Weak population structure and no genetic erosion in Pilosocereus aureispinus: A microendemic and threatened cactus species from eastern Brazil

Abstract

Succulent cacti (Cactaceae) are among the most threatened taxonomic groups assessed to date. Here we evaluated the genetic diversity and population structure of a narrow endemic columnar cactus Pilosocereus aureispinus. This species is only found in a small area of c. 300 km2 of rocky savanna from eastern Brazil and it is currently classified as vulnerable (VU) on the International Union for Conservation of Nature (IUCN) red list. Eight microsatellite loci were genotyped for 91 individuals from four localities of the known P. aureispinus range. In contrast with expectations for narrow endemic species, we found relatively high levels of genetic diversity (e.g., HE = 0.390 to 0.525; HO = 0.394 to 0.572) and very low population structure based on the variation of six loci. All the analyzed individuals were clustered in one unique genetic group in assignment tests. We also generated the sequences of two plastid markers (trnT-trnL and psbD-trnT) and found no variation on a subsample of 39 individuals. We used Landsat 8 images and Normalized Difference Vegetation Index to estimate a potential extent of occurrence of c. 750 km2 for this species. Our results showed that P. aureispinus is not suffering from erosion of nuclear genetic variability due to its narrow distribution. However, we advocate that because of the extremely limited extent of occurrence, the ongoing anthropogenic disturbances in its habitat, and phylogenetic distinctiveness of P. aureispinus, this species should be classified as endangered (EN) on the IUCN Red List.

Revisiting phylogeny, systematics, and biogeography of a Pleistocene radiation

“…Despite the time of the first flowering of Pilosocereus species being approximately 5 to 11 years (G. Olsthoorn, personal observations based on greenhouse plants), clonal reproduction in the wild may promote overlapping generations by increasing the longevity of some individuals. This event may have contributed to the long‐term maintenance of genetic diversity in Pilosocereus populations (Khan et al, 2018) and other cactus species (Fraga et al, 2020; Franco et al, 2022). Both the rapid diversification resulting in short internal branches and the long‐term maintenance of genetic diversity might favor extensive incomplete lineage sorting and high gene‐tree discordance.…”

Evolutionary Genetics of Cacti: Research Biases, Advances and Prospects

“…The trnK , matK , trnL-F , and trnL were the most used cpDNA markers. The combination likely occurred due to a low mutation rate of cpDNA markers compared to nrDNA regions [ 36 , 47 ] and low sequence variation of cpDNA among closely related species or among conspecific populations (e.g., [ 21 , 48 , 49 ]). Even so, the use of multiple independent molecular markers has been a successful strategy to resolve phylogenetic relationships within rapid and recent divergent groups of Cactaceae [ 21 , 50 , 51 , 52 ].…”

Population expansion and genetic structure in Cephalocereus nizandensis (Cactaceae), a microendemic cactus of rocky outcrops of the Tehuantepec basin, Mexico

“…High genetic diversity is common in columnar cacti (Pachyceerinae and Stenoceerinea tribes; Hamrick et al 2002;Palleiro-Dutrenit 2008;Cornejo-Romero et al 2014), even in species with restricted or patchy distributions, such as C. nizandensis (Ledig et al 1999(Ledig et al , 2001Moraes et al 2005;Figueredo et al 2010;Bonatelli et al 2014;Khan et al 2018;Silva et al 2020). This diversity has been linked to common life history traits in this group, such as long-life cycles and bat-and bird-mediated pollination (Valiente-Banuet et al 2002) or self-incompatibility (Mandujano et al 2010).…”