RELICTOAK

"The genetics of enduring isolation: diversity, gene flow and offspring performance in glacial relict tree populations"

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 Obiettivo del progetto (Objective)

'The response of species to changing environments is likely to be determined largely by population responses at range margins. In contrast to the expanding edge, the low-latitude limit of species ranges remains understudied, and the critical importance of its populations as long-term stores of species’ genetic diversity and foci of speciation has been little acknowledged. Here we propose to study a set of 23 low-latitude marginal populations of the widespread European forest tree Quercus robur (Pedunculate oak) in central Spain in order to elucidate how these were able to sustain their genetic diversity and viability through multiple glacial cycles. For this purpose, we investigate how genetic diversity is distributed and transmitted across populations. Because gene dispersal plays a central role in this process, we examine patters of historical and contemporary gene flow involving three levels: within populations, among populations, and between species. Finally, germination and growth experiments under controlled conditions will be used to assess whether low levels of genetic variation actually result in reduced fitness and resistance to abiotic stress. This study should help improve our understanding of how glacial relict populations manage to persist under adverse conditions and provide valuable background information for developing appropriate strategies for their conservation and management in a changing climate.'

Introduzione (Teaser)

The aim of the RELICTOAK project was to gain a better understanding of how populations of a species that was once abundant over a large area during the ice age, but now only occurs in a few small areas, can persist under adverse conditions. The work is of major importance as populations act as long-term stores of a species' genetic diversity and evolutionary history.

Descrizione progetto (Article)

Funded by the EU, RELICTOAK investigated a series of 23 low-latitude marginal populations of Quercus robur (Q. robur) in central Spain. The species is a wide-spread European forest tree commonly known as the Pedunculate oak. Scientists studied how genetic diversity was distributed and transmitted across these populations in order to discover how they maintained their genetic diversity and viability through several ice ages.

As gene dispersal was a key part of this process, researchers studied historical and contemporary gene flow at three levels. They were: within populations, among populations, and between species whereby hybridisation with the more common Quercus pyrenaica (Pyrenean oak) was investigated.

A comparison of Q. robur genotypes with those of the Q. pyrenaica revealed that hybridisation between the two species is not uncommon. This could explain the observed high diversity and weak geographical structure of Q. robur populations.

Researchers found that long-distance gene flow through pollen dispersal was extensive in Q. robur populations. As a result, even the smallest stand of trees produce abundant crops in some years and display continual regeneration. An additional study into the link between populations and landscape-scale patterns of pollen gene flow revealed that acorn size, a parameter that affects seed dispersal, germination and seedling growth, is determined by the mother tree rather than the population of origin.

Project members demonstrated that efficient pollen exchange between small and isolated Q. robur populations, aided by hybridisation with the much more abundant Q. pyrenaica, enabled the examined stands of oak to sustain a high genetic diversity and reproductive potential. The diversity and viability of Q. robur populations at the edge of their range, together with their potential to acquire genes from the more drought-resistant Pyrenean oak could provide a powerful mechanism for adapting to a warmer and drier future climate.

The work conducted by RELICTOAK will provide valuable data for developing appropriate ecologically based strategies for conserving and managing relict populations in the face of a changing, drier climate.