Two Steps Away From Extinction: Do You Believe?

Forest fragmentation can have detrimental effects on plant populations, reducing population sizes and depleting genetic diversity, as a consequence. As a matter of urgency, it is crucial to assess the effects of forest fragmentation on genetics and ecological processes, particularly for threatened species on the brink of extinction. Here, we examined the responses of Dinizia jueirana-facao G. P. Lewis & G. S. Siqueira (Fabaceae, Caesalpinioideae) - a rare and critically endangered tree species endemic to the Brazilian Atlantic Forest-, to forest fragmentation. Based on theoretical predictions for barochory plant species with small population sizes, we hypothesized that forest fragmentation would reduce gene flow, erode genetic diversity, and negatively impact demography. Using neutral SNPs (Single Nucleotide Polymorphisms) derived from ddRADSeq (double-digest restriction site-associated DNA sequencing), we found that pollen dispersal occurred within short distances, with the majority of outcrossed pollination events occurring locally. Furthermore, contemporary estimates of gene dispersal distances were lower than historical ones, indicating a seasonal shift in the scale of gene flow due to recent forest fragmentation. Our results also indicated no evidence of inbreeding and loss of genetic diversity. In terms of ecological process, the demographic structure of fragmented populations of D. jueirana-facao followed a reverse J-shaped size class distribution, with more than 45% of plants found in small diameter classes. While a more in-depth understanding of ecological and evolutionary processes at fine-scale is still needed to safeguard this unique plant species, our infant study plays a crucial role to help keep the evolutionary potential of D. jueirana-facao. We stress that the approach used here would be useful to guide conservation and management efforts for species on the brink of extinction.