Search

Warm‐edge populations, that is, those usually small and isolated populations at the boundary of species maximum temperature range limit, are of particular scientific and conservation interest. This is especially the case for those that have long been geographically isolated, possibly through multiple glaciations, as they can contribute significantly to species' overall genetic diversity. However, distinguishing between glacial relict and more recently established warm‐edge populations is difficult especially in the absence of a continuous fossil record. In this study, we investigate the origin of anomalously low‐elevation warm‐edge populations of the dominant cool temperate Japanese tree Fagus crenata in the northeast Kanto (NEK) region. We sought to determine whether these populations are glacial relicts or, rather, were established via dispersal in the Holocene using chloroplast and nuclear genetic data, species distribution modeling and comparison with populations in a well‐established glacial refugia (south‐central Kyushu [SCK]) and of mid‐late Holocene age (southern Hokkaido [SH]). Whole chloroplast genome "mining" revealed a similar amount of haplotype diversity in NEK and SCK while there was no chloroplast variation in SH. Populations in NEK, particularly the lowest elevation sites, harbored unique haplotypes providing evidence for their persistence since the Last Glacial Maximum as supported by species distribution models under two of three general circulation models. NEK populations also lacked the genetic signatures of recent expansion that characterize the most northern‐edge populations in SH. We conclude that warm‐edge populations in NEK are most likely relicts of glacial refugia and should be given high priority for conservation. [ABSTRACT FROM AUTHOR]

In plant populations, limited seed dispersal may generate the aggregation of related individuals, which is referred to as spatial genetic structure (SGS). If short-distance pollination frequently occurs in populations with SGS, it may lead to frequent mating between related individuals (biparental inbreeding). In this study, we examined patterns of pollen dispersal and inbreeding under such conditions in a population of the wind-pollinated tree species Fagus crenata Blume using microsatellite analyses of adult trees and dispersed seeds. The population showed weak but significant SGS and the pollen dispersal in the population involved a combination of distance-dependent (largely short-range) dispersion at the local scale and long-distance transport. Although SGS and distance-dependent pollination co-occurred, individual inbreeding coefficients for both adults and seeds were almost zero, suggesting that mating generating sound seeds was genetically random with little or no inbreeding, probably because of the weak SGS, long-distance pollen dispersal, and postpollination mechanisms including self-incompatibility and inbreeding depression. The production of sound seeds through genetically random mating may be important for maintaining F. crenata populations because the resulting seedlings may be less affected by inbreeding depression than those resulting from the mating of related individuals. Key words: dispersal kernel, Fagus crenata, inbreeding coefficient, outcrossing rate, paternity analysis, wind pollination. Resume: Dans les populations vegetales, la dispersion limitee des graines peut generer une agregation des individus apparentes, phenomene que l'on appelle structure spatiale genetique (SSG). Si la pollinisation sur de courtes distances survient frequemment dans les populations avec SSG, ceci peut mener a un croisement frequent entre des individus apparentes (endogamie biparentale). Dans cette etude, les auteurs ont examine les patrons de dispersion du pollen et l'endogamie sous de telles conditions chez une population de Fagus crenata Blume, une espece d'arbres a pollinisation anemophile, a l'aide d'analyses de microsatellites des arbres adultes et des graines dispersees. La population presentait une SSG faible mais significative, et la dispersion du pollen dans la population impliquait la combinaison d'une dispersion en fonction de la distance (principalement de courte distance) a l'echelle locale et d'un transport de longue distance. Meme si la SSG et la pollinisation en fonction de la distance survenaient conjointement, les coefficients individuels d'endogamie des adultes et des graines etaient presque de zero, suggerant que le croisement generant des graines saines etait genetiquement aleatoire avec peu ou pas d'endogamie, probablement a cause de la faible SSG, de la dispersion du pollen sur une longue distance et des mecanismes post-pollinisation incluant l'auto-incompatibilite et la depression endogamique. La production de graines saines au moyen du croisement genetiquement aleatoire peut etre importante pour maintenir les populations de F. crenata car les semis resultants peuvent etre moins affectes par la depression endogamique que ceux qui resultent du croisement d'individus apparentes. [Traduit par la Redaction] Mots-cles : dispersion des grains, Fagus crenata, coefficient d'endogamie, taux de croisement eloigne, analyse de paternite, pollinisation anemophile., Introduction Gene dispersal via seeds and pollen strongly influences the genetic diversity and structure of plant populations. Genetic differentiation among populations is reduced by gene dispersal (i.e., gene flow) even [...]

SUMMARY: Standard models of plant speciation assume strictly dichotomous genealogies in which a species, the ancestor, is replaced by two offspring species. The reality in wind‐pollinated trees with long evolutionary histories is more complex: species evolve from other species through isolation when genetic drift exceeds gene flow; lineage mixing can give rise to new species (hybrid taxa such as nothospecies and allopolyploids). The multi‐copy, potentially multi‐locus 5S rDNA is one of few gene regions conserving signal from dichotomous and reticulate evolutionary processes down to the level of intra‐genomic recombination. Therefore, it can provide unique insights into the dynamic speciation processes of lineages that diversified tens of millions of years ago. Here, we provide the first high‐throughput sequencing (HTS) of the 5S intergenic spacers (5S‐IGS) for a lineage of wind‐pollinated subtropical to temperate trees, the Fagus crenata – F. sylvatica s.l. lineage, and its distant relative F. japonica. The observed 4963 unique 5S‐IGS variants reflect a complex history of hybrid origins, lineage sorting, mixing via secondary gene flow, and intra‐genomic competition between two or more paralogous‐homoeologous 5S rDNA lineages. We show that modern species are genetic mosaics and represent a striking case of ongoing reticulate evolution during the past 55 million years. Significance Statement: The evolution of extra‐tropical wind‐pollinated tree genera involves dynamic speciation processes. High‐throughput sequencing of the multi‐copy, potentially multi‐locus 5S rDNA reveals a complex history of hybrid origins, lineage sorting and mixing, and intra‐genomic competition between paralogous‐homeologous loci in the core group of Eurasian beech trees (genus Fagus) and their distant relative, F. japonica. The modern species are genetic mosaics and represent a striking case of at least 55 million years of ongoing reticulate evolution. [ABSTRACT FROM AUTHOR]