Highlights • Signatures of genetic bottlenecks and reduction of populations' fitness were observed in populations of Luehea divaricata in southern Brazil. • Lower levels of observed heterozygosity are correlated with populations' fitness, decreasing germination capacity and increasing the proportion of anomalous germinated plantlets. • Promoting the connection among populations is proposed as a key strategy towards conservation of L. divaricata genetic resources in its southernmost distribution

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... range. Abstract Extant populations growing in regions that were refugia during the last glacial period are expected to show higher genetic diversity than populations that moved from these refugia into new areas in higher latitudes. Such new populations likely faced harsher climatic conditions, being established with reduced population size and experiencing the effects of genetic bottlenecks. In this study we employed data from nuclear SSR markers for detecting molecular signatures of genetic bottlenecks, and germination experiments to evaluate reduction of populations' fitness in natural populations of Luehea divaricata Mart. et Zucc., growing in the southern range of the species distribution (around 30°S latitude). Signatures of genetic bottlenecks and reduction of populations' fitness were observed in all populations. Lower levels of observed heterozygosity are correlated with populations' fitness, decreasing germination capacity and increasing the proportion of anomalous germinated plantlets. Promoting the connection among populations is proposed as a key strategy towards conservation of L. divaricata genetic resources in its southernmost distribution range. The offspring from crosses among populations would significantly increase the observed heterozygosity and fitness of multiple populations.