Genetic structure of dioecious and trioecious Salix myrsinifolia populations at the border of geographic range

P Mirski,B Ostrowiecka,J Kotowicz,I Jędrzejczyk,E Brzosko,A Wróblewska

doi:10.1007/s11295-016-1096-6

Abstract

Gene flow in plant populations is heavily affected by species sexual systems. In order to study the effect of sexual systems on genetic structure, we examined plastid and nuclear DNA of 12 dioecious (males and females) and 18 trioecious (males, females and hermaphrodites) populations of Salix myrsinifolia—a boreal shrub with slow range expansion. Populations were located along latitudinal gradients across submarginal and marginal parts of the range. Individuals of each sex morph were all hexaploid. We identified 10 chloroplast DNA haplotypes and scored 205 polymorphic bands with amplified fragment length polymorphism. We found dioecious populations that differed from trioecious populations via the presence of four unique haplotypes and significant difference in Nei’s gene diversity index (0.119 vs. 0.116) and down-weighed marker value (1.17 vs. 1.02). The latter parameter, together with haplotype and nucleotide diversity, significantly decreased with latitude similar to the expansion front. Also, we found that 89% of hermaphrodite individuals belong to one distinct in tree parsimony network haplotype. This frequency significantly decreased with latitude towards the expansion front. We suspect that the presence of hermaphrodites in trioecious populations may represent a trade-off between the possibility of producing progeny by single hermaphrodites and genetic variability loss through autogamy. S. myrsinifolia benefits from trioecious sexual systems under colonization events. This phenomenon is no longer a gain closer to the core of the species range.

Highlights

Patterns of species’ geographic range and genetic diversity are strictly shaped by life history traits such as reproduction type, breeding system(s) and dispersal mechanisms as well as natural processes or human impacts (Hamrick and Godt 1996; Barrett and Husband 1990; Gitzendanner and Soltis 2000; Nybom 2004)
Given the potential of S. myrsinifolia to expand its European geographic range, we studied the consequences of sexual systems on phylogeography and population genetic structure using chloroplast DNA and nuclear molecular markers
The genome size estimated for males, females and hermaphrodites of S. myrsinifolia was 2.172, 2.164 and 2.160 pg/2C DNA, respectively, with no significant differences between these groups (Online Resource 1)

Summary

Introduction

Patterns of species’ geographic range and genetic diversity are strictly shaped by life history traits such as reproduction type, breeding system(s) and dispersal mechanisms as well as natural processes or human impacts (e.g. isolation, fragmentation, climate changes) (Hamrick and Godt 1996; Barrett and Husband 1990; Gitzendanner and Soltis 2000; Nybom 2004). Species harness evolutionary potential and adopt various strategies enabling survival, reproduction and geographic expansion. Phenotypic variation positively affects adaptive potential of expanding species and the source of this plasticity lays in genetic variation. Different patterns of genetic variation during range expansion can be found both in theoretical assumptions and experimental studies. There was an increase in genetic differentiation in 70.2%. During human-mediated introductions, newly established populations most often suffered losses of allelic richness and heterozygosity, but rarely underwent significant increase in both parameters (Dlugosch and Parker 2008)

Methods

Results

Conclusion