Search

Adaptive genetic variation is a key factor in evolutionary biology, but the detection of signatures of natural selection remains challenging in nonmodel organisms. We used a genome scan approach to detect signals of natural selection in the Black alder ( Alnus glutinosa), a widespread wind-pollinated tree. Gene flow through pollen dispersal is believed to be high in this species, and we therefore expected to find a clear response to natural selection. In combination with two different landscape genetic approaches, we determined which environmental variables were most associated with the inferred selection. This analysis was performed on a regional scale (northern Belgium) and on a continental scale (Europe). Because climate-related differences are much more pronounced at the continental scale, we expected to find more selection-sensitive genetic markers across Europe than across northern Belgium. At both spatial scales, a substantial number of genetic loci were considered outliers, with respect to neutral expectations, and were therefore identified as selective. Based on results from our combined approach, four putative selective loci (or 2.5%) were recovered with high statistical support. Although these loci seemed to be associated with different environmental variables, they were mainly temperature-related. Our study demonstrates that the use of complementary methods in landscape genetics allows the discovery of selective loci which otherwise might stay hidden. In combination with a genome scan, the selective loci can be verified and the nature of the selection pressure can be identified. [ABSTRACT FROM AUTHOR]

1. Resurveys of regional floras allow assessment of long-term floristic change and to pinpoint driving forces behind these changes. Causes of floristic decline derived from such resurveys depend on the considered landscape, but are often associated with human activities especially in urbanized areas. Much could be learned from comparisons of contrasting landscapes. 2. Vascular plant abundance categories from a detailed, late 19th century flora were matched with distribution data from a late 20th century plant database in a rural area (Thiérache; 1673 km2) in northern France. Floristic change was characterized both in absolute numbers of extinct and extant species and by a measure for relative change in range size. Knowledge of land use changes and ecological correlates of floristic change permitted the causes for species change to be inferred and to identify which traits are associated with species vulnerability. Extinction rates were compared with similar studies from contrasting landscapes, taking into account the negative relationship between standardized extinction rates and log-transformed size of the study area. 3. Of the 959 species from the historical list, 186 (19.4%) may be considered regionally extinct. Most extinct species were already rare historically. Differences among habitats indicated strong declines for aquatic species and arable weeds and least change for forest species. Percentage species loss per year in Thiérache equalled 0.22, which was higher than two other similar sized predominantly rural landscapes. 4. Across the main habitat groups, relative species decline was always associated with relatively higher stress tolerance and lower competitiveness and biased towards therophytes. The main causes of species decline were management intensification, eutrophication, secondary succession in semi-natural open habitats and land use change. 5. Synthesis. Rural landscapes with no population density increase, no urbanization and a stable landscape configuration are believed to be less vulnerable; yet, on a relatively short time scale, without nature conservation measures, these landscapes may suffer strong species loss comparable to that in urbanized landscapes. Effective management of landscapes for biodiversity conservation whether they are urbanized or rural requires the development of a network of nature reserves. [ABSTRACT FROM AUTHOR]