Variable time lags in genetic response of three temperate forest herbs to 70 years of agricultural landscape change

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Abstract Context Agriculture-driven land-use changes over the past decades have not only reduced the amount of habitat for species but also influenced the genetic exchange among the remaining fragmented populations. Many recent studies have found a delayed response in population genetic diversity and differentiation of species in fragmented habitats to past landscape disturbances, a so-called time lag. However, the specific role of species’ individual reproductive traits and the population genetic measures used remain poorly understood. Objectives We examined the impact of past and current agricultural landscape composition in temperate Europe on the population genetic structure of three long-lived, slow-colonizing forest herb species – Anemone nemorosa, Oxalis acetosella and Polygonatum multiflorum, which vary in their reproductive traits. Methods We considered four time points in history (mid-1900s, 1985, 2000 and 2017) to identify the potentially different length of time that is needed by each species to respond to landscape change. We also explored the impact of using different genetic measures in quantifying the time lags. Results Our findings show that despite substantial landscape alterations about 70 years ago, the mid-1900s landscape composition was not reflected in the current genetic diversity and differentiation of the three species. This indicates a possible unexpected quick genetic adjustment of these species. Nevertheless, by combining the signals of multiple genetic measures, we found that O. acetosella, which reaches sexual maturity earlier than the other two species and is self-compatible, showed signs of faster genetic adjustment to these landscape changes. In contrast, A. nemorosa and P. multiflorum, which take longer to reach sexual maturity, might exhibit longer time lags that were beyond this study’s time frame. Conclusions This study underscores the importance of considering the species’ reproductive traits and especially the role of temporal scales of different genetic measures when investigating the impact of landscape history on current population genetic structures.

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