Genetic diversity in micro-endemic plants from highland grasslands in southern Brazil

Abstract

Population genetic structure results from the interaction between historical events, current ecological conditions and life traits. The genetic structure and gene flow between populations are important to species dynamics, mainly for rare and endangered species that are more vulnerable to landscape changes and fragmentation. Here we evaluated the genetic diversity, population structure and gene exchange in Petunia bonjardinensis, P. reitzii and P. saxicola, three rare species endemic to subtropical highland grasslands in southern South America. We analysed the genetic diversity and structure considering historical events, such as founder effect and climate changes, and biological traits of each species. We also estimated the conservation status for these three species. We collected samples from all adult individuals and occurrence sites that could be found at the same flowering season and genotyped them for 13 nuclear microsatellite markers. Our results indicate that rarity is probably historical for these species, given that we found no genetic evidence for recent bottlenecks. Petunia bonjardinensis, with the largest occurrence area and population sizes, displayed the higher diversity indices. The other two showed lower genetic diversity and are geographically most restricted. Gene exchange among these species was low, although they share some ancestral genetic polymorphism. Historical migration, founder effects and Pleistocene climate cycles ae the main factors explaining genetic diversity, and this was also influenced by reproductive biology and recent habitat loss, whereas the landscape influences the structure. Based on IUCN criteria, the three species are endangered, and the main risk for their survival is probably anthropic activity in the occurrence area. We recommend an urgent programme for the preservation of these species in situ and ex situ.

Disentangling the causes of high polymorphism sharing in sympatric Petunia species from subtropical highland grasslands: insights from nuclear diversity

“…We retrieved genetic information based on eight nuclear microsatellites, amplified with previously published primers ( Bossolini et al, 2011 ; Table S2 ). We re-evaluated the original data ( Souza et al, 2022 ; Soares et al, 2023 ) by visualizing and scoring the alleles with GeneMarker v.1.97 software (Softgenetics LLC, State College, USA). We used Micro-Checker ( van Oosterhout et al, 2004 ) to identify possible null alleles, significant allele dropout, and scoring errors due to stutter peaks.…”

“…These species are interfertile, as demonstrated by experimental pollinations and bee-pollinated, with the same solitary bees’ genera already observed visiting their flowers ( Stehmann et al, 2009 ). Nuclear and plastid data were previously published for these species revealing high polymorphism sharing among them ( Lorenz-Lemke et al, 2010 ; Souza et al, 2022 ; Soares et al, 2023 ). Species share a common ancestor ( Reck-Kortmann et al, 2014 ), diverged recently, and evolved under the Pleistocene influence in an allopatric process due to landscape fragmentation ( Lorenz-Lemke et al , 2010 ).…”

“…in Santa Catarina; P. reitzii that occurs at 800-1000 m a.s.l. growing on the walls of small cliffs beside rivers, hanging freely in space in Santa Catarina; and P. saxicola, which inhabits humid and shadowed rocks, in the forest borders, at 800 m in elevation also only in Santa Catarina ( Stehmann et al, 2009 ; Lorenz-Lemke et al, 2010 ; Souza et al, 2022 ; Soares et al, 2023 ).…”

“…Species share a common ancestor ( Reck-Kortmann et al, 2014 ), diverged recently, and evolved under the Pleistocene influence in an allopatric process due to landscape fragmentation ( Lorenz-Lemke et al , 2010 ). Moreover, has been suggested that the nuclear polymorphism sharing could be due to hybridization with another Petunia species widely distributed in the same area ( Souza et al , 2022 ). Testing such hypothesis regarding multiple hybridization events under landscape changes served as starting point to re-evaluate the microsatellite data.…”

Shades of white: The Petunia long corolla tube clade evolutionary history

“…or more), it has been proposed an allopatric speciation, strongly influenced by climate changes during the late Pleistocene ( Lorenz-Lemke et al, 2010 ; Barros et al, 2015 , 2020 ). Pleistocene effects were also implicated in the intraspecific diversification of some species ( Backes et al, 2019 ; Souza et al, 2022 ; Soares et al, 2023 ). Additionally, for ST lowland species (elevation < 500 m), ecological factors and geomorphology were the most important features, even when the species are parapatric ( Ramos-Fregonezi et al, 2015 ; Segatto et al, 2017 ).…”