Morphological Stability of Rural Populations Confirms Their Use As Controls in Urban Ecology Studies

Abstract The expansion of urban environments and how animals may be affected by them are being increasingly investigated, leading to a surge in urban ecology studies. Many urban ecology studies involve a direct comparison between rural and urban populations, or the use of urban gradients along a continuum from rural to urban areas. The implicit, although not properly investigated, assumption in these rural vs urban comparisons is that the rural populations offer a control that represents a lack of the anthropogenic stressors affecting the urban populations. Here we used museum skulls from 14 rodent species to conduct two separate studies, measuring fluctuating asymmetry (FA) as a proxy of developmental stress to assess the effect of anthropogenic disturbance. First, we compared urban and rural specimens of house mice (Mus musculus) to validate our methodological approach. Second, we compared rural specimens from 14 rodent species collected during the last two centuries across Austria. We hypothesised that FA in rural populations has not increased over the last two centuries, which would support the use of rural populations as a proper control in rural vs urban comparisons. We found higher morphological asymmetry in urban populations of Mus musculus compared to rural populations, which is consistent with similar studies in other species. However, we did not find any significant increase in FA over time in rural populations for any of the studied species. This supports the common practice of using rural populations as a control in rural vs urban comparisons when assessing the effects of urbanisation.