Genetic differentiation, local adaptation and phenotypic plasticity in fragmented populations of a rare forest herb.

Rodolfo Gentili,Aldo Solari,Gianna Serafina Monti,Sandra Citterio,Stefano Armiraglio,Silvia Assini,Cecilia Duprè,Martin Diekmann

doi:10.7717/peerj.4929

Rodolfo Gentili, Aldo Solari + Show 6 more

Open Access

https://doi.org/10.7717/peerj.4929

Copy DOI

Abstract

BackgroundDue to habitat loss and fragmentation, numerous forest species are subject to severe population decline. Investigating variation in genetic diversity, phenotypic plasticity and local adaptation should be a prerequisite for implementing conservation actions. This study aimed to explore these aspects in ten fragmented populations of Physospermum cornubiense in view of translocation measures across its Italian range.MethodsFor each population we collected environmental data on landscape (habitat size, quality and fragmentation) and local conditions (slope, presence of alien species, incidence of the herbivorous insect Metcalfa pruinosa and soil parameters). We measured vegetative and reproductive traits in the field and analysed the genetic population structure using ISSR markers (STRUCTURE and AMOVA). We then estimated the neutral (FST) and quantitative (PST) genetic differentiation of populations.ResultsThe populations exhibited moderate phenotypic variation. Population size (range: 16–655 individuals), number of flowering adults (range: 3–420 individuals) and inflorescence size (range: 5.0–8.4 cm) were positively related to Mg soil content. Populations’ gene diversity was moderate (Nei-H = 0.071–0.1316); STRUCTURE analysis identified five different clusters and three main geographic groups: upper, lower, and Apennine/Western Po plain. Fragmentation did not have an influence on the local adaptation of populations, which for all measured traits showed PST < FST, indicating convergent selection.DiscussionThe variation of phenotypic traits across sites was attributed to plastic response rather than local adaptation. Plant translocation from suitable source populations to endangered ones should particularly take into account provenance according to identified genetic clusters and specific soil factors.

Highlights

In recent years, human-induced habitat loss and fragmentation have caused severe reductions in biodiversity so that many formerly widespread plant species have become rare and are persisting in isolated populations (Lienert, 2004; Magrach, Larrinaga & Santamaría, 2012; Marcilio-Silva & Marques, 2017)
With regard to genetic mechanisms, it is known that some local environmental factors, such as those linked to soil characteristics, can exert a selective pressure on the life history traits of resident populations, causing local adaptation and affecting fitness under the new environmental conditions (Ellis & Weis, 2006); neutral genetic differentiation can be explained by environmental factors (Al-Gharaibeh et al, 2016)
We used complementary approaches: (a) we measured a set of morphological traits to assess phenotypic population differentiation in the field, correlating local and landscape conditions with the population characteristics; (b) we investigated genetic diversity and genetic differentiation among populations by examining FST values; (c) we assessed the patterns of local adaptation, in terms of level of divergence of quantitative traits, by applying a PST approach

Summary

Introduction

Human-induced habitat loss and fragmentation have caused severe reductions in biodiversity so that many formerly widespread plant species have become rare and are persisting in isolated populations (Lienert, 2004; Magrach, Larrinaga & Santamaría, 2012; Marcilio-Silva & Marques, 2017). Previous studies highlighted that plants growing in small and fragmented populations may be subject to genetic erosion. This can increase the frequency of (biparental) inbreeding, which can lead to an inbreeding depression where the genetic load of deleterious recessive alleles reduces individual fitness (Pluess & Stöcklin, 2004; Rosche et al, 2017). Alteration of environmental conditions accompanying fragmentation (i.e., in abiotic factors such as light regimes, soil conditions, humidity, etc.) may induce changes in the demographic dynamics of populations (Richards, Emery & McCauley, 2003) and a shift in several phenotypic traits (Jacquemyn et al, 2012). Fragmentation did not have an influence on the local adaptation of populations, which for all measured traits showed PST < FST, indicating convergent selection. Plant translocation from suitable source populations to endangered ones should take into account provenance according to identified genetic clusters and specific soil factors

Objectives

Methods

Results

Discussion

Conclusion