which the landscape varied between agricultural land in arural setting and natural woody vegetation, rivers, roads and a city (Moro-goro). We sampled M. natalensis across 10 localities and genotyped 15microsatellite loci from 515 individuals. Hierarchical STRUCTURE analysesshow a K-invariant pattern distinguishing Morogoro suburbs (located in thecentre of the transect) from nine surrounding rural localities. Landscapeconnectivity analyses in Circuitscape and comparison of rainfall patternssuggest that neither geographical isolation nor natural breeding asynchronycould explain the genetic differentiation of the urban population. Using theisolation-with-migration model implemented in IMa2, we inferred that asplit between suburban and rural populations would have occurred recently(<150 years ago) with higher urban effective population density consistentwith an urban source to rural sink of effective migration. The observedgenetic differentiation of urban multimammate mice is striking given theuninterrupted distribution of the animal throughout the landscape and thehigh estimates of effective migration (2NeM = 3.0 and 29.7), suggesting astrong selection gradient across the urban boundar