Optimal habitats enhance establishment, but do not influence gender frequencies or genetic diversity of Silene acaulis in Svalbard (Norway)

• Main Author: Svoen, Mildrid Elvik
• Format: Master Thesis
• Language: English
• Published: 2014
• Subjects: Establishment; performance; female; advantage; gender; frequency; gynodioecy; habitat; optimality; population; genetics; Silene; acaulis; Svalbard; vegetation; cover; Arctic; Norway; Arctic Archipelago; Silene acaulis; Spitsbergen
• Online Access: http://hdl.handle.net/10852/43531; http://urn.nb.no/URN:NBN:no-47900

Plant reproduction in the Arctic is challenging, and tight energy budgets, short growing season and the limited number of pollinators favour self-pollination. Self-pollination over time will, however, have a negative effect through reduced genetic variation and increased risk of inbreeding depression. In gynodioecious species, hermaphrodites and male-sterile females co-occur. This breeding system allows for selfing by hermaphrodites, but enforces outcrossing through females. To maintain the gender polymorphism, females must be fitter than hermaphrodites. This female advantage is predicted to cause improved establishment performance of female offspring, in particular under harsher environmental conditions. This study aims to evaluate how changes in habitat optimality, represented by vegetation cover at different successional stages, affect population dynamics in the gynodioecious pioneer species Silene acaulis (L) Jacq. in the high arctic archipelago Svalbard (Norway). Open pioneer habitats are predicted to be optimal for this species. As a result of increased inter-specific competition, S. acaulis populations in suboptimal closed habitats are expected to show i) decreased establishment performance and ii) increased female frequency due to female advantage, which further should affect iii) patterns of genetic diversity and structure. Two approaches were taken to test these issues further. A large-scale study including 17 populations (4136 individuals) from the south-western to northern parts of Spitsbergen assessed establishment patterns and female frequency of S. acaulis in different habitat types on a broad scale. A small-scale study including two populations (1036 individuals), one in an open habitat and one in a closed habitat, assessed these issues in more detail, including analyses of microsatellite genetic diversity and structure (224 individuals). Demographic patterns were assessed through generalized linear modelling (GLM) and significance tests, while genetic diversity and structure were investigated by estimation of inbreeding coefficients, heterozygosity measures, analysis of molecular variance (AMOVA), Mantel s tests and principal component analysis (PCA). Average plant cushion size was significantly smaller in open habitats compared to suboptimal closed habitats. Female frequencies were slightly but not significanty higher in suboptimal closed habitats. Inbreeding levels were fairly high, and not significantly different between the two habitat types. Low levels of genetic differentiation were detected between and within sites and plots. The results show that closed habitats reduce general establishment performance, while no significant association with habitat type is detectable for female frequency and genetic diversity measures. It is suggested that establishment performance is affected by environmental conditions changing over local scales, while gender frequency is mainly influenced by large-scale climatic conditions, which are severe for all sites included in this study. Overall high inbreeding levels are suggested to reflect pollinator deficiency in this high arctic system, leaving considerable spatial and temporal seed dispersal as the most likely cause for low differentiation levels between and within the two populations.