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.

Keywords: Rattus norvegicus; brown rat; genetics; mating behavior; microsatellite; multiple paternity; polyandry; urban slums..

Figure 1.

The 3 valley study area of Pau da Lima. White triangles indicate the location where pregnant rats (included in this study) were caught. White dots show the location of inferred sires. Straight white lines and numbers indicate distance (m) between pregnant rats and inferred sires. Black dots indicate all other rats sampled during May and July of 2013. Black lines indicate the location of streets. Topography generated by a digital terrain model is shown in different categories of elevation.

Figure 2.

Paternal contributions to litters are indicated on the x axis and total number of offspring per litter on the y axis. Column color/pattern depicts the number of sires per litter and how many offspring each father sired.