Distinctions in Fine-Scale Spatial Genetic Structure Between Growth Stages of Picea jezoensis Carr.

Keiko Kitamura,Chunlan Lian,Atsushi Nakanishi,Susumu Goto

doi:10.3389/fgene.2018.00490

Abstract

Conifers in northern forests, such as fir and spruce, preferably regenerate on coarse woody debris, including fallen logs, stumps, and snags. In northern Japan, the sub-boreal conifer species Picea jezoensis is completely dependent on coarse woody debris for seedling establishment. To understand the fine-scale spatial genetic structure (FSGS) of this species, a 5-ha plot was established in central Hokkaido, and 531 individual trees were categorized into four life-stages (seedling, sapling, juvenile, and mature) on the basis of age and size. The FSGS of the established seedlings and later growth stages was investigated using 11 nuclear simple sequence repeat loci. A STRUCTURE analysis of seedlings and saplings established on fallen logs revealed that genetically related individuals were spatially localized between adjacent logs. We also found a significant FSGS in early life-stages based on a decline in the kinship coefficient calculated between individuals over shorter to longer spatial distances. Furthermore, the estimation of dispersal kernels indicated the frequent occurrence of short-distance seed dispersal. These results indicated that genetically related seedlings and saplings regenerated on the same or nearby fallen logs. In contrast to the results for the early stages, mature-stage trees showed no significant FSGS. We ran a simulation to examine the hypothesis that the FSGS could be eliminated by demographic thinning during life history processes. We calculated values for simulated offspring generated under three sets of conditions; i.e., by removing (i) inbred individuals, (ii) randomly chosen individuals, and (iii) all individuals on the specific fallen logs. However, the results for the FSGS were significant for all simulated data sets. This indicated that inbreeding depression, stochastic loss, or eradication of establishment sites by local disturbances alone could not explain the lack of FSGS among mature-stage trees. Therefore, it is possible that the colonization history of mature trees present on the study site might differ from that of the current offspring.

Highlights

Sub-boreal conifer forests are widely distributed throughout the northern hemisphere, including North America, northern Europe, and western Siberia, and are mainly dominated by the genera Picea, Abies, and Tsuga
The STRUCTURE analysis indicated that adjacent areas of coarse woody debris (CWD) accommodated genetically related progeny at the center of the study plot (Figures 1E,F)
This might reflect limited seed dispersal capacity and a limited number of established sites (CWD), both of which decrease the effective number of seed parents and, strengthen the fine-scale spatial genetic structure (FSGS) in this species

Summary

Introduction

Sub-boreal conifer forests are widely distributed throughout the northern hemisphere, including North America, northern Europe, and western Siberia, and are mainly dominated by the genera Picea, Abies, and Tsuga. These coniferous species successfully regenerate at safe sites, which are most often decaying logs and areas of coarse woody debris (CWD) (McCullough, 1948; Harmon, 1987; Suzuki et al, 1987; Nakamura, 1992), and some are so strongly dependent on CWD for their establishment that they are highly susceptible to changes in the environment. In contrast to the numerous studies undertaken on regeneration on CWD, few studies have investigated the demographic processes from seedlings to mature trees for CWD-dependent species

Methods

Results

Conclusion