Proc B. Special Issue: Urban Hubs of Connectivity: Contrasting Patterns of Gene Flow Within and Among Cities in the Western Black Widow Spider

In my recent contribution to the special issue on urban evolution in Proceedings B, my co-authors and I share our findings on contrasting patterns of gene flow (paper here). This is one of several posts on the recent special issue on urban evolution in Proceedings B.

Urbanization in the Western United States is significantly rapid and encroaches on natural landscapes, creating a heterogenous landscape. This urban expansion typically fragments the natural habitat, resulting in population declines and reduced gene flow. However, the Western black widow spider (Latrodectus hesperus) is considered an urban adapter that is thriving in the urban habitat and our previous broad-scale study showed that urbanization facilitates gene flow.

Figure 1 from Miles et al (2018). (a) Geographic sampling of the broad-scale samples with the highlighted locales in blue and yellow reflecting urban and non-urban, respectively. Fine-scale samples are boxed and are shown for (b) Albuquerque, (c) Las Vegas, and (d) Phoenix, with circles for urban and diamonds for non-urban and the color scale representing percent impervious surface.


In this study, we compared fine-scale sampling of 3 Western US cities to our broad-scale sampling of 10 urban and 11 non-urban locales distributed across the geographic range of Western black widow spiders.


We found that patterns of gene flow differed between our three cities, revealing that some cities have higher rates of gene flow between them than other. Additionally, we find that when we look at patterns across all sampled locales, some urban areas contribute significantly more to genetic connectivity than others, which results in hubs of connectivity.

Figure 3 from Miles et al (2018). Social network popgraph analysis among urban (blue) and non-urban (yellow) locales for the broad-scale sample, as well as the fine-scale sample from Albuquerque (black), Las Vegas (light grey) and Phoenix (dark grey) cities).

Our results challenge the use of cities as replicates of urban evolution. Each of our sampled cities has varying levels of genetic connectivity among them, as well as different levels of urbanization, however, these two measures are not correlated in our results (e.g. high connectivity does not mean highly urbanized).  

Check out the full manuscript:

Urban hubs of connectivity: contrasting patterns of gene flow within and among cities in the western black widow spider
Lindsay S. Miles, Rodney J. Dyer, Brian C. Verrelli
DOI: 10.1098/rspb.2018.1224

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