Physical and ecological isolation contribute to maintain genetic differentiation betweenfire salamander subspecies

Landscape features shape patterns of geneflow among populations, ultimately determining where taxa lay along thecontinuum between panmixia to complete reproductive isolation. Geneflow can be restricted, leading to populationdifferentiation in two non-exclusive ways:“physical isolation”, in which geographic distance in combination with thelandscape features restricts movement of individuals promoting genetic drift, and“ecological isolation”, in which adaptivemechanisms constrain geneflow between different environments via divergent natural selection. In central Iberia, twofiresalamander subspecies occur in parapatry across elevation gradients along the Iberian Central System mountains, while inthe adjacent Montes de Toledo Region only one of them occurs. By integrating population and landscape genetic analyses,we show a ubiquitous role of physical isolation between and within mountain ranges, with unsuitable landscapes increasingdifferentiation between populations. However, across the Iberian Central System, we found strong support for a significantcontribution of ecological isolation, with low genetic differentiation in environmentally homogeneous areas, but highdifferentiation across sharp transitions in precipitation seasonality. These patterns are consistent with a significantcontribution of ecological isolation in restricting geneflow among subspecies. Overall, our results suggest that ecologicaldivergence contributes to reduce genetic admixture, creating an opportunity for lineages to follow distinct evolutionary trajectories.GV-A was supported by FCT–Foundation for Science and Technology (CEECIND/00937/2018). This research was supported by the European Science Foundation (Frontiers of Speciation Research, Exchange grant 3318), and by the European Commission (Synthesys grant ES-TAF-1486), granted to RJP. Partial funds were additionally provided by grants EVOVIV: PTDC/BIA-EVF/3036/2012 (FCT, Portugal) to GV-A, and CGL2017-83131-P (FEDER/Ministerio de Ciencia, Innovación y Universidades–Agencia Estatal de Investigación, Spain) to IMS.Peer reviewe