Comparative analysis of the complete plastid genomes of desert trees Neltuma and Strombocarpa genera

Abstract Neltuma alba (Algarrobo blanco), Neltuma chilensis (Algarrobo Chileno) and Strombocarpa strombulifera (Fortuna) are some of the few trees found in small highly fragmented populations, throughout the Atacama Desert, indicating their drought resistance. We found that the complete chloroplast genomes of N. alba and N. chilensis are larger in size compared to species of the Strombocarpa genus. However, the Strombocarpa species presented slightly more GC content than the Neltuma species. Therefore, we assume that Strombocarpa species have been exposed to stronger evolution than Neltuma species. We observed high variation values in the number of cpSSRs (chloroplast simple sequence repeats) and repeated elements among Neltuma and Strombocarpa species. Very low nucleotide diversity values were found in Neltuma , while ten highly variable regions found in Strombocarpa , can likely be used to resolve uncertainties in phylogeny, and for DNA barcoding. Although in general our study supports the phylogeny of other studies, the biggest inconsistency was the nesting of Prosopis cineraria within the Neltuma clade and showed a divergence time of 1.85 Mya. With this study we provide valuable information about isolated populations of tree species that provide important ecosystem services in hostile environments before they disappear, due to an ongoing fragmentation of their populations.