Abstract
Increasing anthropogenic environmental impacts lead to rapid transitions of ecosystems and species. Species persisting in changing environments may respond to changes by altering phenotypic traits across space and/or time. Here we tested whether the frequencies of three color morphs in the ground beetle Harpalus affinis differed across spatial and temporal gradients. The gradients extended from urban to rural regions, and from the early 20th century until today, in the Berlin-Brandenburg area, Germany. Specimens comprised beetles from the entomological collection of the Museum fur Naturkunde, Berlin and recently collected material. As a result of differing environments, we expected to observe differences in color frequencies in beetles between habitats and across time, responding to different levels of urbanization. Our results revealed sexual dichromatism in H. affinis as well as some habitat dependent differences in trait frequency. Frequencies of color morphs remained generally constant in males across space and time. Females likewise showed no differences in color frequencies between habitats, urban and rural regions, and between different time periods in rural regions. In contrast color morph frequencies changed in urban regions over time in females: Bronze color decreased, whereas green color became more dominant over time. We assume that bronze color was selectively advantageous in times with high levels of soot pollution in the city, whereas green is more cryptic and thus advantageous in times with less polluted air. The color change of females thus could have been driven by natural selection. In contrast, the persistence of predominately green males through all times and habitats, more likely can be explained by sexual selection.
Highlights
Increasing levels of urbanization and agricultural land use, mostly due to rapid population growth (Bairoch and Goertz, 1986; Antrop, 2004), cause rapid environmental transitions from natural to degraded or novel ecosystems and are of major ecological and socio-economic interest (Hobbs et al, 2013; Jeltsch et al, 2013)
Our study focused on changes in frequencies of color morphs in the diurnal ground beetle species Harpalus affinis in the Berlin-Brandenburg area, Germany, an area experiencing increasing urbanization and agriculture intensification during the last 125 years, with heavy air pollution in the early twentieth century due to industrialization, but with decreasing levels of air pollution after the Second World War (UBA, 1998)
In females the frequencies of color morphs changed in urban regions over time, resulting in a decrease of “bronze,” and an increase of “green” color morphs whereas color frequencies remained nearly constant in rural areas over time as well as between regions and habitats
Summary
Increasing levels of urbanization and agricultural land use, mostly due to rapid population growth (Bairoch and Goertz, 1986; Antrop, 2004), cause rapid environmental transitions from natural to degraded or novel ecosystems and are of major ecological and socio-economic interest (Hobbs et al, 2013; Jeltsch et al, 2013). Due to human induced environmental changes (Figure 1), the native fauna and flora will be heavily impacted by habitat degradation, fragmentation, and conversion, as well as the invasion of new species, and the creation of new habitats (Ribera et al, 2001; Haila, 2002). There are some native species that persist throughout these environmental transitions (Van’t Hof et al, 2011; Doudna and Danielson, 2015). How these species deal with the changing environments, especially if rapid transitions triggered any changes in their phenotypes or if particular (pre-)adaptations enable these species to persist, whilst other species disappeared (Palkovacs et al, 2011), has been so far mostly neglected
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