Data from: Trapped within the city: Integrating demography, time since isolation and population-specific traits to assess the genetic effects of urbanization

Urbanization is a severe form of habitat fragmentation that can cause many
species to be locally extirpated and many others to become trapped and
isolated within an urban matrix. The role of drift in reducing genetic
diversity and increasing genetic differentiation is well recognized in
urban populations. However, explicit incorporation and analysis of the
demographic and temporal factors promoting drift in urban environments are
poorly studied. Here, we genotyped 15 microsatellites in 320 fire
salamanders from the historical city of Oviedo (Est. 8th century) to
assess the effects of time since isolation, demographic history
(historical effective population size; Ne) and patch size on genetic
diversity, population structure and contemporary Ne. Our results indicate
that urban populations of fire salamanders are highly differentiated, most
likely due to the recent Ne declines, as calculated in coalescence
analyses, concomitant with the urban development of Oviedo. However,
urbanization only caused a small loss of genetic diversity. Regression
modelling showed that patch size was positively associated with
contemporary Ne, while we found only moderate support for the effects of
demographic history when excluding populations with unresolved history.
This highlights the interplay between different factors in determining
current genetic diversity and structure. Overall, the results of our study
on urban populations of fire salamanders provide some of the very first
insights into the mechanisms affecting changes in genetic diversity and
population differentiation via drift in urban environments, a crucial
subject in a world where increasing urbanization is forecasted.