How diverse can rare species be on the margins of genera distribution?

Abstract

Different genetic patterns have been demonstrated for narrowly distributed taxa, many of them linking rarity to evolutionary history. Quite a few species in young genera are endemics and have several populations that present low variability, sometimes attributed to geographical isolation or dispersion processes. Assessing the genetic diversity and structure of such species may be important for protecting them and understanding their diversification history. In this study, we used microsatellite markers and plastid sequences to characterize the levels of genetic variation and population structure of two endemic and restricted species that grow in isolated areas on the margin of the distribution of their respective genera. Plastid and nuclear diversities were very low and weakly structured in their populations. Evolutionary scenarios for both species are compatible with open-field expansions during the Pleistocene interglacial periods and genetic variability supports founder effects to explain diversification. At present, both species are suffering from habitat loss and changes in the environment can lead these species towards extinction.

The demographic and ecological factors shaping diversification among rareAstragalusspecies

“…The substantial increases in population size following divergence may be the result of the opening of new habitat or local adaptation following environmental change (see below for more discussion of local adaptation). Although additional genomic research of this genus is needed, our findings are consistent with the hypothesis that vicariance events and genetic isolation of local demes contributes to rapid diversification of Astragalus following climate change (Gavrilets & Vose, 2005; Simões et al., 2016), similar to diversification patterns in other rare and narrowly distributed plant species (e.g., Backes et al., 2019; Godt et al., 1996; Kropf et al., 2006).…”

Threatened and understudied: the lack of genetic data of endangered Brazilian plant species

“…This general observation corroborates the results of Torres-Florez et al ( 2017) in a review study on conservation genetics studies in Latin America, which found the use of SSRs in 33,1% of the articles. Solanaceae, with a series of studies of endemic and endangered Brazilian species without effective commercial use (LORENZ-LEMKE et al, 2006;FRANCESCHINELLI ET AL., 2013;BACKES et al, 2019;JOHN et al, 2019). Brummitt et al (2015) estimate that one out of every five plant species evaluated in the world is threatened with extinction.…”

Population genomics indicates micro‐refuges and riverine barriers for a southern South American grassland nightshade

“…This scenario proposes that species or their ancestors could have fragmented their distribution and isolated lineages, promoting allopatric speciation (Lorenz‐Lemke et al, 2010). In contrast, the colder and drier climate during the glacial periods would allow the expansion of grassland domains, such as Pampa and Chaco, leading grassland species to expand their distribution from the persistent populations (Backes et al, 2019; Latrubesse et al, 2012; Mäder & Freitas, 2019; Reck‐Kortmann et al, 2014).…”

“…Our results revealed that the P. parodii evolutionary history agrees with the proposal for ancient lineages (Avise, 2000). The ancestor of the Petunia genus has originated in the Pampa, and the Quaternary climate shifts strongly influenced its species distribution and diversification (Barros et al, 2015(Barros et al, , 2020Ramos-Fregonezi et al, 2015;Reck-Kortmann et al, 2014), with posterior migration to the north and higher elevations (Backes et al, 2019;Lorenz-Lemke et al, 2010).…”