Multiple Paternity in the Norway Rat,Rattus norvegicus, from Urban Slums in Salvador, Brazil

Abstract

The Norway rat, Rattus norvegicus, is one of the most important pest species globally and the main reservoir of leptospires causing human leptospirosis in the urban slums of tropical regions. Rodent control is a frequent strategy in those settings to prevent the disease but rapid growth from residual populations and immigration limit the long-term effectiveness of interventions. To characterize the breeding ecology of R. norvegicus and provide needed information for the level of genetic mixing, which can help identify inter-connected eradication units, we estimated the occurrence of multiple paternity, distances between mothers and sires, and inbreeding in rats from urban slum habitat in Salvador, Brazil. We genotyped 9 pregnant females, their 66 offspring, and 371 males at 16 microsatellite loci. Multiple paternity was observed in 22% (2/9) of the study litters. Of the 12 sires that contributed to the 9 litters, we identified 5 (42%) of those sires among our genotyped males. Related males were captured in close proximity to pregnant females (the mean inter-parent trapping distance per litter was 70 m, ±58 m SD). Levels of relatedness between mother-sire pairs were higher than expected and significantly higher than relatedness between all females and non-sire males. Our findings indicate multiple paternity is common, inbreeding is apparent, and that mother-sire dyads occur in close proximity within the study area. This information is relevant to improve the spatial definition of the eradication units that may enhance the effectiveness of rodent management programs aimed at preventing human leptospirosis. High levels of inbreeding may also be a sign that eradication efforts are successful.

Spatial population genomics of the brown rat (Rattus norvegicus) in New York City

“…Rats have been observed moving over 150 m in a day (Glass et al., ; Recht, ), but their home range is often as small as 30–40 m in urban settings (Davis et al., ). Additionally, paternity tests (Costa et al., ; Glass et al., ) and radio tracking (Taylor & Quy, ) indicate that male rats regularly expand their range of movement to find mates, often moving hundreds of metres. Our study describes distances separating related pairs of individuals that may be due to dispersal or regular home range movement by one or both rats in each dyad.…”

“…Previous studies have found that only a small percentage of urban rats move between study sites, with greater movement identified by genetic methods (6.5%, Gardner‐Santana et al., ; 6.8%, Kajdacsi et al., ) than capture–mark–recapture studies for rats caught above ground (0.003% between city blocks, Davis, ) or below ground (0.0% between sewer systems, Heiberg et al., ). Movements by adult males presumably maintain gene flow between nearby colonies (Costa et al., ; Glass, Klein, Norris, & Gardner, ), but results on sex‐biased dispersal have been mixed (Gardner‐Santana et al., ; Heiberg et al., ; Kajdacsi et al., ). However, urban rats are capable of moving several kilometres during relatively rare long‐distance dispersal events (Creel, ), indicating the possibility of gene flow across entire cities.…”

Significant Genetic Impacts Accompany an Urban Rat Control Campaign in Salvador, Brazil

“…Norway rats exhibit colonial social systems, where individuals within a colony are more related to each other than at random among the population (Calhoun, 1963;Costa et al, 2016). However, drastic reductions in population size may disrupt this social structure, leading to shifts in relatedness if some colonies are hit harder than others, or if the residual individuals remaining after the campaign come from a subset of colonies and inbreeding increases (Calhoun, 1963).…”

Using fine‐scale spatial genetics of Norway rats to improve control efforts and reduce leptospirosis risk in urban slum environments

“…However, the sharp break in genetic similarity between Valley 2 and Valley 4 indicates the potential for such adaptive divergence to either arise or explain the observed genetic break. Outbreeding avoidance may also contribute to this divergence, where rats are more likely to breed with more closely related individuals coming from within the local population, rather than immigrants from other areas of Pau da Lima or Salvador (Costa et al., ). There are an increasing number of examples of evolutionary divergence at microgeographic scales, including in response to complex urban environments and their natural selection regimes (Richardson et al., ; Saccheri, Rousset, Watts, Brakefield, & Cook, ; Selander & Kaufman, ).…”